Power Quality Symptoms & Solutions e-book is is written from an electronics point of view, rather than a power engineering one. And in so doing, provides the bridge between theory and real life. According to the book introduction more and more lecturers are using this material as a reference in their courses. You can find lots of interesting reading here for many industry fields and links to other resources.
48 Comments
Tomi Engdahl says:
Mitigating harmonics in electrical systems
http://www.csemag.com/single-article/mitigating-harmonics-in-electrical-systems/0fdc552157dd758226bc8f757fe2b252.html
Although devices using power electronics can produce distortion in electrical distribution systems, it’s up to the engineer to apply effective solutions to mitigate them.
Tomi Engdahl says:
Southern Fried Transformer
http://www.designnews.com/author.asp?section_id=1368&doc_id=273075&cid=nl.dn11
It is common practice to connect a three-phase generators and transformers in this configuration, wye-wye-delta. The delta connected transformer’s secondary absorbs the harmonic distortion from the generator, which is typically just a few percent. And that’s good because it cleans up the waveform. This particular generator had about 5% distortion, not bad at all, but the generator and transformer are usually the same size. Ours weren’t.
But 5% of our generator amounts to several hundred percent of our poor little transformer, and the better transformer, with its lower impedance, were even less able to resist the harmonic current. And that’s why it burned up so much quicker.
Tomi Engdahl says:
Welcome to Open Power Quality
http://openpowerquality.org/
Open source hardware, software, and data for low cost, crowd-sourced power quality monitoring, storage, and analysis
OPQBox: Low cost, open source hardware
Our first generation OPQBox costs less than US$75, and the schematics are published under an open source hardware license if you want to build it yourself.
OPQHub: Cloud-based, open source software service
Each OPQBox sends power quality events and data to OPQHub, an open source cloud-based service.
Tomi Engdahl says:
Home made power quality analyser
https://www.youtube.com/watch?v=x5BWcP8UZnQ
Built from a scrap step-down transformer and a few resistors, and a lot of software finesse.
Demonstrates some truly terrible power quality, including harmonic distortion, commutation notches and other problems.
Tomi Engdahl says:
Understanding Power Quality
https://www.youtube.com/watch?v=qUGgOm6s0aM
ONEAC AC Power, a business of Emerson Network Power, demonstrates the dramatic difference an ONEAC power conditioner can make in your power quality and protecting your system from power disturbances.
Tomi Engdahl says:
Monitor Ground Fault Leakage Currents
http://ecmweb.com/content/monitor-ground-fault-leakage-currents
Most power quality problems are due to incorrect connections of an electrical system. Using CTs and leakage current monitors, you can check an electrical system during acceptance testing of the installation and also during maintenance and renovation of the system. Watch out for partial or complete short circuits between neutrals and your grounding network. They’ll often create power quality disturbances
Most power quality problems are due to incorrect connections of an electrical system. Using CTs and leakage current monitors, you can check an electrical system during acceptance testing of the installation and also during maintenance and renovation of the system.
Yes, there’s a certain amount of normal leakage current going from the neutral and the phase conductors to ground in all electrical systems. Usually, the level of this leakage current is from about 10mA to some 100mA, depending on the size of electrical system.
Voltage differences are between different grounding points.
Because of contact between the neutral and ground at Point A, the return current flowing from the load also flows through the grounding network and the grounding circuits in Devices D1 and D2.
This current may disrupt their operation because the voltage difference and resulting current are often quite high.
So, how does ground noise enter a sensitive electronic device? Current flowing in a neutral conductor consists of many kinds of disturbances such as harmonic waves and distortion, high frequency disturbances, transients, etc.
As you can see, a filter or surge suppressor circuit does not prevent disturbances from entering the device. Often sensitive electronic devices are connected to a reference ground. The problem above results from the devices’ grounding conductor connected to the conduit (which is also serving as a ground) rather than to a dedicated reference grounding system tied to the main grounding point.
Sometimes the shield of the communication or data cable connects to conductive parts of the building.
Watch out for magnetic field interference. In a normal electrical system, ground current produces a low frequency (60 Hz) magnetic field. At this frequency, a clean electrical system has a magnetic field between 0.1 mGaus to 45 mGaus. In an industrial working environment the magnetic flux density can be much higher, anywherefrom 20 mGaus to 15 Gaus. Normal sources of stray magnetic fields are transformers, large motors, and various industrial production machines. However, the major significant cause for magnetic stray fields is often a faulty grounding connection or an equipment failure in an electrical system.
Relatively small magnetic fields cause disturbances to sensitive electronic devices. For example, fields higher than 13 mGaus can disturb a computer monitor.
In the U.S., definitive standards on electric magnetic fields aren’t yet established. However, in Europe, the Cenelec (European Committee for Electrotechnical Standardization) EMC Standard EN-50082-1 gives limit values for residential, commercial, and light industry environments. The maximum value of magnetic flux density is 38 mGaus for industrial situations and 13 mGaus for computer monitoring locations. In a facility’s electrical system, you may see very high peaks of magnetic flux density during starting current impulse. These peaks can directly effect the circuits of sensitive devices.
How do you monitor ground leakage current to avoid problems? To prevent electronic noise from disturbing electronic devices, you can use different kinds of noise attenuation circuits, such as filters, isolation transformers, photo-couplers, etc. But one of the most important aspects in preventing electronic noise from disturbing electronic devices is to evaluate the wiring and grounding systems first. This can often be expensive and time consuming. The simplest and most economical method is to continuously monitor leakage current of the whole electrical system or the most critical parts of electrical system.
Tomi Engdahl says:
Save Energy Through Smart Feeder Design
http://ecmweb.com/electrical-testing/save-energy-through-smart-feeder-design
Energy savings is often thought of something extra you do, after the fact, to reduce thermal losses.
Let’s look at a very common area of error: nominal voltage. Commercial and industrial facilities typically use some combination of 480/277V and 208/120V. Often, the electric utility provides 480V at the service. A center tap on that service transformer provides 277V.
For offices and general receptacles, you need 120V, so stepdown transformers supply 208/120V. Sometimes, this is just one big transformer and one big panel. While that arrangement saves the design engineer time, it typically increases the cost of construction and definitely increases the cost of operation.
Ideally, you will distribute 480V as far inside the building as you can — so far that all feeders are 480V and only branch circuits are at a lower voltage. First of all, it costs less in labor and materials to carry that same power at 480V than at 120V (smaller wire due to lower current, smaller raceway due to smaller wire, etc.). More important, the distribution itself is more efficient at 480V. The closer the 120V transformer is to its 120V loads, the more energy-efficient your system will be. Thus, it’s smart to:
Use several small, strategically situated 480V-120/208V transformers instead of one large, centrally situated one. The idea here is to get the shortest 208/120V branch circuits that are practical.
Use a similar approach for 277V. Rather than a center tap off the service transformer, use several smaller 480V-480/277V transformers. Better yet, see if you can replace 277V with 480V, since the typical uses (lighting and reheat boxes) are available in 480V versions.
Tomi Engdahl says:
Branch circuit power meter delivers data center power-quality data
http://www.cablinginstall.com/articles/2015/04/bcpm-data-center-power-monitor.html
TrendPoint Systems Inc. recently launched Branch Circuit Power Meter 2.0, the newest version of its branch circuit power meter (BCPM) product that the company says “delivers utility-grade power data.” TrendPoint provides a monitoring platform for high-density power consumers including data centers.
“BCPM 2.0 is the latest evolution of TrendPoint’s exceptional technology, delivering power quality data down to the branch circuit level,”
“The BCPM 2.0 meter is the first of its kind to offer waveform capture, along with harmonics. [It] improves upon the industry’s method of using three-phase PQM meters for switchgear, switchboards, and distribution panels.”
http://www.trendpoint.com/
Tomi Engdahl says:
From the Ground Up
Answering five of the most frequently asked questions on grounding and ground-fault current
http://ecmweb.com/power-quality/ground
Although it’s one of the most important aspects of electrical design and installation, grounding continues to be one of the least understood and most misinterpreted concepts in the industry. It’s also one of the most expensive when errors are made. The dollar value of equipment in-operation and/or loss — not to mention the potential liability — associated with ground-fault arcing can be staggering. So if grounding implementation problems leave you dazed and confused, don’t worry. You’re not alone.
Electrical contractors, plant/facility electrical maintenance personnel, and electrical engineers continue to demand more complete and concise information on grounding-related issues. That’s why interest in grounding and ground faults has not diminished throughout the various Code cycles.
Question No. 1: What are the advantages and disadvantages of the various grounding methods for medium-voltage systems in power plants? Also, what practices are adopted by electric utilities both nationally and internationally?
Answer: You can broadly classify medium-voltage (MV) grounding systems into four categories: solidly grounded, low-resistance grounded (LRG), high-resistance grounded (HRG), and insulated neutral (ungrounded) systems. A good reference is ANSI/IEEE Std. 242 (Buff Book), “Protection and Coordination of Industrial and Commercial Power Systems.”
With the solidly grounded system, as shown in Fig. 1, there is no intentional impedance in the neutral-to-earth path. Instead, the neutral is solidly connected to earth.
The protective device closest to the fault must trip and isolate the circuit as fast as possible.
With LRG systems, as shown in Fig. 2, the ground-fault current is controlled and normally limited to between 25A and 1,000A. The voltage to ground on the un-faulted phases can increase up to the phase-to-phase voltage level, so you must use adequately rated insulation systems and surge suppression devices. You also must detect and isolate the ground fault. Since the ground-fault current is smaller and controlled, ground-fault relaying still has the requirement of fast tripping.
With an HRG system, as shown in Fig. 3, the ground-fault current is in the 10A range. The intention here is to allow the system to operate without tripping, even with a phase-to-ground fault on one phase. When a ground fault does occur, only an alarm is raised. This permits time to locate the fault while power continuity is maintained.
If the fault is in a rotating machine, there usually is no iron damage in the stator.
With the insulated neutral (ungrounded) system, as shown in Fig. 4 on page 36, there is no intentional connection of the system to ground. In effect, the three phases of the system float. When a ground fault occurs, the fault current is contributed by the system capacitance to earth on the un-faulted phases. This is usually small, and the system can be operated without tripping. Because the system is floating, if the ground fault is of the arcing or intermittent type, then there is the possibility of substantial transient overvoltages, which can be six to eight times the phase voltage.
The standards and best practices in various countries generally follow ANSI or IEC standards. The technical literature supports these practices. In power plant applications, MV systems occur in two places: generation and station service. In practice, both station service and generators are low- or high-resistance grounded.
Tomi Engdahl says:
System
Grounding Impact on reliability and Safety
http://southern-alberta.ieee.ca/files/2011/12/mar-11_presentation1.pdf
May 11, 2009
Transient Overvoltages on Ungrounded
Systems from Intermittent Ground Faults
http://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/ia08700001e.pdf
Tomi Engdahl says:
GROUNDING CONSIDERATIONS
FOR INDUSTRIAL POWER SYSTEMS
http://www.hv-eng.com/2010IASGrounding.pdf
Tomi Engdahl says:
How important is clean power?
https://www.youtube.com/watch?v=FD_2RKpWkYw
Clean power is said to be critical to the performance of high-end audio equipment, yet is that so? Power expert Paul McGowan gives us a slightly different viewpoint on the subject, one that’s going to be surprising to many
Tomi Engdahl says:
Introduction to Harmonics – Effect of Harmonics on Power System
https://www.electricaltechnology.org/2018/02/harmonics.html
Tomi Engdahl says:
Sensors and Power Conditioning for Industry
https://www.eeweb.com/profile/steve6366/articles/sensors-and-power-conditioning-for-industry?utm_source=newsletter&utm_campaign=link&utm_medium=EEWebEngInsp-20191219
Power conditioning acts as an interface between the power source and the load, which in most industrial applications performs critical functions, providing equipment protection and output waveform correction against noise, voltage fluctuations, radiofrequency, and electromagnetic interferences.
The increasing industrial use of electrical and electronic equipment has led to a rise in the demand for electricity, which in such applications must be as much freedom as possible from disturbances, drops, or undesirable harmonic components. In industrial production processes, it is mandatory to guarantee the availability of electricity uninterruptedly and regularly — an equipment downtime would, in fact, result in lost productivity, with inevitable consequences on the company’s profits. To mitigate these risks, the most commonly adopted solution is to install a power-conditioning system. This electronic device has the task of monitoring the input voltage (tri-phase voltage from the electrical distribution network), ensuring that the connected loads are safely protected by spikes, surges, sags, ground noise, undesired harmonics, and other types of phenomena that can interrupt the functioning or damage the sensitive electrical and electronic equipment. A power-conditioning system for industrial applications is able to detect any anomalies in the supply voltage. By applying the appropriate corrective actions in a very short time, it ensures the supply of a regular and reliable three-phase power source. The response times are very fast (in the order of milliseconds), while the output power varies from a few hundred VA up to about 1,000 kVA, with an input voltage between 380 and 415 VAC. In summary, power conditioning acts as an interface between the power source and the load, which in most industrial applications performs critical functions, providing equipment protection and output waveform correction against noise, voltage fluctuations, radiofrequency, and electromagnetic interferences.
Tomi Engdahl says:
https://www.electricaltechnology.org/2021/01/capacitor-bank-calculator-kvar-microfarad-pf-correction.html
Tomi Engdahl says:
https://www.enertec.fi/natiivi/2508/teollisuusmuuntajien-toimintakunto-valvontaan?fbclid=IwAR3mKNPnYv5um5Ny_nzUGYa3TX8nLjlx6Yp1iBIpuvukB_HtQUDe15g2-Os
tanohu says:
ACSR is short for Aluminum Cable Steel Reinforced. ACSR conductor are widely used for electrical power transmission over towers. Because they are suitable for long overhead line spans.
Tomi Engdahl says:
Defining “Clean Power” Systems
By Arthur S. Kelm
https://www.ground1.com/whitepaper1.htm
Tomi Engdahl says:
Introduction of Custom Power Devices For Power Quality Improvement
https://www.electricaltechnology.org/2023/02/power-quality-improvement-dstatcom-dvr-upqc.html
Custom Power Devices
The Classification of custom power devices can be done into two major categories, one is network configuring type and the other is compensating type.
The network configuring type devices changes the configuration of the power system network for power quality enhancement. SSCL (Solid State Current Limiter), SSCB (Solid State Circuit Breaker) and SSTS (Solid State Transfer Switch) are the most representative in this category.
The compensating type devices are used for active filtering; load balancing, power factor correction and voltage regulation. Compensating devices include DSTATCOM (Distribution Static Compensator), DVR (Dynamic Voltage Restorer) and Unified Power Quality Conditioner (UPQC).
In the power system, nonlinear loads results in production of harmonics due to which load current waveform gets distorted. The power-quality problems include voltage sags/swells, load voltage harmonic distortions, and unbalancing.
Tomi Engdahl says:
Distortion (THD) in Power Systems
https://www.allaboutcircuits.com/technical-articles/understanding-thd-total-harmonic-distortion-in-power-systems/
https://www.electronics-tutorials.ws/accircuits/harmonics.html
Tomi Engdahl says:
https://www.meanwelldirect.co.uk/glossary/what-is-power-factor-correction/
Tomi Engdahl says:
Is voltage between neutral and earth normal or could there be a fault? A rule-of-thumb used by many in the industry is that Neutral to ground voltage of 2V or less at the receptacle is okay, while a few volts or more indicates overloading; 5V is seen as the upper limit.
Source: https://diy.stackexchange.com/questions/167020/acceptable-voltage-between-earth-line-neutral-single-phase
Tomi Engdahl says:
What is the voltage limit for neutral to ground?
0.5 volts to 2.0 volts
Neutral to earth voltage normally varies from 0.5 volts to 2.0 volts. It’s the voltage drop on neutral wire. More values of N to E voltage would mean overloading in circuit
https://www.quora.com/What-is-the-acceptable-voltage-between-neutral-and-earth-in-a-single-phase
The acceptable voltage between neutral and earth in a single-phase system is typically around 0 volts. In a properly wired and grounded single-phase electrical system, the neutral conductor should be at the same potential as the earth ground, resulting in a voltage difference of approximately 0 volts between the neutral and earth. Any significant voltage difference between neutral and earth could indicate an issue with the grounding or wiring of the system.
This answer is based on UK 230V single phase.
The voltage between neutral and earth is equal to the resistance of the wire between neutral and earth multiplied by the current it is carrying. This resistance needs to be low in order to not waste energy. The live supply wire also needs to be low for the same reason and to be able to supply enough current when a fault occurs to be able to blow the breaker or fuse. Typically they will be under one-tenth of an Ohm each.
There is a parameter known as the prospective fault current which is the current which would flow under short circuit conditions with a 230V 100A supply this has a maximum value of about 16kA. this figure would give a supply resistance of 230/16000 = .014 Ohms. which is the practical minimum likely to be encountered.
A current of 100A flowing through 0.1 Ohms would give rise to 10 Volts
A current of 100 A flowing through .007 Ohms (only dealing with one wire) would give rise to 700mV
Somewhere between these values would be normal under full load conditions.
If we only had a 2kW load then these voltages would be reduced to a tenth.
Depending on the local supply wiring your neighbours may be able to inject voltage onto your neutral but in general, with the 3 phase supply distributed between neighbouring properties with similar demands these will cancel out owing to phase differences.
Neutral to earth voltage normally varies from 0.5 volts to 2.0 volts. It’s the voltage drop on neutral wire. More values of N to E voltage would mean overloading in circuit. In that case length of neutral to be shortened by reducing off take points per circuit.
Without going into calculations regarding loading and wire sizes. Less then 2 Volts for a MEN system.
I have worked on many LV cable faults over the years, and in the case the Neutral fails it goes up to around the 20 Volts value, measured towards an independant Earth pin.
What is the standard of neutral-to-earth voltage?
Technically, there should be no voltage difference between the neutral and earth voltage, because that is the very purpose of earthing the neuteal point of the system. Through this earthed neutral connection an unbalance current is passed from the three phase system to the earth.
Now due to aging or loose connection in the earthing connection of the three phase system a resistance is developed. This resistance causes a voltage difference between the neutral wire and the main earth point of the system.
Development of such voltage is not only unwanted for the systen, but also dengerous gor the working perdonnel. So, to limit this situation, some countries has fixed various limits for this neutral voltages.
In general, this voltage should not exceed 10v in any cases, though for some sensitive electronic equipment the required standerd is below 5V.
In most of the countries the standerd is less than 1V.
Happy reading!.
What can we conclude if neutral to earth voltage is more than 5v? Is it about safety or a healthy system, and how?
You can conclude that current is flowing in the hot to neutral circuit and that current is causing a voltage drop of 5 volts between the neutral line and earth ground.
The earth ground line normally has no current flow so it will be measured as being at an earth ground level of 0 volts.
Any further conclusions requires knowledge of the gauge of the wire used as well as the length of the wire run and the material the wire is made of, usually copper or aluminum.
Knowing all of the above a calculation of current can be done and a power calculation done to get an idea how much heat is being generated and if that heat poses a danger.
If you are talking about a EU or Asian mains of 220 volts AC a drop of 5 volts should not pose an issue. Even a USA mains of 110 volts should not be an issue.
In any case a properly rated circuit breaker will trip before hazardous heating and fire happens. Defeating a circuit breaker by forcing it to stay closed CAN lead to fire.
In an older fused circuit replacing a properly rated fuse with a higher current rating or shorting the fuse with a metal disc CAN lead to fire.
Electrical power is wonderfully safe if people don’t due unwise things.
If unsure I suggest contacting a licensed electrician and have them give you their recommendations.
I personally have a bachelor’s degree in Electronics Engineering Technology. I also have practical experience with house wiring.
However!!!
I am not a licensed electrician so I can not advise you on your local electrical codes which may require things I have not mentioned.
What voltage is perfect when we check neutral and earth?
It depends on where you are. Where are you?
In the US the nominal range that they consider ideal is 114 to 126 VAC which is 120+/-5% with a target of 120V
They consider 104.4 to 127.2 (-13%, +6%) acceptable for short term deviations as load may be added and removed and before adjustments are made.
This is at the entrance panel. But within your house due to wiring resistance and loads, you might see another 3 V or so lower drop.
That is for Line-neutral.
I see the question says neutral and earth. They should ideally be at the same voltage. which is zero from earth to Neutral. In practice there is often some difference of a few volts which is due to the fact that neutral carries the same current as Line but Earth should carry no current. Therefore at places along the Neutral (esp. near the load on long branches) it may be elevated by say 3 V or so above Earth. Because as Neutral lines are generally 12 Ga or so, they are not perfect zero ohm conductors.
What is the voltage between neutral and earth in a 3phase system?
What is the voltage between neutral and earth in a 3phase system?
In a 3ph/3w system, there is no neutral, so the question is not applicable.
In a 3ph/4w system, the 4th wire (neutral) is the earthed star-point of the distribution transformer.
Close to the source – the transformer – the voltage of the neutral should be very near to zero.
If the load on the system is balanced 3ph, then there should never be any neutral current, so the neutral voltage wrt earth remains at zero.
If there are unbalanced (single phase) loads, then the out-of-balance currents need to flow through the neutral to get back to the transformer. The voltage of the neutral will be the product of the vector sums of the neutral currents and the resistance of the neutral wire. This voltage will tend to get larger as the distance from the transformer increases.
The maximum neutral voltage permissible will depend on the standards of the distribution company, but should never exceed a few volts in a 400/230v domestic supply.
Is it any problem if a single phase 220V electrical supply neutral to earthing voltage shows 2.4v?
Yes and no!! Most regulators require the Neutral line to be earthed at the connection to your house. In this case, any voltage on the Neutral implies a poor connection to earth and this is bad.
Some regulators only connect Neutral to earth at the nearest substation which may result in a small voltage on the Neutral line at your premises. Anything below 10v is acceptable.
However.. Sensitive electrical equipment often misbehaves if the Neutral in not well earthed.. Examples are devices that are controlled by remote controllers (garage doors, ceiling fans, TV sets etc)
I recommend that an electrician is employed to strap the Neutral to a quality earth at your DB board.
How can we reduce the voltage between the neutral and ground less than 1V?
Ground the neutral effectively to achieve less than 1 volt or even zero volt between NEUTRAL and GROUND.
In AC systems, there are two kinds of Neutrals. One is from a Wye System where three transformers are connected in Y and the common point is the Neutral. The other kind of Neutral is from a Delta System where one of the three transformers is providing a 120/240 volts in addition to the three phase 240 Volts. The mid-point of the 120/240 Transformer is the Neutral. There are two kinds of Delta Systems: Closed and Open Systems.
In Open Delta System where two transformers are used, one of them can be connected such that it will provide single phase 120/240 volts, similarly, the mid-point of this transformer is the neutral and such transformer is rated bigger than the other. This Open Delta connection is common if only a smaller three phase load is supplied with power and a larger single phase 120/240 volt load is included.
Both Closed and Open Delta Systems are providing three Phase, 240 Volts and single phase 120/240 volts. These two systems provide 180 volts hot legs that might cause technical problems for inexperienced electricians since the leg that provide 180 volts might be mistaken for another 120 volts.
By the way, another system is the Single Phase 120/240 Volts where only one Transformer is used. The mid-point of the 120/240 volts is the neutral.
The National Electrical Code requires that all neutral shall be effectively grounded. What is discussed above is typical household utility voltage standard in the United States and some Countries with U.S. influence on Electric Systems.
What is the voltage between neutral and earth connection in 3 phase power supply?
If the load on the 3-ph system is perfectly balanced , then the voltage between neutral,N and earth, E will be 0. Practically in our 3-ph, 4 wire domestic supply system the loads are not perfectly balanced in all the 3 phases, so there will be currents through different sections of the neutral wire producing an impedance drop (ZI). This causes the voltage between neutral and earth to be present. Higher this voltage more will be the load imbalance.
How can we reduce the voltage between the neutral and ground less than 1V?
On a modern (TT) electrical installation there is a very good reason the neutral isn’t at earth potential.
If it was, there would be no easy way to detect a fault condition in the case where neutral is shorted to the protective earth (as current would be just as likely to carry on flowing through the neutral too).
No potential difference means that certain types of circuit breaker will not work correctly (GFCI/RCBO types).
I’ve tried to keep this answer as “layman friendly” as possible, basically there is nothing to worry about if you can measure a small voltage between neutral and earth, only if it creeps up would it indicate a fault with the earthing of the building.
What is the voltage between neutral and earth in a 3phase system?
There should be ZERO volts between neutral and Earth but there is usually a volt or two. Problem is that although the neutral or STAR point of a transformer is also the origin of the Earth connection, if there is a sudden break in the neutral return to the star point, the load side of the neutral break will rise to near coil voltage of 240 volts in a 415/240 system, due to loads that are switched on, but inoperative due to the break of the neutral cable. I’ll say that again, the broken neutral cable will be near 240 volts above the earth.
What should be ground to neutral voltage?
When there is no load the value should be very close to zero, I’m guessing maybe a volt or two of noise. When the line is loaded then you have the I-R drop of the current in the neutral line resistance. This will make Neutral to ground perhaps as much as 10–15 volts, this would be the high end and more than about 10 Volts you probably need to look at your wiring because you have a problem. Below 10 volts is probably not a problem.
The actual value will depend on the load and the length and the gauge of your circuit wiring in your home.
What is the difference between earthing, grounding and neutral?
Earthing and Grounding are two different simple concepts which people often gets confused. Let me explain both of these things in simpler manner.
Earthing means connecting the dead part (it means the part which does not carries current under normal condition) to the earth. For example electrical equipment’s frames, enclosures, supports etc.
While grounding means connecting the live part (it means the part which carries current under normal condition) to the earth. For example neutral of power transformer.
The purpose of earthing is to minimize risk of receiving an electric shock if touching metal parts when a fault is present.
While the purpose of grounding is the protections of power system equipment and to provide an effective return path from the machine to the power source. For example grounding of neutral point of a star connected transformer.
Ground is a source for unwanted currents and also as a return path for main current some times. While earthing is done not for return path but only for protection of delicate equipments.
Tomi Engdahl says:
https://crsc.ca/wp-content/uploads/2015/12/Neutral-to-Ground-Voltage-Causes-and-Cures-White-Paper-202.pdf
Tomi Engdahl says:
Neutral-to-Earth/ground Voltage- Causes, effects, and solution
https://www.electricalclassroom.com/neutral-to-earth-ground-voltage/?utm_content=cmp-true
Ideally, the voltage measured across the neutral and the earth/ground must be zero. But sometimes there exists some measure of potential difference between them. Here, in this article let us analyze the causes of neutral to earth/ground voltage, its effect, and how to mitigate it.
Modern domestic power sockets consist of line, neutral, and earth connections. The picture shows a multi meter reading the neutral to earth voltage. It can be seen that there is a minute voltage of 0.4V across them. This voltage is very little to cause any adverse effect.
What is the acceptable voltage level between neutral and earthing?
Ideally the neutral to earth must be less than neutral to earth 0V. Neutral is earthed at the transformer end. It could be possible that at the load end, some amount of voltage may present, depending on how far the neutral earthing is, how much load is connected the system, presence of power electronic devices that induces harmonics to the system and the load distribution across the three phases. It is recommended to maintain it below 3V.
Causes of neutral to earth voltages
If your multi-meter indicates a neutral to ground voltage, that could be due to any one of the following causes:
Improper earthing, caused due to loose earthing rods, wire breaks, or corrosion.
Improper earth pits.
If you measure 120V or 230V across the neutral and the earth and 0V between the line and the earth then the line and the neutral wires have been reversed.
Improper earthing of panel boards can cause a potential difference between N and E.
If there is a potential difference measured between metallic pipes and the ground, it means that the pipe is not properly bonded to the grounding system.
Cable insulation damages.
In a three-phase system with neutral, imbalance loading can cause neutral voltages. Unbalanced loads may cause heavy neutral currents.
Short circuits.
The line to ground faults.
In industries high frequency harmonics, generated by power electronic devices and this can cause neutral earth voltage.
Insulation failures and poor body panel earthing.
Effects of neutral to earth voltages
Neutral to earth voltage can be either due to improper wiring or due to improper earthing. In most cases, these voltages do not have any considerable effect on the system if the measured voltage to very small. It might have some effect on the electronic circuits but might not affect some others. Below are the few effects of neutral to earth voltages.
Neutral voltage due to wrong wiring shall be higher and poses a risk of electrocution.
Malfunctioning of electronic devices.
Small neutral to earth voltages can light up LED lights even when switched off.
Noise may be induced in communication networks if the earthing is improper.
Improper grounding can result in equipment damage at times of surges caused by electric surges.
The solution to neutral to ground voltage problems
The solution to neutral to earth voltage issues begins with diagnosing the cause. Ultimately, there can be only two reasons: improper wiring and improper or lack of earth. Once the cause is traced, the problem can be solved. Here are a few steps to fix the issue:
For industrial connections:
If you are engineer or an electrician, you might already know how to diagnose earth faults and fix them. Below are a few additional things that might need your attention.
Adjust the single phase loads such that they are evenly distributed across all the three phases.
Make sure all equipment are properly bonded.
Make sure that there is no insulation failures in the system.
Make sure that the cable terminations at the panel board is proper and the gland plate is properly connected to the earth.
Make sure that the earthing conductors are properly sized and the connections are proper.
Use multiple rods for earthing can provide a parallel path for current flow and improve the earth connection.
Make sure that proper power factor compensation is done.
Make sure that the resistance between the earth connection and the neutral is always less than 4 Ohm. Higher resistance means poor neutral earthing.
Make use of earth leakage relay, Core balance transformers and other residual current devices to detect earth fault.
Tomi Engdahl says:
Causes of Neutral-to-Ground Voltage
and Proper Remediation Methods
https://www.ametekesp.com/-/media/ametekesp/downloads/white-papers/esp-surgex_white-paper_causes-of-neutral-to-ground-voltage-and-proper-remediation-methods.pdf
Effects of N-G Voltage on Electronic Equipment
While measuring N-G voltage is relatively easy, the effects it has on
electronic systems are hard to diagnose because N-G voltages may
affect some equipment and not others. It might even affect a piece of
equipment only if it is connected to another piece of equipment. It
really has to do with the design of the circuitry inside the device.
Troubleshooting the effects of N-G voltages can be difficult. Some
equipment that might be impervious to N-G voltages when used by
itself can be susceptible to N-G voltage and becomes unstable when
connected to other pieces of equipment via data communication ports.
Consider a system where Equipment A has a circuit architecture where
the internal DC power supply and circuitry is isolated from chassis
GROUND by design. One might have no issues if installing it in an
environment with N-G voltage issues. However, Equipment A contains
an RS-232 port for communication with Equipment B. Equipment B
has been designed where its DC power supply is referenced to chassis
GROUND. Through the data communication cable, Equipment A is
now referenced to GROUND which was not intended by the designer,
causing unstable behavior in data communications between the two
pieces of equipment and/or system lockup.
Solutions for N-G Voltage Problems
As N-G voltage problems are caused by internal wiring issues, the best
way to solve the problem is to ensure proper electrical distribution
inside the building. Have a licensed electrician rewire the branch circuit
to your equipment to provide an independent, dedicated set of wires
from the breaker to the outlet. The dedicated circuit should consist of
(3) individual conductors (L-N-G). All conductor’s wire gauges should
conform to recommendations set by the National Electrical Code that
minimizes wire resistance for the specific wire length between the
breaker panel and outlet, as well as supplies the required current to the
electrical load. This may require oversizing the wire 1 to 2 gauge sizes.
Use certified National Electrical Code practices for connecting
oversized wires to wiring devices and circuit breakers. Have the
electrician check to the NEUTRAL connections in the distribution
system, especially at the buss bar in the breaker panel.
There may be situations where the wire from the breaker to the outlet is
just too long for increasing the wire gauge to be effective, or replacing
the wire is not feasible. In these situations, there is an accepted
practice for creating a new NEUTRAL to GROUND bond at the point of
use.
An Isolation Transformer is a 1:1
transformer that galvanically isolates
the source from the load.
When an
isolation transformer is used, it is acceptable to NEC and IEEE
standards to reestablish the NEUTRUAL – GROUND bond that is
found inside the breaker panel. This is the only acceptable method for
bonding NEUTRAL to GROUND downstream from the breaker panel.
In addition to cancelling N-G voltages due to insufficient wire sizes and
load imbalances in systems that share the NEUTRAL connection, it has
the added benefit of cancelling out common mode N-G noise voltage
created by Electro-Magnetic Interference and Radio Frequency
Interference (EMI/RFI). Using an isolation transformer is a good
practice in professional and residential audio/video systems requiring a
very low noise floor to enhance performance.
Tomi Engdahl says:
https://electronics.stackexchange.com/questions/415969/high-neutral-to-ground-voltage-and-other-problems
Tomi Engdahl says:
https://www.fluke.com/en/learn/blog/electrical/diagnosing-power-problems-at-the-receptacle
https://cr4.globalspec.com/thread/30792/Neutral-Ground-Voltage
Tomi Engdahl says:
Clearing Up Neutral-to-Ground Voltage Confusion
Feb. 2, 2007
Because effects from N-G voltage can range from nonexistent to significant, you must learn to identify true common-mode events
https://www.ecmweb.com/power-quality-reliability/article/20890303/clearing-up-neutral-to-ground-voltage-confusion
Power quality questions continue to revolve around one underlying issue related to electronic equipment: its ability to withstand the effects of electrical interference. If equipment sensitivity was always well known and defined, then we would have few, if any, doubts. In this perfect world, we would also know with a high degree of certainty that a voltage sag of a known amplitude and duration would have either no effect or a significant impact on equipment. Unfortunately, we seldom are privy to such information. Therefore, the possible effects of neutral-to-ground (N-G) voltage are often left up in the air.
Tomi Engdahl says:
neutral to earth voltage, and high voltage Concerns
https://www.youtube.com/watch?v=yIAGecSyxEg
neutral-to-earth voltage, and high voltage Concerns
It’s important to clarify that neutral-to-earth voltage, in itself, doesn’t inherently damage equipment more than high voltage. Both situations can create problems, but the damage and likelihood differ. Here’s a breakdown:
High Voltage:
Direct danger: Exceeding the intended voltage rating of an appliance will directly stress its components, leading to overheating, insulation breakdown, and even fire. This risk is significant and why most equipment has built-in voltage protectors.
Neutral-to-Earth Voltage:
Subtler effects: This refers to a voltage difference between the neutral and earth wires, which should ideally be zero. While small imbalances may go unnoticed, larger ones can cause:
Ground currents: This can lead to unintended paths for current flow, potentially causing overheating in wires and components not designed for it.
Electromagnetic interference (EMI): Fluctuations can create EMI, disrupting sensitive electronics and causing erratic behavior.
Component stress: Depending on the design and tolerance of equipment, prolonged exposure to even small neutral-to-earth voltage can contribute to premature wear and tear.
However, it’s important to consider the magnitude and context:
Small values (up to 5V): Often considered tolerable for most modern equipment, especially with built-in protection.
Medium values (5-20V): May start causing issues like EMI and ground currents, depending on equipment sensitivity.
High values (above 20V): Can lead to more significant problems like component damage and overheating, becoming similar to high voltage in impact.
Therefore, neutral-to-earth voltage alone isn’t the sole deciding factor for damage. High voltage directly exceeds equipment ratings, while neutral-to-earth voltage creates other concerns, potentially leading to issues like overheating or component degradation over time.
So, what to do?
Monitor and investigate: If you suspect high neutral-to-earth voltage, get it checked by a qualified electrician. Identifying the cause and correcting any underlying issues (e.g., faulty wiring, unbalanced loads) is crucial.
Invest in protection: Surge protectors can offer some protection against sudden voltage spikes, but may not address chronic neutral-to-earth voltage issues.
Remember, electrical safety is paramount. If you have any concerns, always consult a qualified electrician for diagnosis and solutions.
Tomi Engdahl says:
How to test voltage between neutral and ground
https://diy.stackexchange.com/questions/184255/how-to-test-voltage-between-neutral-and-ground
I’m not an electrician. Per, https://www.apc.com/us/en/faqs/FA158817/, I want to test the outlets in a room for the following:
Overloaded neutral wire (>5 Volts AC measured between Neutral and Ground).
Reversed polarity (hot and neutral wires are reversed).
Missing ground wire. (Note: this also includes using a 3 prong to 2 prong adapter)
I’ve found simple plug-in devices on Amazon that I’m confident can test for #2 and #3, but what sort of tool do I need for #1, to measure the voltage between Neutral and Ground?
A simple multimeter can help you verify all three, as well as many other voltage related troubleshooting. It’s a real must have for… anyone really.
To measure between neutral and ground, you will set the meter to AC voltage, 200V range, and stick one probe into the neutral slot of the socket (the wider slot for USA standard sockets, on the left if the ground hole is on the bottom) and one probe into the ground slot (the D shaped hole).
A common digital voltmeter will do everything you need. Quality should be reasonable since you will be sticking this thing in electric sockets.
You should be wary of the 3-light testers. While they do provide a simple pass/fail test for most outlets, the legend describing the likely faults for “fail” conditions are misleading and wrong. Many hours have been wasted because people believed the legend’s interpretations of the fault. I just saw a labeled “hot-ground reverse” which was in fact a lost neutral. (night and day, like reporting a bad fuel injector when the problem is actually a flat tire).
Tomi Engdahl says:
Why are we not allowed to measure voltage from the neutral wire to the ground wire in an electrical wiring system?
https://www.quora.com/Why-are-we-not-allowed-to-measure-voltage-from-the-neutral-wire-to-the-ground-wire-in-an-electrical-wiring-system
Measuring voltage from the neutral wire to the ground wire in an electrical wiring system is not recommended because it does not provide meaningful information about the electrical system’s operation.
The neutral wire and the ground wire serve different purposes in an electrical system:
Neutral wire: The neutral wire is part of the circuit and carries the return current back to the power source. It is designed to have the same voltage potential as the earth ground.
Ground wire: The ground wire provides a low-resistance path to earth ground. It is used as a safety feature to divert any fault current away from the user in the event of an electrical fault or short circuit.
Measuring the voltage between the neutral wire and the ground wire would typically result in a very small voltage difference, often less than 1 volt. This small voltage difference is normal and does not indicate any issues with the electrical system.
The more meaningful voltage measurements in an electrical system are:
Line voltage (hot wire to neutral wire)
Voltage between hot wire and ground wire
Voltage between neutral wire and ground wire at the service entrance
These measurements can provide valuable information about the electrical system’s performance, grounding, and potential safety issues. Focusing on these standard voltage measurements is generally more useful for troubleshooting and analyzing the electrical system.
If you can measure voltage from Ground to Neutral, then they are not bonded correctly (at least to the National Electrical Code (United States)).
I was very tempted to join the fun here, but am opting for a straight answer. There is no reason you can’t measure the voltage between ground and neutral. It usually does not tell you what you want to know. With a load on the circuit, there will be a voltage drop in the neutral but none in the ground. Neutral and ground are connected together at the breaker panel, so the difference there is zero. With a heavy load, like a window air conditioner or space heater, the difference might exceed one volt at the outlet. Much more than that might indicate a connection problem between the panel and the test point and should be investigated. I’m assuming residential wiring where wire distances are under 50 feet. At the RCA Solid State facility where I worked, there were outlets hundreds of feet from where the power came into the building and neutral to ground voltages over two volts were not unusual.
I have to wonder who disallowed you to measure the voltage between the neutral and equipment ground and what the heck they were thinking.
There are reasons why you’d want to take a voltage reading between the neutral and ground. The primary objective is that you want to not have a voltage between the two. There will sometimes be a small 1 to 2 volts or so between the wires but that’s due to voltage drop. That’s normal. Anything higher than that and you’ll want to investigate why there’s a voltage on the neutral in respect to ground.
Seriously, when testing electrical work, check voltages across all pairs of wires. This will give you the most informed and fullest picture of where things stand. Don’t listen to anyone that says not to do so. They’d be a hack for saying so.
Not Allowed? It is actually something people measure. The neutral wire carries current and therefore will have a voltage drop along its length. Sometimes you want to know what that drop is. A way to measure this is to place an AC volt meter across neutral to ground.
It has nothing to do with what you are “allowed to do,” it’s a matter of what works most dependably and safely.
As an ex electrician, the most straightforward answer is, the neutral will not have any measurable voltage unless a device (lightbulb, toaster, TV, etc.) is turned on, completing the circuit between the “hot” wire and the neutral bar (or ground bar) in the electrical panel.
So unless at least one outlet (typically there are 8–10 outlets/receptacles on a normal household circuit) is in use, using a two-pin circuit tester between the neutral and the ground will detect nothing. For most people, using the three-prong, plug-in type of circuit tester is the best solution. Easy, safe (no shocks), and reliable!
Its zero where the ground and neutral are bonded together. The bond it supposed to be one point at the source end of the circuit (the service usually). The neutral is a load carrying conductor even though it reads a small voltage to ground under load. It will be show voltage potential to ground of a small voltage if there is a normal load on the circuit as you measure points between the source end and the load end. This is because the neutral really has full load current in it. The resistance of the wire causes a voltage to ground due to the current of the load going through it. That voltage will be highest at the load end of the circuit. If the neutral opens on an energized circuit the load end of the break will go to full supply voltage up to the break point potential with the load connected. Be extra careful when troubleshooting an open neutral!!!
The ground wire is at ground potential if functional. Its only purpose is to cause a hard fault if the circuit should happen to come in contact with something not part of the circuit. An example might be a motor housing. It does this by draining the dangerous potential from the contact point back to the source through the safety return path it forms. That’s the ground wire’s only purpose. It must be sized big enough to then cause a breaker to trip if the circuit is in trouble. This keeps the motor housing of this example from becoming a lethal shock hazard.
All that said, if you measure the voltage between the neutral and ground the meter may pass a few thousandths of an amp from what point you are measuring to ground just to read that voltage. If the circuit you measure is protected by a ground fault interrupter breaker (GFI) the measurement itself may cause the breaker to trip as the meter then becomes a partial ground fault.
Again,I will refer to the Australian standards because their wiring rules applies to me, since we have an M.E.N. (multiple earthed neutral) Link inside of the main switchboard or circuit breaker enclosure including the metering system there should be Zero volts between earth & neutral since the M.E.N. link ties the neutral & earth links & conductors together so that the circuit protection devices can operate in the event that an earthed enclosure becomes live.
So, we’re not legally allowed to have an earthed enclosure where the enclosure is live due to an active conductor,etc shorting out to earth,the protective devices are supposed to take the Active out of circuit in an event where the earth fault occurs !
There is no such rule that one can not measure the voltage from neutral to ground. We do measure it often to ensure that neutral is properly grounded and there is no voltage in between the two. In fact there should not be any voltage in between 4wire neutral grounded system as neutral of the transformer of Delta star transformer is grounded other by solid earthing to get a low domestic supply of 220 volt in India for residential purpose.
There are different grounding arrangements and not all of them are connected to the neutral back at the meter. In TT earthing the ground wire is only physically connected to the live/neutral circuit when there is a short to ground fault. The only reliable voltage reading is accross live and neutral at the main switch.
Besides that you don’t want to be deliberately bridging the live wire to the ground wire for any reason. The gound wire is bonded to anything metal in the premises like plumbing or central heating pipework.
I have a plug-in device which checks for wrong or missing wire connections but also contains two volt meters. It has a little screen which displays the hot-neutral voltage and the neutral-ground voltage. It’s useful for checking voltage at the end of a long run and can help diagnose neutral-to-ground leaks.
You are allowed to measure voltage from any point to any other point. There is no restriction imposed on making measurements. Any voltage measurement (using a high resistance voltmeter) does not tamper with the working of the circuit in any perceptible way. However, do not measure the current between two points of any circuit unless you know exactly what you are doing. For example you can measure the voltage between live and neutral. Now while the measurement device has one prod touching live and the other touching neutral, lets switch the device to measure current instead of voltage. No marks for guessing what would happen!!
On many home systems, neutral and ground are attached to the same bus in your breaker box. They are for all practical purpose the same wire. In the last decade or so, ground goes to ground and neutral to the neutral bus. Unless there is a problem, there should not be any voltage there either.
One quick follow-up. There is NO NEUTRAL in a 120 volt circuit. In a 120 volt circuit, the white wire is NOT a neutral.
The NEC officially designates it as a “grounded” conductor. (The black wire is designated the “ungrounded” conductor. Green or bear, is the “grounding” conductor).
A neutral conductor only carries the unbalanced load in a 240 volt circuit. (In a 120 volt circuit, the white wire carries 100% of the load; as does the black conductor).
Common misconception, but calling a 120 volt circuit’s white conductor a “neutral”, doesn’t make it so.
A neutral is allowed to be reduced in carrying capacity (can be reduced in size) in comparison to the phase conductors. In a 120 volt circuit, the white is sized for the full load permitted by the branch circuit rating (same size as the black or red conductors).
Ordinarily, there will be “0” voltage difference between a Neutral and Grounded conductor. As others have noted, the two wires are bonded (tied) together at either the transformer or the main breaker panel.
However, there may be exceptions found in troubleshooting a faulty circuit. The most commonly-found one, If there IS voltage between the two, is that somewhere in the wiring the Neutral wire is broken/disconnected – maybe cut, poor make-up in a wire nut, or not landed in the panel, etc. This will have a “floating” neutral and the result may be damaged appliances or equipment because of unwanted voltage elsewhere in the circuits. The circuit needs to be searched to find the break, turned off once found, and repaired.
The other situation is more specialized: large inverters feeding rooms. I found this one because sensitive audio equipment was on the circuit and the audio technician asked me to find out why it was picking up a low “hum.” The inverter output had a neutral that was “floating” above the ground. The equipment was picking up the ~2 volts of difference as hum that was being recorded. The solution was to move the circuit to a “regular” power source, not the inverter.
So, in a perfect world, there won’t be any difference. In the real world, it can be found and is usually a bad problem.
Tomi Engdahl says:
Checking Voltage from Neutral to Ground
https://www.youtube.com/watch?v=t-Epjx5wN2w
Tomi Engdahl says:
Measuring neutral to ground with the power on will give some strange readings if there is a load on that circuit. It sees the voltage drop from the current flowing and goofs up the resistance measurement.
Tomi Engdahl says:
Voltage between ground and neutral increases as resistance increases – as the line voltage drops, neutral to ground voltage increases. It’s normal to have some, but if it’s excessive it can be a problem. Normally you’re looking for no more than 5% volt drop which would be about 6V.
Tomi Engdahl says:
Identification of the source location Neutral to Earth Voltage (NTEV) rise on the commercial building
https://www.sciencedirect.com/science/article/pii/S2090447919300589
The Neutral to Earth Voltage (NTEV) rise are categorised one of power quality (PQ) problems in the commercial building. Usually, the NTEV rise occur due to the neutral conductor problems. Theoretically, the neutral problems give an adverse effect to the network system where the phase voltage and harmonic distortion become more imbalance, heating on the conductor cable, and the electrical appliances prone to damaged. This paper presents a novel technique to identify the source location of NTEV rise in the commercial building due to the loose and open neutral conductor. The proposed technique able to identify the problems that occur either on the upstream or downstream location which respected to the measurement points. In addition, the characteristics of neutral problem due to the loose termination and open conductor are also explored based on the 13-nodes distribution system. The results show the source of NTEV rise can be correctly identified.
Power quality (PQ) problems especially Neutral to Earth voltage (NTEV) rise in commercial buildings has become more complicated issue in recent years. Usually, the NTEV rise is caused by the neutral conductor problem. Theoretically, the neutral conductor problems give adverse effect and hazardous to electrical network systems, electrical appliances, humans and also animals [1], [2], [3]. The effects of open conductor and loose termination in the distribution network is introduced in [4], [5], where the system network is exposed to unsymmetrical and damaged faults, and fire could easily occur. Referring to the regulation IEEE std 1965, the tolerable NTEV magnitude in electrical network should be below than 10 V [6]. However, it’s magnitude can exceed the benchmark value of 10 V due to the problems which have related on the neutral conductor such as loose termination, open conductor, cable damage, and improper wiring. Thus, the source location of NTEV rise should be identified where the effort of conservative work to solve the problems on the neutral conductor can be minimized quickly.
Tomi Engdahl says:
Open neutral or broken neutral on a service transformer or service cable into a facility can result in serious overvoltage or undervoltage. Relative magnitude of loads on each phase and return path resistance determines which phase experience over voltage or undervoltage.
https://voltage-disturbance.com/power-quality/open-neutral-voltage-fluctuation-and-stray-voltage/
Multi point neutral grounded System: In multi grounded systems, open neutral ‘forces’ return current to flow through earth electrode back to service transformer. This ‘earth current’ flows from customer to earth and can take many paths some of which could be through ground-neutral connection of other customers fed from same service.
Panelboard Neutral-Ground BondFig 1b: Panelboard Neutral-Ground Bond
Current can also flow through CATV shields, metallic water, gas pipes that are typically connected to ground at each customer’s panel. This can cause local or remote ground potential rise (GPR) resulting in stray or tingling voltage on grounded surfaces such as refrigerator handles, control panel enclosure etc. This issue is discussed later in this article.
When neutral wire gets accidently disconnected from transformer as shown in figure 2, neutral return current has no choice but flow through physical earth (ground) to reach back to transformer [source]
Open Neutral and Ground Potential Rise
During open neutral condition, return current is forced to flow through ‘earth’. This leads to two things that is of interest:
Rural Electric Distribution
Local Ground Potential Rise (GPR)
Current flowing through local earth rod will create local ground potential rise, magnitude of which will depend on current and earth resistance. Say earth resistance is 20Ω and 5A flows which results in 100V of GPR. All the grounded objects (ex. refrigerator) in that customer premise will also be elevated to 100V potential. A person standing on kitchen floor (at earth potential of 0V) touching refrigerator will experience 100V of shock.
Remote Ground Potential Rise (GPR)
Earth currents can ‘leak’ through ground-neutral connection of neighboring customers. This can cause local ground potential rise (GPR) at a non-faulted customer premise that is fed from the same source transformer. This is manifested as ‘tingling’ voltage or stray voltage when person touches on grounded appliance like refrigerator door handle. Often customer will call an electrician and will not find an issue at his location. Until and unless electric power company finds the location of open neutral and fixes the issue, tingling stray voltage issue will persist.
Read: Voltage Regulation
This is especially a problem in many European or Asian distribution systems where a single distribution transformer powers hundreds of customers. An open neutral on any one customer can cause tingling voltage at many other ‘innocent’ customer locations. Magnitude of tingling voltage will depend on earth resistance at that customer service and amount of ground current.
Note that when earth resistance is zero ohm then no voltage variation is seen as expected. This is because earth is functioning as neutral conductor with no resistance.
Cable TV shield is connected to electrical groundFig 6: Cable TV shield is connected to electrical ground
If there are any alternate ground paths like CATV shields, telephone lines, water, gas lines etc. then majority of neutral current will flow through these paths instead of earth. Neutral current will flow through these alternate paths, get to neighbor’s Ground-Neutral bond and back to service transformer.
In the process cable TV shield, telephone wires will likely get damaged. Remember that CATV shields are grounded at each customer and thus is a good parallel path for neutral current, same is the case for metallic water, gas lines and telephone grounds. A severely burned CATV shield is usually is good indication of open neutral. It is not easy to detect and troubleshoot open neutral condition when one transformer feeds multiple customers. Any one of them could be experiencing open neutral.
Single point neutral grounded system: This is not a common practice where neutral is grounded (earthed) only at the transformer however such installations do exist.
Open Neutral Damages
Over voltage due to open neutral condition can lead to surge arrestor (MOV) failure, insulation failure, transformer overheating and possible fire.
MOV Damage due to open neutralFig 9: MOV Damage due to open neutral
Under voltage due to open neutral condition can lead to air conditioning or refrigeration loads to shut down, motor overheating etc.
Customers can purchase and install automatic voltage protection devices at their service to prevent damages resulting from open neutral condition. These devices should detect an unbalanced voltage condition and open the circuit. When voltage is restored, the circuit should be capable of resetting automatically.
Ground Potential Rise [GPR]
Ground potential Rise (GPR) per IEEE Std 80 is defined as “The maximum electrical potential that a substation grounding grid may attain relative to a distant grounding point assumed to be at the potential of remote earth. This voltage known as GPR is equal to the maximum grid current times the grid resistance”.
https://voltage-disturbance.com/power-engineering/ground-potential-rise-step-and-touch-potential/
Tomi Engdahl says:
How serious is a Loss of Neutral?
https://www.sollatek.com/loss-of-neutral/
A loss of neutral in the grid isn’t a cause for concern, however, there are places around the world where this scenario can become a reality with potentially life threatening consequences. A broken neutral is an electrical fault that can have a devastating impact on households and businesses. As power flows in and out of your premises from a distribution network, it enters via the active cable and leaves via the neutral cable within a circuit. If the neutral cable is broken, it can cause an influx of voltage that can damage electronic equipment and, in extreme cases, cause excessive levels of voltage. If there are problems with the neutral line, electricity may travel through different paths to escape. This can be though the ground wire, earth or any conductive material that is in contact with the circuit, resulting in unpredictable and dangerous conditions such as overvoltage, unfixable equipment damage and electrical shock hazards.
What Causes Loss of Neutral?
Loss of neutral is a serious condition. A break in the neutral conductor will simply result in a loss of the energy supply which leads to an Irrespective of load balance.
There are a number of situations that can cause a loss of neutral, however firstly we must understand what is meant by “loss of neutral”. In a three-phase electrical system, the neutral point serves as a reference point for the three phases. It is connected to the center point of a 3 phase transformer, and is grounded to provide a path for fault currents. A loss of neutral occurs when the neutral connection in the circuit becomes disconnected or broken which will result in an unbalanced voltage and current distribution in the system. Voltage fluctuations and extremely high voltage will most likely occur which can result in the damages of electrical equipment that can result in electrical fires.
Effects of Loss of Neutral
In the event of loss of neutral, the single-phase voltage will rise to the three-phase level subjecting your equipment to >400V instead of 230V. This results in over voltage and can be catastrophic for your appliance. Any electronic appliance connected to the wiring will most likely be damaged due to overheating.
If there are problems with the neutral line, electricity may travel through a different path. This may be via water pipes, stoves and metal taps or any other conductor of electricity. This can be very dangerous, and you may suffer a serious electric shock if you touch something where electricity is present.
Tomi Engdahl says:
Neutral-to-Earth Voltage (NEV), NEC 2020, (44min:40sec)
https://www.youtube.com/watch?v=a_nv_Q9WbeE
Thanks for watching, in this video Mike Holt discusses Neutral-to-Earth Voltage (NEV).
Tomi Engdahl says:
Finding a bad neutral on a Service – Raw footage
https://www.youtube.com/watch?v=fpAD80FPNac
Tomi Engdahl says:
https://electrical-engineering-portal.com/floating-neutral-impacts-in-power-distribution
If the is opened, broke or lost at either of its source side (Distribution Transformer, Generator or at Load side – Distribution Panel of Consumer), the distribution system’s neutral conductor will “” or lose its reference ground Point.
If the is opened, broke or lost at either of its source side (Distribution Transformer, Generator or at Load side – Distribution Panel of Consumer), the distribution system’s neutral conductor will “
” or lose its reference ground Point.
The floating neutral condition can cause voltages to float to a maximum of its Phase volts RMS relative to ground, subjecting to its unbalancing load Condition. Floating Neutral conditions in the power network have different impact depending on the type of Supply, type of installation and Load balancing in the Distribution.
or would damage to the connected load or create hazardous at equipment body.
Tomi Engdahl says:
https://c03.apogee.net/mvc/home/hes/land/el?utilityname=elpaso&spc=pq&id=3269
Stray Voltage Sources
The most common source of stray voltage is an elevated neutral-to-earth voltage (NEV) at the service panel. Neutral-to-earth is an elevated voltage on the neutral bus when that voltage is measured relative to an electrode placed in the earth. Neutral-to-earth voltages are a direct and unavoidable consequence of the mechanisms used to distribute electrical power. Even when wiring is up to code, neutral-to-earth voltages may be sufficiently high to cause stray voltages. Many times, elevated neutral-to-earth voltages are caused by such things as:
Faulty electrical equipment,
Improper or faulty wiring, and
Induced or coupled voltages.
Often, these sources result in increased neutral-to-earth voltages; and the elevated neutral-to-earth voltages, in turn, lead to stray voltages.
Damaged equipment and damaged or faulty wiring create the potential for a problem known as ground faults. Ground faults are those conditions where electric current flows to the earth and thereby creates a neutral-to-earth voltage. Ground faults caused by wiring that is partially shorted to ground could also result from connections that are damaged or wet.
Properly grounded equipment has a green insulated or bare wire that safely conducts the fault current back to the electric panel. If however, the ground wire is broken or not installed, or the connections are corroded, there is little or no path for the fault current which causes neutral-to-earth voltage.
Tomi Engdahl says:
https://www.toppr.com/guides/physics/difference-between/earth-and-neutral/
Tomi Engdahl says:
TT system neutral to earth voltage
https://engx.theiet.org/f/wiring-and-regulations/29903/tt-system-neutral-to-earth-voltage
Minimum would be 0.0V. Maximum could be almost anything (up to Uo). The classic problem with TT systems is that during an earth fault, all the fault current returns via the source electrode, multiplied by the soil resistance, can give a very substantial potential difference between true Earth and the transformer’s star point (i.e. supply N) – the exact figure depending on the resistance of the consumer’s electrode (and any parallel paths – e.g. bonding to extraneous-conductive-parts) as much as the source electrode itself. If the fault isn’t cleared promptly (e.g. due to a faulty RCD or just because it’s on the distribution network) that N can reman at a hazardous voltage for a long time. Hence all isolation devices need to open N as well as L on TT systems.
There are no recommendations of N-PE voltage from safety standards.
However, there are recommendations for EMC (although not from standards) – which have, in some cases, been as low as 5 to 10 V.
There is a solution to this … although not without cost … which is to use transformers to permit the filters to perform as they would in a TN system. This is recommended in the standards for VSDs, and also in BS EN 60204-1. The transformer secondary neutral is earthed, thus forming TN-S circuits in the TT installation.
On a single phase system, 11v is probably on the borderline of being acceptable. In contrast, by the time it reaches 20-50 you almost certainly have an unrealised fault somewhere. The thinking is as follows – the voltage drop in the LN loop may be right at the limit, as high as ~ 10% of supply (20 odd V) Half of this is lost on the live on the way out, and the other half in the neutral wire on the way back. TN-S would be the same, for the same reason. However this is neutral to true earth voltage – there may be an additional offset between true earth (an electrode far away from the near field of your local one and carrying negligible current) and your TT installation electrodes – if there are significant currents running into the electrodes then the metal work of the whole installation may also be a few volts off terra-firma earth voltage. It may be worth installing a test electrode, or even a garden fork or un-insulated screwdriver in the ground a few m from the building and seeing how far off the building earth voltage that is.
Be aware in a TT system can go a bit wild if your user electrodes are lower resistance than the ones at the substation. – if this happens, when the fault to earth comes on, the voltage is divided between the series connection of your electrodes, and the substations transformers electrode(s).
Normally we assume the substation neutral voltage rises a few volts, and most of the 230V or whatever, is dropped in the earth around your your local one, but it can be the other way about – so that the phase you have shorted to ground is nearer true earth if your earth is good enough, then the the whole transformer, neutral and everyone else’s supply bounces up to near 230V for the neutral and upto about 400V for the other phases. So while you have the test electrode in the lawn or flower beds, also check the phase voltage/voltages. you may not have a fault, but your neighbours just might.
Mike.
Just to be clear, there is no limit in BS 7671 on touch-voltage to the general mass of Earth in this regard … only in terms of selection of protective devices and combined resistance of protective conductor and earth electrode alongside this.
Which are explicitly co-ordinated so that a touch voltage of >50V cannot persist – reg. 411.5.3 (ii).
The touch voltage can of course exceed 50V for very short durations, but that’s the same with supplementary bonding where the fault current exceeds Ia.
Which are explicitly co-ordinated so that a touch voltage of >50V cannot persist – reg. 411.5.3 (ii).
Not disputing that, although only true in some circumstances, such as RCDs in TT systems … it’s unlikely that a high touch-voltage will persist in other cases for faults in the installation, ignoring PE faults and leakage currents.
The reason for pointing this out, is that there’s a common misunderstanding that BS 7671 actually serves to limit touch-voltage values (although as you correctly point out, for the most part, it’s aims to limit the time those touch-voltages may persist).
Tomi Engdahl says:
https://shishirameng.com/why-1-5-v-to-3-v-voltage-between-neutral-earth-electrical-neutral-neutral-leakage-problems/
Tomi Engdahl says:
https://en.wikipedia.org/wiki/Stray_voltage
Tomi Engdahl says:
https://zandz.com/en/news/20210717/is-voltage-between-the-neutral-and-grounding-acceptable/
http://www.ste.lanera.com/strayvoltage/strayvolt/sect2/file32g.html
Neutral-to-Earth Voltage
The voltage measured between the neutral conductor (or a ground lead connected to the neutral conductor) and a remote point on the earth is the highest gradient voltage possible in most cases. Neutral-to-earth voltage may be measured either on the supply circuit (also known as the utility or primary neutral-to-earth voltage) or on the utilization circuit (also known as the customer or secondary neutral-to-earth voltage).
The neutral-to-earth voltage is a special voltage gradient measurement in the earth.
Neutral-to-earth voltage is not stray voltage. This is an important difference. Stray voltage is a voltage gradient measured between two points that a cow may contact at the same time (two nearby steps in a stairway). Neutral-to-earth voltage, on the other hand, is a gradient measured over a distance too great for a cow to reach. Neutral-to-earth voltage is the maximum gradient. Measuring neutral-to-earth voltage typically involves locating a reference point on the earth far from the area of concern and outside of the electrical system’s influence. Usually a cow cannot contact the neutral conductor, or some object connected to the neutral, and a remote point on the earth at the same time and is therefore not exposed to neutral-to-earth voltage.
The neutral-to-earth voltage changes slightly from location to location on the neutral system. The resistance of the wires and connectors allows for these slight and regular changes in voltage along the neutral conductor.
Locating the reference ground rod can be a difficult task. If not done properly, considerable variability and errors in measurement may result.
Some portion of the neutral-to-earth voltage appears on all metallic structures that normally are bonded to the farmstead neutral system (i.e., waterlines, stanchion pipes, etc.). Many of these structures are the grounding electrodes that allow current to flow from the neutral to the earth or vice versa
Tomi Engdahl says:
Acceptable voltage between earth, Line,Neutral – Single Phase
https://diy.stackexchange.com/questions/167020/acceptable-voltage-between-earth-line-neutral-single-phase
5
I have a 240V+-10V 2 Wire Single Phase (UK) supply with TT earth bonding (earth rod).
Normal case:
Live-neutral: around 240v
Live-earth: around 240v
Earth-neutral: around 0v
With neutral and live swapped:
Live-neutral: around 240v
Live-earth: around 0v
Earth-neutral: around 240v