Index

Electrical Wiring Surge Suppression

    General information

    Spikes, surges, zaps and transients are all terms used to describe temporary over-voltage power line disturbances. Today's computerized appliances and electronics can be damaged or destroyed by over-voltage surges or spikes. Classic surges are 8/20 microsecond events. Any electronic device that contains a microprocessor or other complicated is susceptible to damage from transient voltages. Most surges occur when devices with motors - hair dryers, refrigerators, water pumps shut off. Suddenly the energy these devices were consuming is diverted elsewhere in the form of excess voltage. Surges also happen when the electric company switches power from one geographic area of the grid to another as supply and demand in the region changes. Thunderstorms and lightening are the most dramatic and destructive causes of power line problems. Typically around 60% of all electrical surges or transient voltage activity is generated within the home. Surges are caused by elevators, air conditioners, vending machines, copiers, large computers, even lights turning on and off will cause rushes of power and transient voltages back up the line. The rest of the problems (40%) are generated outside the home or office by events such as lightening, utility grid switching, line slapping, mis-wiring, etc. Surges can be viewed as ideal current sources; not voltage sources. Incoming surge will increase voltage as necessary to get tothe appliance or earth ground. But surge protection is aboutmaking a lower voltage connection to earth. Less voltage(because current is shunted to earth on a low impedanceconnection) means a surge (now at less voltage) will not seekalternative destructive paths through appliances. But toomuch impedance to earth ground (such as through wallreceptacle outlets) means the surge must find destructivepaths via adjacent appliances. This is basic circuit theory. One must display knowledge of basic concepts such as impedance, common mode transients, and etc to make a credibleclaim about surge protection. Surge disturbances can be addressed with transient voltage surge suppressors (TVSS). Transient Voltage Surge Supressor, they have many forms ofconstruction and have one function. To reduce the chance of a voltagespike damaging the equipment that is connected to it. They havedifferent ratings in number of Joules dissapated, bigger numbers arebetter, to a point. The typical devices used as shunting element are voltage sensitive.This means that at normal voltage they are very high impedance (Opencircuit). When a surge reaches the voltage at which the deviceactivates, the device goes into low impedance state (short circuit).As soon as the voltage drops to normal, the device stops conductingand goes back into open circuit state. This clamps the voltage at thefiring voltage of the device during a fault condition.Surge protectors do not stop, block, or absorb surges. Theyare called shunt mode devices for good reason. Their job isto simply shunt (connect, distribute, short) a surge from onewire to all others.To work effectively they need to be connected to ground very well with a short wire. No earth ground means no effective surge protection.The reason why a typical plug-in protector has no effectiveearth ground connection (via green safety ground wire or whiteneutral wire) is that wire has impedance. A 50 foot 20 ampwire measuring 0.2 ohms resistance may also be 130 ohmsimpedance to a surge current. Sufficient to safety ground 60Hz power (20 amps times .02 ohms is less than 1 volt) butinsufficient to earth a surge (100 amps times 130 ohms is13,000 volts).The reason why a typical plug-in protector has no effectiveearth ground connection (via green safety ground wire or whiteneutral wire) is that wire has impedance. A 50 foot 20 ampwire measuring 0.2 ohms resistance may also be 130 ohmsimpedance to a surge current. Sufficient to safety ground 60Hz power (20 amps times .02 ohms is less than 1 volt) butinsufficient to earth a surge (100 amps times 130 ohms is13,000 volts). A surge protector with no short, dedicated, and independentconnection to earth ground can mean sometimes more problems. The plug-in surge protector can provide the surge with more paths to findearth ground - possibly destructively through adjacent appliances. In very small surges, the plug-in adapter might help because the current with those paths on small surge case are not very huge. But when a large surgew gets in, large scale damage can occur. A good quality surge supressor notes the critical importanceof earthing. A surge protector is only as effective as its earth ground. For effective TVSS, the devices have to be installed at the service entranceor very close to it, not where equipment is connect to the wall sockets. There are surge suppressors which fit to wall sockets, but those are nowhere that good than a proper TVSS installed to service entrance. This applies to both mains power, telecommunication and radio/TV services. Those surge suppressors that are connected service entrance work best on protecting the whole house form powerful surges from external sources. The surge protection capability of the protectors that go to the outlet is less, but can help to fight agains in-house power surges. For successful lighting protection for that you need a lightning arrestor system that makes sure that the the lighting does not hit directly to your equipment. Lightning seeks earth ground. Divert lightning to earthbefore it can strike your building and equipment. Well proven by centuries of experience.If lightning finds acircuit path to earth via household electronics, then surgedamage result. Again well proven is to earth the surge, atservice entrance, before surge can enter a building. This kind of devices are called 'whole house' surge protectors.A surge protector is only as effective as its connection to surge protection - earth ground. No short connection to earth ground (which isthe problem with plug-in or point of use surge protectors)means no effective connection. A properly installed and grounded surge protector can stop the surge or at least reduce it considerably so that damages are limited. Surge protectors are classifed into grades, classes and work in differentmodes, based on their design, scale, type of protection.Suppression devices have all their limits in protection they can give. Transient Voltage Surge Supressor will not stop the effects of direct lightning. Direct lughting hits are fatal, and it is pretty impossible to completely protect against them. A lightning bolt can carry as much as 30,000 amps. Even a resistance of one tenth of an ohm will drop 3000 volts, and the resistance of ground is typically significantly higher. The peak voltage drop can be calculated from the formula: E = L di/dt; where L is the total inductance of path (in uH); di is 18,000 amps (average strike current, abbreviated 18kA); and dt is 2us (rise time). When selecting surge protection devices you need to condier what kind of equipment you are protecting. There is huge difference if the equipment is connected only to one one place with one-link(like only cord to mains outlet) or to two different places (like phone line and mains connection, referred as two-link connection). Examples of one-line connection appliances include TV with "rabbit ears" antenna, portable radio receiver, table lamp and computer with no modem nor remote accessories. A computer with modem is a two-link system, and so is every telecom equipment powered with mains power and connected to telephone line.VCR or TV with connection to common antenna networks, cable TV or satellite dish is also a two-link device. Surge problem with two-link appliance is that a surge coming in from one of the two systems (power or communications) can damage the appliance, because of a difference in the voltage between two systems when the surge occurs. If you have a two-link system, it is a good idea to find a special type surge protector against the problem. A simple solution to the problem of voltage differences for two-link appliances is to install a special surge protector that incorporates, in the same package, a combination of input/output connections for the two systems. Each link, power and communications, is fed through the protector which is then inserted between the wall receptables the input id the appliance to be protected. This type od surge protector is readily availavle in computer and electronics stores. A proper grounding is important for proper lighting surge protection. It is always dangerous to have independent earth grounds due to aphenomenon called ground bounce. All grounds have to be tied to acommon point to earth ground using special very thick bondingconductors that are low impedance. Some protector makers don't just sell thedevice, but also an insurrance with it. If anything is damaged, they'll pay the damages.

    Mains surge protection

    The effectiveness of the multiple earth neutral wiring forlightning protection is quite limited. In multiple earth groundingthere is a ground rod at the service entrance panel of the buildingand there are other ground rods connected at other buildings to theneutral in a similar manor. But as far as lightning isconcerned the wire between those ground points has too much inductance to looklike much of a ground to lightning Any appreciable length of ground wirelooks like a large inductor to the lightning (most energy at DC to 1 MHZ).Then don't forget that the hot wires carrying the ac are not grounded.Lighting facts from Polyphaser "grounds for lightning and EMP protection" book:The average lightning strike will have a peak current of 18kA for thefirst impulse (stroke) and less (about half) for the second and thirdimpulses. Three strokes is the average per lightning strike.50% of all strikes will have a first strike of at least 18kA, 10% willexceed a 65kA level and only 1% will have over 140kA. The largest strikeever recorded was almost 400kA.Disconnecting everything when a storm is approaching is of course one way toavoid damage but that doesn't always get done. There are many "plug in" surge devices sold. They are not veryeffective for proecting agains direct strikes. The biggest problem being that there is no ground for them.The ground lead at the ac outlet is too far away from the ground rods to do anygood. The impedance of the ground line is too high in normal mains wiring.To be effective they need a short good ground connection.Plug-in devices without very good grounding can protect somewhat devicesagains small small overvoltage spikes and devices connectedonly to mains (no telephone line connection etc.).Protection from direct strikes without damage even to the surgeprotector is 'system normal' throughout the world since the 1930. Butsimple standards define how the 'system' must be wired. The singlepoint earth ground is necessary so that incoming surges on buriedwires do not enter the building. Earthing incoming utilities, througheither a direct wire to earth or via a surge protector, will beuseless to earth borne wire surges IF not using the single point earthground concept. And better quality plugs, sockets, and cable wouldnot help.When protecting sensitive electronics like PC, look for a suppressor that offers a response time (the time it takes for the suppressor to react to a surge) of 10 nanoseconds or less and energy dissipation rating of 200 joules or more. A failure indicator light that tells you when the suppressor is on the blink is also important. If you are still using a dial-up modem, you want to be sure the suppressor blocks electricity that can come in from the phone lines, too. Finally, be sure that the suppressor you buy meets the local safety ratings (has compliance stamps). In USA be sure that the suppressor you buy has a UL compliance stamp and look for a suppressor that meets the UL 1449 specifications. Some brands of surge suppressor include an equipment protection guarantee that covers components damaged if the device fails to do its thing.When designing larger systems, the system grounding needs to beconsidered also.All equipment involved in a system should physically be located as close as possible to one another. This reduces the potential that is developed between the ground site and the individual components of the system during a lightning strike. This single point grounding greatly reduces the potential for lightning damage to electrical equipment. If you are unable to achieve single-point grounding due to large distances between equipment or other variables, other means of lightning protection must be considered. Consult a reputable lightning protection company.The typical design of mains surge protector is something like this: The shunt element in the protector is designed to fire at anywherebetween 260 to 700 volts depending on the design. It is connected between the phase and neutral and/or ground connection. The shunt element will shunt the surge to neutral and/or ground wire when it gets fired by the surge. The typical devices used as shunting element are voltage sensitive.This means that at normal voltage they are very high impedance (Opencircuit). When a surge reaches the voltage at which the deviceactivates, the device goes into low impedance state (short circuit).As soon as the voltage drops to normal, the device stops conductingand goes back into open circuit state. This clamps the voltage at thefiring voltage of the device during a fault condition. Now if there isa fuse or breaker and the surge is long enough in duration, the shuntelement (which is actually shorting your AC mains) will cause enoughcurrent to flow that will cause the fuse to blow or breaker to tripand thus interrupt the supply and protect the shunt element. If thesurge is short duration, the short is momentary and does not blow thefuse or trip the breaker. (This is because a fuse or breaker respondsrelatively slowly to the fault condition) so all that will happen isthat the voltage clamps to the firing voltage of the shunt element.Protection from direct strikes without damage even to the surgeprotector is 'system normal' throughout the world since the 1930. Butsimple standards define how the 'system' must be wired. The singlepoint earth ground is necessary so that incoming surges on buriedwires do not enter the building. Earthing incoming utilities, througheither a direct wire to earth or via a surge protector, will beuseless to earth borne wire surges IF not using the single point earthground concept. And better quality plugs, sockets, and cable wouldnot help.

    Surge in 12V power systems

    Under the hood of a vehicle is an electronics nightmare. EMI spraying and RFI sparking is everywhere, and electrical transients run amuck, zapping the embedded electronics. Electronics located in that environment must withstand 600V transients, and load dump situations.

    ESD surge protection

    ESD surge protection is essential in many electronics devices for then to withstand real-life use. Typical protection measures for the actual electronics are metal case or well insulating cases.Usually the most demanding places for ESD protection are the electrical interfaces. Typical protection schemes used for this include galvanic isolation, using internally protected components (with can withstand needed amount of ESD) and surge protection components (transzorbs, zeners etc.).The usual simple protection methods (transzorbs etc) will usually lead to large surge current passing trough the circuit ground.This is usually not acceptable, because this kind of high current can cause problems in microprocessor circuit operation (most typically crashes the CPU). This kind of probles are generally solved by carefully designing which routes those surge currents take in the circuit (preferably far away from other components and signal wires) and by limiting the surge current (series resistors and coils in input lines). Usually the only proper protection in hard environments (for example in heavy industry) would include galvanic isolation (usually expensive alternative).

<[email protected]>

Back to ePanorama main page ??
 
| Submit site | Info | Advertise | Feedback | Disclaimer | Privacy | Ad. FAQ | Legal Notice |
Copyright © 1994-2011