Newsgroups: rec.audio.tech
Subject: Re: Burned out sound card...
References: <[email protected]> 
"James Lehman"  writes:

> Here in the USA we have three prong AC outlets.

In many European countries we have to pin ungrounded outlets 
and then grounded outlets that have an extra ground connection in 
addition to the two power carrying pins. The shape and position of the 
ground connection varies from country to country, at some countries it 
is third pin on the plug, on some other countries it is pin sticking 
out of outlet and on many countries two metal contacts on the sides 
of the plug that nake connectact to two "spring" contacts on the outlet 
(SCHUKO outlet). 

Some examples:
http://kropla.com/!c.htm
http://kropla.com/!e.htm
http://www.kropla.com/!f.htm
http://kropla.com/!l.htm


There are countries where you can plug grounded connector 
equipment to ungrounded power outlet. For example that 
SCHUKO plug goes nicely to the ungrounded two pin outlet. 
http://kropla.com/!c.htm
http://www.kropla.com/!f.htm

Doing that gets your computer powered up, but not beging grounded 
to anyhting. This is a common situation that happens in many 
european countries every day. When computer is ungroudned, the 
case is floating ar potential set by the leakage currents on 
the filtering capacitors (around 110V AC potential, less than 1 mA 
leakage current). This is not considered bery dangerous, because 
this leakage current is low and even possibilitty to get it 
on your fingers is not very common, because those locations 
where ungrounded power outlets are installed, there should not 
be any easily touchable grounded thigns and the materials 
shoudl be insulation... So even on case gets to mains potential 
because of some fault, it is unlike that it will kill 
(you will be shocked but current will be quite low because you 
are standing on insulation floor material). 
Grounded outlets are put on those location which are considered 
potentially dangerous (wet locations, non insulating floor/walls, 
grounded metal object reacahble etc..). Ungrounded outlets are 
only put where there are no such dangerous things 
(expections to this is that grounded antenna outlets and 
grounded central heatign radiators are not considered as 
grounded metal objects that would make room dangerous). 
Anyways the thigns have changed nowadays so that for many 
years in the country I live in the new buildings have always 
been installed with grouded power outlets everywhere. 

The computer manufacturers recommend usually that the computer 
should only be connected to grounded power outlet.

If you connect the computer to ungrounded outlet, you have the 
case floating somwthing like 110V AC potential when freely floating. 
If you happen to make connection between the real ground and equipment
case, typically a leakage current of around 0.5-0.7mA (0.1mA..1mA depending
on equipment). When you have several equipment (like computer, monitor 
and printer) interconnected, the total leakage current is easily 
in 1-3 mA range with perfectly working and up to the regulations 
devices. If you make connection to ground with your had, you cna 
definately feel this current as a slight shock, but it will not 
kill you (unless your equipment are damaged and considerably more 
current gets through). This few mA current and 110V AC voltage 
when combined with the capacitances on the equipment filters 
(those same that cause the leakage), it is possible to 
get currents and voltages that when they make direct contact 
to equipment input/output connections can damage ICs in them 
(unless theu are well protected). 

I have seen those damages happen. I have learned the damages 
on the costly and hard way. And then learned how to avoid them. 
I have damaged, years ago, at least one VGA graphics card and 
two sound cards (one input, one output). This kinds of things 
happen unless you are careful and know more than what is said 
on the equipment manuals. 

The question to manufactuers is when this kind of damages happen, 
who is to blaim, the user od the manufacturer. The average user 
might not be expected to know all the secrets of interconnecting 
everythign in every different setup without damageng them. 
Usually the equipment are not protected well enough to survive 
this kind of commonly happening overvoltage occurences 
(I think for proper consumer equipment those outlets should be 
better protected, should not be too expensive). And usually 
the interconnections on the manual are not so clearly described 
and not so clearly warned, that the average user woudl no the 
tricks to safely make the connection or avoid the unsafe connection. 
I think on this light is is perfectly OK to ptu the blaim to 
the manufacturers... if their equipment fails on this kind of 
considered normal use on then it is OK to put the equipment 
to the bring thr equipment to the warranty service to be repaired 
becasue is stopped working as expected! It is up to the manufacturer 
to point out if the user operated the equipment improperly and 
that the manufacturer either clearly warned that this should not
have been done or the user should have with common sense understood 
that this kind of connection would result equipment damage not 
covered by warranty. If the equipment is not properly designed and 
built to withstand the normal expected use, there is a fault in 
it and if that causes fail then it is manufacturer's problem 
to pay the repairs. If this becomes too expensive to the 
manufacturer, they should make their products so that this 
kind of damages become less common. 


> It is very typical for things like computers to have a real Earth ground
> from the chassis to the ground pin in the AC outlet.

It is very typical in many european countries that when computer 
is connected to the grounded outlet, the case has a real Earth ground
from the chassis to the ground contact (pin or whatever shape used) 
in the AC outlet.

But in case the same computer is plugged to ungrounded outlet (which are 
very common in buildings mode than 10 years old), then the the computer 
case is not connected to any real ground! 

> It is also very typical for home audio equipment to have only two prongs and
> a floating ground.

This is very typical in Europe as well. 
This kind of equipment typically are designed as double insulated 
equipment and use to pin electrocal power connector called EURO plug
(you can see image of it at http://www.powercords.co.uk/pc109.htm )
This particular connector plugs nicely to both grounded and ungrounded 
electrical power outlets in most parts of Europe (all the outlet types 
listed above). 

The double insulated equipment are designed in such way that it is 
very very unlikely that there becomes a short circuit between the 
mains input wires and equipment case / touchable parts. 
The consruction is also such that possible leakage currents from 
the mains inlet to case are very low. The leakage currents are a 
fraction of mA typically, you can barely feel them and very unlikely 
that they damage any properly designed equipment input/output.

> I have seen some really horrible things happen when a three pronged device
> is connected to an amp with a floating ground.

Can you give examples of those horrible things you have seen to happen ?

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/