Random electrocution?

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bob_v5

Member
2005-09-04 5:38 pm
"This is reinforced by you saying that there are missing connections inside the player and you get tingles from certain parts of the insides."
This made me think. When mucking about with a/v stuff, (dvd players etc) I often get electric shocks when swapping interconects between differnt devices when they are plugged in and running. (maybe not a wise thing to do?) I dont belive it is static, as it lasts for as long as I leave my finger on whatever is zapping me. Anyway, I was wondering if anybody could tell me why this happens. As far as I understand it, there is just not enough power flowing in an interconnect to hurt me. This seems to happen a lot, even on gear at other people houses that I have never taken apart! I read somewhere that it is something to do with switch mode supplys. I dont want to think about what would happen if I had a pacemaker!
 

gareth

Member
2008-01-31 3:38 pm
I think it could be either bad ground problems on your interconnects, wherein you are becoming part of the circuit. This is perhaps unlikely when there is no more than 2volt and some milliamps running through them. Having said that only 30mA is enough, under the right conditions, to kill. (BS7671 wiring regulations).

Another possibilty is that a static charge is being built up on the cables perhaps through stray capacitance or something . There are other things that can cause this aswell.

You say that this happens when you touch other peoples equipment too. Do you wear lots of man-made clothing? Or walk on many man-made objects? This may sound silly but all man-made objects have the ability to produce static charge.

Humans tend to be negatively charged and thus we tend to attract electricity, we are also made of carbon and contain lots of water. All of us have varying resistance to electostatic discharge and electrocution. If you can get your hands on a good Fluke multimeter you can measure resistance over different areas of your body and compare readings.

I hope this kind of answers your question.
Gareth

:att'n:
 

OzMikeH

Member
2007-03-18 9:22 am
If you check with your multimeter you'll see it's half of your mains voltage. It's only a couple of mA to ground but it's very unpleasant when you're on a wet concrete floor with bare feet. Forcing an involuntary breath out through clenched teeth kind of unpleasant.

It's something to do with a slightly dodgy mains filter in double insulated appliances. (no earth pin)

I have an LG DVD/VCR combo in a spare room that livens the whole antenna distribution up in my house. You could see the sparks when you plugged the antenna into a grounded device.

I connected the outer of the coax to the building frame and it stopped the shocks and tingles unless I'm messing with the DVD player and it's antenna is not connected.
 
There is capacitance between pretty much any two things in the universe. That includes your transformer windings, and the rest of the chassis. And you. If left to its own devices, the chassis will assume some voltage, depending on the capacitive and resistive leakage from the transformer windings, and the difference is what you feel if you lightly run your finger across the chassis. This assumes no safety ground. Once you tie the chassis to ground, there should be no stray voltage on it. So, do all your components have a safety ground? Didn't think so. FWIW, the chassis of components having 2-wire plugs is often at 40-60 VAC, until it gets connected to something to bleed this off. There isn't much current available, but it's not a good situation. It used to be common to reverse the plugs of each piece of equipment, measuring to ground, to find the orientation with the least chassis voltage. The assumption was that this would give minimal current flow in the cable shields, and the best hum performance. I've also seen surprisingly high voltages on cable TV shields that weren't properly grounded. IMO, there are some issues between getting the absolute best hum performance from audio equipment, vs. having everything properly safety grounded. Generally it's not a big problem unless you have very high gain, or components plugged into distant outlets.
 

gareth

Member
2008-01-31 3:38 pm
OzMikeH said:
If you check with your multimeter you'll see it's half of your mains voltage. It's only a couple of mA to ground but it's very unpleasant when you're on a wet concrete floor with bare feet. Forcing an involuntary breath out through clenched teeth kind of unpleasant.

It's something to do with a slightly dodgy mains filter in double insulated appliances. (no earth pin)

I have an LG DVD/VCR combo in a spare room that livens the whole antenna distribution up in my house. You could see the sparks when you plugged the antenna into a grounded device.

I connected the outer of the coax to the building frame and it stopped the shocks and tingles unless I'm messing with the DVD player and it's antenna is not connected.


If you are seeing sparks when you plug your antennae in then this is more likely to be some kind of inductance, possibly from the transformer. In theory there should be nothing of the kind though as double insulation takes the circuit earth from the centre tap of the secondary side of the transformer. The centre tap in theory being 0 volts.

This may suggest some sort of fault in the power supply area of your LG combi and is probably worth looking at.

Try measuring your antennae cable with a good meter. You should be in the region of 12 volts and with close to 75 ohm provided the cable is properly terminated.

Thanks
Gareth
 

OzMikeH

Member
2007-03-18 9:22 am
I was talking about voltage between cable screen and protective earth. There's a thread talking about

DC resistance will most likely be anything but 75 ohms, but that is another discussion.

About multimeters: to Misquote Croc Dundee.
"That's not a meter........
(Whips out a HP974a and HP8920)
"THATS a meter." :D
 

gareth

Member
2008-01-31 3:38 pm
This is co-axial cable ? Why don't you try to measure any voltage/current flowing in the outer braid then? Surely you can work back to where the fault lies ?

Have you tried new cable to connect your combi to your splitter. I would have thought you have. It could be a breakdown of the inner insulation. (25kV rating though).

As to your choice of multimeters, hmmm....not expensive enough.

Gareth
 
Please stop non-sense.

Every off-line switching mode power supply has at least one small capacitor (100pF to 1nF, safety rated) connected between primary side ground, which is mains live, and secondary side ground, which is signal ground too in A/V stuff.

This capacitor serves EMI filtering purposes and allows some AC current to leak from mains line to signal ground in the process. This capacitor is almost mandatory, EMI would be too high without it, except with some specially designed low-power SMPS transformers.

Furthermore, bigger switching mode power supplies witn a safety earh connection also include two more EMI filtering capacitors that are similar to the previously mentioned one but of a slightly higher value. They are connected from line to earth and from neutral to earth. Since safety earth is usually connected to the metal case of appliances and to secondary side ground (also signal ground in A/V stuff), if the safety earth wire in the plug is left unconnected, this will cause half of mains potential to appear at signal ground and the metal case.

Fortunately, the AC current leaking through these capacitors at mains frequencies isn't high enough to do you any harm. This is unless the signal grounds of several pieces of equipment without safety earth are connected together, because leakage current is cummulative and it may become high enough to shock you.

Power supplies employing conventional transformers are not free from mains leakage either. All transformers will exhibit some leakage capacitance (cummulative too) and some appliances will still include EMI filtering capacitors from line and neutral to safety earth.
 
I don't know about where you all are, but here the electrical code is very specific about how you have to ground an antenna cable and mast. In short, you have to tie it to your mains ground at the service entrance, or if you sink another ground rod for the antenna, you actually have to wire the ground rod back to the ground at the service entrance- a potentially expensive piece of heavy wire. IMO, doing it correctly is very worthwhile, as it will prevent damage from nearby lightening strikes, and may prevent a fire from a secondary or main strike. It also avoids those annoying shocks.
 
bob_v5 said:
"This is reinforced by you saying that there are missing connections inside the player and you get tingles from certain parts of the insides."
This made me think. When mucking about with a/v stuff, (dvd players etc) I often get electric shocks when swapping interconects between differnt devices when they are plugged in and running. (maybe not a wise thing to do?) I dont belive it is static, as it lasts for as long as I leave my finger on whatever is zapping me. Anyway, I was wondering if anybody could tell me why this happens. As far as I understand it, there is just not enough power flowing in an interconnect to hurt me. This seems to happen a lot, even on gear at other people houses that I have never taken apart! I read somewhere that it is something to do with switch mode supplys. I dont want to think about what would happen if I had a pacemaker!


Buy one of the 3 bulb outlet checkers. Test lots of your outlets. The two outer bulbs should light, nothing more. (my tester is setup that way, others may arrange the bulbs differently.)

Measure your neutral to ground voltage. It should be less than 2 volts give or take.

Measure your ground to a baseboard pipe, steam pipe, kitchen sink...

If any of these fail, call the electrician. It may be that you have lost the neutral feed to your house.

Cheers, John
 

bob_v5

Member
2005-09-04 5:38 pm
jneutron-
I wont be bothering to do this. The reason is that I'm currently a hundred miles from the house that this happens most often. Maybe I should call and tell them, but I really hate to imagine what would hapen if my electricaly incompetent family started poking sockets with multimeters! (this is why I am always the one that gets the wonderfull job of setting up dvd's etc...) I dont think it would be appreciated if I sugested calling an electritian for a problem that might not exist (and they wouldnt do it anyway). Having said that there could be something wrong, as when the new kitchin was installed, some pretty horific wiring faults were discoverd. The shower was bodged into the same circuit as the mains plugs, extra mains plugs had been fitted atached as spurs instead of into the mains loop, wrong size circuit breakers, a real mess.
Also, it happens to me at many peoples houses. I dont have the time or money to visit all of them checking the mains!
 

gareth

Member
2008-01-31 3:38 pm
bob_v5 said:
jneutron-
I wont be bothering to do this. The reason is that I'm currently a hundred miles from the house that this happens most often. Maybe I should call and tell them, but I really hate to imagine what would hapen if my electricaly incompetent family started poking sockets with multimeters! (this is why I am always the one that gets the wonderfull job of setting up dvd's etc...) I dont think it would be appreciated if I sugested calling an electritian for a problem that might not exist (and they wouldnt do it anyway). Having said that there could be something wrong, as when the new kitchin was installed, some pretty horific wiring faults were discoverd. The shower was bodged into the same circuit as the mains plugs, extra mains plugs had been fitted atached as spurs instead of into the mains loop, wrong size circuit breakers, a real mess.
Also, it happens to me at many peoples houses. I dont have the time or money to visit all of them checking the mains!


Hi Bob,
If your still getting these faults I would recommend a GOOD electrician to have a look. I am serious about this. I am a BS7671 16th Edition qualified electrician myself and whilst you could go connecting all sorts of equipment to a common earth YOU WILL NOT correct the fault, at source, as the fault can only be corrected by due evaluation and process. Linking equipment together, equipotential bonding, IS NOT a good way to go in this instance. Next year BS7671 will be removing the section on this completely. (BS 7671 is the code of practice for electrical installations on land and sea).

I cannot stress GOOD electrician enough!! Fault finding can be a tasty subject and requires good background knowledge and reasoning skills, as you would imagine.

And yes youre shower should never have been connected into your ring-main (showers average 8kW - 10.5 kw, pretty nasty) and kitchen fitters are notorious for the...'yeah it'll be alright' approach and start adding all sorts of electrics, food mixers running from the lighting etc etc etc, trust me I have seen all sorts of random guesswork.

Hope you get everything sorted out for yourself
 
Conrad Hoffman said:
I don't know about where you all are, but here the electrical code is very specific about how you have to ground an antenna cable and mast. In short, you have to tie it to your mains ground at the service entrance, or if you sink another ground rod for the antenna, you actually have to wire the ground rod back to the ground at the service entrance- a potentially expensive piece of heavy wire. IMO, doing it correctly is very worthwhile, as it will prevent damage from nearby lightening strikes, and may prevent a fire from a secondary or main strike. It also avoids those annoying shocks.

Codes are usually written by politicians or people sitting in front of a desk with no experience on real life disasters. They are usually ambiguous, for example:

A grounded antenna will attract lighting more than a non grounded one.

If lighting gets to your antenna, you will get fried antenna, TV sets, and amplifier/mixer, no matter if they were on or off, and no matter if the antenna was grounded or not. This happened to me.

If the antenna is grounded, the risk of being shocked when connecting antenna wires to appliances is higher because the appliance side is nearly always live (through SMPS capacitors) while the antenna side is always grounded. A non experienced person is very likely to touch both sides at the same time (not to mention the jump reaction after the shock).
 

gareth

Member
2008-01-31 3:38 pm
Eva said:


Codes are usually written by politicians or people sitting in front of a desk with no experience on real life disasters. They are usually ambiguous, for example:

A grounded antenna will attract lighting more than a non grounded one.

If lighting gets to your antenna, you will get fried antenna, TV sets, and amplifier/mixer, no matter if they were on or off, and no matter if the antenna was grounded or not. This happened to me.

If the antenna is grounded, the risk of being shocked when connecting antenna wires to appliances is higher because the appliance side is nearly always live (through SMPS capacitors) while the antenna side is always grounded. A non experienced person is very likely to touch both sides at the same time (not to mention the jump reaction after the shock).


Hi Eva, undoubtedly what you say about political intervention when writing codes of practice is undoubtedly true, the 'Reg's' here in the UK are written by Electrical Engineers, many of whom have vast amounts of knowledge and are members of the IEE.

The message I was trying to convey was that there may be a more serious underlying problem as to why the random electrocutions are being recieved. Under extreme circumstances, which cannot be foreseen, this may arise to being a bigger problem for which preventative techniques would resolve.

Thanks
Gareth
 

bob_v5

Member
2005-09-04 5:38 pm
gareth-

"The message I was trying to convey was that there may be a more serious underlying problem as to why the random electrocutions are being recieved. Under extreme circumstances, which cannot be foreseen, this may arise to being a bigger problem for which preventative techniques would resolve."

If you would like to pay for the GOOD electritian, I wont stop you. (no insult meant, but as I said in my last post the sugestion would not be liked, or acted on)

The kitchen fitter was the guy that discoverd the faults. He was also the guy that corrected them. As he was a friend of the house owner, and getting paid no extra for correcting the faults, I see no reason to doubt him. The bodge jobs were made by the local council.

The minor "electrocution" seems to be a common thing, I really dont think there is anything wrong with the wiring in the house I talked about, it has happend to me in other houses.

"(random electrocution) Something all politicians should be subjected too !!"
I have to agree, not deliberatly provoking things here, but... ( insert anti ROHS comment here) My friend makes custom guitar amps, using the parts he aquired in the past 40 years, and now has to throw much of his stock in the bin if he wants to keep it legal....
Arg, going off topic in a thread I started, not good!
 
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