Residual voltage in the sockets, OFF switch

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Residual voltage in the sockets, OFF switch




by Christophe » 15/06/09, 16:45

Uh I think we have a problem with our electrical network !!

There is residual voltage in the sockets of the luminaires, switch OFF.

For the moment I have only measured 2 and here are the results:

a) E27 socket only: 22 V AC empty, voltage which drops to 0.003V AC if a 12V 20W bulb is placed on it

b) Luminaire with 3 GU10 spots: 140 V AC empty (!!), voltage which drops to 60V AC with a 3W led

How did I spot this problem? Well on the light b) during a test of LED bulbs ... the LED flashed when the switch was off (off!) And this permanently! Bigre an electric ghost!

The fact that the voltage drops to 0.003V AC indicates that there is not really any power flowing but it is still a problem and it is enough to "blink" a 3W led bulb. If it is, we have a few tens of watts 24/24 pumped by all the plugs ... for queudale!

What do building electricians think?

Is it a grounding or switch problem?

I had already measured "shady" things during various works of the phase-earth style = 60 V AC ...

I'm lost :? : Cheesy: What to do? Is this really a problem or is it linked to static electricity (bigre) or other EM disturbances (bigre bis)?

Thanks for your advices...
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by delnoram » 15/06/09, 17:06

About twenty years ago, a work colleague called me because he had one of the sorting phases with a current of around 140V.

In fact, it only measured the current induced by the 2 other phase wires, the other was simply disconnected.
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by perplex » 15/06/09, 17:34

I have a little the same problem : Shock:

At two very distant places in the house, unrelated to each other
The switches on off, after a few minutes I have a barely noticeable but present flash (visible only at night)
The flash cycle is not regular (sometimes ten minutes between 2 micro flashes, the bulb does not light, we simply see in a furtive way, a brief passage of the current!)
I tested the nickel switches,
I have no serious explanation

Ps; are conventional bulbs (60 Watts, anyway), it's not LEDs! : Mrgreen:

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by Christophe » 15/06/09, 17:40

delnoram wrote:In fact, it only measured the current induced by the 2 other phase wires, the other was simply disconnected.


To complete this somewhat laconic explanation: if 2 electric cables (unshielded) are in the same riser (or sheath) and quite "close" (which is generally the case), then a cable of the 2 cables acts as an inductor " generator "on the other.

The greater the length "side by side" and the greater the intensity in a cable, the greater the induction effect.

I just checked it: I cut the only "big load" near the luminaire b) (it was my PC) and the "no-load" voltage "miraculously" drops to 0.4V AC ...

Delnoram you were therefore right: the cause is found ... Bravo and thank you!

As for the flashing solution ... apart from pulling new shielded cables I don't see any! Note that it only flashes with 1 or 2 LED bulb on the spots (it flashes faster when there is only one). When you put a fluorescent bulb it stops.

How does it work in homes with electric heaters (or even with an electric balloon)? Are the cables systematically shielded or are they separated from each other? Are there standards?

I made a video with the blinking, I will put it on youtube. You'll see it's funny :)
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by elephant » 15/06/09, 18:30

I bet you did your measurement with a digital voltmeter.

the very high input impedance causes the device to pick up induced currents (the wire is an antenna)

That said, beware: it is not because you cut one of the phase wires with the switch (which is generally the case in interior lighting) that there is not a potential difference between the other phase and earth, which can shock you.

Finally, an uncle of my wife who worked in the high voltage cabins explained to me that he discharged the disconnected wires using an insulating pole connected to the ground because a long cable has a capacity. Under 11000 volts, the energy thus stored is far from zero.

Good electricians always have with them a good old needle voltmeter, who does not dream.
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by Christophe » 15/06/09, 18:35

Well ... the measurement I made above all ... with the naked eye :)

Okay, I'm processing the video, you'll see!

For galvanometric measurements, I agree ...
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by C moa » 15/06/09, 18:48

Christophe wrote:
delnoram wrote:In fact, it only measured the current induced by the 2 other phase wires, the other was simply disconnected.


To complete this somewhat laconic explanation: if 2 electric cables (unshielded) are in the same riser (or sheath) and quite "close" (which is generally the case), then a cable of the 2 cables acts as an inductor " generator "on the other.

The greater the length "side by side" and the greater the intensity in a cable, the greater the induction effect.

I just checked it: I cut the only "big load" near the luminaire b) (it was my PC) and the "no-load" voltage "miraculously" drops to 0.4V AC ...
Honestly I have big doubts about your conclusion.
Indeed, that there is an insulation problem between two circuits (2 phases or phase / earth) why not even if it is worrying but to have a voltage generated by induction, I do not believe it too much.
First of all because Messrs Ampère and Tesla had indeed noticed that there could be phenomena of attraction between two conductors traversed by different voltages and intensities but they had especially noticed that to generate a current, it was necessary to have a strand (what a coil) and an exciting element (a magnet or an electromagnet).
In addition, you tell us to always have a tension while the computer is stopped, it does not stick too much with induction.

On a "general public" circuit, this is unlikely.

Personally, I would rather prefer a lack of insulation. When was your installation? If these are still textile cables, we might even have to worry a little more ....

To be completely sure, you can do the following tests:
- Unplug everything on the socket of your computer to be sure that there is no return current (or better to drop the circuit breaker or remove the fuse from the circuit). If you always keep a tension (however weak it is) it is that there is a bp of insulation.
- You can test your switch (or even unplug it) to see if the problem is not caused by it.
- If you have a junction box through which all these charming sons pass, open it to see if there is not one that is disconnected or broken and that will tickle a cousin.

On the receiver side, you can do a test with a plastic two-ball socket to see what's going on. The fault can also come from poor insulation of your wall lamp.

How does it work in homes with electric heaters (or even with an electric balloon)? Are the cables systematically shielded or are they separated from each other? Are there standards?
The cables are not shielded, the standards (NFC 15100 in France but I believe that roughly the same is the same everywhere in Europe except in Italy : Mrgreen: given the state of the installations) say that the light circuits and sockets must be separated so everything is fine.
You still need to know that cable shielding is not so common. Even in the industry where the forces at play are much greater there are very few cases where we have to screen the cables and yet a lot of circuit pass next to each other without worrying too much .
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by I Citro » 15/06/09, 18:51

: Arrow: I too am part of the "club". : Lol:
I realized this by installing a LED lighting in the WC. Even when off, there is enough residual voltage left to light up the LEDs.
When the little girl was younger, they left the door open, and it was a nightlight for her to go to the toilet at night.
8) : Lol:
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by C moa » 15/06/09, 18:52

elephant wrote:Finally, an uncle of my wife who worked in the high voltage cabins explained to me that he discharged the disconnected wires using an insulating pole connected to the ground because a long cable has a capacity. Under 11000 volts, the energy thus stored is far from zero.
You're right but here we are talking about 240V not 11000. And then on the high voltage lines, there is also a large accumulation of static electricity due to the weather, charge / discharge phenomena ...
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by elephant » 15/06/09, 18:52

In general, the natural twisting of the cables is already sufficient to greatly reduce the inductions.

As for the armored, armored power cable (in Belgium VFVB) its use has been completely abandoned, even prohibited.
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