Residual voltage on a ground wire

  • Thread starter robertito
  • Start date
11
1
Summary
Ground wire touching live wire, but feeling current anyway, even if the wire is grounded.
Dear All,

Hope you are fine! Hope this is the right place for this question. If not, my apologies.
We just replaced the complete wiring of our apartment with three wires (live, neutral and ground + new circuit breakers + residual current device). Last week I noticed some tickling on my fingers when emptying the dryer while touching the inner drum with my humid hands. I called the electrician and after evaluating the situation he told me that there was some voltage leaking from the live wire into the ground wire because both wires were too close together inside one of the sockets. He measured 30V on the drum. He fixed the issue and now everything works.

My question is: If there was current leaking from live to ground, why was I feeling it on my fingers when touching the machine's drum? Isn't the current supposed to go to ground without me feeling anything? Why if the machine is grounded I can touch the drum without feeling anything, but it doesn't happen the same with the cable that's directly connected to the ground if current is passing through in both cases?
If someone could point me to some books to read on the subject as well, I would highly appreciate it.
Thank you in advance for your help and wish you a great day!
Robert
 
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Your concern seems seems well founded. Three questions:
  1. What exactly were you touching to get the tingle (all of your phalanges)?
  2. Did the electrician work on the outlet into which the dryer was plugged?
  3. Oh yeah what country?
 

Baluncore

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I called the electrician and after evaluating the situation he told me that there was some voltage leaking from the live wire into the ground wire because both wires were too close together inside one of the sockets. He measured 30V on the drum. He fixed the issue and now everything works.
I think the earth connection had not been properly made. That explains why there was a small voltage on the drum and why you sensed the limited leakage current.
 
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Your concern seems seems well founded. Three questions:
  1. What exactly were you touching to get the tingle (all of your phalanges)?
  2. Did the electrician work on the outlet into which the dryer was plugged?
  3. Oh yeah what country?
Dear hutchphd,
Thanks for replying. To answer your questions:
1) Just the tip of my fingers. I was taking out the dry clothes (well not 100% dry), and rubbed the tip of my fingers against the drum.
2) No, the problem was on another outlet on the same cable.
3) Luxembourg.
Thank you!
Robert
 
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It does sound like a faulty ground connection on that cable (presumably between the dryer and the fuse box). Also there would need to be something causing leakage either an internal fault in the dryer or the wiring itself (as your electrician indicated).
 

Baluncore

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It does sound like a faulty ground connection on that cable (presumably between the dryer and the fuse box). Also there would need to be something causing leakage either an internal fault in the dryer or the wiring itself (as your electrician indicated).
In the MEN system the voltage on the active and neutral is asymmetric as the neutral is earthed at one point in the breaker/distribution box. The earth wire lies with neutral and active in the same long cable bundle and so forms a three way capacitive divider. The small capacitive reactive current of all the cables to outlets returns through that one earth-neutral link.

If an appliance was plugged in but switched off, and the earth connection was faulty, being open-circuit near the distribution box end of that cable, then the earth wire may be expected to pick up about half the active voltage. The capacitance of the appliance to it's earthed environment will reduce that to a lower voltage. Note that the appliance only needs to be plugged in, it does not need to be operating, have any internal fault leakage, or even be switched on at the socket.

I would ask why continuity of the earth wire to the outlet socket was not tested on completion of the installation or rewiring process.
 
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I agree with Baluncore.

Luxembourg-in Europe?-then the earthing [grounding] it has to be as per IEC 60364 and I think TN-S system.

The socket-the outlet in the wall- is provided with 2 holes-one for live and one for neutral and two strips for earthing.

If the electrician worked on the socket only then it is possible the screw - from the back side of the outlet-for the earthing strip connection with the protection wire was disconnected.
Luxembourg earthing socket.jpg
 
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I would ask why continuity of the earth wire to the outlet socket was not tested on completion of the installation or rewiring process.
Usually electronic equipment (in Europe, at least) has half line voltage (with high impedance, so no problem happens when somebody touches it) on the ground point if the ground is not connected. In case it is connected but not properly (or has another connection to some kind of ground, like water pipes of a washing machine) it's lower. 30V measured on the ground point likely means the letter, since the current required to reach 30V on a proper PE line would mean enough current to trip the fuse.

Call for an expert and check the PE line (and all extenders too) .
 

Baluncore

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Usually electronic equipment (in Europe, at least) has half line voltage
We just replaced the complete wiring of our apartment with three wires (live, neutral and ground + new circuit breakers + residual current device).
Live, neutral and ground suggests the MEN system, not a balanced supply with two half voltage active lines such as used in USA.
In Multiple Earthed Neutral (MEN), the neutral is earthed at each consumer service point.
 
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Live, neutral and ground suggests the MEN system, not a balanced supply with two half voltage active lines such as used in USA.
For being ready for any circumstances like swapped live<=>neutral (possible with some types of plugs) or missing ground (whatever reason), the EMI filter at the power input tends to be symmetrical => with a missing ground (and no additional connection towards the ground) the chassis will be at half line voltage, at high impedance.
 
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Your neighbour may have a 'ground fault' which is below the 'trip' threshold, but can be felt thus...
 

sophiecentaur

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Usually electronic equipment (in Europe, at least) has half line voltage
Not in the EU. The system uses three phases and neutral. Each phase is 240V (or whatever is the local arrangement) and the Neutral should be only a few Volts from Earth.
The slight tingling sensation is very common (my laptop supply makes the laptop case feel slightly live) but you can't easily measure the available current to Earth as it's very high impedance and doesn't trip my RCD.

The OP should call the Engineer and tell him that it needs sorting out; It's not up to you to test his work. They charge 'professional fees'.
 
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Not in the EU.
- Could you (too) please quote the whole sentence next time? While what you wrote is true for the quoted part, it has lost any connection to what I did wrote.
- What I wrote is true exactly in the EU. See #10
 

sophiecentaur

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- Could you (too) please quote the whole sentence next time? While what you wrote is true for the quoted part, it has lost any connection to what I did wrote.
- What I wrote is true exactly in the EU. See #10
I don't see how "Double Insulated" (the UK term) equipment can suddenly become balanced unless there's a transformer. There's a lot of double insulated equipment around and it has mains filters but perhaps you could describe more fully what you mean by "half line voltage" and where it comes from. Are you referring to the effect of the filter on High Frequency current waveforms?
 
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I don't see how "Double Insulated" (the UK term) equipment can suddenly become balanced
I don't see where that 'double insulated' comes from. The topic is about equipment which is not double insulated, but supposed to (but actually not) grounded.

Here on the first page there is an example of commonly used EMI filter for electronic devices. Could you please give an estimate for the voltage of the ground (chassis) on the device side in case the line side does not connects to the actual ground and it has no any other connection towards to any ground?
 
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sophiecentaur

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I don't see where that 'double insulated' comes from.
It's the universal term for equipment (legitimate devices) that uses no Earth connection. Look it up and you'll see that it's a well known term. Such appliances are made with 'more' insulation - nothing more. Very often, the case is plastic. This is not what happens with static mounted White Goods, in which the case should be firmly screwed down to Earth. Reversing L and E, is of very little consequence in either case, though.
Unless there's some series impedance in both live and neutral legs, the volts (relative to Earth) on the device will be 240 and 0, same as if an (unused) Earth conductor is there. Low power devices can get away with a mains filter with significant series R but a 1kW motor cannot. So where would any unbalance produce "half line volts" anywhere (except half way through the load resistance)? I think your use of the word "gets" is misleading. That would imply the volts across the load, which is where the misunderstanding comes from and I didn't take a lot of notice of what followed, I'm afraid.
The source of the tingle, from the two capacitors connected to the Earth wire is understandable when there is actually a connection to the case. In Two-Pin connected devices, there should be no such connection to the case (which is insulated from any of the electrics). It seems that the wrong sort of filter could be in my (and a lot of other) equipment and the 0V conductor of the DC out is connected to some internal C's. A built-in tingle - naughty.
 
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I refuse to discuss anything else here but dryers (and possibly, washing machines): especially till I get answer to my question stated in the second half of #15.
 

sophiecentaur

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I refuse to discuss anything else here but dryers (and possibly, washing machines): especially till I get answer to my question stated in the second half of #15.
The unloaded volts on an unearthed earth would be half line volts, of course but that is not the same a "gets half line volts", with no stated context. It was just badly worded - particularly not where it's written and before introducing the possible filter design. We always need to consider how our statements can be interpreted before getting cross with the responses.

Edit: Just measured the (AC) volts between the 0V and Supply Earth with DMM. It shows about 17V. DC volts are around 150mV. fwiw. For my laptop charger.
 
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Dear All,

Thank you for your many answers! I'm extremely grateful! I'm reading them and trying to understand.
Yes, Luxembourg in Europe.
We replaced all the wiring because it was composed of only two metal wires (L + N, each one wrapped with a tiny cloth sock instead of plastic) without RCD and the neutral was originally connected to the ground (earth) in each outlet. Besides the circuit breakers were very old, made of porcelain from the 50s. I'm giving some background because Babadag was writing about the TN-S system, topic I'm reading about now to understand.

Thank you!
Best regards,
Robert
 

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