Question: Where does the potential come from in the socket on the grounding wire?

  • Jan 13, 2021
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This is exactly what the title of the question from the reader Alexander sounded like.

I continue to publish the questions that readers asked me. For new dear readers who have come to my channel for the first time, I inform you that this is already the 20th (anniversary) publication of this kind.

Consider in this part 20 a question from Alexander. It is quite simple and fairly typical (I am asked it relatively often in different variations):

Good day! The question is the following. Periodically, a potential of 100-150 volts appears on the ground contacts in the sockets. Where from?

Photo for illustration
Photo for illustration

I consulted Alexander within the framework of my knowledge and qualifications as follows:

Hello! I want to ask you a question - in relation to what do you measure the potential difference? If you measure a terminal (clamp) relative to a neutral conductor, then the presence of the same 100 - 150 V is a normal situation. Since when any electrical device is plugged into a power outlet, current will flow in the neutral conductor and a certain potential will arise. Which should fix the voltmeter relative to the ground.

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If you take measurements relative to any point on a grounded structure, which in normal operation is not conductor of electric current, then there is damage to the insulation of some electrical equipment connected to electrical chains.

In the event of natural aging or mechanical damage to the insulating coating or dielectric base, part of the potential may transfer to the case electrical equipment, supporting structures, etc. In this case, a certain voltage level will appear in the protective conductor, depending on the conductivity of the dielectric in place of damage. This situation poses a real threat to the life and health of residents.

To eliminate this situation, you need to identify the defective electrical equipment. It is more convenient to navigate by the electrical equipment plugged into the outlet, so please note that plugged into the socket or from the rocker switch at the moment of detecting potential at the terminal (clamp).

Then "ring the circuit" between the socket outlet leads to the safety terminal in each of the connected electrical appliances. In the event of a defect in the insulation, the multimeter will show "presence of a circuit" between the phase and protective conductors, or between neutral and protective.

Due to the fact that not every commentator or just a reader can sensibly understand the purpose and essence of my advice and my answers to specific questions from other readers, after each publication I will publish the following disclaimer (Disclaimer):
My information is just information for thought. Electrical work performed without skills and appropriate experience is very dangerous! The materials of the publication are only advisory in nature and are provided for informational purposes only. I am not responsible for the application of the information provided in real conditions!
For a detailed solution of the issue, you must definitely contact a qualified person who will come and solve your problem on the spot.
P.S. Dear Readers! If you have your own version of the answer to this question, please write it in the comments. It will also be interesting for me to read it and, if necessary, discuss it.

P.S. Link to some past parts - Part 19, Part 18, Part 17, Part 16, Part 15.