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Recently i tried gathering voltages from few AC outlets in my house. I got following readings using a dmm Phase-Ground = 398V-400V (should be around 240V) Phase-Neutral = 230 V Neutral-Ground= 210 V (should be around 1-2V)

I tried in the whole house but got same results and i can't figure out where the problem lies. I know for certain that my ground is fine.

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  • \$\begingroup\$ for clarification where are you located, and where does your electricity come from (eg from the city, from a SWER line, or from a generator that you maintain) \$\endgroup\$ – Jasen Jan 19 at 22:42
  • \$\begingroup\$ Your neutral should be at ground voltage unless there are very significant currents flowing on it. I would examine your neutral and ground connections all the way back to the panel, expecting to find a misconnection/break somewhere along the way. If you meter neutral to ground in your panel, where they are directly connected, and where your panel should be connected to your bond/ground plate/rod/pipe/bus, you should have 0V. \$\endgroup\$ – K H Jan 19 at 23:52
  • \$\begingroup\$ You could also perform a continuity test on the neutral. Power down the system, connect a 14/12AWG wire to the neutral bus and draw it out to the outlet in question. Meter resistance from the wire you have drawn to the neutral in the box. There should be no significant resistance. Be sure to use a NCVT on every box/conductor you approach, even if you have powered down the affected circuit. The bond wire should attach to all bond screws and all other bond wires in every box, and a given neutral should attach to all neutrals of every circuit it serves in every box. \$\endgroup\$ – K H Jan 19 at 23:54
  • \$\begingroup\$ Note that not every white wire is a neutral (some may be switch legs/return conductors) and it is important that a neutral must not be joined with other neutrals unless they serve the same circuit. The same principal follows for neutral connections upstream of your system, although you should not attempt to access those. Metering at the entry point to your electrical system should reveal if the problem is upstream. Because the neutral should be connected to ground inside your panel, it seems unlikely to be a problem coming in from your supply, although it affects your whole house. \$\endgroup\$ – K H Jan 19 at 23:59
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First off you mention 240V so I'm guessing you're in the UK, it's notoriously difficult to get meter probes into a UK BS1363 socket and have them connect. The best way of connecting is to (with all due care an attention) use a BS1353 to IEC320 C13 lead (commonly referred to as a kettle lead) the female C13 connector is very easy to fit meter probes in, but again be careful. [you can get BS1363 plugs with 4mm meter sockets on the back if you want to do this safely].

Worryingly your results are self consistent and suggest a fault with your electricity supply.If you have a TT connection from your supplier (eg the power comes in on two wires overhead from a pole), then it's possible that something near either your house or the transformer is pushing the earth potential up that high. You say you've checked your earth connexion - do you mean you've checked that the sockets have a low resistance to a measuring stake you've driven in near the ground (or if you're boding it the lead/copper pipe bringing water into your house).

If you want to check your observations, you can buy cheap devices with leds/neons arranged between all the conductors. (eg https://www.screwfix.com/p/lap-ms6860d-socket-tester/91596 others are available and are better/cheaper)

or any device used to do a Part-P test would be able to check your measurements.

If your measurements are correct you'll be putting extra strain on the insulation in any of your devices that use switch mode power supplies, and I'd expect any surge suppressors in your house to have gone bang.

Either way this definitely warrants further investigation.

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  • \$\begingroup\$ Thanks for answering, I called the power company and you were right it is the faulty transformer as all my neighbors have same issue. But too bad for me that the power company is not taking any responsibility as they are saying that we are only concerned with Phase-Neutral voltage that is 230V. They also said that in your neighborhood only you are complaining so we can't change transformer just for you. I have a PC that started developing problems when i took it with me to this new house but light bulbs, fans, electric motor seems to be working fine. \$\endgroup\$ – BumbleB Jan 21 at 19:00
  • \$\begingroup\$ Wow - which country is this in? I would get their statement in writing, so that you have something to show your insurance company. \$\endgroup\$ – james Jan 21 at 22:43
  • \$\begingroup\$ Update: Very strange that the problem seems to be fixed now and no one even replaced the transformer. Now the voltages are normal and the neutral is not hot anymore. This indicates that the problem was either at power distribution or at LV overhead distribution. Found this topic electrical-engineering-portal.com/… \$\endgroup\$ – BumbleB Jan 23 at 22:38

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