15V on Earth circuit!!

25 Aug 2006
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United Kingdom

I was replacing a wall lamp last week and I tested the earth wire with my phase tester. I was shocked when it lit up!! I then went around the house and tested the washing machine, the dishwasher, the metal electric ketal and the oven casing and they all lit my phase tester. I bought a multimeter and measured the voltage. With respect to the neutral it is sitting at 15V. I then touched all of the things previously tested and verified that touching them alone doesn't give a shock. However i am a bit concerned that this is not normal!! Should the earth circuit not be sitting if not exactly, then very close to the neutral voltage level (i.e. 0V with respect to neutral)? Is 15V normal?

Advice please.

I should add that I live in Italy, hence the post in the "outside of UK" forum.

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I recon your house has its own earth electrode/stake and no earth from the suppliers, check that the stake is connected. the only other thing is the italians might not reference there supplies so then there will be no connection from neutral to earth.
I had a similar fault in Spain.
The 2-pin plugs can be reversed, so the polarity of the equipment may be opposite to the manufactures intention.
The gas hob had a mains-powered spark ignition.
The wash-machine had a capacitor on the motor.
Reversing the plugs to these items cured the 'voltage on earth' problem.
I could guess the cause, but I prefer to say I don't know.
This can happen when heavy loads are used within the installation and the live & neutral cables are not very large for the load it is carrying. When this happens the live feed and the neutral act as part of the load circuit and become a resistor hence there can be a few volts dropped in the cables giving a slight voltage between neutral and earth. If the supply to your home is a small cable this can also cause it. Try testing the voltage with less load being used and you should get lower readings.
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There are international and local differences in earthing systems.

It sounds like a "TT" supply i.e. there is no connection between your supply neutral and the local earth, which would be provided via ground rods.

These supplies are also used in the UK, just not generally in urban areas, so you may be unfamiliar with them.

Normally the entire installation will be connected to a large RCD (e.g. 500mA) and all of the sockets etc on a 30mA RCD for added safety.

The potential difference (voltage) between live and neutral will be 220-230V but the Neutral's floating, it's not grounded so it could be 15-20V.

Normally, it's important, particularly in an unfamiliar system, to treat the neutral as potentially live.

Don't make any connections between Neutral and Earth. The local supply system isn't TN-C and wasn't designed to have its Neutral used as a reference point for your protective earth.

Connecting them could be very very dangerous.