Floating earth wire is live

I originally posted this as a follow on to two other streams of correspondence, but it doesn't seem to be registering so let's start again.

In summary, I have had the same problem as the two previous guys. Using a neon screwdriver, I am detecting current in a ‘floating’ earth wire in a lighting circuit. I am off to get a decent voltmeter to check just how much voltage there is in the earth. I want to make sure that I have understood the advice given in previous replies. So here goes. I check the voltage between the neutral and the earth. If this is below (what?) 30V this is ‘normal’. I should then connect the earth wire to a good earth. The induced current should run off down the earth without tripping the circuit breaker at the switchboard. Have I got this right?. Thanks. IanC.

Look, what you really want to know is, what is the continuity of your earth wire. You should have something in the region of 0.1ohms (i.e. not a lot) between any point in your system and the main earth bond point.

You cannot measure this with a b****y neon screwdriver. Don't even bother trying to measure the voltage with a 20,000ohms per volt voltmeter. Use the resistance scale.

If you don't understand this and the reasons for it .... deep breath, I was about to say, don't do it. However I will calm down and say come back and ask.

also whilst on the subject, throw the neon screwdriver in the bin and invest in something better.

Some people just have a thing about neon. Why can't they use a different gas?

If the earth wire is truly 'floating', that means it is not electrically connected to anything. This is a bad thing. It should most definitely be connected to earth at the supply end.

If you touch a neon screwdriver against any unearthed piece of metal running alongside cables (metal conduit for example) then there is a good chance the neon will light. This is because a very small leakage current can flow betweenn nearby conductors. This works with a neon because it uses only a very small current to light. If on the other hand you connect a dial voltmeter you may get an entirely different result. The result is not terribly meaningful, except as a warning to check your earth continuity.

If on the other hand you connect a dial voltmeter you may get an entirely different result. The result is not terribly meaningful,

Click to expand...

If you connect a moving coil volt meter you'll probably read nothing. If you use a digital voltmeter you may well get a varying reading.

If you are going to measure earth continuity use a continuity tester and measure ohms.

Please use the right equipment for the right job. This is like weighing apples with a watering can.

LOL - yea you need a 'loaded' meter, or the old school moving iron meters.

IanC100 said:

I originally posted this as a follow on to two other streams of correspondence, but it doesn't seem to be registering so let's start again.

In summary, I have had the same problem as the two previous guys. Using a neon screwdriver, I am detecting current in a ‘floating’ earth wire in a lighting circuit.

Click to expand...

No - you are not detecting current, you are detecting a voltage, magitude unknown, with an extremely high impedance voltage indicating device.

Before fiddling with any other test equipment, please rectify the floating earth wire - that is far more important.