I have three wires coming from the wall that used to power a lamp. Now I want to connect a different lamp but my problem is how to determine which wire is neutral and which is earth.
Since I have a GFCI installed on my electrical fusebox, a quick and dirty way to do it would be by connecting the lamp to hot and one of the mystery wires. If GFCI trips then I have connected it to earth, if it doesn’t trip then I have connected it correctly to neutral.
Is there another way to do it?
I guess that you could use a digital voltmeter to measure AC voltage between each lead and an actual contact to earth–a concrete wall, a water pipe or something like that. Hot will have the highest voltage by far. The neutral wire will **probably **have a voltage that is higher than earth due to capacitance/resistance in downstream where it is carrying current, and the earth will **probably **have the lowest voltage.
That said, I’d much rather play it safe and do a final check by tripping the GFCI.
What colors are the wires? If this is in North America the ground will be either bare or green. Unless it was wired by a nimrod. Or is really really old.
If it’s just a piece of SO or zip cord or something similar, there may not be color-coded wires.
The wires are painted over several times. As far as I can see the hot is black and the other two are grey.
If the GFCI is in the breaker panel, than they way you originally proposed is both fast and sure. Do it.
If you have a wiggie voltage tester test between hot and one wire. If the GFI trips then you have found the ground.
If your neutral is not white or the ground not bare or green then be carefule of any wiring in the house. It is really old or wired by a nimrod.
If it’s zip cord in the walls you have bigger problems than fixing a switch.
You may have a ground and a neutral. You may have two neutrals, or you may have a switched hot or even a switched neutral. There are different ways of wiring up a lamp, and even a few more ways when you consider that whoever wired it up may not have done it right.
If you figure out that one of the gray wires is ground, wrap some green electrical tape around it. Alternately, if you figure out that one of the gray wires is a switched hot, wrap black tape around it. The next guy who has to work on that connection will appreciate having things color coded correctly.
What voltages do you measure between all three wires with the switch on and again with the switch off?
I am in Europe and the wires are solid core, probably 1.5mm[sup]2[/sup], inside a flexible PVC conduit tube.
As far as I can tell, there’s no switch. The cable probably goes straight to the breaker box.
Generally, in Europe the hot wire is red and the neutral is blue.
I carefully scraped some paint and the colors are actually grey and yellow. So I guess the yellow is earth and grey is neutral.
I’m in the U.S. but it was my understanding that the newer European stuff (last decade or so?) is brown, black, and gray for hot phases, blue for neutral, and yellow/green striped for earth ground. Older European just uses brown for all hot phases, I think.
This makes me think you have two hot phases and earth ground but no neutral.
The yellow wire probably has a thin green line on it.
Are you sure the gray wire is really gray or could it be light blue?
No, these colors are correct according to an older local standard. Black = hot, grey = neutral, yellow= earth.
While color coding is convenient, don’t always assume that it’s right. There’s a lot of wiring in place out there that was put in by idiots.