How to find earth

[John Asdf]

Hi,

I'm trying to put up some new wall lights and it would appear that the three wires are not correctly identified - can anyone tell me a simple way to find which of the two low potential wires is earth - only tool I've got access to is a multimeter.

Is it simply the case that I need to connect a cable to the outside earth (pole in the ground) to one terminal of the multimeter and the other to each of the offending wires coming out of the wall (the zero volts ones) and choose the lowest resisance one.

Out of interest what would the consequences be if I connected these incorrectly (no RCD or earth leakage trips in the fusebox)

Thanks John

[Christian McArdle]

Throw the double pole isolator on your consumer unit and unplug every appliance in the house, particularly those with metal cases, such as white goods and computers. Turn off any immersion heaters at the isolators. Then resistance check the cables to be tested to nearby radiator pipework. The neutral should show a high resistance, whilst the earth should show a low one. If you don't isolate the neutral by throwing the isolators and removing the plugs, you will also get a low resistance in the neutral, so won't be able to tell the difference. If you have plastic pipes, or both tests are high resistance, test to the earth terminal of a 3 pin socket.

It would work, but it would be dangerous.

Christian.

[Andrew Gabriel]

You might be right, but you have given no clue why you suspect this to be the case.

Trace back to the other end of the cable and ensure it it connected up properly. A multimeter isn't going to help much. It sounds like the wiring might need reinstalling correctly.

No. You need to verify that the wiring in the circuit you are working on is correctly connected all the way back to the supply.

Someone might get killed.

[BigWallop]

Find out at the switch end. Are the cables to switch colour coded correctly ? Does the switch have both live and neutral from the main lighting circuit passing through it ?

If you do find both live and neutral at the switch, then it is just a case of putting your multimeter on Ohms check, and test between each end of the pieces of cable going to where the light fittings are.

[Chris Holmes]

Third rock from the Sun.

WRT what bigwallop wrote, if he has neutral connections at his light switches, I would suggest he also calls in an electrician! (Unless of course he's deliberately wired his lighting circuits in a different manner to the rest of us. (Switches should have Live ,switched Live and Earth, not Neutral).

[BigWallop]

If you have a junction box under the floor in the middle of the hallway, with all the switch wires and a feed cable in it. You then have an after thought of fitting some wall lights at the other side of the living room. You'd only take a feed (Live and Neutral and Earth = One Cable) from the junction box, to the point on the far wall of the living room where you want a switch for the wall lights. You would then connect each lighting point back to the feed at the switch. Life is easier that way.

I don't think you'd go to the trouble of lifting all the floors and taking a cable from each wall light position and the new switch position, all the way back to the junction box in the middle of the hall. Life's to short for all that.

Or maybe "you" would. :-))