with a multimeter how can i properly identify old black wires in a house

[johnnyfalcon]

How do i find wich is the neutral wire with multimeter

Non contact voltage detecters arent that reliable in discernment

Thanks!

[MorningStar]

Assuming US residential wiring standards: look at incoming power feed to the fuse box and study how the fuses (or breakers) are wired with the incoming feed. If the neutral is not marked in white, you should be able to discern two "hot legs" (to use electrician's lingo) in black and a third wire common to both, which would be the neutral wire.

Voltage across the black or hot legs would be 240 VAC, from neutral to hot leg 120 VAC, but better to understand your system by observation, described above, than by experiment with a multimeter. Remember, messing in fuse box could be deadly and one false move could easily be your last.

Post a picture, if you can, and maybe others can provide move insight.

[Iotayodi]

A vague question. The panel box should be obvious as to the hot and neutrals.
I assume you have a junction box, outlet or switch where the wires arent put together. If thats the case make sure the wires are separated and the breaker or fuse is on. Take your meter and check the wires to ground. A neutral should have no voltage or minor transient voltage..

[citfta]

Hi Johnny,

I am going to assume a couple of things in order to give you an answer. First I think you are probably asking about an old house that does NOT have a ground wire run to the outlets. My second assumption is you are NOT asking about the wiring in the main panel. If you are trying to find which is the hot wire at an outlet or switch and you don't have a ground wire that can be difficult to figure out. You will need to run a temporary wire from a good ground or from the known neutral connection in your panel. Then you can check from the wire you ran to each of the others to find the hot or black wire.

Carroll

[Iotayodi]

If its just a 2 wire system you can use your digital meter. The Hot red probe on a neutral will show a negative voltage. That will be your neutral wire.

[ewizard]

Almost sounds like a trick question. Black wires will have black insulation on them. But if you mean 'hot' which normally is what black wires are then you can hook up a long wire to neutral at your breaker box and identify each outlet as to which side reads about 120 volts. That normally should be the right side of the two prong outlet - it should read 120 volts when you have one of your meter wires hooked to ground and the other in the right side of the outlet. As others have said - lethal voltages so be careful - wear gloves if possible.

[citfta]

Wire colors

Hi ewizard,

I have worked on old houses before. Many of them have wire that is cloth covered with a black insulation between the cloth covering and the actual wire. When the cloth gets really old it will take on the color of the black insulation and be very hard to tell from the real black wire. Also some of the old homes have been rewired with breaker panels and the person doing the wiring may not have gotten all the wires connected correctly.

I don't understand the comment made to take a digital meter and the red lead will read negative when touched to the neutral. Can someone explain how that is supposed to work. We are talking about AC here so there shouldn't be a negative or positive side.

Carroll

[Iotayodi]

We are talking about AC here so there shouldn't be a negative or positive side.

My bad on thinking DC.
You can always do a continuity test back to the panel. You can also wire up a 3 prong outlet with alligator clips and use a plug tester. The small slot on the outlet is the hot and the larger slot is the neutral.
Depending on its location you could run a separate ground wire as citfta mentioned. That might be the easiest.

[ewizard]

Hi ewizard,

I have worked on old houses before. Many of them have wire that is cloth covered with a black insulation between the cloth covering and the actual wire. When the cloth gets really old it will take on the color of the black insulation and be very hard to tell from the real black wire. Also some of the old homes have been rewired with breaker panels and the person doing the wiring may not have gotten all the wires connected correctly.

I don't understand the comment made to take a digital meter and the red lead will read negative when touched to the neutral. Can someone explain how that is supposed to work. We are talking about AC here so there shouldn't be a negative or positive side.

Carroll

Yes I considered that might be the case that the black is not easily identifiable and may be the reason for the OP question. Thanks for mentioning that. Right there is no + or - here with AC.

[johnnyfalcon]

They are either wires coming out of a receptacle or an outlet or wires at the light fixture

Never mind though i can always rig a gfi tester to it .

[johnnyfalcon]

If i take red prong to neutral and black prong to hot and vice versa i get around 120