How do I tell a white wire from a black wire, when both are black?

Question

I've got a lamp, and the switch broke. I'm trying to install a new switch. I understand the installation process, but I have to keep things straight between the black (hot) wires and white wires. However, on the lightbulb end, I have two black wires, one of which has white letters. On the power source end, I have only yellow/translucent wires, and one has black letters. Does anybody know for sure which is which?

Do the black letters on a yellow wire mean it's black? Do white letters on a black wire mean it's white? Or do letters, in general, indicate one color or the other?

Answer 1

It is scary an electrician (fdk479) would say the lamp terminals are interchangeable. And to the others that think that, it is wrong!! It is very important that you get the wires right, or you will have a screw shell of the lamp HOT. The neutral needs to connect to the screw shell and the hot needs to be switched. If you have any doubt after doing the wiring, test with a meter to make sure they are correct.

Now, there are many other ways that the "identified" (neutral) conductor is identified. Being white is the most well known. Another answer mentioned the ridges (common on "zip cord", you can feel the ridge on one side and not the other, the ridge side is the neutral). Other methods to identify the neutral: white strips on other than green insulation, grooves, tracers, and tinned (if one copper conductor is tinned and the other isn't, the tinned one is the neutral).

For your specific case, the yellow/translucent wires sound like zip cord, and the neutral had a ridge on it. Do not go by the writing. If you test with the plug (which is polarized) the neutral is connected to the wider blade. The other, white letters is not in the code as a method. I would think there is some difference you aren't noticing. You can check with a tester--the neutral is connected to the screw shell, the hot is the center contact in the bottom of the lampholder.

Answer 2

Lettering on wires does not tell you if it is a hot or neutral. Always test for which wire is hot, don't depend on the color.If you determine which wire is hot it should go to the center part of the lamp socket. The outer shell of the lamp socket should be hooked up to the neutral. This is standard practice for screw in bulbs. The purpose of this is that if power is on when you screw the bulb in and touch the metal outer shell of the bulb, you don't get a shock if you are grounded.

Answer 3

You can either open up the lamp and find the junction and visually trace the wires, or run a continuity test with a multi tester.

See if one of the wires in each pair has a longitudinal ridge on it. That will be the positive one.

Answer 4

If your wiring a lamp with only 2 wires,, it doesnt matter, the switch is/usually only breaking one wire, goes like this, wire from lamp to one wire on switch, other wire from switch back to the lamp.

Answer 5

if this lamp uses an incandescent bulb(regular old fashioned bulb), it makes no difference which wire you attach to which.
the reason for this in simple terms is since the power source is AC (alternating current) the current is just going back and forth through the filament, and the bulb doesn't care from which wire the current starts or ends.

hope this helps
p.s. i am an electrician

Answer 6

If its just a lamp it doesn't matter,Its a concern when your completing a circuit like installing an outlet..

Answer 7

Plug it in, touch it to your tongue.