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I have an older mobile home, 80's model. the light switch in a bedroom busted out of the wall so I went to replace it only I am confused about the wiring.

Normally I am fine with this when replacing new lights and stuff but I think this was done wrong. There are two sets of wire bundles in the wall, each with a copper black and white. The switch had a black one the bottom side screw then a copper on the screw above it both from the same line. Then the two whites are put together. Then on the top screw is a wire with black on it and and not positive cause it got pulled out but the copper wire might have been on that same screw and if it wasn't then it was just there in the open.

What is going on? Does that mean two things were hooked up to the switch? But then what?

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1 Answer

The standard wiring pattern in USA (but not necessarily elsewhere in the world) for 110/120 AC is

black - hot
white - neutral
bare or green - ground

The hot wire brings the current to the outlet or fixture, often through a switch.

The neutral completes the circuit back to the panel.

The ground is a safety mechanism that, hopefully, will shunt the hot current to the ground (literally) rather than through a person if there is a short.

The terminals of a single pole switch (the only switch in a circuit and turning on/off one device or one set of devices) get the black wires, one on each terminal. Many switches also have a grounding terminal. This is not one of the switch terminals, but is usually a green screw on the metal strap of the switch frame, often on the opposite side from the terminal screws.

In general the white wires in a box should always be connected to each other, and never to or through a switch.

Similarly, the ground (bare) wires should be connected to each other and to the ground screw if the switch has one.

In your case, one set of wires (black, white, bare) are the source of the power, and one set (also black, white, bare) go to the fixture.

More complicated systems are possible with more colors, more switching choices and other configurations, but they don't apply in this case.

To work on this, make sure that the power is off (a non contact tester is best), before handling any wires.

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what confused me was the way it was hooked up, maybe it was wrong then, because it was the whites together but on the side it was a black on bottom and a bare on top and then at the ground screw it was a black and i believe a bare on top, either that or the bare was just their not hooked to anything, like i said it was pulled out. thank you for your time. –  jen Jul 16 '13 at 14:10
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@jen The bare should never be connected to a black wire or to an active switch terminal. Sounds like the existing wiring was incorrectly done. To be safe, check the fixture to make sure that the black goes to the hot lead of the fixture (connected to the bottom of a standard bulb) and the white goes to the neutral (connected to the side of the bulb) and the bare goes to the metal frame of the fixture (not either of the hot or neutral connectors). If not, the fixture may need rewiring too. At that point, you may need a pro. –  bib Jul 16 '13 at 14:17
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Lets be careful when specifying color codes. Questions can come from anywhere in the world. I do believe everyone is on the same page here, but if the OP were in South Africa, black is neutral and some power wires are white. –  bcworkz Jul 16 '13 at 23:42
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@bcworkz Excellent point! This advice is US based only (as it says in the first line). If you are elsewhere, you need to check local codes and conventions. –  bib Jul 16 '13 at 23:52
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