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I have three lights with the power to the first light and passing through the other two and then to a switch. How is this wired?

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  • Where are you on this planet? Also, are all three lights controlled by the switch at the "end" of this circuit? Apr 16, 2017 at 1:40

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If you are in the U.S.A. and the wiring was installed before 2011, it probably looks like this. Note the colored tape or paint mark on the white wire used as a switched hot: BX and Romex era

NEC 2011 and later calls for a neutral wire to be present in each switch box (to accommodate smart switches) so if your wiring is new it might look like this: current standard

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Most commonly the line power enters the box with the switch and then goes to the light fixture. By analogy with water pipes it is easy to see that the switch can control the light because it is "between" the two. But it is sometimes the case that the line power cable first enters the box of the light fixture and then goes to the switch. The switch controls the light even though it would not at first glance appear to be "between" the two, but actually it is.

In the latter case, the neutral of the line (white in the US) is connected to the neutral connection of the fixture, and the hot of the line (black) is connected to the black of a cable going to the switch. The white of the second cable is connected to the hot connection on the fixture and marked with a piece of black tape to indicate that it has been "converted" to a hot. (White is usually neutral.) At the switch the black of the second cable is connected to the line connection and the white to the load connection. The white should be marked with a piece of black tape to indicate it is a hot, even though it will be hot only when the switch is on.

In the case of several lights controlled by a single switch, the converted white conductor from the line side of the switch goes to one fixture, and then another cable goes from there to the second fixture, to the third, etc. This part is no different from the case where the power enters the switch box first.

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