[robinbabcock]

Trying to install security lights and found a 3-wire in the attic. The bare wire and the white wire complete a circuit. What can I do?

[ma0641]

It is possible the white wire is hot if it is part of a switch loop. Where does it connect? Where does it come from? What is the other wire-you mentioned 3.

[ballengerb1]

What is the third wire?

[donf]

Just exactly how do the white wire and the bare wire complete the circuit? "Bare" is the
Equipment grounding conductor and is NOT part of the circuit.

A normal circuit is made up of a hot conductor (usually black) and a Neutral conductor (usually white)

The bare conductor keeps all of the metal in the circuit at the same potential level so you do not get a shock if you touch the metal. It also functions to clear a fault or short circuit.

[ma0641]

Just exactly how do the white wire and the bare wire complete the circuit? "Bare" is the
Equipment grounding conductor and is NOT part of the circuit.

A normal circuit is made up of a hot conductor (usually black) and a Neutral conductor (usually white)

The bare conductor keeps all of the metal in the circuit at the same potential level so you do not get a shock if you touch the metal. It also functions to clear a fault or short circuit.

If the white wire was hot from a switch loop, the ground would complete the circuit and measure 120 on a VOM if white and ground connected.

[donf]

Agreed, but the OP did not provide a full description of the wiring. If the supply is going directly to the switch, then a 120 v between the supply's neutral and the bare EGC would indicate a serious problem.