Circuit testing 101
If you’re new to running electrical circuits and are working on your own, it’s a good idea to test electrical work at rough-in. You can test from box to box, but it’s simplest to test the whole circuit (tied together but not hooked to the panel).
On the last box in a circuit, strip the ends of the hot and neutral wires, and wire-nut them together. Using a multimeter or similar tool, test the resistance/continuity of the insulated wires at the other end of the circuit; continuity shows the wires aren’t broken. In multiwire circuits, test pairs of wires, using the neutral or a selected common wire. While wires are tied together, test an insulated wire against the green/bare equipment ground wire; you should not show continuity, confirming that there is no short between the ground and insulated wires.
Next, tie one insulated wire and the ground wire together. Be consistent in your wire choice to avoid any risk of confusion. Test that insulated wire and the ground; continuity confirms that the ground isn’t broken. Test that insulated wire against the other(s) and, in a circuit with more than two insulated wires (such as a three-way switch leg), against each pair of insulated wires; you should not show continuity, confirming that there is no short occurring between the insulated wires.
Found a problem? It could be a connection or a defective cable. To find a broken cable, disassemble tie-ins in the boxes, and test from box to box. Look for an obvious problem, such as a staple through the cable insulation.
Errant nails and screws can still damage the wiring, but repairing a mistake made during rough-in is best tackled while the wiring is still easily accessible.
Bill Houghton, Sebastopol, CA