Originally Posted by timchi29
I just pulled the Christams Tree lights from storage (the icicle kind) and each string has 4 sub strings and I need to determine where the bad bulbs are since they are all out on a particular string. Will the non-contact AC current and voltage detector solve the problem? I read that if you take this tool on the wire on each side of the light socket, you will be able to tell which one is bad if there is no current on one side.
Probably not. Detectors that clamp on the wire and measure current won't measure anything in the individual wires between dead sockets if current is not actually flowing which means the lights are on. It is not possible to have current flowing on one of the two wires going to a socket and not flowing on the other wire; if a lamp burns out*, current stops flowing in the entire loop (circuit; substring). Non-contact continuity detectors that generate a tone when you connect one test lead to a plug prong and touch the probe to the outside of the wire will likely give a false reading because of the wires of the correctly working substrings so closely spaced.
Also you need to be careful when measuring continuity from one socket to the next. Many strings are wired with sockets alternating, as:
Very confusing when the two wires (dashed lines above) are twisted together
*Miniature Christmas tree lamps have a jumper inside to keep the current flowing if the filament burns out but this is not foolproof.