Inductive Coupling On Floating House Wire: Possible ?

Question

Hello:Have a length of 3 conductor (and Gnd. wire) No. 14 AWG running around my house.Would like to use the red, third conductor, to interconnect some smoke alarms.This red wire is at present, to the best of my knowlege, totally floating.Believe that there is nothing hooked to it now.(but, it is hard to trace totally, and there might possibly be "something" connected to it  that I am unaware of ?)Anyway, my question is:Assuming that it is toatally floating, how likely, or possible, would it be for this wire topick up, e.g. 2 V AC, via inductive coupling, RFI, or... ?I ask this because I measure 2 V AC on it, which I cannot account for.Thanks,B.

me · Accepted Answer

Did you use a high impedance digital multimeter? Try an analog meter,The voltage may disappear. A light bulb may also be used to dissapateinductive coupled energy.

John G · Answer

In most jurisdictions, power wires are for power and signal wires are for signals and should be in separate conduits,etc. and certainly not in the same jacket.

Paul Hovnanian P.E. · Answer

There are AC powered smoke detectors that interconnect via a dedicated conductor (i.e. the red one) in an NM cable. The detectors need to be approved for this kind of wiring. If the ones you are using have low voltage alarm outputs, you need to provide wiring separate from the 120 VAC system.

The 2 VAC that you see could be caused by capacitive (rather than inductive) coupling from local fields and will be picked up by high impedance voltmeters. Try holding one voltmeter probe up in the air and you might get a volt or two. Unfortunately, you would also read a volt or two if you were measuring the voltage to ground on a grounded conductor carrying neutral currents.

Inductive Coupling On Floating House Wire: Possible ?

Join the Discussion

Didn't find your answer?