From the desk of WECA Instructor Jimmie Slemp. Names have been changed to protect the innocent and not-so-innocent.
I got a call from a student. He needed some help. The apparent problem? Kitchen counter-top receptacles not working, and kitchen dishwasher not working. Also, there seemed to be a circuit in the panel that while turned off was still reading approximately 30 volts.
Upon arriving on the scene I made a couple of observations. The first was that there were two 12 AWG conductors that were not connected in the panel. Second, the conductor that was reading 30 volts (even when turned off) was part of a multi-wire circuit that was improperly connected to a 20 amp “tandem or dual” circuit breaker. A tandem or dual circuit breaker is a circuit breaker that connects to one space (single pole) in the panel and has two independent devices on it. The problem is that to truly be a multi-wire circuit, the conductors are supposed to share the grounded conductor and this is accomplished by using two OC devices that are on separate opposite poles.
So, Question #1: What is the major problem with connecting a multi-wire circuit to a single pole “ tandem or dual” circuit breaker?
Back to the receptacles, which were simply not working. Luckily I had brought my circuit tracer with me and after a little investigation it seemed that half the kitchen was fed by the 12 AWG mutli-wire circuit that had been disconnected. It ran down the wall to a switch box and then split off - one circuit to the counter-top receptacles and the other to the garbage disposal and dishwasher. Apparently someone had been in the panel and pulled the original circuit breaker to replace it with a “quad 20/50” breaker and never finished the job. (Who knows???).
Well, the major problem was fixed, another problem had been identified, but what about the strange 30 volts I had mentioned? Something that I was wondering was, “Is the voltage coming from the circuit breaker, or is it some sort of back feed coming from the wire?” After disconnecting the wire from the breaker it became apparent that the voltage was on the wire itself, but where was it coming from? Well, we traced the circuit to the clothes washing machine in the garage. From there one circuit fed the washing machine and the other split off to the other half of the kitchen. We totally disconnected the home run at this junction box. So at this point let me describe, (to the best of my ability), what we are dealing with. We have a 3 wire 12 AWG romex with the black and white conductors connected at the panel and the red wire disconnected - on the other end of the 12-3 the circuit is disconnected and there is still 30 volts on the red conductor.
Question #2 - Where could these 30 volts be coming from?
Answer 1 – the major problem with improperly connecting multi-wire circuits (connecting both hots to the same 120v leg)is that the grounded conductor (neutral) does not carry the unbalanced current as intended … instead the currents of the two circuits add together on the grounded conductor and could potentially overload the conductor. In this case two 20 amp circuits could potentially put 40 amps on the neutral (12 AWG) conductor.
Answer 2 – Remember that I had mentioned this was a 12/3 conductor. As it turns out the 30 volts in the Red conductor were an “induced” voltage caused by the 120 volts in the Black conductor running next to it. Induced voltage or “Ghost voltage” is basically when the energy in one conductor is transferred into another … kind of like in a transformer. Something to be aware of – today’s electronic meters are very sensitive (but not always smart) and will often read any voltage.