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Old 12-17-2012, 02:24 PM   #1
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weird wiring and wierd voltages on 3 dual switches...


In our 1969 home that we've had 7 years, we have a mystery. There are 3 dual switches in one switch box by our back door (so 6 switches total), and until recently, we could not find anything that they control. We just found that ONE of the switches controls some outdoor light boxes from which the lights had been removed. In searching for the circuit breaker to this switch and these lights, we found that TWO circuit breakers power it. I opened up the switch box and found that each dual switch has two circuits feeding it (a separate line to each of the two switches), but the jumper between the two switches was never removed.

Is there a reasonable explanation for what can be going on here, such that this is actually correct? SHOULD I GO AHEAD AND REMOVE THE JUMPERS??

I detached the line wires from the switches to sort out exactly which breakers are feeding which switches, and I'm getting really weird voltage readings in one aspect. The top switch of two of the dual switches is fed by the same breaker, and they seem normal...the voltage across the line wires to their load wires is 120V as expected. The weird part is that for the bottom switches that are fed by another breaker, the voltages across those line wires to their load wires on the switches, are zero and 35V, but oddly the voltages across the line wires to the load wire from the OTHER switch is 120V.



More info: There are no neutral wires in the switch box...just a line wire and a load wire for each switch. The two breakers that power each switch are not tied together. They are not on top of each other (but are on the same side of the circuit breaker box).

Is there any rational explanation for these voltages and why these switches would be wired this way? Or was it just someone incompetent? Help!

Thanks a million for any insight you have!!

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Old 12-17-2012, 03:47 PM   #2
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weird wiring and wierd voltages on 3 dual switches...


Don't measure across the two terminals of a switch; that does not give useful results.

Measure voltage from hot to neutral (either side of the switch to neutral, record both values) or from hot to ground, the latter may need electrical experience to interpret if it seems unusual.

What do you mean by a dual switch with a jumper? Post a picture of it.

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Last edited by AllanJ; 12-17-2012 at 03:50 PM.
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Old 12-17-2012, 04:57 PM   #3
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weird wiring and wierd voltages on 3 dual switches...


I think he means one of these.

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Old 12-17-2012, 05:37 PM   #4
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weird wiring and wierd voltages on 3 dual switches...


Yes, that is what I mean.

Also, I cannot measure across the neutral, as there are no neutral wires in the box. I get 0 volts with respect to the metal box itself.
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Old 12-18-2012, 07:54 AM   #5
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weird wiring and wierd voltages on 3 dual switches...


If you are correct about the two circuits then yes the jumper should be removed.
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Old 12-18-2012, 12:37 PM   #6
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weird wiring and wierd voltages on 3 dual switches...


Getting zero volts from all conductors to a metal box almost always means that the box is not grounded, which is against today's code but may be grandfathered. You can get a reference neutral for measurement or test purposes by stringing a long single conductor (14 to 20 gauge) from the panel neutral bus up the stairs and across the floor to where you are working. You can get 18 or 20 gauge wire from Radio Shack too.

Grounding the metal box (bonding it to the house grounding electrode system) is a separate topic.

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Last edited by AllanJ; 12-18-2012 at 12:39 PM.
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