Light switch using a neutral maybe double fed

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haywire

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Milpitas, ca
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Electrician
This is the problem. No voltage at switch when in off position. Flip on switch one wire has power. Only one set of wires in switch box. At the light there are only two individual black wires coming into the box. when the switch is off there's voltage reading on both wires when the switch is turned on only one of the wires has voltage. I haven't been to the site yet I was on the phone with the people as they were checking the wire with a voltage tester when I get there I will use a meter on each of the wires. I'm wondering what could do that I know another switch in the house the guy was switching the neutrals. Any ideas would be appreciated
 
I suggest plugging an extension cord into a known-properly-wired receptacle to find the true hot and grounded conductors, and testing with a solenoid tester, not a volt-meter.
 
haywire said:
I haven't been to the site yet I was on the phone with the people as they were checking the wire with a voltage tester when I get there I will use a meter on each of the wires.
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I take it this means that they were using a non-contact tester?

haywire said:
At the light there are only two individual black wires coming into the box. when the switch is off there's voltage reading on both wires when the switch is turned on only one of the wires has voltage.
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If the neutral was being switched it would show that behavior. When the switch was off, the switch leg conductor would be fed with voltage through the light, and so both wires to the light would show voltage being present. And when the switch was turned on the switch leg would be pulled to the neutral, and therefore the tester would not indicate any voltage on it.

haywire said:
No voltage at switch when in off position. Flip on switch one wire has power. Only one set of wires in switch box.
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I'm having a hard time understanding how this behavior could be possible. But if you change the word "off" to "on" and vice-versa, then switching the neutral would exhibit exactly this behavior. When the switch was turned on then both of its wires would be at neutral potential, and therefore no voltage would be indicated on either wire. But when the switch was turned off there would be voltage present on the switch leg that is being conducted through the light, but there would be negligible voltage on the neutral wire that's connected to the switch.
 
synchro said:
I take it this means that they were using a non-contact tester?


If the neutral was being switched it would show that behavior. When the switch was off, the switch leg conductor would be fed with voltage through the light, and so both wires to the light would show voltage being present. And when the switch was turned on the switch leg would be pulled to the neutral, and therefore the tester would not indicate any voltage on it.


I'm having a hard time understanding how this behavior could be possible. But if you change the word "off" to "on" and vice-versa, then switching the neutral would exhibit exactly this behavior. When the switch was turned on then both of its wires would be at neutral potential, and therefore no voltage would be indicated on either wire. But when the switch was turned off there would be voltage present on the switch leg that is being conducted through the light, but there would be negligible voltage on the neutral wire that's connected to the switch.
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If I’m understanding correctly, I thought that’s what he was saying. I have seen a switched neutral in a older house before.
 
Thanks everybody... When the switch is on and light disconnected I get about 120v across the 2 wires (the wires at the light). Switch off, light disconnected there's around 20.6v across the wires. My main question now is if I should leave it alone and wire up the new switch location the same way? Old switch box as j box run new wire connect to new switch.
 
haywire said:
Thanks everybody... When the switch is on and light disconnected I get about 120v across the 2 wires (the wires at the light). Switch off, light disconnected there's around 20.6v across the wires. My main question now is if I should leave it alone and wire up the new switch location the same way? Old switch box as j box run new wire connect to new switch.
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If it was working beforehand I'd run the new switch connect the wires in the jbox to the new wire you ran, put the switch on the new wire and keep getting it assuming it works correctly.
 
haywire said:
Thanks everybody... When the switch is on and light disconnected I get about 120v across the 2 wires (the wires at the light). Switch off, light disconnected there's around 20.6v across the wires. My main question now is if I should leave it alone and wire up the new switch location the same way? Old switch box as j box run new wire connect to new switch.
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Use a low impedance meter if your not already doing so.
 
haywire said:
Thanks everybody... When the switch is on and light disconnected I get about 120v across the 2 wires (the wires at the light). Switch off, light disconnected there's around 20.6v across the wires. My main question now is if I should leave it alone and wire up the new switch location the same way? Old switch box as j box run new wire connect to new switch.
Click to expand...
Seen this effect when someone has spliced neutrals from multiple circuits that have passed thru a common jbox and a device is turned on the other circuits, then getting neutral current taking "all available paths". This can cause you some issues if installing LED on the switch. Also you might have a potential code with the spliced multiple circuit neutrals if you have them.
 
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