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See Diagram

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I have a switch that controls a light as seen in this diagram. There is no neutral at the switch, instead, it picks that up from somewhere else. In the light receptacle it pigtails into the light and continues to the garage.

I measure 120v between the source hot and ground, and 120v when the switch is on between the hot lead and ground. In the light box, with the light disconnected I get 19v from neutral to ground. with or without the light, I get 90v between the hot to neutral.

In the garage, the outlets read out 120v and everything connected to them seem fine (work).

What is the right way to diagnose this? Any ideas why I'd be getting 20v in the neutral?

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  • Can you post some photos of what's going on here?
    – ThreePhaseEel
    Commented Nov 4, 2016 at 22:22

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Basically the neutral has current trying to return back the the transformer and is dropping voltage due to how a neutral is simply a series circuit.

When the source hot passes thru the light (as a parallel circuit), it continues out the neutral without dropping voltage.

The problem with this circuit is the neutral and hot do not originate in the same junction box and is very confusing not only DIY's but also electricians, not to mention a Code violation.

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    Thank you for this. Your comment about the neutral not originating in the same box got me thinking. I started tracing wires and discovered this neutral was connected to a 3way switch that was miswired. I also got to find another light that was used as a jbox and packed with cloth wiring... Ugh.
    – Will
    Commented Nov 9, 2016 at 23:01

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