Detect common neutral with K & T wiring

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Old 08-16-16, 09:34 AM
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Detect common neutral with K & T wiring

I recently discovered, accidentally, that two circuits in my house use a common neutral. Is there some reliable method to detect if there are other circuits with common neutrals?
 
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Old 08-16-16, 09:58 AM
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Two circuits sharing a common neutral are called multi-wire branch circuits.
At the panel they originate with two breakers.... usually next to each other.... and utilize three wire cable with a ground.
 
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Old 08-16-16, 11:51 AM
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The two circuits I found with a common neutral are knob and tube. There is nothing in the panel indicating the common neutral. Both circuits originate from the panel with a hot and neutral. I want a method that will detect similar wiring in other circuits.
 
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Old 08-16-16, 12:28 PM
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If it's K&T pretty much assume there are shared neutrals throughout the house. It was standard practice to grab a wire from where ever it was convenient.

You can put a clamp on amp meter on the suspected shared neutral and turn off the hot that is supposed to be associated with it. If you still read current on the neutral it's coming from some other circuit. When doing this test you'd want to make sure that something is plugged in an turned on on each circuit.
 
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Old 08-16-16, 08:16 PM
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Both circuits originate from the panel with a hot and neutral.
If each circuit originates with it's own neutral then they aren't shared.

It sounds like it's time to move towards removing the K and T wiring.


I added K & T to original title as it makes a big difference.
 
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Old 08-17-16, 03:22 AM
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Here is a simplified version of what I believe is going on--a shared neutral even though both circuits originate with a neutral (k&t indicated by the raggedy nature of my drawing):

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Old 08-17-16, 10:00 AM
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You're asking how to determine where the two neutrals are connected ?
No easy way to locate or test.
The splice is probably somewhere in the wall requiring the opening of the wall.
 
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Old 08-18-16, 05:06 AM
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It is not unusual for a knob and tube multiwire branch circuit to have one hot wire daisy chaining through receptacles along the front of the house, the other hot wire along the back of the house, and the neutral running through the middle of the house.

You might be able to trace the routes of conductors using a wireless two piece toner set. This will be trial and error; an appliance or light still plugged in and turned on will cause additional wires in the walls to be sensed as part of the conductor path being tested.
 
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Old 08-18-16, 10:23 AM
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I recently discovered, accidentally, that two circuits in my house use a common neutral. Is there some reliable method to detect if there are other circuits with common neutrals?
How did you determine that two circuits share a common neutral?
 
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Old 08-18-16, 09:56 PM
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How did you determine that two circuits share a common neutral?
When my electrician disconnected H2 and N2 from the breaker box, the light second from the left went out, but the far left light stayed on (see my diagram below). I was surprised he didn't get shocked.
 
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