no resistance between hot and neutral?

[ndrose]

Hello--

Today I was working on an old door jamb switch which I thought had gone bad. (As it turned out, the strike plate just needed adjustment, and is working correctly now.) My question pertains to the routine testing I did while I had the switch disconnected.

With the circuit on, I had the expected 110-120 volts between the two wires to the switch.

With the circuit OFF: I had zero resistance between the two wires(!)

With the circuit off and the light bulb removed: back to infinite resistance.

I tested this several times with the bulb in and out; I was consistently reading a connection between the two wires as long as the bulb was in. I don't understand how this could be without shorting the circuit.

Any ideas?

Additional information: since this is old BX wiring, I have the circuit on an arc-fault breaker. There was one place in the house when I first moved in where the ground sheath was the return path for a particular fixture. Once I put the arc-faults in, turning on that light would throw the breaker, which is how I discovered the problem.

Thanks for any advice

--Nathan Rose

 

[Dennis Alwon]

I am closing this thread, in accordance with the Forum Rules.

This site is designed for:

• Contractors
• Electricians
• Engineers
• Inspectors
• Instructors
• Other electrically related individuals

* This NEC? Forum is for those in the electrical and related industries. Questions of a "How-To" nature by persons not involved in the electrical industry will be removed without notice.

If you feel this action to be in error, feel free to contact me via PM to explain.

A reminder to all members, if you see a questionable post, feel free to report it by clicking the

button at the bottom left corner of the post.