Advice on knob and tube wiring - mystery short


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Old 01-16-14, 12:05 PM
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Advice on knob and tube wiring - mystery short

I own a 2-story 1906 house with a modern breaker panel. There is still an active K&T circuit for the downstairs ceiling fixtures. All the wall outlets have modern wiring back to the breaker. The K&T circuit is tied into a subpanel (modern wire from a 15A breaker, black tied to hot K&T, white tied to neutral K&T). The downstairs K&T circuit just developed a short (trips the breaker and won't reset). If I disconnect either the hot or neutral at the subpanel, I can reset the breaker, so the short is in the K&T section. I disconnected all the wall switches that run to K&T ceiling fixtures, and all the "unswitched" (pull chain) fixtures, made sure the wires were separated, but the breaker still trips, and I get a ~300kOhm short when I test between the hot and neutral (using a cheapo multimeter/tester). I took down all the ceiling fixtures, they are all old K&T wiring, so it does not look like there was a splice added to the K&T circuit during a remodel. All fixtures and switches have just 2 wires (hot in/out at the switches, and hot/neutral at the fixtures), so there are no junctions at the fixtures (each one appears to be the endpoint of a K&T branch). I had an electrician come out and he came to the same conclusion, that there is a short between the hot and neutral, and suggests a rewire to the tune of $3-$5k (and probably that much again to patch the openings he will cut). But I just don't understand where this short could be, given that the hot and neutral of K&T should not be in physical proximity to each other. Any advice, additional troubleshooting to do, or is a rewire the only/best option? Thanks
 
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Old 01-16-14, 12:37 PM
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All fixtures and switches have just 2 wires (hot in/out at the switches, and hot/neutral at the fixtures),
The power has to come in somewhere and if only two wires at both the switch and light the power has to come in somewhere other than the switch or light. Your short may be at the "other than" location. You need to find that place. Hopefully it is a junction box. Best guess it is a junction box that was added during the rewire to connect the lights to a new cable.
 
 

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