This one has me confused!!!

[jemsvcs]

Currently doing the finish work on an old structure that still uses knob and tube wiring. During the rough-in the local inspector asked me to clean up some open romex to knob-and-tube splices I had found in the attic that were done at some time in the distant past. Tracing out the circuit showed that one continuous run (approximately 80 feet) of old romex was spliced on one end between knob-and-tube and on the other between some old BX. At the knob-and-tube end my Greenlee Voltage Detector indicated that there was no voltage on the circuit. However, when I test the BX end the Detector registered voltage for the first ten feet after the splice!!! The Detector also registers voltage on the grounded conductor!!! What gives? This one has me totally confused.

[ November 12, 2003, 09:06 PM: Message edited by: jemsvcs ]

 

[noxx]

Re: This one has me confused!!!

Non-contact voltage testers are about as accurate as carpet bombing. They're fine for letting you know voltage is present, but generally do not distinguish between 120VAC, and 4 volts roaming around a loose neutral looking for a home.

You'll have to open up those splices and take some real readings on your multimeter to determine where the current is entering this "system" such as it is. Either way, knock the whole thing down, and meg out any wiring that you intend to leave in service. I find a megger provides excellent re-inforcement for abandoning K&T wiring, as it usually wont stand up to 500VDC.

let us know when you have some more info.

 

[big john]

Re: This one has me confused!!!

Jemsvcs,

On my very first side job, I was installing a seperate receptacle for a garage door opener. Using my hot-stick (non-contact voltage sensor) as my main trouble-shooting tool in trying to figure out what circuits were in this j-box. No matter what I turned off, I my hot-stick was still telling me I had power in the box. Unfortinately, I believed it and kept trying to trace these circuits. After ninety minutes of running back and forth flipping breakers and peering behind drywall with my flashlight, I finally decided to go get a multimeter and take some hard measurements, only to discover that some of these circuits had been off the whole time. That's how I learned the hard way that hot-sticks are almost worthless as a trouble-shooting tool.

As long as you're not trying to get a reading off of any metal raceway or armored cable or similar, if the hot-stick doesn't indicate voltage, chances are good the circuit is dead. That's about the only thing it's good at telling you. Otherwise, check everything with a tester/multimeter.

-John

 

[noxx]

Re: This one has me confused!!!

On a bit of a side-note, I prefer a meter with an NCV built into it, this way I never find myself with "just" a hot-stick. I use the Ideal 702 as my everyday tester, great meter for not too much money, covers all the functions I ever need for troubleshooting.