# Knob & tube polarity ID



## Tinstaafl (Jan 6, 2008)

I've never been able to visually discern the difference between hot and neutral on the old K&T wiring--but of course it's all covered with dust and crud these days.

Did they actually do anything to ID them?


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## griz (Nov 26, 2009)

I do not believe so.

In those days it did not matter which way the plug went into the receptacle.

Every so often I have seen one of the wires with a white stripe down it.

Have no idea if it really meant anything.


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## rrk (Apr 22, 2012)

There was a white tracer or a red tracer.


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## CarpenterSFO (Dec 12, 2012)

Sometimes a little white paint on a lead, in a box. Not that I'd trust it. Up in the attic or in the basement, I don't think I've ever seen any marking, although you can usually tell from where the conductors go which was which.


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## hdavis (Feb 14, 2012)

rrk said:


> There was a white tracer or a red tracer.


Yup, you just have to wash it good to see it.


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## rrk (Apr 22, 2012)

just asked my electrician, initially cloth covering was black; the wire for neutral was bleached to a natural color. Then the had red or white strands of cloth in the cloth covering of the black and stopped the bleach because it deteriorated the cloth. Then they just dipped the wire in paint about the time armored cable started. 

He reminded me about the wooden wire raceways we used to see mounted on the ceilings.


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## Inner10 (Mar 12, 2009)

I remember seeing red fibers in the jacket of the wire when I stripped it...never knew it was for polarity.


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## Dave in Pa (Oct 10, 2009)

I have seen and worked on a few! The wires as old as they are, I can't with my old eyes see any difference! Then try tracing back the leads! THAT is worse!! Just walk away, and recommend a re-wire!


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## Tinstaafl (Jan 6, 2008)

rrk said:


> He reminded me about the wooden wire raceways we used to see mounted on the ceilings.


I just pulled one of those off the wall of a garage last year. Kind of hated to do it in a way.

Guess I'll have to get my toothbrush and some liquid cleaner out the next time I get to play with some K&T.


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## SectorSecurity (Nov 26, 2013)

The better question is how often are you running into knob and tube wiring?


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## hdavis (Feb 14, 2012)

SectorSecurity said:


> The better question is how often are you running into knob and tube wiring?


Hopefully he sees it before that happens.:whistling


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## Tinstaafl (Jan 6, 2008)

SectorSecurity said:


> The better question is how often are you running into knob and tube wiring?


Somewhere between never and all the time; just depends on how the jobs happen to fall. There's still a _lot_ of it in use in old houses.


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## Inner10 (Mar 12, 2009)

SectorSecurity said:


> The better question is how often are you running into knob and tube wiring?


Still a decent amount left in ottawa.


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## GettingBy (Aug 19, 2010)

Maybe it's 1 in 3 that the colors are wrong. The older the house, the more likely it's 50-50 that the color is wrong.

The wire that has less than 2vac on it when measured with respect to any earth ground (soil, concrete, a cold water pipe, a faucet) is the neutral.


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## CarpenterSFO (Dec 12, 2012)

SectorSecurity said:


> The better question is how often are you running into knob and tube wiring?


We're sorting out a K&T job right now. I traced an old circuit, still live, from a ceiling box, out in a 60-foot detour around the house, where the conductors are mashed by water and gas pipes and ducting, and are getting in the way of new work, back to a box about 3 feet from the original one, in the same joist bay. There isn't a single currently active outlet, any connection, anywhere along that 60-foot detour; where there once were are some little tails with wire nuts. We'll wire between the 2 boxes and pull all the old wires. We run into this sort of thing frequently.


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## Tinstaafl (Jan 6, 2008)

CarpenterSFO said:


> back to a box about 3 feet from the original one, in the same joist bay.


Sometimes you just have to wonder. :laughing:

I'll do just about whatever I can to avoid even replacing a fixture wired with that stuff. The insulation's usually so brittle you need the hands of a neurosurgeon to touch it without cracking it. And cracking it. And cracking it.


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## Quad Racer (Jun 2, 2014)

Lick fingers and apply liberal pressure to each while standing bare footed in water. If you're lucky you won't feel anything the first try. :thumbsup:


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## CarpenterSFO (Dec 12, 2012)

Tinstaafl said:


> Sometimes you just have to wonder. :laughing:
> 
> I'll do just about whatever I can to avoid even replacing a fixture wired with that stuff. The insulation's usually so brittle you need the hands of a neurosurgeon to touch it without cracking it. And cracking it. And cracking it.


I went back to the shop at lunch today and brought an extra fire extinquisher back to the job.


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## hdavis (Feb 14, 2012)

I think all the brittle stuff I've come across was from getting hot, either in a light fixture, box, something. The runs of air insulated wires usually are still gummy if you try to cut then out. It could be different in a hotter climate...


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## Quad Racer (Jun 2, 2014)

Me too. I've found the most brittle when swapping light fixtures. Appearantly most old timers would just screw in a 100 watter and call it good.


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