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#193582 - 04/08/10 02:36 PM Knob and tube grounded conductor bond?
crselectric Offline
Member
Registered: 09/24/06
Posts: 133
Loc: albany, ca
whats the risk? was doing some crawl space replacement of K&T circuit, as it was the type k's every 8 feet on bottom of joists and beams, evidence of rat infestation and needing some heat ducts replaced, tried to correct polarity on natural k&t ins. but circuit blew when I hooked up to breaker so there is a short down stream of black to earth, or possibly combined returns in k&t system works ok as originally connected....tried arc fault it wouldnt stay on....been like that for 80 years? Is it worth the needle in a hay stack isolating of the feeds up to find the short? Chris


Edited by crselectric (04/08/10 02:37 PM)
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#193584 - 04/08/10 04:05 PM Re: Knob and tube grounded conductor bond? [Re: crselectric]
HotLine1 Offline


Member
Registered: 04/03/02
Posts: 6776
Loc: Brick, NJ USA
Might be cost effective just to replace it with current Article 300 wiring method.

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#193592 - 04/08/10 07:28 PM Re: Knob and tube grounded conductor bond? [Re: HotLine1]
Rewire Offline
Member
Registered: 02/23/08
Posts: 165
Loc: Missouri
having pulled out miles of K&T you are much better off just replacing the circuit than trying to repair.
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#193594 - 04/08/10 07:57 PM Re: Knob and tube grounded conductor bond? [Re: Rewire]
crselectric Offline
Member
Registered: 09/24/06
Posts: 133
Loc: albany, ca
my thoughts too but getting access and moving antiques to upgrade is the question of level of importance, safety? chris
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#193596 - 04/08/10 10:38 PM Re: Knob and tube grounded conductor bond? [Re: crselectric]
Jim M Offline
Member
Registered: 08/10/01
Posts: 457
Loc: Chestertown, MD, USA
Sometimes K&T had a switched neutral. You need to check before making too many changes to the system.
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#193597 - 04/08/10 11:43 PM Re: Knob and tube grounded conductor bond? [Re: Jim M]
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9038
Loc: Estero,Fl,usa
I agree. They were really fast and loose with keeping the pairs separate in K&T and if it is working you are usually better leaving it alone until you are ready to rip it out.
My bet is you have a borrowed neutral somewhere that is giving you your bolted fault when you "fixed" the polarity problem. That will also give you a parallel neutral path that trips AFCI/GFCIs.
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Greg Fretwell
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#193598 - 04/08/10 11:56 PM Re: Knob and tube grounded conductor bond? [Re: Jim M]
crselectric Offline
Member
Registered: 09/24/06
Posts: 133
Loc: albany, ca
switched neutral is possibly why the white wire was hot. but just reversing the polarity shouldnt trip the breaker unless there is a short to ground downstream of the panel. Is there a tool that will locate a short, Ie inspector 2 or 3 and measure leakage? this house had some remuddling done before I arrived and just added new circuits as needed. otherwise my knowledge would tell me that somewhere there has to be a grounded box with the return wire bonded to it to make a dead short when polarity was switched, or would a possible old three wire k t circuit trip a breaker if one phase was swapped with the neut.? previous owners had new K&T wires pulled to old fpe panel for new kitchen remodel, prior to 1990, and a new 200amp panel for new remodel circuits, but kept the K&T, I've bypassed the fpe but trying to ring out the old circuits has been trying.
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#193599 - 04/09/10 12:06 AM Re: Knob and tube grounded conductor bond? [Re: gfretwell]
crselectric Offline
Member
Registered: 09/24/06
Posts: 133
Loc: albany, ca
thanks greg the borrowed neut. is possibly it, I just dont want to have floating voltage on a screw plate or water pipe but if it was bonded downstream you would only see that if you lost the neutral/return path, I am trying to talk them into ripping it out, but that may be a year away...chris
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#193601 - 04/09/10 06:51 AM Re: Knob and tube grounded conductor bond? [Re: crselectric]
Rewire Offline
Member
Registered: 02/23/08
Posts: 165
Loc: Missouri
I removed a K&T circuit that had the neutral looped back to the panel so both ends were connectewd to the neutral buss.
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