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Knob and tube grounded conductor bond? #193582 04/08/10 04:36 PM
Joined: Sep 2006
Posts: 155
C
crselectric Offline OP
Member
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

Last edited by crselectric; 04/08/10 04:37 PM.
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Re: Knob and tube grounded conductor bond? [Re: crselectric] #193584 04/08/10 06:05 PM
Joined: Apr 2002
Posts: 7,233
HotLine1 Offline
Member
Might be cost effective just to replace it with current Article 300 wiring method.



John
Re: Knob and tube grounded conductor bond? [Re: HotLine1] #193592 04/08/10 09:28 PM
Joined: Feb 2008
Posts: 165
R
Rewire Offline
Member
having pulled out miles of K&T you are much better off just replacing the circuit than trying to repair.

Re: Knob and tube grounded conductor bond? [Re: Rewire] #193594 04/08/10 09:57 PM
Joined: Sep 2006
Posts: 155
C
crselectric Offline OP
Member
my thoughts too but getting access and moving antiques to upgrade is the question of level of importance, safety? chris

Re: Knob and tube grounded conductor bond? [Re: crselectric] #193596 04/09/10 12:38 AM
Joined: Aug 2001
Posts: 457
J
Jim M Offline
Member
Sometimes K&T had a switched neutral. You need to check before making too many changes to the system.

Re: Knob and tube grounded conductor bond? [Re: Jim M] #193597 04/09/10 01:43 AM
Joined: Jul 2004
Posts: 9,569
G
gfretwell Offline
Member
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.


Greg Fretwell
Re: Knob and tube grounded conductor bond? [Re: Jim M] #193598 04/09/10 01:56 AM
Joined: Sep 2006
Posts: 155
C
crselectric Offline OP
Member
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.

Re: Knob and tube grounded conductor bond? [Re: gfretwell] #193599 04/09/10 02:06 AM
Joined: Sep 2006
Posts: 155
C
crselectric Offline OP
Member
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

Re: Knob and tube grounded conductor bond? [Re: crselectric] #193601 04/09/10 08:51 AM
Joined: Feb 2008
Posts: 165
R
Rewire Offline
Member
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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