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
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.
#193598 - 04/09/1001:56 AMRe: Knob and tube grounded conductor bond?
[Re: Jim M]
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.
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