induction on knob and tube

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tdjs

Member
Whats the correct way to splice a 240 volt knob and tube to nm wire? Would you get induced induction from phase A and B going through the knock outs on a metal j-box or would a non metallic box be the preferred method?
 
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scook56

Member
Location
Allentown, PA
K&T Splice

K&T Splice

I use a sleeve of NM covering on K&T conductors, w/ NM connector or NM-two screw connector to box.
Gnd. metal box NM w/GEC.:happyyes:
PVC box, wire nut GEC.
 
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lakee911

Senior Member
Location
Columbus, OH
K&T should enter the same knockout in a box to prevent inductive heating of the metal. Usually done, back in the day, with a cloth sleeves around the wires. Plastic box, enter any which way.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
While 300.20 would require the K&T conductors enter the same opening on a ferrous metal box, I have never seen that in any K&T installation. The conductors always entered in separate opens. I don't see a real world issue if you enter via two openings, just a code issue. There is a lot of information out there, including the Canadian Electrical Code, that says this is not really an issue unless the current exceeds 200 amps.
 
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