minimum bending radius THHN

[ChristianD]

i am looking for the minimum bending radius for THHN like a #12 no specific size. i know the minimum radius for romex is 5 times the diameter. could someone help me with stranded cable. code reference and example please. thanks christian

 

[iwire]

Re: minimum bending radius THHN

I do not believe there is min allowable radius given for single conductors.

There are minimum bending space rules in 312.6

 

[roger]

Re: minimum bending radius THHN

Christian, what are you asking specifically?

If you look inside a standard device type of box, these conductors are practicaly kinked.

Other than that, open your code book to article 312.6.


Roger

 

[ChristianD]

Re: minimum bending radius THHN

what i am looking for exactly is i have always been tought i guess since when i was back in scool the the code tries to lead you away from makeing any more bends than needed by haveing restrictions on some bending radius. i have also been told by one inspector that making a 90 on termination in a panel is illegal with no reerence on his part. i make up a lot of control panels that may have over 100 wires. and i bend them or sweep them in with no 90's because i have been tought that or "told that since i was in school i just wanted to know if there was any restriction on that, the only 1 i have found is for over 600 volts. i guess i was just under the assumption there was restrictions on the radius bends of single conductors also
thanks christian

 

[jim dungar]

Re: minimum bending radius THHN

If we cannot make a very sharp 90 degree bend in #12 and smaller wire, how it it possible to wrap it around a wire binding terminal/screw?

Actually, per UL508A for control panels, wire bending space for #14-10 is not specified. However, for field terminations a wire binding screw for #10 and #12 must be at least a #8 (4.2mm or 3/16" dia).

edit: reference

[ July 21, 2005, 08:56 AM: Message edited by: jim dungar ]

 

[ChristianD]

Re: minimum bending radius THHN

NMB has a minimum radius of five times the diameter so i guess when the cable is stripped no rules are applied to the conductors? that would make sense. i guess what i have been reading is that in NMB it is to protect the cable itself. other than thhn I also use a lot of twisted sheilded cable 18 to 22 AWG so i will have to check on that. just trying to educated myself a little. thanks guys
christian

 

[George Stolz]

Re: minimum bending radius THHN

ChristianD, welcome to the forum.

Originally posted by ChristianD:
...the code tries to lead you away from makeing any more bends than needed by haveing restrictions on some bending radius.

I don't believe the restrictions are to keep unnecessary bends out of the cables. I think the requirements are there to prevent damage to cables by extreme turns that would pinch the cable, causing heat buildup in a spot in the cable.

For example, take a piece of #14, put a little scratch in it with your dykes. If you start bending the conductor back and forth in that area, it will break there. That's a weak spot.

While not a rock-solid analogy for the principle I visualize, I assume it's something along those lines. When you take a hard, abrupt turn with a cable or conductor...

...Picture a pipe. Bend it in half, at a hard 90?. In general, there is more material at the inside of that bend than the outside. Now run current through it. I'd imagine the resistance of one edge of that bend in the pipe is different than the other. In the difference is heat difference. In the difference, there's stress. There's heat, stress, bad things for a current carrying conductor.

It's a flimsy analogy, but it's kinda what I picture when I think of a kink in cable.

When you say, "unnecessary bends", it brings to mind the 360? rule as it applies to conduit, and that's definutely a different concept than the one in place for cables.

Hopefully some better analogy-makers can pitch in and correct me or augment my statements.