410.67(C)

[dana1028]

I was taught the intent of this section is to 'thermally isolate' the old 60 degree C knob & tube conductors from new fixtures that require 75-90 degree C conductors. [and this section apparently prohibits the use of NM to accomplish this 'isolation'].

410.64 says 'fixtures installed in recessed cavities in wall or ceilings shall comply with 410.65 thru 410.72'.

What about surface mounted fixtures requiring connection to 75-90 degree conductors? Is there not a 'thermal isolation' requirement for them?...or does this fall to 110.3 'per manufacturers listing'?

 

[physis]

Re: 410.67(C)

I think 410.67(C) is meant to address lighting in suspended ceilings where you can't support the conduit.

 

[curt swartz]

Re: 410.67(C)

Dana,

I don't think that 410.67(C) was intended to apply to most current designs of recessed lights which are pre-wired. Older recessed lights were not pre-wired so the field wiring had to connect directly to the socket. Most building wire was only rated for 60C or 75C but the connections to the socket had to be high temperature wire so a junction box and short section of high temperature wire needed to installed in the field. I guess the 18" minimum length of the tap conductors is what was found necessary to dissipate the heat before connecting to the branch circuit conductors. The reason type NM cable is not listed is that most if not all of these fixtures required the wire temperature to be higher than 90C and up until the early 80's type NM cable was only rated for 60C.

I personally don't see a problem using type NM-B to transition between K&T or old NM as long at the recessed fixtures are rated for direct connection of type NM cable.

Curt