I run #12 NM using 3 wire to run 120V smokes and share with a lighting circuit. The smokes have #18 wires to tie into. I am wondering about this reduced wire size being an issue. I know the things dont use much juice, but it seems odd to tie in #18 to a 15 or 20 Amp circuit. Is this a bad design or do the smokes' wires in the J-box count as part of the internal workings of the fixture?

Is there an article on this issue I can read up on?

Thanks in advance.

[This message has been edited by Joule-E (edited 08-30-2002).]

Treat it like a light fixture. Don't worry about protecting the small wire from overloads.

OTOH, the 18AWG conductors are considered adequately protected for short circuits by a 20-amp overcurrent device. It’s sort of a juggling act, I agree.

I don’t know if the detector and 115V pigtail can fail in any mode to start a fire. {?}