said by evil_gusgus:Actually, I'm pretty sure plastic boxes are fine, at least in Ontario... In fact, my Knight book specifically mentions them, as an option, rather then using a metal box and vapour barrier, in exerior walls.
You arn't allowed to use plastic boxes in Canada for this use. The only time you use them is when their are outdoors. I would recommend that you use metal ones.
That said, I just about always use metal... And to the comments about grounding above, every plastic box I've seen has come with a metal bonding strip in it, that does require grounding.