How to hard wire a furnace blower?

Nov 09, 2005 4 Replies

My wood furnace requires a dedicated 20 amp circuit, and is hard wired (i.e. not a 3-pin plug I can plug into a wall outlet).



It has a connection box on the side of the furnace. Do I wire all the way from the breaker box to the furnace without interruption?



Dean


I'm not sure of the code and I'm sure others will jump in, but I'd put a disconnect device near the stove.

Well, it is best; any connection can fail. But it is not a big deal if you need to put a junction box in.

I am a bit disturbed that they wired my dryer with #6 aluminum, and used a junction box about 5 feet from the breaker box; presumably they were using up a short cable. It is just a problem waiting to happen; but after 22 years I figure I am better off leaving it alone, as there is no easy fix. But that is aluminum; with copper it is not as serious.

Well that's a good idea. Indeed most of the powerful things in my basement have a labelled switch right next to them. I think I'll do that.

Cheers,

Dean

(2002) NEC Section 422.32 requires that all motor-driven appliances over 1/8 HP have a disconnect. In your case, a regular 20 amp switch rated for at least 3/4 HP will suffice. When you buy the switch, if it is HP rated, it will be stamped on the switch. You can run PVC down the wall to the switch box, then use flexible conduit (Greenfield) from the switch box to the unit connection box.

If the furnace came from the factory with a unit ON/OFF switch, NEC Section 422.34 permits that switch to be used as the disconnect, in which case you can wire straight to the connection box.

If the nameplate on the furnace says "use fuse only" or similar statement, you _must_ provide one as required by NEC Section 422.11. A circuit breaker is _not_ sufficient in that case. In other words, when you are done, you will have a circuit breaker in the electric panel, but will also have to provide a fuse at the furnace. Usually a combo switch/fuse is used with the proper fuse installed. The combo switch/fuse is available at most stores that sell electric supplies.

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