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?
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.
(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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