Can a furnace used to heat a home be plugged into a switched outlet on a single, dedicated circuit?

Not the way that I read 400.7.

BTW, you hit one of my pet peeves.
There is no definition of "dedicated", no matter how many times people think that it's in the Codebook.
I have had "dedicated receptacle" and "dedicated circuit" called for on many, many jobs...and it never meant the same thing one each one.
It either only has 1 load, or 1 type of load, or only feeds 1 area, or only feeds 1 room.
I've even taken to responding to requests for dedicated circuits with "what do you mean 'dedicated'? Does that mean that it always votes Republican"? At least that wise-acre answer opens up a discussion that if I don't know what they really want, I can't give it to them.

I think that your question was intended to mean ...switched outlet on a separate circuit.

My answer is still nope.

422.16 is probably more on point. You really bump into this language " ... the appliance is intended or identified for flexible cord connection."
You *might* be able to use the "vibration" and "service" language (with tongue firmly in cheek) otherwise.
I doubt any furnace manufacturer "identifies" his equipment as being suitable for cord and plug connection.
I suppose if you could get a letter from the manufacturer's engineering department, you would be good to go.

Out West, it is quite common to connect a furnace with a cord and plug. This has been particularily true when the electricity is only used to power a fan and an electriconic igniter.

I see a requirement that the furnace be on a 'dedicated circuit.' I understand this to mean that the breaker serving the furnace serve only the furnace, an associated equipment. For example, folks are installing electronic air cleaners, humidifiers, and the like into a 'air treatment assembly.' (to coin a phrase).

Now, there is the matter of controlling the furnace. I would have no problem with a timer, or occpancy sensor, being connected to a furnace. Indeed, a person might want a remote "disconnect" to shut off the furnace when the property was vacant - as in a holiday lodge. Many hotels also have a central control that can disable the individual thermostat in each room.

We want a dedicated circuit, so that an unrelated fault will not disable the heating equipment.

My concern with a switch controlled receptacle being used is the accidental disabling of the furnace. While I don't think the code specifically addresses this isue (so technically it would be allowed), I question the wisdom of this design.

I had a request to install a setup like that once, so that the furnace (gas) could be plugged into a portable generator during a power outage.

I ran it by the AHJ, and he was fine with it, as long as I used rough service cord and a twistlock plug/receptacle. Had to make up a special extension cord with a mating twistlock for use with the generator, as well. Setup is still in service, AFAIK.

As was already said, it would depend on the manufacturer's instructions.
Here we hard wire them in off of a single pole switch that is used as the disconnect. Usually located at the bottom of the stairs so if the furnace is on fire you don't have go close to it to cut the juice. It is on its own cicuit. We put a red switch plate on it that says "emergency" so you remember what it is for and don't accidentally turn it off.
http://www.tnb-canada.com/en/catalogues/online/comresconstruction/pdf/c1/boxes_18_eng .pdf

This is code here in Canada when the panel, which would normally be the disconnect is in the vicinity of the furnace. They don't want you to have to walk by the furnace to disconnect it if there is an emergency. Allot of times the panel is in the vicinity of the furnace so that is why we do it here.

No switch required if the panel is located between the furnace and the point of entry to the area where the furnace is located.

I know you are not from Canada but thought I would write it anyway because I like the reasoning behind our rule.

[This message has been edited by RobbieD (edited 01-19-2007).]

Why would the receptacle be switched?

If the furnace was wired with a cord, then the cord would meet the required disconnecting means.

I've never had to wire a furnace this way.

I second what renosteinke said, out here in California, we plug the FAU into a receptacle that's on an INDIVIDUAL (The correct term for dedicated) circuit.

And as ShockMe77 says, why add the switch, it's not needed.

The New Jersey way, as I know it;
Branch circuit from panel to furnace location. Hard wired to furnace. May have a single receptacle at/by/on furnace for accessory. May have a duplex if two accessories. (Single recept in 'unfinished basement area) Safety switch (disconnect) on/at/by furnace.

Furnaces installed in attics may have an additional safety switch by the point of entry into the attic.

As noted above, the switch at the top of the basement stairway for "emergency use' USED to be the norm, but has faded away.

The "safety" switches were required either by the Fire Code, or Mechanical Code, but not NEC to the best of my knowledge.

I have never seen a furnace cord and plug connected here, but...hey you never know.

John

Robbie's description is what I remember from Md. We always had a switch wioth a red plate, at the entrance to the furnace "space". If it was in a utility room the switch was at the door. If it was out in the open in an unfinished basement it was usually at the top of the stairs.
A lot of times it would be taped up so you couldn't hit it by accident.

Down here there is no such thing as a furnace. All we have is toaster wire in the air handler or a couple 2.5Kw wall heaters.

Around here, we hard-wire gas furnaces, with a single-pole switch as a disco. I don't know why it wouldn't be OK to do it with a cord-and-plug connection, as long as the cord is kept away from the flame. Yes, 400.7 does cast doubt on the legitimacy of that, but you have to admit, it would give people one less reason to backfeed their houses with portable generators, if they could simply plug the furnace into the generator.

Oh, yeah, the red plate. "Gas Burner Emergency Switch". I remember those. We don't use them around here.