Is a dedicated circuit to gas furnace always required?

Question

USA NEC 2014.

Is there any way to dodge the requirement for a dedicated circuit for a gas furnace? I need to hang one more small hardwired load right near the furnace, and would rather not run a new circuit.

The other load is not HVAC related, and this is an office outbuilding not a domicile.

This is on the side of the furnace and supplies the furnace.

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Could you pull a feeder to a small subpanel? The branch circuit would just be from the subpanel to the furnace then, correct? — Hari, Apr 05 '18 at 00:30
What is providing the service disconnecting means for the furnace at this moment? — ThreePhaseEel, Apr 05 '18 at 00:30
@hariganti no nearby wall to install sub at proper height and clearance. — Harper - Reinstate Monica, Apr 05 '18 at 02:27
Is there simply not enough space there to provide clear working space around a subpanel, no matter where it was put? — ThreePhaseEel, Apr 05 '18 at 03:05
@threephaseeel there's no wall to mount it to, furnace is in center of room. — Harper - Reinstate Monica, Apr 05 '18 at 03:12
The nearest wall is nearly as far as the panel, so I might as well go there. — Harper - Reinstate Monica, Apr 05 '18 at 03:18
@Harper -- I can't find anything in articles 312 or 408 that would prohibit slapping a surface-mount loadcenter (panelboard+enclosure combo) on the furnace itself, provided it can be attached securely to the furnace — ThreePhaseEel, Apr 05 '18 at 03:46
I would consider mounting the panel on the unit, I have seen panels mounted on equipment many times in industrial equipment, not so much in residential because there is room in most cases. Three phase make that an answer I will up vote — Ed Beal, Jun 13 '18 at 15:39
I am reluctant to attach anything to the furnace since it's somebody else's "baby". I also wanted to get this building wrapped up. Since the other load is a fridge, I decided to "walk my talk" and put the fridge on a dedicated circuit. I only had 2 circuits in the conduit so still 1 more without derate (not that it'd hurt anything to derate fridge and furnace to 15A). — Harper - Reinstate Monica, Jun 14 '18 at 15:13

ThreePhaseEel · Answer 1 · 2020-01-09T03:56:00.193

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Put a subpanel here

Provided there's enough clear working space out from that side of the furnace, you can replace that fusible mini-disconnect (switched fuse cover) with a small subpanel (a "spa panel" type of disconnect is large enough for this job, although GE makes? or at least made the TL510RT that is basically perfect for a 120V only application if you can get it, and SqD has the QO24L50TTS that will do the trick here as well), that has 2 15A breakers on the same leg, one for the furnace and one for the other circuit. (You can also put the service receptacle for the space on this panel, if one is not already present.)

Or, if this is all in conduit...

If this circuit is run entirely in conduit, then there should be enough space for another 15A circuit (hot+neutral) in there for the remaining loads, allowing the furnace to be left alone on the existing circuit, or vice-versa, with the furnace moved to the new circuit and the other loads left on the existing circuit.

edited Jan 09 '20 at 03:56

answered Jun 14 '18 at 07:04

ThreePhaseEel

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It's in EMT.... I'd have another circuit run before you could get back from the store, having spent not even $5 in wire, while you're spending +$50. - How to dodge and not have to run a new circuit? Spend fifty bucks. – Mazura Jan 09 '20 at 02:02
@Mazura -- if it's in conduit all the way, pulling another circuit would be an option, but we don't know that from just the photo given – ThreePhaseEel Jan 09 '20 at 03:53
True, or if there's a whole bunch of junction boxes. They ended up running a new circuit, +1 – Mazura Jan 09 '20 at 04:15

score 1 · Answer 2 · answered Apr 06 '18 at 08:12

I don't think you can dodge the requirement with Gas Furnace; the code is quite clear about this so dodging it is not possible unless an inspector is blinded by a vision of Ben Franklin (not an endorsement of using such a method, just saying something not right would have to be going on to 'dodge' the code) .

The potential for a "potential" for a serious problem due to overheated wiring and overloaded wiring - not too mention the spikes from other items on the same circuit might be hazardous (even if YOU do know what you are doing - some other wingnut might not). I think this was the reasoning behind the rule and it does make a whole lot of sense. I remember working with industrial size gas roasters and some jobs I just could not do with out a Gas Certification - and that was for good reason too.

score 0 · Answer 3 · answered Apr 06 '18 at 11:09

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Absolutely not, and for good reason too. Who's to say the next person won't assume what you've done and add-on to your add-on.

And probably the main reaaon why: people can be seriously hurt, even die w/out heat.

answered Apr 06 '18 at 11:09

Kris

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Code is about electrical safety not if you have heat or not. There are ways to do this such as creating a sub and then the additional load is on its own circuit from the sub. In addition to this it is not a living space commercial/ industrial requirements are less restrictive. – Ed Beal Jun 13 '18 at 15:42

Jeff · Answer 4 · 2021-11-29T06:23:04.670

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In addition to the code making it a requirement, there's a considerable amount of line noise that may come from even a small residential furnace. I'm not sure why there's so much noise, but the noise is likely to affect some what you might connect, including lighting. This is from personal experience. A good understanding of electronics enabled accurate diagnosis and correction of the problem - accomplished by restoring it to compliance. I won't make the same mistake again.

edited Nov 29 '21 at 06:23

answered Nov 29 '21 at 06:07

Jeff

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Realize as well that noise potential IS a two way street. You don't want something adversely affecting your furnace. It's too risky, expensive, and could be dangerous. I know the people who created the codes know more than I do. – Jeff Nov 29 '21 at 06:31

Is a dedicated circuit to gas furnace always required?

4 Answers4

Put a subpanel here

Or, if this is all in conduit...

Linked