question on wireing furnace, legal or not

We have experienced power outages lately. With the temperatures in the 20’s, I am looking to remedy my heating problem. At this time my forced air furnace is hard wired to my breaker box. I have a generator that is big enough to handle the furnace, sump pump, refrigerator and a few lights. I am trying to do this as inexpensively as possible, but (most importantly) safely.
I want to have the romex from the furnace circuit (where breaker is) end in a box with a receptacle close to the furnace. Then the romex from the furnace end in a box, (about a foot away from the receptacle) joined to a cord (with wire nuts) with the male end which gets plugged into the receptacle. This setup would be permanent. When there’s a power outage, switch off breaker then plug in extension cord from my generator to furnace. When power returns, unplug extension, plug cord back into the receptacle and switch breaker on. No grid involved. But is it legal, as in code?


A small transfer switch would be required for something to code -

I am sure someone from the electrical side can give you some wire by wire guidance

While I agree with you that setup would be no different than a garbage disposal with a plug, garage door openers with a plug, large 220 volt window HVAC units etc.

Main problem is that items that are permanently installed must be wired as same except for the items that are exceptions to the rule

Small transfer switches are not that expensive



I am sure many of us ( electricians ) could talk you through this but you will have a better chance over at as this is not really a DIY forum here and I am sure NACHI does not want the liability from telling a DIYer how to do something like this.

My furnace disconnect switch is a double pole double throw type. It is mounted in a 4"X4" box on the furnace. One side is connected to the house romex and the other is a 12" cord and cap. Furnace runs normally until switch is flipped from normal side to the cord side. Plug in the generator cord and voila! It’s legal because it transfers both the hot and the neutral wires from house power to generator power. This isolates any chance of back feeding generator voltage to the power company grid. That protects linemen from a potential shock hazard from your generator. The switch cost about $10. aregular manual transfer switch does the exact same thing. Make sure the generator is a good distance from the house. You don’t want any CO to find its way in.:mrgreen: :mrgreen:

As per Paul’s suggestion, I’ve been doing electrical work for 30yrs. I recommend this being done by a qualified person. A life may be on the line.:smiley:

P.S. You can’t use Extention Cord as permanent wiring and you can’t place a MALE attachment cap onto a romex wire and remain legal.

I can’t condone a jumper CORD made out of extention cord or the like as a permenant fix…sorry…

While it may be something YOU are aware of…it is the person who will mess with it potentially at risk…you are not ALWAYS potentially going to be the one to make this cheap fix.

Would not the manufacturers installation instructions and requirements for the furnace include its wiring? As such, wouldn’t deviations such as those suggested, be in violation?

Paul when you have 5k worth of meat in a freezer as I have been through numerous ice storms you do what you have to do. 14 degrees outside ambient. My furnace and my freezer most important.I will be running a generator no matter what. I could place my meat outside but the varmints would be into it country living you know. I feed my main panel with a home made # 8 from the 50 amp 220 volt outlet on the generator and just turn off the breakers I don’t want on. (Temporary Temporary)

Dude…I dont DEAL in WHAT IF’s…I can only deal in what I consider SAFE and LEGAL.

No cutting corners for the sake of saving some MEAT is not the right choice.

however, legally you can tell the guy whom is a DIYer to do it and IF by chance the guys burns his house down or kills himself…tell it to his son or daughter…whom could SUE the board.

lol…Ok…not coming down on you Charle…BUt you have to understand legal responsibilities of telling a person (DIYer) how to do something…wrong or technically illegal.

Now…if he just goes and does it because he HAS to do what he has to do…then not post about it…then I may agree.

Sites like has liability insurance for those types of questions…my site has coverage from my professional licence and covered…but I dont think NACHI has this insurance.

Please dont think i am coming down on ya…just explaining I can’t use the " do what ever is needed" approach to this type of question…sorry

or…Charley you could send ME about 2 K of that meat…ask Stephen in Seattle…I EAT alot…:slight_smile:

Dude…I don’t DEAL in WHAT IF’s…I can only deal in what I consider SAFE and LEGAL

I can understand your point of view but the gentleman was not asking how to wire it. He was just asking if it was code and its not. He had already made up his mind as to what he was going to do regardless of what you stated.


Just for information – how the heck can a 2 hp garbage grinder be wired on a plug under the sink and a furnace with equal or less current demand be required to be permanent??

Do not understand the code – Both are perm. at about the same current and if the furnace were to be on a plug one could just plug it into the generator with no problem and have heat safe an legal??

Just a question – not a debate



hmmm…just giving my opinion…I did direct him/her to a forum that possibly could explain to him how to legally do it…:slight_smile:

Ah…i thought I made a statement about it not being to code…at least I thought I did…

You basically answered your question…the Disposal is designed to be wired this way and and approved for such…if the furnace is wired in this manner then not a problem…

Careful I dont like generators running in the house…but thats a different thing I wont go into.

I was only making a statement to ensure the person does not put a male plug on Romex…and not to use any extention cords or FLEX as perm. wiring…thats all…

Sorry Charley…just figured he would want an opinion from an electrician and an electrical educator on why he should not do it that way…hell I get PAID for that advice…sorry if it was misguided.

Consider it some FREE consultation poster…feel free to do as you wish:)

Hope that makes all my HATERS happy…:slight_smile: ( I am teasing guys…honestly )

Come on OTHER electricians…here’s your chance to JUMP in and BERATE the GURU…i am sure they are lurking under many screen names…:slight_smile:

Not legal and I would not tell some one on here how to do it .
Would I do it sorry I do not have a furnace.
I have electric heat and a gas fire place .
We electricians can get in trouble with out trying .
Sorry go and buy the proper switch.
Every year we hear of Power outages and some poor person gets hit with a back feed .

Roy Cooke

Good transfer switch are less that $100.00 – cost of doing it correctly is probably less that doing it wrong


Sorry Charley thats The Tuna Commercial

Paul I wasn’t looking for an apologize You were absolutely right in your advice and I was just stating what I do in a crisis.
If you have never lived through a Hurricane, Tornado or Major ice storm you would have no clue as to the true devastation a person can feel and to what extent or even risk that you might be willing to endure for a little normallicy in ones life. My hat and a little sympathy goes to the gentleman for at least trying to prepare in advance of a crises thats more than most folks do.


Doesn’t the ground and any neutral have to be broken, as well as the line? If not, a back feed into the municipal grid could kill someone working on the line.

And a double pole breaker on a 120vac furnace doesnt cut it either. No fused neutral allowed.

Now, if the furnace is a plug in type (I see these in condo’s a lot and R Ray talks about them in CA), would a separate generator line to an outlet at the furnace be OK?

You can put O/C protection on the neutral if it also opens any ungrounded conductors. That can’t be a “fuse” but it can be an internal trip breaker with sufficient poles. The only problem with using the DPDT switch is it’s listing. It is not listed as transfer equipment. In the grand scheme of things that is not the worst violation you can have with generators. The other idea, cord and plug connected blower/thermostat is a source of discussion from time to time. It is, again, a technical violation but perhaps the safest alternative for a homeowner since there will be no connection to building wiring when the generator is used. You should be using a hard service cord, not Romex.

There is no requirement that the equipment ground ever be switched and better not to be. The only issue is the neutral and the possibility of parallel paths. This can get pretty complicated in language but the end result in a properly wired installation is that in any configuration of switching that there is only one bonding jumper point where neutral and ground connect. The easiest way is to unbond the generator and do not switch the neutral. Then the building electrode system and main bonding jumper is still your grounding path. You may still be driving a local rod at the generator but it will only be connected to the equipment ground. That grounding conductor musty be 6ga or larger to satisfy article 250 “bonding of electrodes”.