Running furnace from generator

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  #1  
Old 10-29-06, 04:12 PM
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Running furnace from generator

I would like to rewire my forced air furnace to run off of a generator when needed. I am not looking to install a manual transfer switch at the panel, as I only want to be able to run the furnace if the power goes out. Anything else I need powered can be done via extension cord. Can I just terminate the existing furnace supply wiring to an outlet and wire in a plug to the furnace itself? If not is there a more permanent and just as safe to the utility crew method?


Thanks,

Eric
 
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  #2  
Old 10-29-06, 04:23 PM
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You could do this. First you must have a three (3) position switch (disconnect). This way there will be absolutely no chance of a back feed.

Myself, I am interested in others opinions. Before I go further.
 
  #3  
Old 10-29-06, 04:29 PM
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No need for a switch if you terminate the furnace wiring with a plug.
I would recommend two junction boxes.. Put a receptacle on the panel side. Put a short piece of cabtire out of the furnace side to plug into the receptacle or the generator extension cord. It would not be code to put a plug directly on the end of the NM cable.
 
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Old 10-29-06, 05:10 PM
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Think about the tech out there.

How easy would it be to add a rec/cord cap to back feed the furnace/boiler?
Quite easy.
How easy, in this manner would it be to screw up?
Quite easy.

How easy would it be to knock on the families door, or know that you sent the mesenger?

Probably the hardest thing you have ever done in your life.
 
  #5  
Old 10-29-06, 05:17 PM
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lectriclee,
I did not understand a word you said in the last post.

It sounds like joed is saying I can basically make the furnace plug-in, although I do not know what cabtire is. Are you agreeing or disagreeing with him?

Thanks,

Eric
 
  #6  
Old 10-29-06, 05:43 PM
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#I did not understand a word you said in the last post.#

You absolutley, do not want any generator power going back into the power grid (utility supplied power). This is a back feed. The utility people are working on lines presumed off. Stray voltage Kills.

I suggested a 3 position switch to iliminate this possibilitey.
Perhaps Joed can elaborate on his point.
There are other options.

I'm thinking safety for all.
 
  #7  
Old 10-29-06, 05:54 PM
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It would not be code to do this any other way than a transfer switch. This can be as simple as a single pole/double throw switch wired into the furnace circuit.

The safest thing is a single transfer switch from folks like Gen-tran.

http://www.gen-tran.com/eshop/10Expand.asp?ProductCode=200120
 
  #8  
Old 10-29-06, 07:35 PM
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You would need a trasnfer rated switch.

Cabtire is a trade word for SO type flexible cord.
 
  #9  
Old 10-29-06, 08:35 PM
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Originally Posted by lectriclee
Think about the tech out there.

How easy would it be to add a rec/cord cap to back feed the furnace/boiler?
Quite easy.
How easy, in this manner would it be to screw up?
Quite easy.

How easy would it be to knock on the families door, or know that you sent the mesenger?

Probably the hardest thing you have ever done in your life.
I don't understand this either. The method i described makes the furnace a plug in device. You either plug it into the receptacle from the panel or you plug it into an extension cord from the generator.
Under no circumstance should you make a suicide cord with a male plug on both ends.

Cabtire is a flexible cord like an extension cord.

http://www.wirecableandcords.com/Cabtire.html
 
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Old 10-30-06, 04:25 AM
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Once again we have no location info on the OP, so I can only say that in the US you cannot use flexible cord as permanent wiring in a situation such as this.

By the time one might get all the material to do this safely without a transfer switch; including the cord, cord caps, SPDT switch, etc., you could have bought and installed the $110 transfer switch. In much less time and with MUCH less hassle.
 
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Old 10-30-06, 04:50 AM
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I agree with Petey, the cost is negligible when you think about all the other materials you will have to buy and put together to attain the 110v to the fan blower. Transfer switches are too cheap not to use one. And, you may want to expand it at a later date.
To further lectriclee's comments, we had one of our local poco employees killed during Hurricane Ivan a couple of years ago, because some numb skull (that's as descriptive as I can get on the forum) hooked up his generator directly to his lead-in lugs. Back fed 120 volts and created 12000 volts by the time it got to his hands.
 
  #12  
Old 10-30-06, 05:20 AM
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I most areas in the U.S. it is against code to have a plug on the airhandler. In most areas they must be hard wired.
 
  #13  
Old 10-30-06, 08:24 AM
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A few years ago I did exactly what the OP is proposing. This works well for me when we have a power outage and I need to run the furnace. I just unplug the furnace from the supply line and plug a suitable #12 extension cord from my generator. I don't see any possibility of back-feeding into the power grid. What is the reason for code calling for the air handler to be hard-wired? Is there a hazard that I may not be aware of?
 
  #14  
Old 10-30-06, 10:00 AM
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You just shouldn't be using flexible cord where the application should be using nm.
 
  #15  
Old 10-30-06, 10:00 AM
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It's not that difficult.

The parts list for this project is a three way switch, flanged inlet (excepts female end of extension cord) Go here for picture <http://www.twacomm.com/catalog/model_5239.htm?sid=A68B2FC035FE66934647F014CCCEEC4B>, handy box for switch, four square by 2&1/8 deep box for flanged inlet, raised cover with the opening selected to mount the flanged inlet, 2 close nipples. If there is already a shut off switch on your furnace then replace the single pole switch with the three way switch. Connect the ungrounded conductor to the furnace to the dark colored common terminal of the three way switch. Connect the ungrounded conductor of the branch circuit that supplies the furnace to one of the lighter colored screws on the switch which is usually brass in color, preferably the one that is connected to the common when the switch is in the up position. Connect the brass colored terminal of the flanged inlet to the other lighter colored terminal of the three way switch. The flanged inlet is the only thing that you couldn't buy with pocket change and it will run between twenty and thirty dollars.
 
  #16  
Old 10-30-06, 04:02 PM
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Originally Posted by thiggy
A few years ago I did exactly what the OP is proposing. This works well for me when we have a power outage and I need to run the furnace. I just unplug the furnace from the supply line and plug a suitable #12 extension cord from my generator. I don't see any possibility of back-feeding into the power grid. What is the reason for code calling for the air handler to be hard-wired? Is there a hazard that I may not be aware of?

Yes, I did this in my last house and it worked well during an extended power failure. There is no chance of back feeding, if you put the male plug on your furnace, it is then like a toaster, up plug it in and it works, you unplug it and it does not not, you are just using a differnet power source - generator vs power company. I was also told this set up was against code, and the reason was something like .. essential devices must be hardwired in so that someone does not forget to plug it in when you're not there or that it accidentialy falls out and the house freezes ...

Someone had later told me that you could make it code if you used a special plug in connecter that had a push and twist to lock plug connector, but I never followup to verify.

P.S. some thermostats require a transformer, if yours does that will need power also.
 
  #17  
Old 10-30-06, 05:34 PM
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Thanks everyone, I did not know transfer switches existed for just one item, figured I would have to put one on the panel, although looking at instructions it seems pretty easy, a keck of a lot easier than it was to replace my outdoor garage light last week. I will just go with the transfer switch. Now, the big question is, can the transfer switch be a ways from the furnace, the hot water heater and associated NG hardline is in the way of getting to the side of the furnace. It appears the transfer switch comes with 18" of conduit and line, so I would want to run that into a junction box, then romex to the furnace as it is now. By the way, I am in upstate NY.

Thanks,

Eric
 
  #18  
Old 10-30-06, 06:13 PM
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The transfer switch is typically located at the panel. For a single circuit unit it can be at the appliance as well.
I would rather see it at the panel though as intended.
 
  #19  
Old 10-30-06, 06:24 PM
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Originally Posted by Speedy Petey
The transfer switch is typically located at the panel. For a single circuit unit it can be at the appliance as well.
I would rather see it at the panel though as intended.


You can also use a simple 3way switch as a appliance transfer switch. I would use 20amp though. Under 5$
 
  #20  
Old 10-30-06, 06:52 PM
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Read back a few posts. It's been suggested.
It is also not simply $5. There is A LOT more to it than just the switch.

Also, I question the legality of a simple 3-way, although I can't put my finger on a code article just now.
IMO a SPDT, center off switch would be required.
 
  #21  
Old 10-30-06, 07:14 PM
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I am talking the gen-tran $99 switch that was suggested in one of the first posts, that is the way I will go given all this feedback. Except I will use a Reliance one circuit switch since it has the normal (5-20?) plug rather than the round one so I don't have to fool around with a converter, just plug the generator into the switch and stay warm. I would put it at the panel but the hot gas water heater is on the circuit as well, running both may overwhelm my modest little 3Kv generator that I am looking at. Of course if I am careful, and only run the furnace when needed and leave it off other times, and unplug the hot water heater until I need more hot water, hum, maybe that would be a better bet.

OK, going to do this "right" way, you have all convinced me.

Thanks,

Eric
 
  #22  
Old 10-30-06, 07:20 PM
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The generator is a separately derived source, so there are some special rules concerning grounding the neutral to prevent current from flowing through the ground. For this setup, you pretty much have to switch the neutral, there's no way around it. Hopefully that switch does it the right way, since that's how it's marketed!
 
  #23  
Old 10-30-06, 07:36 PM
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DPDT would be the switch to use then. 2pole on-off-on But the transfer switch is the way to go for sure. They are cheap enough too.
 
  #24  
Old 10-30-06, 07:43 PM
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I'm NOT sorry I started this discusion.

(See post #4)
In a small (any)community, so safe, alot of DIYrs.

Storms come, we all want power.
(not that this has happend)
1 Neighbor wants power on outages, so they connect a generator.
Their neighbor is out in the storm trying to restore their power.
Some where something goes wrong. The fixer is Killed.

Long story short, Another neighbor had to go and tell the fixers family of this needless "accident".

They all knew each other.

Sorry I had to explain.
 
  #25  
Old 10-30-06, 08:13 PM
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lectriclee,

you have made a very good point, but the discusision so far has been about cord and plug connected, or three way switching.

these are safe ways to connect the generator.

you are absolutely correct. but the other posters have not suggested anything unsafe either.

Jeff
 
  #26  
Old 10-30-06, 08:51 PM
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I was not suggesting that the options were unsafe.

Just trying to illustrate how important this can be.
I personaly feel that a cord and plug, with multiple boxes leaves to much to chance.
In this vein, I would think the switch to be the best solution, for a DIYr.

There MUST be a definitive break between the two sources.
 
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