Generator feeding back up outlet to gas furnace


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Old 10-11-10, 06:19 PM
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Question Generator feeding back up outlet to gas furnace

Hello, I am wondering what all I would need to worry about on code with a small project.

A friend of mine has power go out often enough during the winter months. And living out here in the sticks, it rarely is taken care of quickly. He lives in a single wide home. The 120v feed wire is just dropped into the furnace opening and is just secured down the side of the paneling. Could I cut this wire. Install an outlet and mount to the wall on power side of wire. And install a male plug on the furnace side of the wire. Then run a proper 120v wire down through the floor and outside through the skirting where he would keep his generator. That way if he ever lost power he could just unplug from main house outlet and plug into the outlet ran from the generator outside? I do not know of any issues that would make this against any codes. But that is why I am asking here.

Also, do some generators run dirty voltage and how picky are some of the cheap furnaces installed in mobile homes when it comes to dirty voltage.

Thanks
 
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Old 10-11-10, 06:34 PM
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JerseyMatt introduced us to a better way to power a gas furnace in a power outage in another thread. This is what he showed us, it's pretty slick and I'd use this rather than what you have proposed.

TF151W @ Electric Generators Direct - Your Online TF151W Superstore!
You can probably buy these from a variety of sources.
 
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Old 10-11-10, 06:41 PM
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I mentioned that to him also. But on the line of an auto transfer switch. Which are more expensive, and I think what made him want to do it the other way. The manual switches aren't that bad though. Will bring that up to him again. Thanks.
 
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Old 10-11-10, 07:52 PM
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I know you mention automatique transfer switch they will cost more than manual transfer switch and also with most recent code change the automatique transfer switch sizeing that will get ya you have to sized the unit { generator } to sized to the main breaker size { I know I have heard this before and it kinda stink but try to correct that code issue when the next edition come out }

The manual verison is not too bad you can use most common size generator but really I advise to make sure you have at least 5 KW or larger so you have more than enough power to get the furance kick on especailly with motours load.

My place I have two generators so it was not a issue for me.

Merci.
Marc
 
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Old 10-12-10, 02:42 AM
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Originally Posted by cutnell View Post
Hello, I am wondering what all I would need to worry about on code with a small project.

A friend of mine has power go out often enough during the winter months. And living out here in the sticks, it rarely is taken care of quickly. He lives in a single wide home. The 120v feed wire is just dropped into the furnace opening and is just secured down the side of the paneling. Could I cut this wire. Install an outlet and mount to the wall on power side of wire. And install a male plug on the furnace side of the wire. Then run a proper 120v wire down through the floor and outside through the skirting where he would keep his generator. That way if he ever lost power he could just unplug from main house outlet and plug into the outlet ran from the generator outside? I do not know of any issues that would make this against any codes. But that is why I am asking here.

Also, do some generators run dirty voltage and how picky are some of the cheap furnaces installed in mobile homes when it comes to dirty voltage.

Thanks
Dammit I had a post all typed out explaining dirty power then my browser crashed when I hit post.

Im just gonna copy it from my post in another thread because I really dont feel like typing the whole thing over again..

That isn't an inverter generator, so it can't be modified sine. Any cheap generator (including the one the OP said he has) produces true sine wave. The problem with them lies in the fact that the sine wave frequency is tied directly to the engine RPMs. So you wind up with one of two problems: if the governor on the engine is set improperly the frequency will be either high or low.. Or, when a heavy load kicks on (like the well pump) that maxes out the alternator, it puts so much drag on the (undersized) engine that the engine slows down, which causes the frequency to dip out of range until the engine can recover. THAT is what is ultimately meant by 'dirty power' when talking about a generator, and THAT is what will cause issues with your electronics. Line conditioners can help with over/undervoltages and noise, but they can't do anything to correct line frequency fluctuations.

That being said, I personally have never had any issues with my electronics or the controller in my furnace. But I use a 10kW generator for about 6kW max worth of load. It has a larger engine so it isn't badly bogged down when something turns on. I also don't have a well pump. It just powers lights, TV, computer, microwave, refrig, freezer, gas range, and gas high efficiency furnace. I've watched the output on a scope, and when something kicks on, the worst the frequency drops to is 57Hz (within spec for pretty much anything out there). Basically the bottom line is you have to oversize the generator for the application to make sure its output remains as clean as possible under starting surges.

As far as the furnace being converted to plug-and-cord, you have a few issues with that. First, you can't put a plug on Romex. You would have to install a premade pigtail that uses minimum 14ga wire. Second, I don't know of a furnace manufacturer out there that allows for plug-and-cord installation in their specifications (since manufacturer requirements trump Code). Although in some areas it is common to use a plug-and-cord setup (most likely to facilitate operation with a generator) and in these areas inspectors commonly overlook its use, but it IS a code violation. A furnace does not meet the requirements of 422.16 (a) (the cord is not required to prevent transmission of vibration, nor is it to facilitate replacement or maintanance of the furnace, because the furnace is not specifically designed to take a cord and the ductwork/hydronics/gas line would not be quick disconnectable), and furnace is not listed in the 422.16 (b) exemptions to 422.16 (a) for permanently installed appliances (dishwasher, garbage disposal, trash compactor, wall oven, cooktop, and range hood).

I would stick with the transfer switch. It is a proven design, listed, and code compliant.
 
 

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