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Old 01-04-2011, 07:58 PM   #1
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Powering boiler with portable generator


In the event of a power failure, I would like to power my boiler with my portable generator. I know that I should disconnect the boiler from the service before doing this. I propose to use a double throw switch with the boiler wired to the common terminal. One throw would connect to the service. The other would connect to a wire terminating in a standard male plug. When the power goes out I simply throw the switch from service to plug and then plug into the generator.

My question is, do I need a double pole switch, so I can switch both the hot and neutral lines, or would it be OK to use a single pole (like a standard "3-way") switch and switch only the hot line, and tie all the neutrals together? That is, does it matter if I connect the generator neutral to the service neutral? Thanks!

p.s. The boiler is fired by gas and draws power only for the water pump and the step down transformer that powers the thermostat control box and the zone valves.

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Old 01-04-2011, 08:00 PM   #2
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Powering boiler with portable generator


What does the NEC state. That would be the first thing, along with the manual that comes with the GenSet would cite which NEC articles for use.

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Old 01-04-2011, 08:21 PM   #3
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Powering boiler with portable generator


This is exactly what my Father wanted to do, he was only worried about heat.

It didn't take long to convince him to install an Inlet on the outside of the house and an Interlock Kit on the panel so that he can safely backfeed a breaker and power anything in the house that he wanted.

The power went out during the storm last week, not only did he have heat, but they had lights, television, internet, etc. Think about it before hacking something together for just the boiler. It'll only cost a little more to do it the right, safe, and legal way.
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Old 01-04-2011, 08:33 PM   #4
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Powering boiler with portable generator


General: Thanks for the great suggestion! Do you know where I can find instructions to do this? Or would I need a pro to do it? My portable generator is not very big, just 3750 watts, so I guess I would have to be careful about what I turn on in the house or I would quickly exceed its capacity!

(I am still curious as to whether it is OK to connect the service neutral to the generator neutral.)

Last edited by piacentini; 01-04-2011 at 08:54 PM.
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Old 01-04-2011, 09:14 PM   #5
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Powering boiler with portable generator


Quote:
Originally Posted by piacentini View Post
General: Thanks for the great suggestion! Do you know where I can find instructions to do this? Or would I need a pro to do it? My portable generator is not very big, just 3750 watts, so I guess I would have to be careful about what I turn on in the house or I would quickly exceed its capacity!

(I am still curious as to whether it is OK to connect the service neutral to the generator neutral.)

This is one of my Square D interlocks, they are not something you can just make, they need to have a UL listing to be a valid interlocking device. Notice how slots 2 and 4 contain a double pole breaker which remains off and cannot be turned on without opening the main?

sorry for the bad pic.
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Old 01-04-2011, 09:24 PM   #6
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http://www.reliancecontrols.com/Prod...il.aspx?TF151W

I have these installed on my furnaces. They use a single pole double throw switch so the neutrals are tied together.
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Old 01-04-2011, 09:36 PM   #7
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Powering boiler with portable generator


Seriously connection to breaker box so as to power house costs about the same. Just turn off breakers in unused rooms to insure that you don't overload genset.
I do beleive that you need to switch neutral. I'll check.
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Old 01-04-2011, 09:55 PM   #8
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These are easy to wire in to your main panel http://www.reliancecontrols.com/Prod...=pt&c=indoor&f= In structions are easy to follow. You can use a larger rated model if you want to pick and chose what you flip on.
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Old 01-05-2011, 05:27 AM   #9
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Just install one of these. Easy and only about $70.

http://www.reliancecontrols.com/Prod...il.aspx?TF151W


Last edited by busman; 01-05-2011 at 05:32 AM.
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Old 01-05-2011, 08:51 AM   #10
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Powering boiler with portable generator


As a DIYer I would put an ordinary 3 way switch in a small metal outlet box at the boiler to act as a transfer switch between the existing feed from the panel (one traveler terminal) and a cord and plug right there (other traveler terminal). This would permit plugging into the generator's regular receptacles, using an extension cord if needed.

If I were to use the above pictured transfer switch (does the same thing) I would include a metal box with some receptacles on the load side (sharing the furnace circuit) so when the generator was in use other appliances and lights can share use of the transfer switch via an extension cord stretched upstairs.
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Old 01-05-2011, 12:38 PM   #11
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Powering boiler with portable generator


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Originally Posted by AllanJ View Post
If I were to use the above pictured transfer switch (does the same thing) I would include a metal box with some receptacles on the load side (sharing the furnace circuit) so when the generator was in use other appliances and lights can share use of the transfer switch via an extension cord stretched upstairs.
What??? if installed to main panel there would be no need to run extension cord upstairs, power would already be there.

OP question if i might is your generator 240V? - if so install a 240v transfer switch(much better)
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Old 01-05-2011, 01:46 PM   #12
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Powering boiler with portable generator


Thanks all for the various insights! To Saturday Cowboy: My generator has a 4-prong locking 240v 20A outlet, as well as 2 regular 120v 3-prong 15A outlets. It is rated at 3750 watts. http://www.homedepot.com/buy/electri...att-77063.html
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Old 01-05-2011, 01:49 PM   #13
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Powering boiler with portable generator


The Easy Tran box pictured above controls one branch circuit. If you decided to install it on the furnace circuit, you might as well add a receptacle box to that circuit downstream so the box can control other things (up to 20 amps for an all 12 gauge wire circuit) as well.

If you don't have any 240 volt equipment, you can make up a portable subpanel that plugs into the 240 volt receptacle on the generator. The subpanel can have receptacles and no breakers if it is only plugged into a 240 volt receptacle breakered at no more than 20 amps. However use of just the 120 volt receptacles with extension cords can use up almost the entire capacity of the generator.
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Last edited by AllanJ; 01-05-2011 at 02:00 PM.
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Old 01-05-2011, 11:52 PM   #14
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Powering boiler with portable generator


Quote:
Originally Posted by AllanJ View Post
The Easy Tran box pictured above controls one branch circuit. If you decided to install it on the furnace circuit, you might as well add a receptacle box to that circuit downstream so the box can control other things (up to 20 amps for an all 12 gauge wire circuit) as well.

If you don't have any 240 volt equipment, you can make up a portable subpanel that plugs into the 240 volt receptacle on the generator. The subpanel can have receptacles and no breakers if it is only plugged into a 240 volt receptacle breakered at no more than 20 amps. However use of just the 120 volt receptacles with extension cords can use up almost the entire capacity of the generator.
I don't mean to get in to it with you but just to make sure we are all on the same page.

EVERYBODY has 240V equipment installed - just the way houses are wired.
Since he has a 240V generator what he should do is to install a box similar to the ones pictured above near his panel or a near by outdoor location, During a power outage the main breaker is opened, and branch circuit breakers turned off, generator plugged in, started, and the gen breaker closed- now everything in the main panel is now hot. Turn back on desired branch circuits. such as furnace, fridge outlets/lights in occupied rooms, keeping in mind the max load of generator.

Cheers
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Old 01-06-2011, 09:01 AM   #15
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Powering boiler with portable generator


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Originally Posted by Saturday Cowboy View Post
EVERYBODY has 240V equipment installed - just the way houses are wired.
Since he has a 240V generator what he should do is to install a box similar to the ones pictured above near his panel or a near by outdoor location, During a power outage the main breaker is opened, and branch circuit breakers turned off, generator plugged in, started, and the gen breaker closed- now everything in the main panel is now hot. Turn back on desired branch circuits. such as furnace, fridge outlets/lights in occupied rooms, keeping in mind the max load of generator.
The generator feed line switch and the switch (main breaker) to the utility lines must be interlocked (part of one method using levers or cams or sliders is pictured somewhat higher up) so both utility lines and generator can never be connected simultaneously. A real generator/utility transfer switch for the main panel is a separate box that would be installed in the service lines between the main panel and the meter and this would be a fairly comprehensive project. A simple switch box quickly installed outside next to a generator pad won't do.

From the looks of it, the Easy Tran box is not meant to feed power into your main panel. It can only be used to choose between panel/utility power and generator power for a branch circuit. You can probably get a similar box for a 120/240 volt circuit aka multiwire branch circuit.

The cam and/or lever interlock system is used when you feed generator power into your main panel "backwards" through a regular breaker in the panel (double wide breaker for 240 volt generators). Much simpler than a real transfer switch for the entire panel. Not all makes and models of panels permit this. Here you would not need an Easy Tran box. The line going to the generator, if not hard wired to the generator, ends at a plain male receptacle perhaps on the side of your house.

With just a 3 to 4 KW generator, chances are great you won't be using any 240 volt appliances. Then you can commandeer the 240 volt receptacle on the generator for 120 volt usage via a portable subpanel. Or include a 240 volt receptacle on your portable subpanel.

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Last edited by AllanJ; 01-06-2011 at 09:25 AM.
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