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Thread: Back-feeding a panel from a portable generator

  1. #1
    Join Date
    Feb 2007
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    Inside the Beltway
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    2,666

    Back-feeding a panel from a portable generator

    Ok, so, here's the scoop:

    I've got a main panel, with a 100 amp main breaker. I've got something like 16 or 20 breakers in there. I'd prefer to leave this panel alone. I've already replaced every breaker in there (except, of course, the main one). I've got a double breaker on there, rated for 50 amps, which goes to a subpanel right next to the main panel.

    I've got 8 slots in that subpanel. Its circuits go to various places: the shop, the upstairs. I still have two open slots, enough for another 50 amp breaker.

    The generator is sitting outside the house, a few feet from the wall where the main panel is, in it's own building.

    Here's the plan: Drill a hole through the brick/cinderblock wall. Run a 6/3 w/g cable through the hole. Put a 220 dryer plug on one end, so it'll plug into the generator.

    Inside the house, I've got a couple options.

    Option one: Put another plug on the "inside the house" end of the cable, which will plug into an outlet permanantly wired to the subpanel, into a new 50 amp breaker.

    Option two: permanently and directly wire the cable into the new breaker on the subpanel. (don't have a whole lot of room on that wall, so can't really move the subpanel around).

    Option three: get a transfer switch. (don't really have the funds for this, and even if I did, I've got too many circuits to run).

    The main advantage to option two: it seems safer, or at least more doofus proof. To get power, I'd need to 1.) turn off the main breaker. 2). engage the 50 amp breaker in the subpanel. 3.) plug in the cable. 4.) start the generator.

    I did think of simply getting a bigger subpanel, but even if I had room, it would be a bear to rewire the heater circuit, etc. onto the new bigger subpanel.

    I hope this is clear. Please let me know your thoughts: any and all advice is appreciated...

    Thanks,

    Bill
    Last edited by Bill Lantry; 01-28-2011 at 09:40 PM.

  2. #2
    Join Date
    Oct 2006
    Location
    somewhere east of Queen Creek, AZ - South East of Phoenix
    Posts
    8,529
    Bill Mine Gen is a bit smaller then your but I back feed my panel through the breaker that would normally feed the 220 to my table saw. I Open the main and the heat pumps and air handlers and the breaker for the table saw, then I plug the generator in start the generator then close the breaker that would normally feed the TS.
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

  3. #3
    Join Date
    Mar 2007
    Location
    Southeast Pa
    Posts
    2,019
    Quote Originally Posted by Bill Lantry View Post
    Ok, so, here's the scoop:

    I've got a main panel, with a 100 amp main breaker. I've got something like 16 or 20 breakers in there. I'd prefer to leave this panel alone. I've already replaced every breaker in there (except, of course, the main one). I've got a double breaker on there, rated for 50 amps, which goes to a subpanel right next to the main panel.

    I've got 8 slots in that subpanel. Its circuits go to various places: the shop, the upstairs. I still have two open slots, enough for another 50 amp breaker.

    The generator is sitting outside the house, a few feet from the wall where the main panel is, in it's own building.

    Here's the plan: Drill a hole through the brick/cinderblock wall. Run a 6/3 w/g cable through the hole. Put a 220 dryer plug on one end, so it'll plug into the generator.

    Inside the house, I've got a couple options.

    Option one: Put another plug on the "inside the house" end of the cable, which will plug into an outlet permanantly wired to the subpanel, into a new 50 amp breaker.

    Option two: permanently and directly wire the cable into the new breaker on the subpanel. (don't have a whole lot of room on that wall, so can't really move the subpanel around).

    Option three: get a transfer switch. (don't really have the funds for this, and even if I did, I've got too many circuits to run).

    The main advantage to option two: it seems safer, or at least more doofus proof. To get power, I'd need to 1.) turn off the main breaker. 2). engage the 50 amp breaker in the subpanel. 3.) plug in the cable. 4.) start the generator.

    I did think of simply getting a bigger subpanel, but even if I had room, it would be a bear to rewire the heater circuit, etc. onto the new bigger subpanel.

    I hope this is clear. Please let me know your thoughts: any and all advice is appreciated...

    Thanks,

    Bill
    I think a transfer switch is the only way to go. Even if you rigged up a manual one. If a system is set up where it can back feed someone will.

    May not be you but you may get injured ands someone comes over to help out your family and doesn't understand...

    Garry

  4. #4
    Join Date
    May 2009
    Location
    Poway, CA, near San Diego
    Posts
    174
    Do it with a proper transfer switch. If you forget to filp the breakers the right way, you can kill a lineman.

    Bob

  5. #5
    Join Date
    May 2007
    Location
    Kansas City, Missouri
    Posts
    13,448
    I'd probably recommend a transfer switch as well. You can usually get a smaller amperage transfer switch cheaper, so if you can single out a few circuits to move over to a backup panel that would be on the generator, it may be more cost effective.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  6. #6
    Join Date
    Dec 2006
    Location
    Carlyle IL
    Posts
    350
    agree: Transfer Switch is the way to go.

  7. #7
    Join Date
    Jun 2008
    Location
    GTA Ontario Canada
    Posts
    12,256
    Bill, I have a few questions to ask regarding your setup.

    What size is your generator?

    What duty cycle is it capable of?

    Is this something you see being needed frequently?


    Depending on the above, besides the concerns raised already which i fully agree with, i would also be concerned about the potential to either kill the gen by running it too long or overloading it given you are hooking it up to the whole house.

    So were you going to go ahead with the gen feed to the whole house via another breaker i would make that breaker closer to the limits of overload rating for the generator. That way should someone accidently turn on that additional item that pushes things over the top, instead of the gen trying to meet your needs and suffering in the process the breaker would trip and alert you to it.

    I think you also have to consider the voltdrops in this equation. The more wire you have to run through from the generator the more loss you have. The generator will be using as feedback to its regulator circuit, the output at the generator itself. It has no way of knowing what the voltage is way up on your second story bedside clock unit for example.

    So you might want to consider the effect of what a low voltage will have on whatever you plan on operating. If its is just lighting and an odd cell phone charger etc, then one thing. If it has to do with the kind of current drain prevalent with heating well thats entirely different.

    In heating its not going to affect the device as much as its output but that kind of load with increase the voltdrop due to current drawn and other items could be affected.

    Personally i dont see a portable type gen being a sustainable and viable change over between supplied power and home gen power for more than an hour or two of provision of lighting and perhaps keeping the fridge freezer going maybe the television. But all that will quickly add up.

    I hear you on the finances side but i would look to make do with however you have it at present and are using it and look into the correct kind of beast and connectivity when finances permit.

    This is more like the kind of unit i would think one should be considering if the power supply from the local authorities is suspect and unreliable.

    Here is a transfer switch set up

    I would strong advise you dont do it the way you thinking and consider your insurance if by accident (and these things happen to the best of us) something went wrong and you have some kind of issue. The setup you thinking of aint gonna be approved.
    cheers

  8. #8
    Join Date
    Oct 2006
    Location
    somewhere east of Queen Creek, AZ - South East of Phoenix
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    8,529
    Just to clear up my previous post. If I need to use this very often I would install a transfer switch, where I'm at it one every couple years for a few hours. Just a note. when I used it last I used my clamp on amp meter to check the load, I had normal lighting, couple of TV some celling fans 2 fridges and 1 stand alone freezer on. On leg measured 11 amps and the other leg measured 9 amps.
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

  9. #9
    Join Date
    Nov 2006
    Location
    Mountain Home, Arkansas
    Posts
    11,832
    When we moved in to this house one of the first things we did was have a transfer switch installed. I called an electrician. All I knew about this thing was what the electric company advertised they wanted you to do to prevent frying their line workers. It was an expense we considered a priority.
    I haven't a clue what you are talking about in most of the post.
    Except your sequence at the end. The instructions that came with my generator (and my previous small one also) said to start then plug in the cords.
    So, when/if, severe weather is threatening I take the wires out under the garage type door of my shop, put the plugs in a plastic bag and leave there. When/if I need the generator I'll go to shop, throw the transfer switch, go outside and start generator then plug in the cords, all the time praying I don't get fried doing this in the rain.
    "Folks is funny critters."

    Think for yourselves and let others enjoy the privilege to do so, too. ~Voltaire

  10. #10
    Join Date
    Mar 2007
    Location
    Long Hill Township, NJ
    Posts
    467
    Bill:

    Check around with the mfg. of your panel.

    I believe Square D has an interlock kit for some of their panels that mechanically link the MAIN breaker to a 2 pole breaker in one of the upper positions.

    With the MAIN "ON" (Connected to Electric Co - or Hydro for you Canadians) the "SPECIAL" breaker is OPEN.

    With the MAIN "OFF" the "SPECIAL" breaker is CLOSED allowing the back feed.

    I have a 5000W Master Generator with a Honda engine. It's loud but will run the stuff I need in case of an extended outage. It ran the house one spring for 3 days after a T-3 Microburst decimated the main power feed into my neighborhood 5 or 6 years ago.

    Cheers

    Jim

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