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Backfeeding a generator on the cheap

Post in 'DIY and General non-hearth advice' started by Dave A., May 25, 2013.

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  1. Dave A.

    Dave A. Minister of Fire

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    It looks promising and is an interesting background read to the idea of backfeeding both legs of the 240v main panel with a 120v gen. But when you add it up, all you get are only two individuals who claim to have done it without any other details or support. Even HB never claims to have done it (successfully or otherwise) himself from what I make of it. Wish there were more support somewhere for this. (see thread http://www.hearth.com/talk/threads/small-invertor-gen-and-subpanel.109909/unread) (message http://www.hearth.com/talk/posts/1450584/)

    Meanwhile have shopped around for an interlock device for my old ITE panel and found one for about $50. In line with backfeeding the two 120v legs of the panel with the gen and keeping in mind the idea of not over investing in something that may rarely if ever happen, would like to do this on the cheap but still safely.

    One way to keep costs down is to not use the 30a plug on my 120v gen but rather just use the regular 20a duplex socket on the gen with two 12/2 w/ground extension cords (I already have them) and backfeed them to each leg of the panel via the duplex plug on the gen and to a dedicated split outside duplex outlet controlled by the breakers controlled by the interlock -- just break off the junction tab on the duplex receptacle and feed each outlet separately with 12-2 romex from each of the 2 interlocked 120v breakers.

    Realize I'd be giving up the full 3000 watt capacity of the gen. But don't really think I need it -- can manage with 2400 watts. All I really want to do is to be able to power (individually, i.e. one thing at most at a time):

    1. Side by side ref/freezer an hour or so a day.
    2. Small freezer, about the same time, just to get it to zero and keep it closed.
    3. Microwave, every now and then.
    4. Desktop computer and accessories (this I'd want on almost all the time for convenience but could turn off monitor and a lot of perifs and probably keep use under 200 watts idling -- but could also run for 15 minute or so stretches on battery backup if necessary.

    5. Also on almost all the time:
    a. a few cfl's
    b. a fan in winter for the blower on the insert (though not required)
    c. in summer a small fan for cooling

    Gas (propane) will handle cooking on stove or outside grill, DHW, HW Boiler (which am not planning on using since insert will heat house and boiler requires elec to run for power vent, ignition, and circulator).

    Cost for the equipment:

    1. $50 for interlock

    2. $10 for outside receptacle, weather proof box, and less than 10 ft 12-2 romex. (I think I have all of these)

    3. $5 for making up the short male/male cords for plugging extension cords into outside box (probably have parts also).

    These (item 3) are the most controversial (potentially unsafe) unless they could be devised to lock into the outside outlet and could only be unplugged from the extension cord side or care needs to be taken in preventing them from being unplugged from the house side while the gen is in operation (to prevent an unplugged but hot male plug). At a minimum they could be taped to the outside outlet along with a warning tag limiting unplugging from the running gen to only expose a hot female outlet on the extension cords.

    The total cost outlay would be for the $50 interlock and maybe some other minor items.

    The problem with using the 30a gen power is the cost of the supply cord $50 for made up cords or even making them up as the male and female's are each close to $20, and the input box and receptacle are about $50 plus 10-3 romex.

    All of the 240v circuits would be kept off as well as any multi wire 120v circuits -- there are a couple of them -- though with all of the latter 20a 12-3 romex and gen max at 20a not a risk of more than 20a on a neutral.

    And also thinking about, after drilling the holes in the panel cover and installing the interlock, leaving it off and only installing it in the event of a power failure. Also leaving the wires for the outside gen outlets unconnected in the panel but wirenutted and labeled. So I could still use those breakers as normal most of the time. They are for a multi wire 120v circuit.

    The reason for doing this rather than use extension cords run from the gen to devices in the house, is the convenience of being able to use just about any 120v device without having to separately unplug it from the house and reconnect to the gen and not need such long extension cords or have them running all over the house

    Questions:

    1. Will it work?

    2. How will the gen distribute the 20a between the two legs on the house panel -- on a demand basis up to 20a total, or split it 10a each, or something else?

    3. What am I missing here?

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  2. woodgeek

    woodgeek Minister of Fire

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    The two 12Ov legs are wired together inside your suicide plug. So 2 is not an issue
  3. Dave A.

    Dave A. Minister of Fire

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    Where do you get that? There are two separate double male (suicide) cords, each runs to a separate leg. The outside house duplex outlet (with the junction bar broken off) has each leg wired to a separate outlet. The only place they are wired together is at the gen (would think).

    But what I now realize is that there is no need for the two cords (lines) anyplace but from the breaker to the outside outlet, if I don't break off the junction bar on the duplex recepacle. So only one extension cord and (short) double male plug cord is necessary.

    And I probably could get away with using 12-3 romex instead of the two 12-2 pieces.
  4. seige101

    seige101 Minister of Fire

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    Why do you insist on doing this the most unsafe way possible. Double male end suicide plugs wired into a regular receptacle?!?! At least get a 20amp 120 volt inlet plug.
  5. fbelec

    fbelec Minister of Fire

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    what is your generator? if it is a 2000 watt 20 amp gen it may run that microwave but the microwave may not like it. the electronics is the worry. i was trying to run my dishwasher on my 5000 watt and technically it should run fine but because of the heavy draw the voltage dropped down just enough to make the thing turn off turn on, turn off turn on. almost blew the board. my point is try not to make your generator work it's max. it won't like it and what your running won't either. what seige101 said is right wire it in the right way with your interlock device and a piece of 10/3 and a outdoor generator box inlet and besides the safety end you would be able with the right cord gen to inlet run any generator from 7500 watt and down. you would be surprised how cheap the parts are. and if you blow your generator and have to borrow or buy a new one your covered. plug in and go.
    raybonz likes this.
  6. woodgeek

    woodgeek Minister of Fire

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    Dave,

    Glad that you decided to pick up a cheap interlock panel for your box. Makes it hard to mess up. The panel will 'interlock' one breaker, so it can only be switched on when the main breaker is off. I think the SOP is to make that a 240V breaker (so it feeds out both 120V phases on its two wires. On the load side of that breaker, you can then connect them both together and to your 120V generator. All your (120) loads are then in parallel on one circuit.

    As for how you do the wiring and connections, respect the amperage rating and do what you want. In the other thread, it was mentioned that you can use a four prong 240V connector, and tie the two hots together in the plug (that you make up). The advantage of that is that said suicide cord could be used with an existing 4 prong 240V outlet (and no interlock, if that's how you roll).

    With an interlock panel, you can use any volt/amp rated outlet cord combo you like. It will be dead whenever the grid is on.

    EDIT: Really didn't understand your post the first time. Its a bit wacky. I'm kinda surprised a 4 prong outlet and plug is that expensive. I really don't see the point of running two 120V cords, instead of one 20A 120V cord (neutral and hot) and then tying both hots together inside your (interlocked) feed outlet.
  7. begreen

    begreen Mooderator Staff Member

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    At a minimum the cord should be sized to the ampacity of the generator. Putting a series of heavy loads on a 16 ga cord is not the best idea. Size up if the cord is long.
  8. woodgeek

    woodgeek Minister of Fire

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    Sorry. Can't brain today. Got the dumb. By 'any volt/amp combo' I meant any volt/amp cable or outlet combo that matched the output of the genny. Thanks BG.

    Ok. I get it how the OP is confused now.

    Here we go. The confusion stems from a bunch of configurations that are commonly used to power up all the 120V outlets in a house through a 4 prong dryer outlet, without an interlock. The OP is not doing that.

    This one is easy. interlock breaker or breakers will have two hots. These will be wired together in the junction box to make a single hot. Of course, running the breakers on grid power would cause a hard short (across 240V) and trip the main, but its interlocked, so its ok I suppose. Now the OP just needs to run 20A and 120V to that line through a three wire cable (1 hot, 1 neutral, 1 ground) rated to 20A.

    I don't see the 3000W rating on your genny anywhere in the prior threads. I would be surprised if the 20A outlet has a separate breakers that trips at 20A versus 25A on the other. My guess is that all the outlets are tied together, and they gave you some choices for how to cable it up. Is the 3000W a surge rating? If so, wire it for 20A and don't worry about it.
  9. Dave A.

    Dave A. Minister of Fire

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    I thought that would be backfeeding without an interlock.

    Been looking for them but can't find any 20a, only 15a. This is the least expensive I've seen but am concerned hooking two positive leads up to it, since it needs to be capable of 20a.

    http://www.pplmotorhomes.com/parts/rv-power-cords/outdoor-receptacle-110-volt.htm
  10. Dave A.

    Dave A. Minister of Fire

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    Champion 3500/3000.

    Guess that's why I'd run things one at a time, make sure there's less of a problem. If there were a problem with the microwave, could always cut the power down to 6 or 5 and just let things cook/heat longer.

    There would be more capacity with the 30a outlet with 10-3 romex rather than trying to save with 12 gauge and my existing 20a breaker. Breaker and wire aren't the costly items though. It's the cables and parts for the locking 30a that are really pricey

    Thing is if I did the 30a outlet, I'd go with the 4 connector one which my genset doesn't support (so I'd be able to use a 240v gen if I got one.) So then I'd need to make an adapter cable to the gen. Even though the adapter cord'd be short, those locking male and female plugs are expensive. The gen didn't cost much more than $200. Didn't expect I'd have to be spending another $300 or more to hook it up.

    So apparently you had it close to being maxed out. The pump and the motor on the dw motor must have very heavy start up draws. And the board you're talking about was the main panel in your house or on the dw?, wonder what might have happened.

    Have heard that before about being careful of starting up draw with appliances with motors and also about problems with certain electronics, too. But have assumed if you have decent surge protectors that should protect your electronic equipment. So like if you were going to run the refrig or the freezer, (or the dw, sure, would be running that too, after a day or so) you'd shut down everything else first, start up the refrig and then put other things back on. (dw would probably set it for air dry)

    Been checking prices for the 30a 4 connector hookup and am definitely not seeing cheap. Am curious where you are seeing the low prices.

    Covered? by whom, insurance. I've got a $500 deductible so that's not going to cover much. Or did you just mean the large capacity outlet would work with another gen.

    But you guys (electricians) are okay with backfeeding both legs of the panel with a 120v gen? I see you said nothing about that. Have you ever done it before or is there anything written about it?
  11. Dave A.

    Dave A. Minister of Fire

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    Actually it just represented the genesis of my thinking in the easiest way to backfeed both legs of the house without going through the subpanel dryer plug. So I thought of using two #12 extension cords from the gen each one to an inside 20a outlet on different legs of the panel.
  12. Dave A.

    Dave A. Minister of Fire

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    It's in my first message in that thread.

    There are two breakers on the gen controlling the three receptacles.
    1. Breaker controls the locking receptacle and the RV receptacle (both at same amperage)
    2. Another controls the duplex 20a receptacle.
  13. woodgeek

    woodgeek Minister of Fire

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    Sorry, only saw refs to a 2400 Yamaha inverter genny.

    I'm just trying to say its easier than your two cord sol'n. If you have an interlock (excellent) then you can just wire the two 120V phases together in the box (on the load side of the breaker), and run that to a single 120V outlet (with a neutral on the other prong). If your long cord and male-male patch cord and outlets are all 20A rated, you can run it all with ONE cord set. Sounds dead easy, cheap and safe.

    The male-male plugs don't bother me....US plugs are not touch safe, as anyone who has ever touched one can attest. And you are only doing everything at 120V. If you were running 240V, then you would want a touch safe setup.
  14. woodgeek

    woodgeek Minister of Fire

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    I'm not an electrician, but this is standard operating procedure with small 120V gennies. When the main breaker is off, both phases in the panels are just 120V circuits. IF you wire them together they are one big 120V circuit, with a bunch of 120V loads on it, connected by amp rated wiring and breakers between the genny and the loads. What is contra safe operation? Your 240V stuff sees a dead short across its two hots == no voltage. A 240V appliance with a neutral (4 prong) might have controls that light up (seeing 120V between the hots and neutral) but the 240V loads will be dead. And you might not even have any 4 prong devices or outlests so that could be a non issue.

    If you ran the two legs through separated cords, plugs and breakers, and one got disconnected, then your 240V loads are seeing 120V, which might be unpleasant for a 240V motor.
  15. Dave A.

    Dave A. Minister of Fire

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    I think F and S are electricians.
    Am really past the 2 cords as I say in message #3 in this thread.

    Glad to hear that, but would really like to see a citation if you/anyone has one. Thing is a lot of people seem to think you can only backfeed one leg of your panel with a 120v gen. The idea doesn't seem to be commonly accepted practice.

    Not saying I don't agree with your logic and thinking, just would feel more comfortable with an authority's confirmation and/or claims by those who've actually done it and can point to any problems or none as the case may be.
  16. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    I'm closing this thing. There is enough information on how to back feed and also why it shouldn't be done on the web. This ain't generators.com.
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