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Generator breaker vs. regular breaker-is there a difference?

Post in 'DIY and General non-hearth advice' started by Badfish740, Mar 27, 2013.

  1. Badfish740

    Badfish740 Minister of Fire

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    We recently got rid of our electric stove in favor of a gas stove, so now I have a 50 amp breaker in my box and about 30' of 8-3 cable that now feeds nothing. The breaker is at the top left of the box. Everything is relatively new-when we moved into our home in 2008 the house had a maxed out 100A service, so as a condition of the sale we had the previous owner upgrade to a 200A service, so the breaker, box, etc...was all replaced. The box is a SquareD and it appears that there is an interlock panel that will work with the box so that I can lock out the main breaker when the 50 amp breaker is closed, and vice versa. The question is, is there any reason that the five year old 50 amp former stove breaker cannot be used to feed generator power into the panel? I'm pretty sure that in this case a breaker is a breaker, but I just want to be sure before I go ahead and assume. The plan is to run the 8-3 cable out the side of the house to a 30 amp weatherproof male receptacle, install the lockout panel, and be able to power the essential circuits in the house with a 4200W generator. Obviously the cable and breaker can handle much more than 30 amps, but even if I upgrade my generator I won't need more than the 30 amp capacity of the receptacle. Does this sound workable?

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  2. jharkin

    jharkin Minister of Fire

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    I believe 8-3 NMB is actually only rated for 40amps, so you might have an issue passing an inspection with the 50 breaker. (#8 individual conductors or SE is rated 50+).

    Other than that I see no reason why this wont work in practice. The 30amp inlet box should be good up to a 7500w genset. (DISCLAIMER - Im NOT an electrician)
  3. Badfish740

    Badfish740 Minister of Fire

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    Thanks-I didn't know that. So basically an inspector might have an issue with the fact that the 50 amp breaker just isn't supposed to be there-not that it's not safe.

    4200W does just fine for me. If I come across a larger one for a decent price I might pick it up, but I couldn't see going with anything larger than 6500. That could even run my 1 ton AC unit.
  4. Highbeam

    Highbeam Minister of Fire

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    You seem to be getting your terms confused. At first you say "interlock panel" and then you talk about a new "lockout panel". An interlock allows you to backfeed your whole panel and choose to power up whichever circuits you want whether they are essential or not. They also sell these silly generator transfer panels that force you to choose about 6 circuits to be backfed from the genset. These transfer panels are inferior in function and in general. Let's just assume you're talking about the better and cheaper interlock device that allows full panel backfeed.

    You can reuse your 50 amp breaker but if you do then you will need to run wire capable of 50 amps. That would be 6 gauge which in romex form is rated for 55 amps. If you go this route then you will need to come up with an inlet plug capable of 50 amps. They make them, common in RVs. You will also need to figure out a way to get power from your genset into the 50 amp inlet. The genset will not have a 50 amp plug so you will have to make an adapter.

    Breakers are really cheap. A 30 amp breaker is very common and is the common choice for this application. Then you can just run plain old 10/3 to the inlet. That's the orange stuff available in rolls for just a little more money than 12 gauge house wire. If you bump up to heavier cable like 8 or 6 gauge the price becomes very high per foot.

    I'd chuck that 50 amp breaker. It's not made of gold.
    basod and jharkin like this.
  5. jharkin

    jharkin Minister of Fire

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    Highbeam gave good advice. The #8 cable is also heavy and still and a real pain to work with in addition to being $$$.

    The rule is that the breaker must be rated at or below the lowest amperage rating of the wires and devices in the circuit its connected to. This is for safety so the breaker pops before something overheats and catches fire.
  6. Badfish740

    Badfish740 Minister of Fire

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    I am talking about an interlock device-any reference to a "lockout panel" was a mistake.

    I get what both of you are saying but here is the situation right now:

    I have a 50 amp breaker installed in the box with 30' of 8-3 romex attached to it that formerly powered my stove. I pulled it out of the floor joists and it is sitting coiled up on the basement floor with wirenuts on the ends of the conductors and the breaker taped in the "off" position and the panel locked with a small padlock that only I have the key to. As it is right now I have more than enough cable to run it to the back of the house and through the rim joist where I would mount a weatherproof male receptacle box. Any excess cable will go to the scrapper, so I'm not worried about the price of the cable as I won't be running any new cable.

    Sure, I understand the concepts at work there, but here is my thought process:

    • The generator is only capable of putting out 30 amps. Any higher current draw will trip the circuit breaker on the generator well before the limit of the wiring/panel breaker got anywhere near overloaded.
    • The generator will be connected to the house via a male (generator end)/female (house end) cord with NEMA Turn-Lock plugs. The turn lock plugs are specific to the amperage and voltage being carried, so a 50 amp plug will not fit in a 30 amp socket, so to me, there is the built in safety system. Though the wiring can handle more than 30 amps, it will never see more than 30 amps because only a 30 amp plug can be inserted.

    Given these two points, I don't see how the wiring could possibly become overloaded. Theoretically one of the conductors could become worn and ground out on something between the generator and the panel while the house is running on generator power, but in that case, the panel breaker would be of no help anyway. The 30 amp generator breaker would be the safety device in that case. Does that make sense or am I missing something here? I'm not trying to be a smartass, just trying to make sure that what I think is common sense isn't actually flawed in some way.

    Finally, I'll put it out there, this will not be inspected. Yes, yes, I know, homeowner's insurance, etc... I realize that building codes are there for a reason, but I would rather do things safely/overkill than worry about catering to what an inspector wants, having them in my home and poking around. I did my stove install myself and consulted codes and a licensed plumber that I know, pressure/bubble tested for leaks, and everything is working fine.
  7. jharkin

    jharkin Minister of Fire

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    Badfish,

    I understand your logic and yeah you are right the odds of a 50 amp current getting onto that circuit are pretty darn low. I guess the bottom line is that for 10 bucks you can swap in a 30amp breaker and make the install completely code legal. Inspection or not you might be glad you did down the line if anything ever went wrong and insurance investigated....
    nate379 and seige101 like this.
  8. Highbeam

    Highbeam Minister of Fire

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    I would reuse the 8 gauge cable if it is salvagable, it is free and legal so long as the breaker is no higher than a 40 amp. The 8 gauge should have no problem mating up with the 30 amp breaker or the male power inlet.

    Is the 8 gauge cable 8/3 or 8/2? It needs to be 8/3 for this application.
  9. Highbeam

    Highbeam Minister of Fire

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    Whoops, you already said 8-3 so yes, you can use it.
  10. Badfish740

    Badfish740 Minister of Fire

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    Thanks for the info guys-I love this forum!
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  11. basod

    basod Minister of Fire

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    What you are asking I think is if the breaker cares which direction the current is flowing - answer is no on standard bimetallic thermal breakers.
    The breaker on the genset can fail and as a good practice any conductor coming into your dwelling swould be matched/oversized to the feeder breaker attaching to the load.

    Don't buy a GFCI 2pole - not only more expensive but it'll trip due to the unbalanced load from your panel feeders.
    A new 40A Square D breaker is ~$12.... alot cheaper than a length of 6/0.
  12. MasterMech

    MasterMech Guest

    This is all assuming that BadFish's 4200W genset has 240V output. Or were you planning on just backfeeding 100V current and disabling half of your panel? (and any 240V loads)

    This has me wondering if your generator has 240V output? 30 Amp breaker on a 4200W unit would imply no? I'm assuming the 4200W is a "surge" or "max" rating and the continuous rating is more like 3200-3500W. 30A @ 120V = 3600W

    If you indeed have a 240V output, then the generator is actually only capable of 17.5A.
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  13. Badfish740

    Badfish740 Minister of Fire

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    It does have a 240V output, but I just checked (hadn't looked at the panel in a while) and it's 240V @ 20A, not 30 ;em. However, I also looked at the generator head and found the following:

    WATTS: 4000
    AMPS @ 120: 33.3
    AMPS @ 240: 16.7

    So the generator itself is labeled 7.8HP/4200W on the sticker, but the generator head is labeled 4000. Wish I had a manual for this thing. Searching the model/serial numbers on Sears' website gets me parts, but not a manual. Searching on Generac (it's definitely a Generac made for Craftsman) gets me nothing...

    *EDIT*

    Did some creative Googling and found a manual, but there are still no raw specifications (ie: max/surge vs. continuous output). It does say that max output is 17.5A@240V as MasterMech said, so is it possible that the numbers on the generator head are the continuous rating? 200W isn't much a difference though...
  14. jharkin

    jharkin Minister of Fire

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    Similar setup to my 3200 watt Generac. It has a 20amp rated 240 twistlock output, but the generator is only capable of about 14-15A and has 15A breakers.

    My Reliance transfer kit came with the parts to make an adapter cable with a 20amp male twistlock on one end to hookup the gen and a 30amp female twistlock at the other end to hookup to the house. That way in the future I could update to as big as a 7500w genset without changing the transfer wiring.
  15. Highbeam

    Highbeam Minister of Fire

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    It doesn't really matter what the genset can make, except of course, it is simpler if it makes 240. The manufacturers have standardized the output plug to be either the 20 or 30 amp twistlock for typical gensets. You'll need to be able to hook it up to your male power inlet on the house.

    The genset can make a zillion amps (not unlike the grid) but your generator inlet breaker at the panel will limit the amount of power that can enter the generator circuit. This is why it is so important to match the generator breaker in the panel with the wire and the wall inlet on the house. The system has to be protected by the breaker.

    Thing is, in the future, some other owner might connect a 15000 watt generator to this system and if you did it right, the panel's generator breaker will prevent overloading the system between the genset and the panel.
    Lighting Up and basod like this.
  16. Badfish740

    Badfish740 Minister of Fire

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    Well whaddaya know...I called the Craftsman generator hotline and found out that my model is rated for 4200W continuous/5000W surge. I had assumed that 4200W was the surge rating and the continuous rating was less than 4000, which means I've actually been running it pretty conservatively. It will be a lot more useful once it's able to be tied into the house.
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