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generator questions

k1c | Posted in General Discussion on December 18, 2011 10:55am

Hello.

Finally getting a generator and I have some questions. 

Generator: Honda EU3000is,   120 volt only,   23.4 amps,   max. output is 3000 watts

I am using interlock assembly at the main service panel for locking out the breakers.  Panel is old Murray, not with orange main breaker. 

Generator output is 120 volts only, so I am using wiring and connections rated for 30 amp/120 v.  I am using 10-2 romex with ground  to connect outside plug to the service panel breaker.

My research for installing generator was based on 240v generators (most usual kind, I think).  Having bought 120v generator, I realized I don’t know much about the breakers.

1.  This is 23.4 amp generator, do I use 40 or 60 amp double arm breaker?  One transfer switch manufacturer recommends 60 amp breaker for generator rated up to 3500 watts.  Does this apply also to 120 v generator? 

2.  If using 60 amp breaker:  this gives 30 amp protection to each leg of the power bus?

3.  For double arm breaker (2 arms connected), if one arm trips, does it take the other arm with it?  Or do I look for 60 amp breaker with arms that are not connected?  Or use 2 single 30 amp breakers?

4.  From outside generator plug, 10-2 wire goes to generator breaker in the main panel.  I was thinking I will split the black wire into 2 power lines in the junction box, then take each power line to the breaker connections.  Is it as simple as this?  Or do I have to use 10-3 and connect the black and red at the generator end?  Powers need to be split at the main panel, and I am getting confused about if this kind of splitting is ok.  For one thing, if wire is split, does each split still carry about 3000 watt?

I wish I knew the answers to ask the right questions, but they never work out that way, lol.  Thank you in advance and I am hoping I can have the answers here than having an electrician come in.

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Replies

  1. User avater
    MarkH | Dec 18, 2011 11:23am | #1

    You bought an excellent generator, but totally the wrong one for what you want to do.

  2. k1c | Dec 18, 2011 11:26am | #2

    re track

    I was eager for answers and I did not search the forum.  I found  a discussion, and specifically about shared neutrals if I use interlock and panel.  I will go with transfer switch, manual 120v.   

    1. User avater
      MarkH | Dec 18, 2011 11:51am | #3

      I would get a generator with more power and 240v.  For what your generator costs, you could buy an automatic stationary generator with 2x to 3x the power and the capability to operate 220 volt devices.  Also it would operate on propane or better yet natural gas which does not spoil like gasoline does, or run out (well, propane will run out if your tank is too small for the generator).  We had a couple extended power outages lasting over a week, and I had an old noisy  5hp 1800 watt generator that could provide fridge and freezer power and lights, but would run about 3 hours per gallon of fuel, and all the gas stations were pretty much powerless, or out of fuel.  It was a drag, but saved my food and kept me out of the dark.  Fortunately it was mild weather in the summer, so I was comfortable.  I'm considering a NG backup unit, but power outages are rare here.  One was caused by remnants of a hurricane (I'm in Ohio!) the other was caused by a tornado.

      your generator was designed for an entirely different purpose, which is quiet, fuel efficient, clean (electrically) power, and portability.  It's an RV or temporary portable power unit, and probably the best of it's type.  But it has no where near the power to power a house even with a minimal power draw. (It would have more than my old one though.) 

  3. Amish Electrician | Dec 18, 2011 12:22pm | #4

    Fools rush in, where angels fear to tread.

    The best way to use the generator you have is to run extension cords to it.

    You simply cannot safely connect this generator to the household electrical system. Period.

    Do not, not, never, ever, connect the 'red' and the 'black' wires .... anywhere. period. The best you can hope for is overloading the white wire if you do. If you can't understand this, take your electrical tools back for a refund, and hire a pro . Your confusion over breaker sizes confirms that you're well out of your depth, and should stay out of the panel.

  4. junkhound | Dec 18, 2011 08:36pm | #5

    You simply cannot safely connect this generator to the household electrical system. Period

    Disagree. 

    While I'd agree that ANY hookup by the OP with limited knowledge would be unsafe, a knowledgeable person can safely install a few typical 3 way light switches to the critical appliances (from either side of the 240) and feed one side from the panel and the other side from a plug in cord to the generator.    This is safe, certain folks code interpretations may differ as to compliance with code. 

    1. DanH | Dec 18, 2011 10:09pm | #7

      A variation on that is one of the small transfer panels that contains breakers for maybe a half-dozen loads.  You wire the loads independently to the panel, so that they are separated from the house wiring when "transferred".  You could safely use one of these panels with the 120V generator, so long as only one "side" were powered.  And it might even be OK to "juice" both sides of this sort of transfer panel from a single 120V generator, depending on the design (and the total load capacity of its neutral bus).

  5. DanH | Dec 18, 2011 10:02pm | #6

    1) The generator should have its own internal overload protection, so you simply need a breaker larger than its capacity.  A 30 or 40A breaker should suffice (though, in general, the smaller the better, down to the extended surge capacity of the generator).  However, it should not be a double (or, at least, half of the double should not be wired).

    2) Unless your house has been very specially wired to run off of a 120V source (basically all neutrals separate or doubled-up) you cannot safely power more than one "leg".

    3) Irrelevant -- you'd not use a double breaker.

    4) No, it's not that simple -- see #2.  Attempting to power both legs off a single 120V source will overload the neutrals and very possibly cause a fire, or, at the very least, expensive damage to the house wiring.

    Unless you're lucky enough to have all critical loads on one side of your 240V service, you should either use extension cords or get a 240V genset.

    1. sapwood | Dec 19, 2011 11:23am | #9

      Please explain...

      You wrote: " 4) No, it's not that simple -- see #2.  Attempting to power both legs off a single 120V source will overload the neutrals and very possibly cause a fire, or, at the very least, expensive damage to the house wiring."

      Why is this so? I'm assuming that the op would be using a cut-out type panel that prevents both a generator and the utility service from being used at the same time. 

      For the record... I'm not thinking of doing what the OP is proposing. My generator delivers 240 into an inspected and approved transfer switch. 

       

      1. DanH | Dec 19, 2011 08:14pm | #10

        It's true because the common neutral in a shared neutral circuit is only designed to handle the max amps of one side, not the sum total of both sides.

        1. sapwood | Dec 19, 2011 10:01pm | #11

          OK, so maybe call me stupid...

          I still don't get it. And this bugs me cuz I thought I had a pretty good grasp of service panels etc. 

          Say the OP connects the black from the generator to one bus bar then jumpers over to the other with another black or whatever. And he connects the white from the generator to the neutral bar. Before doing all this he's disconnected from the grid by whatever means he wants to... probably by using a lockout panel. He turns all his double pole breakers in his panel to "off." He turns off most of the single pole breakers leaving only a couple in use. It happens that these two breakers are on different bus bars. Well, isn't he then "simply" using his panel as a convoluted junction box? A way to get juice to outlets inside the house. It's all 120 volts. Why would the neutrals be forced to carry double amps in this scenario? 

          What am I missing or my assumptions different than what's being discussed?

          Thanks

          1. DanH | Dec 19, 2011 10:59pm | #12

            Say you have a "shared

            Say you have a "shared neutral" circuit -- two hots from opposite "sides" and a neutral.  Draw 20 amps on one side and the current through the neutral is 20 amps, same as the hot.  Draw 20 amps from both sides and the current through the neutral is zero.

            Now wire both "sides" to the same 120V generator.  Draw 20 amps on one side and the current through the neutral is 20 amps.  Draw 20 amps from both sides and the current through the neutral is 40 amps.  That neutral wire won't look very pretty in about 30 seconds.

          2. sapwood | Dec 20, 2011 10:47am | #13

            Ahhh. You're objection to his plan is due to the possibility of shared neutrals. I hadn't picked up on that. For those I understand the problem. Thanks.

  6. k1c | Dec 19, 2011 01:40am | #8

    by Riversong in reply to Anonymous [original] on Wed, 12/31/2008 - 02:08

    you've all convinced me that a regular generator panel is the way to go. I hadn't thought about how a whole-house transfer would have to be 100 amps capacity. I'll just have to make do with only 8 circuits

    You definitely want to use a transfer switch subpanel, but you don't need 100A capacity if you're not transfering heavy loads to those circuits. The transfer panel is basically a subfeed panel with a double-throw, double-pole switch. Only the circuits you move to the subfeed panel will be loading that box. The rest will remain in the main breaker box and be activated only when utility power is available.

    You can get transfer panels with a front power socket for a corded generator supply or without for a hardwired generator supply. Some come with dual wattmeters, but you don't need them since you won't have to balance two legs of a 240v generator.

    You can get a decent transfer panel for less than $250 (such as the Reliant TRC0603D).

    ------------------------------------------------------------------------------------------------------------------------------------

    Thank you very much!  Can I still save the day with above set up?  I am inclined to prewired version.

    I will call in the electrician, if I must, but so many things seem to be factory wired that even electricians just plug and play.  That's why I thought I could do this.  At least, the nature of my questions were confirmed.

    If I use the transfer switch, is this still diy?

    The generators, in general, also had isssues about grounding and bonding.  Does this issue affect this transfer switch?

    Again thank you.

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