Results 1 to 5 of 5

Thread: Portable generators and 4 pole transfer switches

  1. #1
    Join Date
    Mar 2004
    Posts
    297

    Portable generators and 4 pole transfer switches

    Quite often I find clients wanting to be able to power one of their panelboards with a portable generator. This is often accomplished with a transfer switch with a external twist lock receptacle on the line side of the "crucial" panel.

    After reading similar posts and manufacturer's info would it be safe to assume that for the configuration described above, a three pole transfer switch must be used.

    I say this because the owner is unlikely to drive ground rods and connect his grounding electrode conductor (as would be required for an SDS) when he parks the generator and plugs it into the twist lock.

    Related question, if you use a 3 pole transfer switch, the generator's neutral to ground bonding jumper needs to be removed.
    "In this house, we obey the laws of thermodynamics" - H. Simpson.

  2. #2
    Join Date
    Feb 2003
    Location
    New York, 40.7514,-73.9925
    Posts
    3,279

    Re: Portable generators and 4 pole transfer switches

    In a residential scenario (120/240V single phase), a two pole transfer switch for the panel or individual one pole transfers for each branch circuit in the panel is generally available. In those cases, the n-g bond would be removed in the gen, and connected to the "critical" panelboard, as the gen is not a SDS [see 250.34(C) and 250.30(D)FPN]. The fact that you will not switch the neutral in the transfer scheme, makes it NOT an SDS.
    Ron

  3. #3
    Join Date
    Feb 2003
    Posts
    1,257

    Re: Portable generators and 4 pole transfer switches

    Would it be easier to base the # of poles of the transfer switch, on the generator configuration?

    I ask this because I've heard it to sometimes be complicated to remove a neutral bond in some of the smaller generators.
    Todd
    Live Long and Prosper.

  4. #4
    Join Date
    Mar 2004
    Posts
    297

    Re: Portable generators and 4 pole transfer switches

    "Would it be easier to base the # of poles of the transfer switch, on the generator configuration?"

    I don't think its that easy. By going with a 4 pole transfer switch you are setting up a separatly derived system and you must deal with all of the requirements for such. The benefit of the 4 pole switch is that it allows GFI protection systems to operate properly. However, if you use a 4 pole switch you have to ground the generator's neutral just as you would the service entrance.

    "I ask this because I've heard it to sometimes be complicated to remove a neutral bond in some of the smaller generators."

    Why would a small portable generator ever have a neutral bond? It creates a parrallel path to ground if you use a 3 pole transfer switch and if you use a 4 pole switch you would need to create a ground system (rods, building steel, water pipe etc) for the portable generator.

    Answer my own question, maybe if it was not intended for premise wiring but just to run the outlets on the generator panel. I was not talking about something that small in my original post. More like a 80 KVA unit on wheels that you tow behind a truck.
    "In this house, we obey the laws of thermodynamics" - H. Simpson.

  5. #5
    Join Date
    Feb 2003
    Posts
    1,257

    Re: Portable generators and 4 pole transfer switches

    sceepe,
    my post was for argument's sake.
    When I read your post, it seemed to me as if you were basing the generator (SDS, or Non-SDS) on the # of poles in the transfer switch.
    It is the generator bond that determines SDS or NON, and then you would determine how many poles you need in the switch.
    If you want to go with the # of poles first, then you might have to bond or unbond the neutral in the gen. accordingly.


    You can't assume that a small generator does not have the neutral bonded.
    I know that there were some that did.

    Your original post didn't mention 1-ph, or 3-ph.
    But you did mention twistlock receptacle. The twistlock made me think 50amps or below.

    I would imagine for an 80kVa gen., you would be using pin/sleeve entrance.
    I install alot of generator systems. Now, they are mostly 10-12k systems.

    Right before the Y2K scare, I did alot of 3-phase set-ups for some local military units. I believe their portable gen's are 75kVa.
    These were all retro-fit systems on existing services. Some were 240v, some were 480v.
    The cord and plug were almost as heavy as I was.

    Comcast Cable in my area uses a similar set-up.
    They use a 200amp pin/sleeve inlet on their buildings.

    You have it right,
    4-pole for 3phase SDS(bonded neutral)
    3-pole for 3phase Non-SDS(floating neutral)
    Todd
    Live Long and Prosper.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •