Question on wiring diagram for 3500/3000w generator

Discussion in 'General Electronics Chat' started by dcrose, Oct 3, 2013.

  1. dcrose

    Thread Starter New Member

    Oct 3, 2013
    2
    0
    Hope someone can answer a basic question for me on the attached wiring diagram from a 5 or 6 y/o Nikota 3500/3000w generator.

    The genset runs well, producing 240v at the NEMA L14-30 receptacle and 120v at the duplex receptacle. A 4P2T toggle switch selects the voltage between 240 and 120. The wiring to the L14-30 receptacle seems straight forward, with the brown feed from the first phase (call it Phase 1) providing 120v on one terminal, and the blue wire from the other phase (Phase 2) feeding 120v to the opposite terminal. Since the feeds are 180 degrees out of phase, 240v is the result across those terminals. A few years ago, I added a neutral where there originally was none so I also have 120v from the L14-30 receptacle when needed, but that's the only mod that's been done.

    So far so good. What has puzzled me is the way the 120v circuit is wired. As shown on the attached diagram, when the 4P2T is switched to 120v, the brown feed from Phase 1 connects to the hot side of the duplex receptacle, yet the blue feed from Phase 2 connects to the neutral side, on the opposite side of the receptacle. Surprising to me is that the jumper plates are fully intact on both sides of the receptacle. Question: Why doesn’t this yield 240v across the terminals of the duplex, just as it does with the L14-30 when the selector switch is set to 240v? And, even more basically, why doesn’t a ground fault occur due to the blue feed being connected directly to the neutral side of the duplex receptacle by virtue of the intact jumper plate?

    It's been suggested to me that the 4P2T switch may be moving the windings from series for the 240v to parallel for the 120v. Does that sound right? I'm not seeing how that's being accomplished by the switch, nor for that matter, how the windings are in series when in the 240v mode.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
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    With a quick glimpse the Generator windings appear in parallel in the 120v mode, also there does not appear to be any earth ground reference between gen and the receptacle ground pins?
    The windings show in series in the 240v mode the way I read the print.
    Max.
     
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  3. tinkerman

    Member

    Jul 22, 2012
    136
    34
    The windings are series for 240 volt and parallel for 120. Standard for any motor or gen set. Think of the windings as a pair of batteries. Often windings are marked with a polarity mark on drawings. The white would be polarity and brown non-polarity (like positive and negative). The other winding marks would be blue polarity and red non-polarity. The switch is changing the connection between series and parallel. They do this to get full power out of the gen set for either 120 or 240 operation.
     
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  4. dcrose

    Thread Starter New Member

    Oct 3, 2013
    2
    0
    Thanks, Tinkerman and Max. So, to be sure I'm understanding this: (1) With the windings in parallel when switched to 120v, and 120v measured at the duplex receptacle, this genset is wired so that it can (theoretically, at least) produce the full 3000w (nominal) at the receptacle, and (2) the two 13 amp breakers in parallel provide 26 amps overcurrent protection. Do I have that right? Really appreciate your help.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,526
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    Yes, the breakers provide protection for each winding, and are summed when in parallel.
    Max.
     
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