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  1. #21
    mrennie's Avatar
    mrennie is offline Cast Iron
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    Frederick Harvie is bang on....the deciding factor whether to use a 2 pole or 3 pole transfer switch (to either switch just the hots, or the hots and neutral) is whether or not the generator you are using has a bonded neutral or a floating neutral.

    Most portable generators (Honda, Coleman, etc), have a bonding strap between the ground lead and the neutral lead inside the alternator, and are labelled "neutral bonded to ground", and this requires that you use a 3 pole transfer switch to switch both the neutral and the hots. If you used a 2 pole transfer switch by mistake and just switch the hots this results in 2 connections points between neutral and ground (one at the service entrance panel and another in the generator), which can result is different potentials between the grounds and current flow where there shouldn't be.

    In the case where your genset has no strap between the neutral and ground (sometimes found on larger industrial type alternators), this is considered a "floating neutral" type and you need a continuous neutral connection all the way back to the service entrance panel, which is where the bond between neutral and ground is provided. If you mistakenly used a 3 pole transfer switch and switched both hots and the neutral with a floating neutral generator, you would have no connection between neutral and ground when running on the generator and a fault between a hot and ground would not trip the generator breaker.


    Michael

  2. #22
    Frederick Harvie is offline Stainless
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    Further to Michaels comments on bonded neutral. It is my understanding that it is ileagal at least in canada to sell a "Portable Generator" that does not have a bonded neutral. Only generators designed for a stationary application can be sold with a floating neutral.

  3. #23
    Jim Caudill is offline Stainless
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    From my Honda EU2000i manual on page 17:

    "Honda portable generators have a system ground that connects generator frame components to the ground terminals in the AC output receptacles. The system ground is not connected to the AC neutral wire. If the generator is tested by a receptacle tester, it will not show the same ground circuit condition as for a home receptacle."

  4. #24
    jim rozen is online now Diamond
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    Given that there will be a ground loop on the neutral with a two pole Xfer switch
    used with a bonded generator, this is accepted.

    However as far as I can determine, using the a two pole switch where a three pole
    one is called for, still will NOT result in energy being backfed to the line from the
    generator.

    If anyone can point out that this last bit is incorrect, please do so as the subject
    has been discussed at some length here in the past.

    Jim

  5. #25
    mrennie's Avatar
    mrennie is offline Cast Iron
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    Jim Caudill:

    The Honda you have is different from the usual Honda's I am familiar with like the EM5000/EM6500 series, which are bonded neutral and do have a strap between the neutral and ground under the end cover of the alternator (I recently converted all our portable Honda's at work to be "neutral floating" by removing the straps, since our sites use 2 pole transfer switches for use with a 25 kW mobile generator (floating neutral) and we needed the Honda's to work with the existing transfer switches). Is your Honda one of the newer inverter style units?

    Jim Rozen:

    I don't think you could backfeed power into the line using a 2 pole transfer switch where a 3 pole should be used, because this implies that you are not switching the neutral, and since the neutral is "SUPPOSED" to be bonded to ground at your service entrance panel, any stray voltage on the neutral would be pulled to ground at that point and never get any farther into the grid.

  6. #26
    JST's Avatar
    JST
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    In any unit with a ground bond, you should be able to remove the bond in order to use it with a 2 wire switch.

    That removes all question, of course.

    Now, if the transfer switch removes the connection to the service drop, and re-connects to the generator, that obviously has NOTHING to do with the bonding inside the service.

    The bonding in the service remains in either case, unless it is in turn switched, which a 3-pole switch would then have to do, i.e. get into the connection from neutral to ground, not just the drop neutral.

    Merely switching the drop neutral off the drop and onto the generator will NOT affect anything.

    It seems that you MUST use a non-bonded genset regardless.............or remove the bond.

    Much simpler NOT to carry the ground over...... if you merely carry the neutral and hots, you will emulate the 3 wire service.

    In fact, since the service itself grounds (earths) the neutral at every pole, the entire matter is almost moot..... any currents of interest will be between the genset and the service ground bar, and will not involve the premise wiring, assuming the genset has a suitable socket or is wired permanently in a manner similar to the service.

    There is a very real possibility in the case of a normal service, for there to exist significant LOAD currents in the grounding (earthing) system.

    I have tested the grounding system in many houses, and every single one has had anywhere from 1 to 10 amps flowing in the grounding wire from the ground bar to ground (earth). This is load current, affected by turning on and off loads in the house.

    We had a tree fall on our drop, removing the neutral connection, and leaving the hots. If we did NOT have a water pipe ground, we would possibly have no house, since electrical equipment could have caught on fire from overvoltage (240 on 120V). But the good ground, hooked to the neighbors good neutrals, saved the day.

    Until that got fixed (took a while, everyone had power problems) we had 7A+ in the water pipes. Normal is 1 to 2 A.

    The condition that is of concern, is existing in houses all over the US at least, right now.

  7. #27
    mrennie's Avatar
    mrennie is offline Cast Iron
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    Further to what Frederick and I have mentioned, here is a link to a PDF file that explains why it is bad to use a 2 pole switch when you need a 3 pole, and vice versa.

    Also note that we are in Canada and the Canadian code may not be exactly the same as US code for this issue, although I would be surprised if it is different.

    http://www.schneider-electric.ca/www...pl_Note_EN.pdf

    Michael

  8. #28
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    JST
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    AH......... this is NOT the "standby generator" case AT ALL. IT IS QUITE DIFFERENT.

    Both codes would agree IN THIS CASE.

    The confusion I had was not understanding that the case discussed there was anticipated generator power ONLY of certain sub-circuits/ branch circuits, possibly only one. The rest of the circuits would NOT be powered.

    In THAT case, the generator would indeed supply a second bond, which would be a code violation.

    The transfer switch I was envisioning is a complete service transfer to a substantial generator, i.e. a backup sufficient for all circuits, with the actual service wire switched over to it.

    In THAT case the 3 wire transfer makes less sense, since the bond is outside the premises, not on "the load side" of the service box bond. It is difficult to make the switch 3 wire in a meaningful way, and little reason to.

  9. #29
    Jim Caudill is offline Stainless
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    For Mrennie, Yes this is the newer, inverter, model. I assume that all the Hondas with an "i" in the model number are "inverter" type generators. These things are really slick, no longer does the generator have to run at a specific rpm to keep the hz constant. This model has an "Eco" (economy?) switch that allows the unit to idle down and only speed up as much as required for the load demand. There are certain applications where the manual reccommends that you turn the "Eco" switch to off and let the generator run up at its governed rpm.

  10. #30
    Timw is offline Stainless
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    Something as important is generator placement.
    FYI- EVERY storm is seems that someone is killed by CO posioning. If they don't run the gen inside they will put it in their garage or some other place and they become a statistic. And they always blame the storm for these morons.
    Occasionally campers are killed by CO. I think it happened at the Indy NASCAR race. Motorhomes were parked so close together that CO from one killed people in another.

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