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Thread: Portable generator and generator panel incompatibility

  1. #1
    DIY Member luc's Avatar
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    Default Portable generator and generator panel incompatibility

    We just installed a generator panel on a house and we were testing it out yesterday with the portable generator. The generator has a 120/240V 30A receptacle. The receptacle is protected by a 40A double pole GFCI breaker.

    When we came to plug our 120/240 30A extension into the receptacle of the generator it tripped the GFCI breaker. The electricien came and looked over his generator panel installation and everyting was OK. We the contacted the generator manufacturer and they told us that this was normal. The GFCI breaker will trip because the portable generator was not made to be installed on a generator panel.

    Did anyone have this problem before? Is there anyway to get this working?

    Luc
    Last edited by luc; 05-20-2009 at 11:01 AM.

  2. #2

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    On a generator with a GFCI, the neutral and ground are tied together PRIOR to the GFCI on the generator chassis (those I have seen).

    So what happens with a GFCI is that it measures the electricity going out one current carrying conductor and EXPECTS to see the same returning on the other current carrying conductor.

    But if you connect the ground from the generator to ground at the electric panel (bonded to neutral at the main panel as it should be), then some electricity will travel back to the generator via the ground wire to the generator and this will trip the generator GFCI (as it notices not all of the electricity is returning on the other current carrying wire).

    Briggs and Stratton has a transfer switch which switches the neutral "off" from the main panel and connects it to the transfer switch panel neutral at the same time. So you could call this a "switched neutral transfer switch". This solves the problem of a generator with a GFCI. Basically you wind up with a "subpanel situation" where the ground is not bonded to neutral at the panel which is being powered by the generator and this all is disconnected from the main panel which does bond ground to neutral. Then the "main panel" (where neutral is bonded to ground) becomes the generator prior to the GFCI.

    I don't know if Briggs has an automatic switch or not, might want to call and ask them.

    Here is technical info on the Briggs switch...
    http://www.faqs.org/patents/app/20090058191

    Here is a wiring diagram of a generator with a GFCI...
    (Note chassis ground on neutral prior to GFCI)
    http://www.briggsandstratton.com/pdf...0248_0_wds.pdf

    Briggs and Stratton web site...
    http://www.briggsandstratton.com
    Last edited by Billy_Bob; 05-12-2009 at 07:21 AM.

  3. #3
    DIY Member luc's Avatar
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    Thanks Billy_Bob for responding.

    I checked the generator panel and it is wired with a swithed neutral (Cutler Hammer model CPL130G6) for use with generators having neutral bonded to ground. The generator is a Briggs & Stratton 8000PRO series (model 030337) which has neutral bonded to ground.

    Then if everything should work, the problem is in the generator or in the pannel.

    Luc

  4. #4

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    When the transfer switch is switched to generator, the ground and the neutral should NOT be bonded (connected) anywhere.

    You could unplug the cord to the generator and using an ohm meter, there should not be continuity from neutral to ground on the cord going toward the house. (With transfer switch switched to generator.)

    To be double safe when taking this measurement, be sure generator is off and might want to turn power off to the entire house as well.

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by luc View Post
    120/240 30A extension into the receptacle of the generator it tripped the GFCI breaker.
    900' of #14 Romex should trip a 4 mA GFCI because of capacitance between the hot/neutral conductors and the grounded conductor, with nothing connected to it.
    Can you post any schematics you have of the recommended house/generator wiring?
    Last edited by Thatguy; 05-12-2009 at 01:30 PM.

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    DIY Member luc's Avatar
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    Quote Originally Posted by Billy_Bob View Post
    When the transfer switch is switched to generator, the ground and the neutral should NOT be bonded (connected) anywhere.

    You could unplug the cord to the generator and using an ohm meter, there should not be continuity from neutral to ground on the cord going toward the house. (With transfer switch switched to generator.)

    To be double safe when taking this measurement, be sure generator is off and might want to turn power off to the entire house as well.
    Ok this is a good place to start. I will check this out as soon as I can and if I still get the same problem I will try to post the wiring schematic. I will have to scan the sheets because I could not find them on internet.

    Thanks,
    Luc
    Last edited by luc; 05-16-2009 at 11:54 AM.

  7. #7

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    What might make this easier for you is to learn about main electric panels as opposed to "subpanels". Search google.com for the term subpanel.

    Main electric panels intentionally have the neutral "bonded" (connected) to ground. This is usually done by installing a screw provided with the panel. This screw is called a neutral bonding screw (in the panel instructions).

    If you have a main electric panel say outside. Then ANOTHER electric panel say upstairs inside your house. That panel would be called a "subpanel". In this case, you would NOT install the neutral bonding screw. Neutral would not be connected to ground in THAT panel.

    So maybe it is just the case of a neutral bonding screw installed. BUT this is quite important if the panel is a main panel! So don't just unscrew it without checking and considering the entire electric system as a whole.

    This situation is simple, yet quite complex!

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    Homeowner Thatguy's Avatar
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    I have recently found out that AFCIs that use GF sensing use a 30 mA threshold instead of the 4-6 mA threshold for individual GFCIs.
    If whole house GFCIs also use 30 mA then the house wiring capacitance is probably what forces them to go to this higher threshold.

    If you are using your generator GFCI as a whole house GFCI, that may be the problem.
    One solution is to disable your gen. GFCI and use downstream GF protection. In this case I'd make sure your gen. is securely (and probably redundantly, for higher reliability) grounded.

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    DIY Member luc's Avatar
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    We solved half of our problem this morning. One of the circuit had a short between the neutral and ground. The neutral wire was being squeezed between the electrical box and the lighting fixture. With this fixed, the neutral switched properly in the generator subpanel.(It isolates the neutral from the main panel and the generator subpanel)

    We then did our generator test. All the 120V individual circuits were all working properly on the emergency power. When we came to switch the 240V well pump the GFCI breaker on the generator tripped. The pump is only a 1/2 hp and we have plenty of power(8000W generator). We tried the pump individually and it kept tripping the GFCI breaker on the generator.

    Any idea? Is the GFCI made for 240V circuits?
    Would it be the long distances of cables to the well and down the well influence the GFCI? I did not check to see if there was a short between the lines and the ground.

    Luc
    Last edited by luc; 05-16-2009 at 11:55 AM.

  10. #10
    DIY Member luc's Avatar
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    Quote Originally Posted by Thatguy View Post

    If you are using your generator GFCI as a whole house GFCI, that may be the problem.
    One solution is to disable your gen. GFCI and use downstream GF protection. In this case I'd make sure your gen. is securely (and probably redundantly, for higher reliability) grounded.
    We are using the generator GFCI breaker to supply the generator subpanel. We have 9 circuits. If we disable the generator GFCI, is it necessary to have another ground on the generator? The generator 120/240V 30 A extension cord is grounded in the generator subpanel which is linked to the whole house ground.

    Luc

  11. #11

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    What you need is a solution to this problem, but I don't think you would ever get any electrical authority/manufacturer to "say it is OK to remove the GFCI from your generator"...

    I've not gone generator shopping lately, so the question is... Are new generators sold these days which do not come with GFCI's on them?

    And then what is the approved wiring method these days for connecting this type of generator (non-GFCI) to a transfer switch?

    Then if your generator did not have a GFCI and was connected in an approved manner for new generators which do not come with GFCI's, I would ask if that would be the same as it would be for the other non-GFCI generators?

  12. #12
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by luc View Post
    Would it be the long distances of cables to the well and down the well influence the GFCI? I did not check to see if there was a short between the lines and the ground.

    Luc
    1000' of grounded Romex should trip a 4 to 6 mA GFCI due to capacitance between conductors.
    I come to find out there is also a ELCI, Equipment Leakage Current Interrupter, and this can be set from 6 mA to 100 mA. I'd think a pump motor has at least some capacitance from the windings to the motor shell.

    If you have a DVM and a 1/16A fuse you can check leakage to make sure the GFCI is tripping for a valid reason.
    Last edited by Thatguy; 05-16-2009 at 04:49 PM.

  13. #13
    DIY Member luc's Avatar
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    Just took some reading from the well pump circuit:
    - Amps in phase A: around 6.25 A
    - Amps in phase B: around 6.25 A
    - Voltage between Phase A and ground: 2.44V
    - Voltage between Phase B and ground: 2.00V
    - Amps on the ground cable when the pump is OFF: 2.5 mA
    - Amps on the ground cable when the pump is ON: 3.8 mA

    The GFCI breaker has a 5mA trip sensitivity. I think that the 3.8mA added to the amp leakage in the other circuits trips the GFCI.

    I did some research and all portable generators above 5KW need to be protected by GFCI. This is an OSHA standard.

  14. #14
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by luc View Post
    - Amps on the ground cable when the pump is OFF: 2.5 mA
    So is the pump at the end of 500' of Romex?

  15. #15

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    Quote Originally Posted by luc View Post
    ...I did some research and all portable generators above 5KW need to be protected by GFCI. This is an OSHA standard.

    The word is PORTABLE... So what if it was "not portable" is the question!

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