Problem Grounding a Generator

Discussion in 'Electronic Repair' started by Tony Sivori, Nov 15, 2009.

  1. Tony Sivori

    Tony Sivori Guest

    I recently acquired a small portable back up generator for nuisance
    outages. Only paid $200 new. It is 2500 watts continuous, 3250 surge rated
    and no 220 volt outlet, so I won't be hooking it up to a transfer switch.

    Even though I'm going the extension cord method, I decided to properly
    ground it, and use an inline GFI and surge protector. I'm willing to risk
    using a back up computer with it, and I am hopeful that a surge protector
    might clean up the "dirty" generator power.

    Now the problem. I drove an 8 foot ground rod into typical soil, used a
    correct copper clamp (nothing improvised), and connected the rod to the
    generator ground lug with a single strand 12 gauge copper wire.

    Trouble is, the generator outlets still tests as ungrounded.

    I immediately suspected miswired outlets on the generator. So I tried
    checking the resistance from the power receptacle outlet ground to both
    the generator frame and the generator ground lug. Both tests resulted in
    zero ohms of resistance. I'm thinking that would eliminate miswiring on
    the generator as the cause.

    I then removed both ends of the ground wire connection, checked and
    reconnected them.

    Same result, tests as open ground with a three prong plug in tester. I
    also tested the tester, and it shows grounded outlets in my house as
    properly grounded.

    I checked the resistance from the generator end of the ground wire to the
    ground rod itself. It was also zero ohms.

    So it seems to be a case of it has to work, but it doesn't work. Any
    suggestions are welcome.

    --
    Tony Sivori
    Due to spam, I'm filtering all Google Groups posters.
    Tony Sivori, Nov 15, 2009
    #1
  2. Tony Sivori

    PeterD Guest

    On Sun, 15 Nov 2009 17:52:46 -0500, Tony Sivori <>
    wrote:

    >I recently acquired a small portable back up generator for nuisance
    >outages. Only paid $200 new. It is 2500 watts continuous, 3250 surge rated
    >and no 220 volt outlet, so I won't be hooking it up to a transfer switch.
    >
    >Even though I'm going the extension cord method, I decided to properly
    >ground it, and use an inline GFI and surge protector. I'm willing to risk
    >using a back up computer with it, and I am hopeful that a surge protector
    >might clean up the "dirty" generator power.
    >
    >Now the problem. I drove an 8 foot ground rod into typical soil, used a
    >correct copper clamp (nothing improvised), and connected the rod to the
    >generator ground lug with a single strand 12 gauge copper wire.
    >
    >Trouble is, the generator outlets still tests as ungrounded.
    >
    >I immediately suspected miswired outlets on the generator. So I tried
    >checking the resistance from the power receptacle outlet ground to both
    >the generator frame and the generator ground lug. Both tests resulted in
    >zero ohms of resistance. I'm thinking that would eliminate miswiring on
    >the generator as the cause.
    >
    >I then removed both ends of the ground wire connection, checked and
    >reconnected them.
    >
    >Same result, tests as open ground with a three prong plug in tester. I
    >also tested the tester, and it shows grounded outlets in my house as
    >properly grounded.
    >
    >I checked the resistance from the generator end of the ground wire to the
    >ground rod itself. It was also zero ohms.
    >
    >So it seems to be a case of it has to work, but it doesn't work. Any
    >suggestions are welcome.


    You may have high resistance soil, and need more than one ground rod.
    Code typically calls for three, wired together.
    PeterD, Nov 16, 2009
    #2
  3. Tony Sivori

    Tony Sivori Guest

    PeterD wrote:

    > <> wrote:
    >>So it seems to be a case of it has to work, but it doesn't work. Any
    >>suggestions are welcome.

    >
    > You may have high resistance soil, and need more than one ground rod.
    > Code typically calls for three, wired together.


    I think you are probably right.

    A quick Google shows that multiple ground rods are often necessary.
    Although I found the NEC calls for multiple rods only when a single rod
    installation exceeds it says 25 ohms. And it seems that every other
    possible reason has been eliminated.

    --
    Tony Sivori
    Due to spam, I'm filtering all Google Groups posters.
    Tony Sivori, Nov 16, 2009
    #3
  4. Tony Sivori

    Shaun Guest

    "Tony Sivori" <> wrote in message
    news:p...
    > PeterD wrote:
    >
    >> <> wrote:
    >>>So it seems to be a case of it has to work, but it doesn't work. Any
    >>>suggestions are welcome.

    >>
    >> You may have high resistance soil, and need more than one ground rod.
    >> Code typically calls for three, wired together.

    >
    > I think you are probably right.
    >
    > A quick Google shows that multiple ground rods are often necessary.
    > Although I found the NEC calls for multiple rods only when a single rod
    > installation exceeds it says 25 ohms. And it seems that every other
    > possible reason has been eliminated.
    >
    > --
    > Tony Sivori
    > Due to spam, I'm filtering all Google Groups posters.


    I think I know what the problem is. In a house, at the electrical panel,
    the neutral wire is connected to the ground. Your tester maybe assuming
    this and that is why it is not showing a ground connection. Your generator
    probably has a floating output (neutral not connected to the frame ground).
    Which is why the tested shows no ground. This will not pose a problem when
    using the generator, it is still grounded, it's just that the neutral is not
    connected to ground.

    Shaun
    Shaun, Nov 16, 2009
    #4
  5. Tony Sivori

    Tony Sivori Guest

    Andrew Erickson wrote:
    >
    > It sounds as though the generator's neutral leg is not tied to ground at
    > the generator. The outlet tester isn't actually testing that the ground
    > prong is anywhere near ground, merely that current can flow between the
    > hot and the ground leg.


    I wasn't aware of that. Thanks.

    > (In a standard residential setup, the neutral leg is tied to ground at
    > the main breaker box, and all neutral and ground wires go to the common
    > neutral/ground bar.


    That much I did know. I even knew that the only place the neutral can be
    grounded is at the junction box.

    > The outlet tester would still show the outlet is wired properly even if
    > the ground leg were not actually connected to ground.)


    A test with the outlet tester and an ungrounded outlet confirms that
    you're right.

    > By the way, the surge suppressor will do pretty much nothing to clean up
    > the generator output power. It's also rather likely that the output is
    > reasonably clean to begin with; certainly far better than a typical
    > "modified sine wave" inverter output, which is a combination of a couple
    > of square waves. A typical computer, with a switching power supply, is
    > not picky at all about power quality, as the first stage in the power
    > supply is a rectifier and reservoir capacitor, changing whatever the
    > input is into (unregulated) high voltage DC power. They run just fine
    > from the above mentioned modified sine wave inverters, potentially even
    > a bit more efficiently than from sinusoidal inputs.


    I've heard a few anecdotes of generator power damaging televisions and DVD
    players. I thought a pair (one on each outlet) of cheap surge protectors
    might help.

    > Anyhow, you could tie the "neutral" leg of the generator output to
    > ground at the generator, which would be safe provided the generator
    > frame is actually grounded, and which would make the outlet tester
    > happier.


    Unless it would add safety, I'm not at all worried about bonding the
    neutral to ground.

    > Safer, IMHO, is just using the GFI and not worrying about it
    > more. Indeed, code permits GFIs to be used on existing ungrounded
    > circuits to allow three-pronged devices to be plugged in despite the
    > lack of a safety ground conductor (albeit with certain cautionary
    > labeling required).


    I may do that. One of the reasons I was dead set on proper grounding is
    that I knew that the surge protectors can't work without a ground. If the
    surge protectors are useless and unneeded, I could leave the ground
    connected as is, and just use the inline GFI.

    --
    Tony Sivori
    Due to spam, I'm filtering all Google Groups posters.
    Tony Sivori, Nov 16, 2009
    #5
  6. Tony Sivori

    Tony Sivori Guest

    Shaun wrote:
    >
    > I think I know what the problem is. In a house, at the electrical
    > panel, the neutral wire is connected to the ground. Your tester maybe
    > assuming this and that is why it is not showing a ground connection.
    > Your generator probably has a floating output (neutral not connected to
    > the frame ground). Which is why the tested shows no ground. This will
    > not pose a problem when using the generator, it is still grounded, it's
    > just that the neutral is not connected to ground.


    You're right about the floating neutral.

    I found a couple of OSHA pages discussing portable generator grounding and
    neutral bonding.

    http://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf

    although it seems to contradict this one:

    http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=20448

    --
    Tony Sivori
    Due to spam, I'm filtering all Google Groups posters.
    Tony Sivori, Nov 16, 2009
    #6
  7. On 11/15/2009 8:06 PM Tony Sivori spake thus:

    > Andrew Erickson wrote:
    >
    >> (In a standard residential setup, the neutral leg is tied to ground at
    >> the main breaker box, and all neutral and ground wires go to the common
    >> neutral/ground bar.

    >
    > That much I did know. I even knew that the only place the neutral can be
    > grounded is at the junction box.


    Don't say "junction box", as that statement will make all electricians
    wince. You meant to say "breaker panel" or "distribution panel", right?


    --
    Who needs a junta or a dictatorship when you have a Congress
    blowing Wall Street, using the media as a condom?

    - harvested from Usenet
    David Nebenzahl, Nov 16, 2009
    #7
  8. Tony Sivori

    Tony Sivori Guest

    David Nebenzahl wrote:

    > On 11/15/2009 8:06 PM Tony Sivori spake thus:
    >
    >> Andrew Erickson wrote:
    >>
    >>> (In a standard residential setup, the neutral leg is tied to ground at
    >>> the main breaker box, and all neutral and ground wires go to the common
    >>> neutral/ground bar.

    >>
    >> That much I did know. I even knew that the only place the neutral can be
    >> grounded is at the junction box.

    >
    > Don't say "junction box", as that statement will make all electricians
    > wince. You meant to say "breaker panel" or "distribution panel", right?


    A slip of the tongue, or fingers, if you prefer.

    I've found some more pages on the pros and cons of bonding a
    portable generator floating neutral to ground.

    http://blog.rv.net/2009/10/generator-bonding-and-grounding/

    http://blog.rv.net/2009/10/portable-generator-grounding/

    --
    Tony Sivori
    Due to spam, I'm filtering all Google Groups posters.
    Tony Sivori, Nov 16, 2009
    #8
  9. Tony Sivori

    Baron Guest

    Tony Sivori wrote:
    > I may do that. One of the reasons I was dead set on proper grounding
    > is that I knew that the surge protectors can't work without a ground.
    > If the surge protectors are useless and unneeded, I could leave the
    > ground connected as is, and just use the inline GFI.


    No relation to "wtom" ?

    --
    Best Regards:
    Baron.
    Baron, Nov 16, 2009
    #9
  10. In article <>,
    Meat Plow <> wrote:

    > My generator is 2500/3250 surge like
    > yours. And it is brushless. But there was nothing I could do to filter
    > the output well enough where my two 1000va APC UPS units would come
    > back off battery.


    I've read elsewhere that the problem with generators and UPS units, is
    that the generator doesn't hold an exact 60 Hz. You might find a
    generator's frequency will range as much as 63 Hz to 59 Hz from no load
    to full load. The UPS likely depends on a crystal controlled oscillator
    to determine if 60 Hz power is present.

    I wonder if inverter generators like the little Honda EU1000i, will work
    with a UPS?

    Fred
    Fred McKenzie, Nov 17, 2009
    #10
  11. Tony Sivori

    PeterD Guest

    On Mon, 16 Nov 2009 21:39:04 -0500, Fred McKenzie <>
    wrote:

    >In article <>,
    > Meat Plow <> wrote:
    >
    >> My generator is 2500/3250 surge like
    >> yours. And it is brushless. But there was nothing I could do to filter
    >> the output well enough where my two 1000va APC UPS units would come
    >> back off battery.

    >
    >I've read elsewhere that the problem with generators and UPS units, is
    >that the generator doesn't hold an exact 60 Hz. You might find a
    >generator's frequency will range as much as 63 Hz to 59 Hz from no load
    >to full load. The UPS likely depends on a crystal controlled oscillator
    >to determine if 60 Hz power is present.
    >
    >I wonder if inverter generators like the little Honda EU1000i, will work
    >with a UPS?
    >


    Probably would work better. My UPS, a high end high power one, tells
    me the line frequency on it's statistics page. Interesting watching
    the statistics, and seeing line voltage variations, etc.
    PeterD, Nov 17, 2009
    #11
  12. Tony Sivori

    Tony Sivori Guest

    Meat Plow wrote:

    > On Sun, 15 Nov 2009 22:17:57 -0500, Tony Sivori
    > <>wrote:
    >
    >>PeterD wrote:
    >>
    >>> <> wrote:
    >>>>So it seems to be a case of it has to work, but it doesn't work. Any
    >>>>suggestions are welcome.
    >>>
    >>> You may have high resistance soil, and need more than one ground rod.
    >>> Code typically calls for three, wired together.

    >>
    >>I think you are probably right.
    >>
    >>A quick Google shows that multiple ground rods are often necessary.
    >>Although I found the NEC calls for multiple rods only when a single rod
    >>installation exceeds it says 25 ohms. And it seems that every other
    >>possible reason has been eliminated.

    >
    > And good luck trying to clean up the generator output if you intend on
    > using a UPS in the circuit. My generator is 2500/3250 surge like yours.


    Mine is a KingCraft from Aldi. Would you happen to have the same one?

    > And it is brushless. But there was nothing I could do to filter the
    > output well enough where my two 1000va APC UPS units would come back off
    > battery. Both are used in my A/V gear after a about with nuisance
    > outages of short duration but short enough to need to reset a lot of
    > things. Also I had two 9 foot copper ground rods, one on either side of
    > the house connected inside to my ham radio stuff. When hooked to an APC
    > multi outlet filter with a wiring fault indicator, the indicator did not
    > light while on generator power. So I guess in my case the two rods were
    > enough. And they sure reduced my noise level on the HF bands, the main
    > reason for their installation.


    I'd guess that I'm grounded with the one 8 foot rod. I just didn't realize
    how limited the cheap three prong outlet testers are. Live and learn.

    --
    Tony Sivori
    Due to spam, I'm filtering all Google Groups posters.
    Tony Sivori, Nov 18, 2009
    #12
  13. Tony Sivori

    Tony Sivori Guest

    Baron wrote:

    > Tony Sivori wrote:
    >> I may do that. One of the reasons I was dead set on proper grounding is
    >> that I knew that the surge protectors can't work without a ground. If
    >> the surge protectors are useless and unneeded, I could leave the ground
    >> connected as is, and just use the inline GFI.

    >
    > No relation to "wtom" ?


    wtom? Is that a nym?

    --
    Tony Sivori
    Due to spam, I'm filtering all Google Groups posters.
    Tony Sivori, Nov 18, 2009
    #13
  14. Tony Sivori

    Tony Sivori Guest

    Dave Platt wrote:
    >
    > I'd suggest checking your generator manual, to see if you can determine
    > whether it's designed to have a "floating neutral". I suspect that it
    > is.
    > If so, don't modify it.


    Not much in the manual. No mention of the floating neutral, just a
    statement not to connect it directly to any structure's electrical system.

    --
    Tony Sivori
    Due to spam, I'm filtering all Google Groups posters.
    Tony Sivori, Nov 18, 2009
    #14
  15. Tony Sivori

    Baron Guest

    Tony Sivori wrote:

    > Baron wrote:
    >
    >> Tony Sivori wrote:
    >>> I may do that. One of the reasons I was dead set on proper grounding
    >>> is that I knew that the surge protectors can't work without a
    >>> ground. If the surge protectors are useless and unneeded, I could
    >>> leave the ground connected as is, and just use the inline GFI.

    >>
    >> No relation to "wtom" ?

    >
    > wtom? Is that a nym?


    A troll that jumped on anybody that mentioned surge protectors.

    --
    Best Regards:
    Baron.
    Baron, Nov 18, 2009
    #15
  16. In article <>, Meat Plow
    <> writes

    >And good luck trying to clean up the generator output if you intend on
    >using a UPS in the circuit. My generator is 2500/3250 surge like
    >yours. And it is brushless. But there was nothing I could do to filter
    >the output well enough where my two 1000va APC UPS units would come
    >back off battery.


    There was a recent discussion in demon.tech.pc by someone with a very
    similar problem. (If you're aware of w_tom, you'll not be surprised he
    featured in that thread.) We managed to establish that some APC UPSes
    are specified by APC as generator-compatible and also have a button on
    the back which can be used to reduce the UPS's sensitivity to poor mains
    voltage.

    I told the OP in that thread that his problems may be due to the lack of
    a ground reference, but not being au fait with the subject had to bow
    out there. Bear in mind this was a 240V (UK) installation, so I wasn't
    comfortable with discussing tying one side of the output to ground.

    --
    Mike Tomlinson
    Mike Tomlinson, Nov 19, 2009
    #16

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