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Portable Generator Grounding Question

Post in 'DIY and General non-hearth advice' started by BrotherBart, Dec 12, 2013.

  1. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    OK, here is what I got. In the generator shed are twin Chinese Honda clone 3,500 watt 20 amp 120 volt generators like the ones sold under a dozen brands. Backup firepower is a 5,000 watt DeVillbiss gas hog that is seldom fired except the monthly maintenance run. Power supplied to essential items during power failures through 12 gauge extension cords from the shed into the house. The cords and generators are plugged into a pair of Leviton 5500-192 megabucks surge supression PDUs rack mounted in the generator shed. Distribution in the house is via Wiremold J60BOB rack mount PDUs. No connection anywhere, anyhow to house wiring.

    The issue/question. Until this year I have run the generators without grounding rods connected to the grounding lugs on the generators without problems even though the manual says to ground the generators. On the PDUs I have "Power", "Ground Good" and "Protection" leds. All light when running without grounding rods connected to the generators. This year I decided to ground the gensets. With the grounding rods connected I get no "Ground Good" light on the PDUs. Disconnect the grounding rod and "Ground Good" lights up.

    What is happening ground wise here? I know squat about electricity and never will. The web provides a great way to get totally confused about "bonded" and "floating" neutrals with portable gensets. Most contradicting. If the problem is the grounding rods I don't understand why the manual says to ground the things.

    Any wisdom appreciated. I don't want to fry me or any equipment.

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  2. Highbeam

    Highbeam Minister of Fire

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    This is what you'll find. Nobody knows for sure. I would not use the rods since it appears to upset your device.
  3. seige101

    seige101 Minister of Fire

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    You are only supposed to bond the neutral and ground once at the main disconnect in your house most likely at your panel. So technically if you are properly hooking your generator up to the house you should use a floating neutral type.However you are using cords so that doesn't apply. You want the ground and neutral bonded at the generator.

    Personally i have never grounded a portable generator when using it with cords or while connected to my house. If you were connecting through a proper interlock kit the ground would be connecting your house ground to the generator.

    /Electrician

    A far as your good ground light not lighting up, without physically testing with a good multi meter i can only hazard a guess but i will save the ramblings from my mind and technical jargon. More than likely you are still protected
    Adios Pantalones likes this.
  4. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    The main reason for the concern is that Leviton says the surge suppression shunts the surge to ground.
  5. KB007

    KB007 Feeling the Heat

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    Does the manual say if the generators are floating or bonded?

    Sometimes PDUs can be a little too sensitive and pickup a very small voltage and show a fault. I'd be inclined to use the ground rod if the manual says to use it, and you are using only extension cords (ie no connection to the home panel).

    You're sure you don't have any kind of ground wire from any of those PDUs or rack to a house ground by chance?

    Have you ever thought about putting in a transfer switch?
    btuser likes this.
  6. Jags

    Jags Moderate Moderator Staff Member

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    Bro - is your rack grounded to the house wiring?
  7. Matt Ruggeri

    Matt Ruggeri New Member

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    Hah, Join the club! If it is isolated from the house wiring, conventional wisdom says to ground AND bond it to it's own "earth" source, the code book says otherwise! Honda and Yamaha also use the floating neutral, they recommend leaving it alone, unless you're using it as a semi-permanent installation, and for pre-2009 models they''' actually send you the frame bonding kit for free (a short jumper and #8 Ground Screw). This was originally to meet OSHA jobsite requirements, i believe. Maybe some other Electricians can chime in, but it's all about NOT having parallel paths for the return outside of the circuit.
    .... And this was gonna be my next question. See my comment about parallel Neutral paths!
  8. Matt Ruggeri

    Matt Ruggeri New Member

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    Are you a sparky too? I have ALWAYS wanted to know why the Home Depot type Interlok and transfer panels don't Isolate the Neutral from the Utility side? NEC 525.11 deals with multiple sources and bonding, but 525.31 breaks this rule by requiring Isolated Grounds downstream. Trust me, I totally understand grounding and bonding, and grounding vs bonding, but this rule always confused the $^it out of me! Granted, in a perfect world, there is no measurable current or voltage on the ground point!
  9. seige101

    seige101 Minister of Fire

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    Yup another sparky here. Even the larger transfer switches that come with permanent standby generators don't isolate the neutral.

    Typically a permanent standby generator has a ground rod driven right there and connected to the frame, the frame is also connected to the ground that is ran into the panel. Don't know how you would separate them. You could theoretically isolate the neutral, there would need to be another position on the contactor, however it's usually a big no-no to switch the neutral..
  10. oldspark

    oldspark Guest

  11. Matt Ruggeri

    Matt Ruggeri New Member

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    Understood, but it still doesn't mean I don't understand why the NEC constantly contradicts itself when dealing with portable/standby power and bonding! Well, not really understood, i guess!;)
  12. simple.serf

    simple.serf Feeling the Heat

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    On my little gensets I typically don't ground, unless I am at work. On my big girl (the MEP), I drive a ground rod and attach it to the ground terminal if I am using it as a standalone (such as when running a vacuum pump during maple season). When I am running the house through the transfer switch, I jumper the ground terminal to the ground lug inside the transfer switch, which is where the main ground is for the house. Too much going on in this beast for me to be comfortable running w/o ground.

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