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Old 01-11-2011, 03:04 PM   #16
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Portable Generator Electrical Ground


I checked the owners manual. Says to consult OHSA or local agency having jurisdiction. Since the electrical code does not require a dedicated ground, I don't need it.

Generator to house ground is provided by the NEMA 14-50 plug which connects from the generator 50 amp receptacle to the transfer switch 50 amp receptacle.

Thanks guys. You saved me some dollars!
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Old 01-11-2011, 07:13 PM   #17
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Portable Generator Electrical Ground


Where is the genny set up relative to the main panel,
If its close by,
you should be able to connect to the main earth
in the main panel.
This would be a better option.
Seperate ground rods might not always be at the same potental.

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I believe a portable generator connected to a house's electrical system must be grounded. Correct?

I cannot reach the earth ground rod which is under a porch. This prevents me from grounding the generator to ground. Can I sink another copper ground rod and connect the existing rod to the new ground rod using copper ground wire? Distance will be about 12 feet.

Generator is connected to the house via a 200 amp transfer switch.
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Old 01-11-2011, 08:08 PM   #18
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Portable Generator Electrical Ground


Do earth (ground) rods provide any protection in the event of a fault in a portable generating system? I think the answer is no. Grounding is needed at home because the POCOs ground their distributions. Lightning protection. Grounding is different than bonding.

Last edited by jlmran; 01-11-2011 at 08:15 PM.
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Old 01-11-2011, 09:29 PM   #19
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Portable Generator Electrical Ground


If there is no connection between the nuetral and earth on the genny,
Then perhaps not,
But it also depends on where the nuetral and earth bonding is,
in the home wiring, reletive the genny input.

So its a definate may be !

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Do earth (ground) rods provide any protection in the event of a fault in a portable generating system? I think the answer is no. Grounding is needed at home because the POCOs ground their distributions. Lightning protection. Grounding is different than bonding.
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Old 01-11-2011, 09:56 PM   #20
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Portable Generator Electrical Ground


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Originally Posted by dmxtothemax
But it also depends on where the nuetral and earth bonding is,
in the home wiring, reletive the genny input.
How does this relationship matter? If generator input occurs at a point other than the main panel then it still matters not, right? Aren't generator neutral and bonding conductors connected at the generator?

I've seen "grounding lugs" attached to frames of generators and always wondered what their purpose was.
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Old 01-11-2011, 11:35 PM   #21
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Portable Generator Electrical Ground


i would ground it, i work for the local authority and any time we use a gen set we always sink a ground rod
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Old 01-12-2011, 06:22 AM   #22
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Portable Generator Electrical Ground


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i would ground it, i work for the local authority and any time we use a gen set we always sink a ground rod
OK, but why?? Seriously, do you know WHY you do this?

This comment is a boilerplate of "This is the way we always do it. I don't know why, but we do".

What purpose at all does a ground rod serve in this instance?
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Old 01-12-2011, 06:24 AM   #23
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Portable Generator Electrical Ground


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i work for the local authority..............
And out of curiosity, what is "the local authority"?
Do you mean utility? Or are inspectors running generators now?
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Old 01-12-2011, 06:41 AM   #24
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Portable Generator Electrical Ground


Yes, there is a grounding lug on the generator frame. The Generac manual even references its location.

I can't reach the utility meter ground rod since its under a porch. I was going to install another ground rod and run copper grounding wire to bond the two rods to the same ground potential.

Appears its not required since the NEMA plug carries the ground from the generator to the breaker panel.

Maybe the grounding lug is more for lighting strike issues?

So, is the issue bonding to the same electrical ground potential or lightning strike grounding?
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Old 01-12-2011, 06:44 AM   #25
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Portable Generator Electrical Ground


with a generator you are creating your own 120/240 circuit correct? well where do you get that 120 from a 240? it is centre tapped and grounded, well with your house that is a different system than the generator that is why we use them
local authority was suppose to be local utility sorry
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Old 01-12-2011, 06:49 AM   #26
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Portable Generator Electrical Ground


Quote:
Originally Posted by awdblazer View Post
with a generator you are creating your own 120/240 circuit correct? well where do you get that 120 from a 240? it is centre tapped and grounded, well with your house that is a different system than the generator that is why we use them
I understand the idea behind it, it's just if you are only using cord connected loads, then it is NOT necessary, not required, and NOT doing very much at all.

Who knows, it may be required by your utility for some reason. You guys have LOTS of requirements of your own. 99.9% of which are to keep your guys alive. This is just not one of them.
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Old 01-12-2011, 07:16 AM   #27
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Portable Generator Electrical Ground


Quote:
Originally Posted by awdblazer View Post
with a generator you are creating your own 120/240 circuit correct? well where do you get that 120 from a 240? it is centre tapped and grounded, well with your house that is a different system than the generator that is why we use them
local authority was suppose to be local utility sorry
How is the construction of a portable generator center tapped and grounded in order to realize 120V? Where must the grounding occur to get 120V? A generator can be placed on top of a dry plastic box without a ground rod connected, fired up, and there will be 120V at the receptacles.

Additionally, the grounding of a POCO system does not impact the voltages realized.
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Old 01-12-2011, 04:25 PM   #28
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Portable Generator Electrical Ground


Unless the nuetral side of the genny is tied to earth,
Then earthing it will have no effect.

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How is the construction of a portable generator center tapped and grounded in order to realize 120V? Where must the grounding occur to get 120V? A generator can be placed on top of a dry plastic box without a ground rod connected, fired up, and there will be 120V at the receptacles.

Additionally, the grounding of a POCO system does not impact the voltages realized.
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Old 01-12-2011, 09:51 PM   #29
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Portable Generator Electrical Ground


Ok guys .. ya all are making this way too complicated and so do the manufacturers.

Let the generator be your guide ...

The portable generator dictates the transfer switch you need when powering your premise wiring in your home.. By that I mean is your portable neutral bonded to frame or is it not bonded to frame. Remember this while we discuss this subject.

Since portable generators are more job site applicable and the manufacturers tend to make them for that purpose , they configure the generator in most cases to be a separately derived system. In other words it is operating independently of any connection to another electrical source. So out on a job site operating your construction tools by cord and plug it is a separately derived system. And must be grounded in accordance with 250.30. Go back to Speedy's post where he quoted NEC code on portable generators and vehicle mounted generators. Remembering the two criteria of which both must be met. And noticing that connecting to a home via a transfer switch is not addressed.
Now .. would you consider actually driving a ground rod .... the general understanding by most people is..Yes. However this is not true. It is discouraged to use a ground rod with a portable generator because it sets up an electrocution hazard in the event of a fault to a tool metal case. In which case by your holding that tool you provide a path to earth for the fault current and that ground rod makes it way easier for fault current to get back to the generator center tap thru the earth and via the neutral bonding to case which is bonded to the ground rod. Simply put the metal frame of the generator should be your grounding electrode to limit this hazard in the event of a fault to earth from a tool malfunction... and with help your gfci will trip as added safety. The ground rod after all is merely protection from damage by lighting in a job site application or any other application for that matter . Ground rods are and were never meant to protect humans from electrocution. However using one may improve the odds of a electrocution hazard being created unknowingly.

Ok ... so now lets hook this portable generator up to your home via a transfer switch to have an application where the generator supplies standby power to your homes premise wiring which is also connected to your poco transformer as an electrical source.

I read the instructions to my generator or I perform some continuity tests at the generator receptacles mounted on the generator frame and discover that I have a bonded neutral to the frame of my generator. Meaning neutral and ground are bonded as would be required for a separately derived system. So just exactly how do I operate that when I'm going to connect it to my homes premise wiring and thereby be connected to two electrical sources (poco transformer and my generator) ?? Remember to be separately derived I cannot connect to the bonded neutrals of two systems or electrical sources.

If my generator is neutral bonded to ground (metal frame of generator) Then I must use a transfer switch that switches or opens the utility neutral. Thereby making my generator separately derived by breaking connection with the poco transformer. Technically I would then either use the frame of the generator as my grounding electrode or drive a ground rod and connect it to the frame. If your not going to run tools off the generator and power your home circuits then a grounding electrode will to a degree offer equipment protection otherwise it is debatable if it would be useful or needed.

If my generator is not neutral bonded to frame then you would use a transfer switch that doesn't switch the utility neutral but keeps my generator neutral solidly connected to the utility neutral and thereby my portable generator is a non-separately derived system and the generator and poco transformer are treated as the same system. In which case the GES (grounding electrode system) of your home grounds/earths the generator.

The idea between the two systems is to not provide parallel paths for neutral current over the equipment ground which is dependent on whether the portable generator is used with the proper transfer switch in respect to the neutral bonding of your portable generator.

Hope that was clear as mud.


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Last edited by Stubbie; 01-12-2011 at 10:19 PM.
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Old 01-12-2011, 10:25 PM   #30
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Portable Generator Electrical Ground


And who is complicating things? That's a long post...
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