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Portable generator grounding

e hilton

e hilton

Bronze Member
Joined
Jul 2, 2014
Messages
3,152
Location
Virginia
I know there are some qualified sparkies on the forum, so i’m going to ask for some advice.

I have a project to place a container on a concrete pad and connect a portable generator. I need to be a little vague because of some proprietary details. The container is like a 20’ conex full of communication devices, it comes with transfer switch and connection points for power, it’s intended to be moveable. The power connection points are camlocks, 5 of them, the generator provides 120/208 4w+g 30 kW. There will be a ground rod adjacent to the container … question is do i need a ground rod at the generator? Renting it from sunbelt, the power cables will be 50 ft.
 
Do you have a service at the container? What is the status of the bonding at the generator? Likely no but....I would wait for one of the smart guys to chime in if I were you..
 
This is where the incoming power lands, there is space for 2 power sources. On the other side of this is a transfer switch.
1706305062251.jpeg
 
This is very often debated. I would say that NEC would say no, but the manufactures directions may say yes.

I've heard opinions all the way from "absolutely dangerous not to" on one side to "makes it far more dangerous if you do."
 
Its been awhile, but I thank I did an inspection of a large Kohler and the ground rod was below the generator pad with access through the generator door.

Been awhile.
 
Every carnival that I have inspected had two ground rods for a generator. They use welding cable to make the connection.
 
Check out:

Parallel EGC Question

Hi, I'm getting a little confused with table 250.122 and 250.66. My application is I'm running parallel 350 kcmil wiring for a generator automatic transfer switch. The ATS is service rated and I will move the load side of the meter over to it. When I then run the wiring for the 600 amp island...
forums.mikeholt.com

Portable generator

I have MTS that has generator tap box for portable generator for building small bank. I am not sure what the poles of MTS should be. My question is portable generator manufacturer do they come as separately derived system or no separately derived system?
forums.mikeholt.com

Ground Rod Theory

So we all know that if you pound in two ground rods they must be at least 6' apart. When you do some research on the spacing between the rods the prevalent opinion is that further is better, something like twice the length of the rods. So for a standard 8' that is 16' apart at the minimum. So...
forums.mikeholt.com

And I highly recommend Mike Holt's Videos, specifically this one:

Around 20 minutes or so he starts talking about useless ground rods.

He's got a bunch of free video's here, and they are all very good.
 
Being a stand-alone system vs. connected to the grid makes a difference, check out:

NEC
250.30 Grounding Separately Derived Alternating-Current Systems
In addition to complying with 250.30(A) for grounded systems, or as provided in 250.30(B) for ungrounded systems, separately derived systems shall comply with 250.20, 250.21, 250.22, or 250.26, as applicable. Multiple power sources of the same type that are connected in parallel to form one system that supplies premises wiring shall be considered as a single separately derived system and shall be installed in accordance with 250.30.
Informational Note No. 1: An alternate ac power source, such as an on-site generator, is not a separately derived system if the grounded conductor is solidly interconnected to a service-supplied system grounded conductor. An example of such a situation is where alternate source transfer equipment does not include a switching action in the grounded conductor and allows it to remain solidly connected to the service-supplied grounded conductor when the alternate source is operational and supplying the load served.
Informational Note No. 2: See 445.13 for the minimum size of conductors that carry fault current.
 
Joe.B said:
Same question. Is this stand-alone, or is there also a utility connection?
Click to expand...
Ok so it’s a 2 phase project. Phase 1 is to get it set up and running so they can test it, demonstrate to customers, etc. That’s what i’m doing now.

Phase 2 is to get permanent power to it. We are going to do that by tapping into the building electrical system. However … you saw 2 sets of camlock connectors in the picture ... the second set will be used to connect to a permanent generator that supplies backup power to the building. One of the features of the container is that it can be transported to remote sites and powered by 2 generators … one primary and one backup. So when i am finished, the module will draw primary power from the building system, and they can demonstrate to the customer how the ATS works by killing the shore power and watch the generator kick in.

Both the shore power and generator will be connected through the camlocks.
 
Grounding is an overloaded term, it covers both bonding and earthing. Of the two bonding is the more important, but with a 208Y/120V voltage system, you will need to earth the neutral conductor, making it the grounded conductor, to which the non-current carrying metal parts are also bonded.

The electrical system needs to have (a) an earth electrode system that is bonded to the neutral conductor (via one or more Grounding Electrode Conductors) (b) bonding between all the non-current carrying metal parts (via the Equipment Grounding Conductors and possibly Supply-Side Bonding Jumpers) and (c) exactly one (no more, no less) connection between the Equipment Grounding system and the neutral conductor. In particular, part (c) needs to be true in either state of the ATS.

Which means the first question is whether the ATS switches the neutral conductor. If it does, then you have the option for each source connected to it to have its own System Bonding Jumper to fulfill requirement (c) above, with no such jumper in the ATS. Whereas if it doesn't then the only option is to have one System Bonding Jumper in the ATS, with no such jumper in either source.

Cheers, Wayne
 
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