Where do you put the ground rod?

[Brian jojade]

O.K, using a generator for a show this weekend, and am not exactly clear on where ground rods are supposed to be placed. We are running a generator that provides 480 delta 3 phase power, using 4 connectors. (3 phases and ground). This will run about 500 feet to a step down transformer that will give us 208Y 3 phase, 5 conductor. (3 phases, neutral, ground) and out of this, we are running about 75 feet to the main power distro.

Typically, we would ground the generator and run 208 right from there and not ground the power distro, but the long length is necessitating the higher voltage to avoid voltage drop in the line. Are we supposed to ground at the transformer as well? At the final distro? The ground line would tie completely as is. I'm sure it wouldn't hurt to have extra grounding points, but if they aren't necessary, I'd rather save the work.

 

[Jordan Lahr]

Re: Where do you put the ground rod?

Id ground at both the step down transformer and at the genny, those will be the two high value places. I don't forsee anything other than those two places and you could probably get by with just the genny ground, since all your power originates from there.

 

[Tim McCulloch]

Re: Where do you put the ground rod?

Id ground at both the step down transformer and at the genny, those will be the two high value places. I don't forsee anything other than those two places and you could probably get by with just the genny ground, since all your power originates from there.

Sort of, and no.

NEC requires the genset neutral be bonded to the generator frame, but Delta has no neutral. However, Code also required that each unique "point of service" be grounded, so the generator should be grounded. The secondary of the transformer is considered a "separately derived service" that must have its neutral bonded to ground. NEC Article 250 is your friend.

 

[Richard Pyne]

Re: Where do you put the ground rod?

Delta has no neutral

Not always. It is not uncommon for one winding to be center tapped and grounded.

 

[Tim McCulloch]

Re: Where do you put the ground rod?

Not always. It is not uncommon for one winding to be center tapped and grounded.

Never mind.....

 

[Brian jojade]

Re: Where do you put the ground rod?

Thanks. My thoughts were exactly what Tim suggested. Ground at the genny. There is no neutral on the 480 delta, so it's just chasis ground. Bond neutral to ground at the step down transformer, and have a ground rod there as well. Simple enough.

 

[Grant Conklin]

Re: Where do you put the ground rod?

Thanks. My thoughts were exactly what Tim suggested. Ground at the genny. There is no neutral on the 480 delta, so it's just chasis ground. Bond neutral to ground at the step down transformer, and have a ground rod there as well. Simple enough.

Reposting from Bennett. Right near the generator seams about right.

 

[Kevin Graf]

Re: Where do you put the ground rod?

While this is about a separate building, I think that it still applies:

Separate Building Ground

250.32(B) (B) Grounded Systems. For a grounded system at the
separate building or structure, an equipment grounding conductor
as described in 250.118 shall be run with the supply
conductors and be connected to the building or structure
disconnecting means and to the grounding electrode(s). The
equipment grounding conductor shall be used for grounding
or bonding of equipment, structures, or frames required
to be grounded or bonded. The equipment grounding
conductor shall be sized in accordance with 250.122.
Any installed grounded conductor shall not be connected
to the equipment grounding conductor or to the grounding
electrode(s).

Exception: For existing premises wiring systems only, the
grounded conductor run with the supply to the building or
structure shall be permitted to be connected to the building
or structure disconnecting means and to the grounding
electrode(s) and shall be used for grounding or bonding of
equipment, structures, or frames required to be grounded
or bonded where all the requirements of (1), (2), and (3)
are met:

(1) An equipment grounding conductor is not run with the
supply to the building or structure.
(2) There are no continuous metallic paths bonded to the
grounding system in each building or structure involved.
(3) Ground-fault protection of equipment has not been installed
on the supply side of the feeder(s).

 

[Rob Spence]

But note that it does NOT say to connect the ground to the neutral at that location.


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