GEC for seperate building

[Fred G]

This is a rather elongated problem.
Synopsis: We are installing a new classroom at an existing school.
The feed for this new"service" is not the "main" service.
The specs are treating this like a new service entrance, to include bonding the neutral (which we know is incorrect).

The first service, in the new building, is a 277/480v. with the main overcurrent protection set to 300a.
Their spec shows we can use a #4 GEC in the footing. Which to me would be in line with the NEC.
That Service then feeds a transformer with a 600a. secondary. We used a #1/0
for the grounding.
That transformer then feeds a 600a. 120/208 Service. Which we used another #4 bare in the concrete envelope as the ground.

Question:
1) Was the #4 bare acceptable in both services?
2) Was the #1/0 of adequate size to ground the transformer?

The spec drawing showed the gec ufer to be a #4. Below the drawing was a grounding conductor chart which was rated by amps. It specified 400-600a.
to be a #1/0.

 

[RUWired]

Question:
1) Was the #4 bare acceptable in both services?
2) Was the #1/0 of adequate size to ground the transformer?

.

Welcome to the forum Fred.
The # 4 awg cu. for the concrete encased electrode is good at the seperate building and the service. The 1/0 cu at the transformer and seperate building,,,,steel and water pipe if available should be a 2/0 cu.( speculating parallel 350 kcmil conductors for the 600 amp feeder). The grounding conductor in the parallel feeders should be a minimum # 1 awg.

Rick

 

[Buck Parrish]

Ruwired seems to have summed it up..
I will ad some where in the small print in the drawings or prints. It will say every thing to be done by code. This way the engineer covers him self if their is any mistakes.
Nothing against engineers. I wouldn't want to do that stuff all day.

 

[tryinghard]

This is a rather elongated problem.
Synopsis: We are installing a new classroom at an existing school.
The feed for this new"service" is not the "main" service.
The specs are treating this like a new service entrance, to include bonding the neutral (which we know is incorrect)?

I don?t know if I?m following you correctly but it sounds like you believe you?re installing a ?premises? feeder and the school district believes they are having you install a service entrance/lateral?

I recommend you write one RFI asking the EE if this circuit is a service or a feeder.

And a second RFI questioning the feeds complete compatibility to 250.32(B)(2). The concern of course is to avoid parallel neutral current on non current-carrying items.

 

[Fred G]

Thanks....

Thanks....

Thank you for the responses and yes, you understood the problem. The feed coming from the other building was also not the main but another distribution board.

Is it possible to use the service equipment ground bar to pick up the grounding electrode conductor for the transformer? Do I have to use steel or water? Couldn't we consider the ground bar a tap? It's accessible.

Thanks

 

[RUWired]

Is it possible to use the service equipment ground bar to pick up the grounding electrode conductor for the transformer? Do I have to use steel or water? Couldn't we consider the ground bar a tap? It's accessible.

Thanks

The GEC has to be continuous and as close as possible to the electrode. Compression crimps or welds are the only approve splicing methods.


230(A)7(Also see 250.104(D)

(7) Grounding Electrode. The grounding electrode shall be as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system. The grounding electrode shall be the nearest one of the following:
(1) Metal water pipe grounding electrode as specified in 250.52(A)(1)
(2) Structural metal grounding electrode as specified in 250.52(A)(2)

Rick

 

[tryinghard]

Thank you for the responses and yes, you understood the problem. The feed coming from the other building was also not the main but another distribution board.

Is it possible to use the service equipment ground bar to pick up the grounding electrode conductor for the transformer? Do I have to use steel or water? Couldn't we consider the ground bar a tap? It's accessible.

Thanks

Your transformer (SDS) will need to:

• 
  [1]“originate in listed equipment suitable as service equipment” [primary circuit]
  [2]”the [serving/feeding] grounding electrode conductor is of sufficient size for the SDS”
  [3]“the ground bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system”

This is how I understand Exception No. 2 of 250.30(A)(3) & Exception No. 2 of 250.30(A)(7).

So if your primary is originating from service equipment that is listed as such and you meet the remaining criteria you can terminate the GEC at the ground bus.

 

[RUWired]

"So if your primary is originating from" service equipment that is listed as such and you meet the remaining criteria you can terminate the GEC at the ground bus.

The wording of your statement is painting a different picture than that of the exception. The exception is saying if the SDS is originating in equipment that is listed as service equipment. To me that means a part of, not remote from.

Rick

 

[tryinghard]

?The exception is saying if the SDS is originating in equipment that is listed as service equipment. To me that means a part of, not remote from.

Rick

The SDS originates at the beginning of the primary circuit.

I believe his system is a premises feeder anyway, and if so the bonding can take place at the first disconnect, 250.30(A)(1).

 

[Boat211]

I have a similar situation

I have a similar situation

I am not clear if it is even acceptable to put in a seperate ufer. We will of course have to do a ground rod for the transformer. The drawings do not show a ufer but we all know how that is. It also does not show bonding water and steel but I would sure think that needs to be done.