400 amp GEC

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mcclary's electrical

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VA
I looking at the prints for two descent sized department stores. The plans call for (3) 12ft., copper clad, 3/4" ground rods driven in a delta configuration twelve feet apart on center and joined by cadweld w/ 4/0 bare copper 18" below grade with handholes for inspection. Why so big for a 400 amp 3phase service?
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
Agree with Bob.
This often appears on engineered drawings. Not a Code requirement, but the Cadweld folks probably appreciate it.
 

Dennis Alwon

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Chapel Hill, NC
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I looking at the prints for two descent sized department stores. The plans call for (3) 12ft., copper clad, 3/4" ground rods driven in a delta configuration twelve feet apart on center and joined by cadweld w/ 4/0 bare copper 18" below grade with handholes for inspection. Why so big for a 400 amp 3phase service?


IMO, you would be better off with a CEE (Ufer) than you would with that configuration. Of course, you may not have access to the footers if this is not a new construction.
 

TT009

Member
The engineer is covering there butt. I just ran into this on my last project called a counterpoise. We on the other hand had a 3000A service. Which is justifiable for the 4/0 we ran.

Why they spec'ed 4/0 for a 400A service is another question.

Its probably for all of them computers triple grounded, then grounded again. Keep the IT guys happy.
 

benaround

Senior Member
Location
Arizona
IMO, you would be better off with a CEE (Ufer) than you would with that configuration. Of course, you may not have access to the footers if this is not a new construction.


I agree with this all the way. I work in Az. ( the hot, dry place ) and the last three service

sections that were tested ( by a testing company ) had CEE of 5 ohms and less. I don't see

that happening with ground rods.
 
I looking at the prints for two descent sized department stores. The plans call for (3) 12ft., copper clad, 3/4" ground rods driven in a delta configuration twelve feet apart on center and joined by cadweld w/ 4/0 bare copper 18" below grade with handholes for inspection. Why so big for a 400 amp 3phase service?


The engineer belonged to the engineering fraternity in college. The fraternity was call DELTA-DELTA. ;):D
 

TT009

Member
The engineer probable reads 250.56 and says WOW how are we going to get 25 ohms or less? Lets run 4/0 and pound 3 12ft ground rods. Good Idea!

Who cares if its 50 ohms resistance to ground. All you need is Water within 5ft and other electrodes or two ground rods with a at least a #1/0, or other combinations. **If paralleling the 400A**
 

mcclary's electrical

Senior Member
Location
VA
The engineer is covering there butt. I just ran into this on my last project called a counterpoise. We on the other hand had a 3000A service. Which is justifiable for the 4/0 we ran.

Why they spec'ed 4/0 for a 400A service is another question.

Its probably for all of them computers triple grounded, then grounded again. Keep the IT guys happy.

Triple grounded?

The prints show to every receptacle for a computer, gets

One normal sized neutral
One normal sized parallel neutral
One EGC
One isolated EGC

So each 120 volt recepptacle has five wires going to it! That's ridiculous!!
 

iwire

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Location
Massachusetts
The engineer is covering there butt. I just ran into this on my last project called a counterpoise. We on the other hand had a 3000A service. Which is justifiable for the 4/0 we ran.

How so, how is any connection to dirt going to require a 4/0?
 

mcclary's electrical

Senior Member
Location
VA
Please explain the neutrals, that sounds like an NEC violation.

I agree, instead of specs calling for a "super" neutral, they're calling for an "extra neutral" going to any receptacle for computers. They're not calling it parallel.
The grounds say one EGC and one isolated grounding conductor that shall be green w/ white stripe. That doesn't sound right either.
 

iwire

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Location
Massachusetts
I agree, instead of specs calling for a "super" neutral, they're calling for an "extra neutral" going to any receptacle for computers. They're not calling it parallel.
The grounds say one EGC and one isolated grounding conductor that shall be green w/ white stripe. That doesn't sound right either.

It sounds to me like a couple of direct NEC violations.
 

TT009

Member
How so, how is any connection to dirt going to require a 4/0?

It doesn't...but it is more justifiable for a 3000A vs a 400A service to the engineer reading the code. The engineer probably didn't read the whole article 250.66 and sized the GEC per the table.

But specs are specs they over rule NEC any day.
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
...........................................
But specs are specs they over rule NEC any day.

According to ???????
Our guidelines tell us to assure the job meets the NEC. In any given time, I see and reject specs that don't meet NEC.
 

TT009

Member
According to ???????
Our guidelines tell us to assure the job meets the NEC. In any given time, I see and reject specs that don't meet NEC.

I'm mistaken yes we must follow nothing less than the NEC standards, but in this case where the spec has up sized the GEC to a 4/0 you would have to follow this spec.

Correct me if I'm wrong, but if the spec is over and above NEC's standard, and you bid accordingly, you would have to install at least meeting the spec in most cases.

But in no case can you ever be less than NEC's standards
 

augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
From a contractual standpoint, you very well may be held to the specs and I think there are some inspection agencies that require that. Many inspection agencies only inspect to assure NEC.
I don't recall any job I have ever seen where the job followed the specs 100% unless the job included architectural supervision.
 
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