Size of 400Amp GEC?

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davedottcom

davedottcom

Senior Member
Building my 1st 400 Amp service tomorrow! :D

here's my set up:
400 A Milbank Meter / underground fed
3 Double Lugs on secondary side
Using 4/0 AL to (2) 200 Amp Main Breaker panels
2 seperate 2" pvc pipes, 2 seperate feeds,
(no parallel feeds, no tapping.)
# ? GEC from meter can to grounding electrodes

I'm looking at Table 250.66 and according to the chart a #4 solid copper is acceptable for the 4/0 AL Service Entrance Conductor. But, now the Fine Note #1 below the chart is confusing me.

Notes:
1. Where multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No.2, the equivilent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.

230.40 Exception 2 is basically saying that "Tapping" is permitted, Right?

This should have no bearing on my "set up" since I'm not tapping.

I've read it ten times and I can't make sense out of the 250.66 Note #1!
:confused:

Dave
 
infinity

infinity

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Re: Size of 400Amp GEC?

If you're using 2 sets of #4/0 AL on the line side of your Milbank meter then the GEC would be sized according to the equivalent area of the two of #4/0 AL. I don't have the book in front of me but I'm guessing #1/0, the GEC would be sized according to 250.66.

[ June 19, 2005, 09:41 PM: Message edited by: infinity ]
 
davedottcom

davedottcom

Senior Member
Re: Size of 400Amp GEC?

Hmmm, is that typical? Supply house sent single 4/0 lugs for the Line side.
Like I said, I've never done a 400 Amp service before! Will the Utility Co. need double lugs?
I guess I better ask them!

Dave
 
R

redfish

Senior Member
Re: Size of 400Amp GEC?

I think your GEC should be more like #2 copper :) for a 400a service. if you double the circular mils of your 4/0 you would be more in the range of over 250 through 500 in 250.66
 
mdshunk

mdshunk

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Re: Size of 400Amp GEC?

Originally posted by davedottcom:
Ground Rods. Water is in PVC. Single dwelling.

Dave
Click to expand...
Then all you need is #6 to the ground rod(s). Even if you build a million amp service, you're still only required a #6 to the rods.
 
davedottcom

davedottcom

Senior Member
Re: Size of 400Amp GEC?

ok so 4/0 = 211600Cir Mils

211600 x 2 = 423400 cms

That's between 250 & 500!

so #2 CU GEC according to the 250.66 chart.

That sounds more like it!

Dave
 
davedottcom

davedottcom

Senior Member
Re: Size of 400Amp GEC?

Originally posted by mdshunk:
Then all you need is #6 to the ground rod(s). Even if you build a million amp service, you're still only required a #6 to the rods.
Click to expand...
Where can I find this rule?!

Dave
 
mdshunk

mdshunk

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Re: Size of 400Amp GEC?

Reference 250.66(A), where it says:

(A) Connections to Rod, Pipe, or Plate Electrodes.
Where the grounding electrode conductor is connected to rod, pipe, or plate electrodes as permitted in 250.52(A)(5)or 250.52(A)(6), that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.
 
davedottcom

davedottcom

Senior Member
Re: Size of 400Amp GEC?

Mdshunk,
:eek:

I never knew that!

So why are larger GEC's needed for different Electrodes?

Dave
 
mdshunk

mdshunk

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Re: Size of 400Amp GEC?

Originally posted by davedottcom:


So why are larger GEC's needed for different Electrodes?

Dave
Click to expand...
Who knows? Perhaps one of the engineer types here can explain that for you. I was always under the impression that that a driven rod could only handle as much current as a #6 could supply, and a metallic city water line (for instance) could handle much more. It does seem a little counter intuitive to have a zillion amp service with a mega large conductor going to the water line and the building steel, but a little biddy #6 is all that would be required for a driven rod or rods.
 
davedottcom

davedottcom

Senior Member
Re: Size of 400Amp GEC?

I have NEVER ran anything smaller than #4 and they were all 200 Amp or less. I've never even bought #6 solid!
I do see the code reference...just having a hard time believing it!

I guess I'll stick to my #4 and see what Mr Inspector has to say...if anything.

Now back to the second question that has surfaced!

What size lugs will the Utility Co Need?
Like I said, supply house sent single lugs - 4/0.
Anyone here work for FPL?!?! :)

Dave
 
mdshunk

mdshunk

Senior Member
Location
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Re: Size of 400Amp GEC?

Originally posted by davedottcom:
I have NEVER ran anything smaller than #4 and they were all 200 Amp or less. I've never even bought #6 solid!
I do see the code reference...just having a hard time believing it!
Click to expand...
I carry 3 sizes of solid copper. #8 for pools and spas and whirlpools, #6 for ground rods, and #4 for water pipe grounds. Anything (grounding and bonding wise) that needs a bigger conductor than that I measure it up and bring a cut piece. I am aware that many guys use #4 solid everything that would otherwise only require #8 and #6 as the minimum.
 
A

allenwayne

Senior Member
Re: Size of 400Amp GEC?

I guess the individual installations IR: concrete encased electrode, pvc, copper pipe do all have a direct effect on what size ground wire that is used.
First we do allot of homes every year,hense #6 is never used protection thing so the smallest we use is #4.Also it has come more a daily routine to see cpvc used as water supply and concrete encased electrode In one area they require 1/0 as a rule citing 250.66.Which basically sizes the gec to the largest possible incoming feeders :D for underground hook ups $400.00
Guess someone was on the carpet that day :D
 
infinity

infinity

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Journeyman Electrician
Re: Size of 400Amp GEC?

I have NEVER ran anything smaller than #4 and they were all 200 Amp or less. I've never even bought #6 solid!
Click to expand...
The #6 AWG to the ground rod is not required to be solid. And it can be run without protection if it is run along the surface of the building and securely fastened in place. See 250.64(B).
 
A

allenwayne

Senior Member
Re: Size of 400Amp GEC?

How do you leave the structure of the building that you have secured to and safely protected the # 6 and hit the electrode ??,unless you dig a ditch in which case would defeat the cost factor of using # 6 and hit your uffer/ground rod etc.????
Not sure about others but with the amount of homes we do anually it is logistically easier to just cut a 20 ft. piece of # 4 and put it in the rough pack that gets loaded in the truck that`s going to start the next job,yes we load all our guys trucks with material ordered or the next job.
I couldn`t imagine the confusion there would be if we let our guys just grab and run with the material they need.There would be no way to job track,keep tabs on warehouse ordering etc. ;)
 
roger

roger

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Re: Size of 400Amp GEC?

Allen,
Not sure about others but with the amount of homes we do anually it is logistically easier to just cut a 20 ft. piece of # 4 and put it in the rough pack that gets loaded in the truck
Click to expand...
that doesn't go with what you said earlier,
I used 3/o as my gec to be safe.
Click to expand...
You could have stayed with the #6 or #4 regardless of the size service.

You should sit down with the inspector(s) and read 250.66 together in its entirety.

Roger
 
J

jbhindes

Member
Re: Size of 400Amp GEC?

The ohms on your ground rod is only equal to you #6 solid, but you will need 2 ground rods 6' apart without a water ground. Separate grounds to each rod
 
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