Grounding Electrode Question

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C3PO

C3PO

Senior Member
Location
Tennessee
This may be a stupid question, but sometimes I have trouble wrapping my mind around article 250.

I have a 800A service that feeds a 4 unit condo. It is a 4 gang meter base that has 1 200A meter per unit.

It will be fed underground from the utility(not sure what size they are running to it yet).

What size GEC?
 
C3PO said:
This may be a stupid question, but sometimes I have trouble wrapping my mind around article 250.

I have a 800A service that feeds a 4 unit condo. It is a 4 gang meter base that has 1 200A meter per unit.

It will be fed underground from the utility(not sure what size they are running to it yet).

What size GEC?
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Look at Table 250.66. What size conductors are you using. Copper, aluminum etc.

Also are you taking about the GEC to the ground rods or water pipe???
 
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3/0= 167800 cir. mil

4 * 167800 = 671200 cir. mil

Therefore 700KCM would be the equivalent size.

Now use Table 250.66
 
That is the part that is really cionfusing to me. What if a ground rod is all you have? No metal framing or metal water or gas pipe or concrete encased electrode.
 
C3PO said:
That is the part that is really cionfusing to me. What if a ground rod is all you have? No metal framing or metal water or gas pipe or concrete encased electrode.
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If the only grounding electrode present is a ground rod (or 2) then the GEC is not require to be larger than a #6 as Dennis pointed out. Take a look at 250.66(A).

Chris
 
C3PO said:
That is the part that is really cionfusing to me. What if a ground rod is all you have? No metal framing or metal water or gas pipe or concrete encased electrode.
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That's the beauty of it--- # 6 to the ground rod is all you need.

I may be wrong on the other info I gave you-- if this is apartments with separate water line you may be able to run 4- #4 to the water lines-- not sure about that. To me it would be 4 200 amp services not a 800 amp service

Anyway-- in your case just pull a #6 to the rods.
 
That was the way I was leaning, but I wanted to hear some other people's opinions. It is hard for me to understand Article 250 sometimes. Thanks for all of the help.
 
C3PO said:
That was the way I was leaning, but I wanted to hear some other people's opinions. It is hard for me to understand Article 250 sometimes. Thanks for all of the help.
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It's hard for all of us. ;)
 
It's hard for inspectors too kiddo!
go ahead and install that 6awg on your rods for a 1600amp service and watch the inspector treat you like a first year newbie. Makes me so mad.
 
POWER_PIG said:
It's hard for inspectors too kiddo!
go ahead and install that 6awg on your rods for a 1600amp service and watch the inspector treat you like a first year newbie. Makes me so mad.
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I've done exactly that, and the inspector didn't blink.
 
Dennis Alwon said:
That's the beauty of it--- # 6 to the ground rod is all you need.

I may be wrong on the other info I gave you-- if this is apartments with separate water line you may be able to run 4- #4 to the water lines-- not sure about that. To me it would be 4 200 amp services not a 800 amp service
Anyway-- in your case just pull a #6 to the rods.
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If that is the case, is there any requirement that you run four seperate GECs, or can you daisy chain one to all the services to a single set of ground rods?
 
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POWER_PIG said:
It's hard for inspectors too kiddo!
go ahead and install that 6awg on your rods for a 1600amp service and watch the inspector treat you like a first year newbie. Makes me so mad.
Click to expand...

Since you brought it up let me tell you what the inspectors in my area do.
Say you have a 400A service on a house. You come off of parallel lugs and feed two 200A MB panels.

If it is an underground feed they will say the GEC to the rods should be sized per table 250.66 based on the 2/0 or 3/0 ran to the MB panels. Which would be a 4awg.

If it is an overhead service they will say it should be sized per table 250.66 based on the conductors in the mast.(paralleled or 400 or 500) Which would be a 1/0awg

That is why this stuff is confusing to me.
 
C3PO said:
Since you brought it up let me tell you what the inspectors in my area do.
Say you have a 400A service on a house. You come off of parallel lugs and feed two 200A MB panels.

If it is an underground feed they will say the GEC to the rods should be sized per table 250.66 based on the 2/0 or 3/0 ran to the MB panels. Which would be a 4awg.

If it is an overhead service they will say it should be sized per table 250.66 based on the conductors in the mast.(paralleled or 400 or 500) Which would be a 1/0awg

That is why this stuff is confusing to me.
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250.66(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 (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.
Click to expand...

It should not be all that confusing.
 
JohnJ0906 said:
I've done exactly that, and the inspector didn't blink.
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It's not all inspectors, I meant no disrespect to the 90% of the educated inspectors in this indusrty. Just saying that I have had some bad inspectors here in the past and my boss refuses to argue with them, so then I end up having 3/0 running to my rods, and the inspector leaves satisfied that he taught me a lesson...........I guess you can say my boss and the uneducated inspector both are to blame and that just burns my chaps!
 
POWER_PIG said:
. . . I end up having 3/0 running to my rods, and the inspector leaves satisfied that he taught me a lesson . . .
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Well, I'm the boss, so I don't have anyone to tell me what to do, but I'd never run such a conductor when not required just to satisfy an inspector. It sets a very bad precedence.

In my opinion, it's just as illegal to demand something not required as it is to pass something not compliant.
 
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