Service grounding

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Big Guns

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Good Morning

If you have a residential home with 120/240 volts single phase 400 amp service with 2 - 200 amp panels fed off one 400 amp service meter with seperate 4/0 SER what size ground wire is ran for grounding electrodes (rods) and to water main.
 
augie47

augie47

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Size per 250.66 keeping in mind your GEC must connect to or prior to your service neutral buss. Your SER would be a feeder. Size by the servie conductors feeding your service equipment.
 
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Big Guns

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roger said:
Have you read through 250.122?

Roger
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Yes I know what 250.122 states, its for grounding conductors for grounding equipment and raceways. My questions is if they are paralled wires do you have to size wire according to circular mills, this is what an inspector told me...??
 
roger

roger

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jumper said:
Wouldn't 250.66 apply here?
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Big Guns said:
Yes I know what 250.122 states, its for grounding conductors for grounding equipment and raceways. My questions is if they are paralled wires do you have to size wire according to circular mills, this is what an inspector told me...??
Click to expand...

Yes, 250.66 would be correct, that'll teach me to post while dog an cats are screaming to go out.

Roger
 
augie47

augie47

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Big Guns said:
Yes I know what 250.122 states, its for grounding conductors for grounding equipment and raceways. My questions is if they are paralled wires do you have to size wire according to circular mills, this is what an inspector told me...??
Click to expand...

Yes you do. That is covered in the Notes to 250.66.
 
Smart $

Smart $

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Big Guns said:
... My questions is if they are paralled wires do you have to size wire according to circular mills, this is what an inspector told me...??
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What I believe you have is two 200A service panels. There are two ways to run a GEC, either as 1) separate GEC for each panel or 2) a common GEC for both. On the latter, you can tap down to individual GEC size for each panel.

That said, individual GEC is sized to 4/0 Al (#4 copper, #2 Al), common is sized to sum of cmils (#2 copper, 1/0 Al).

As noted, GEC to a single grd rod only has to be #6 copper or #4 Al.
 
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Cavie

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Big Guns said:
Good Morning

If you have a residential home with 120/240 volts single phase 400 amp service with 2 - 200 amp panels fed off one 400 amp service meter with separate 4/0 SER what size ground wire is ran for grounding electrodes (rods) and to water main.
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4/0 ser is not to code. The 4/0 exception applies to a single 200 amp residential service. You have a 400 amp service. The 200 amp panels would require 3/0 copper or 250 mcm aluminum. 'least that's the way it is in SW Florida. Let the beating begin!
 
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Smart $

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Cavie said:
4/0 ser is not to code. The 4/0 exception applies to a single 200 amp residential service. You have a 400 amp service. The 200 amp panels would require 3/0 copper or 250 mcm aluminum. 'least that's the way it is in SW Florida. Let the beating begin!
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Each 4/0 AL SER is a Service Entrance Conductor. The "main power feeder" stipulation only applies on the load side of a service disconnect.
 
jumper

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Big Guns said:
Do you size it for paralleled 4/0 by circular mills...
Click to expand...

Big Guns said:
My questions is if they are paralled wires do you have to size wire according to circular mills, this is what an inspector told me...??
Click to expand...

Your 4/0 AL SER cables are not in parallel by NEC definition.

310.10

(H) Conductors in Parallel.
(1) General. Aluminum, copper-clad aluminum, or copper
conductors, for each phase, polarity, neutral, or grounded circuit
shall be permitted to be connected in parallel (electrically
joined at both ends) only in sizes 1/0 AWG and larger where
installed in accordance with 310.10(H)(2) through (H)(6).
 
jumper

jumper

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Cavie said:
4/0 ser is not to code. The 4/0 exception applies to a single 200 amp residential service. You have a 400 amp service. The 200 amp panels would require 3/0 copper or 250 mcm aluminum. 'least that's the way it is in SW Florida. Let the beating begin!
Click to expand...

What if the calculated load is 180A or less for each panel? Assume 2011 NEC.
 
infinity

infinity

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Smart $ said:
What I believe you have is two 200A service panels. There are two ways to run a GEC, either as 1) separate GEC for each panel or 2) a common GEC for both. On the latter, you can tap down to individual GEC size for each panel.

That said, individual GEC is sized to 4/0 Al (#4 copper, #2 Al), common is sized to sum of cmils (#2 copper, 1/0 Al).
Click to expand...

I'm confused, what size conductors are feeding the meter?

Also why SER?
 
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ActionDave

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kwired

kwired

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A little confusion at the beginning of this thread.

250.66 is for sizing grounding electrode conductors and is based on largest service entrance conductor or equivalent.

250.122 is for sizing equipment grounding conductors and is based on the largest overcurrent protective device that may energize the conductor in question.

OP appears to be asking about grounding electrode conductors so 250.66 is what applies.

Isn't the "equivalent" largest service entrance conductor in OP 2-#4/0 AWG (aluminum?) conductors which is equal to 423200 circular mils?

250.66 tells us this will need #2 copper or 1/0 aluminum GEC.
 
Smart $

Smart $

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kwired said:
A little confusion at the beginning of this thread.

250.66 is for sizing grounding electrode conductors and is based on largest service entrance conductor or equivalent.

250.122 is for sizing equipment grounding conductors and is based on the largest overcurrent protective device that may energize the conductor in question.

OP appears to be asking about grounding electrode conductors so 250.66 is what applies.

Isn't the "equivalent" largest service entrance conductor in OP 2-#4/0 AWG (aluminum?) conductors which is equal to 423200 circular mils?

250.66 tells us this will need #2 copper or 1/0 aluminum GEC.
Click to expand...
The two 4/0 are not parallel but separate service entrance conductors. As I stated earlier, you'd use the sum (423200cmils) to size a common GEC and/or use 4/0 to size individual GEC's.

In questioning the largest SEC, we also have to consider the conductor size feeding the meter, which has yet to be answered.
 
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