grounding a new 400 amp service

[betterelectric]

i have just finished roughing in a new 7500 foot house and i am preparing to ground the 400A service. i am uncertain about the wire size for the cold water GEC. here are the basics...main panel has two (2) 200A main breakers, separately fed from the meter side of the all-in-one, side-by-side panel. one feeding the main panel and one feeding a MLO subpanel in the attatched garage. the cold water entrance is on the opposite side of house, 175 feet from meter. Also, I dont believe any additional grounding is required at the subpanel as it is in the same structure...but i am not certain... any input is appreciated. thank you.

 

[augie47]

Since all your panels are in the same structure, the GES will connect to your service equipment. The grounding electrode conductor to the water system would be szied per 250.66 based on the size of your service entrance conductor. Most often that would end up being a 1/0 cu. #6 is the max you need to ground rods and #4 the max to concrete encased electrodes.
The location of the connection to your water system would depend on if the water piping is a grounding electrode or if you are simply bonding it, however, the wire size would be the same.

 

[wyreman]

Gas bond / structural steel also 1/0


In belief, man can do anything

 

[wyreman]

In a similar situation once many years ago I grabbed the udder also subpanel, since it was all new work.

He had me remove it because you didn't want parallel paths to the ground

was that a valid call?

I still don't think so- you want the lowest impedance possible for that fault current


In belief, man can do anything

 

[wyreman]

Uffer :/


In belief, man can do anything

 

[GoldDigger]

Uffer :/


In belief, man can do anything

It's actually Ufer.
(The inventor's name.)
And as long as the parallel path carries only fault current and not normal neutral current there is no problem.
As stated earlier, parallel EGC paths are common and not objectionable.
But there may be limits on where you can land additional GECs if the only path to the rest of the GES involves wires sized only as EGCs and not as bonding jumpers.

 

[tom baker]

Gas bond / structural steel also 1/0

What is your code reference for sizing the gas bond at 1/0?
FYI the code language is structural metal.

 

[augie47]

What is your code reference for sizing the gas bond at 1/0?
FYI the code language is structural metal.

good point (question) ! I was concentrating on udder grounding, missed that

 

[wyreman]

I have a soares book I think 250.95 says #3 for 400. No exception a on 25066 for gas last I checked with ahj


In belief, man can do anything

 

[augie47]

I have a soares book I think 250.95 says #3 for 400. No exception a on 25066 for gas last I checked with ahj


In belief, man can do anything

There may be no exception by your AHJ but the Code allows a lot of possibilities:
250.104 covers the bonding of "other metal piping systems" which would include the gas pipe. #3 would be correct for a 400 amp circuit, however, the section goes on to say the pipe only needs to be bonded using the rating of the circuit likely to energize the pipe. It goes on to say the the EGC of the circuit likely to energize the pipe can be used as the bonding means.
Seemingly leaves a lot open to the AHJ from allowing the 15 or 20 amp circuit feeding a gas appliance to be the only bonding means to requiring the bond to be as large as 250.122 requires for the main (I've never seen it enforced that way).
Locally the AHJ's either accept the circuit to the gas appliances or rely on a #4 bond between gas and other piping (arbitrary size)