Grounding Electrode Conductor to ground rod

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frankft2000

frankft2000

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I'm looking at putting in a 400 amp service. It is a all wood structure. It looks like I'll be using ground rods. Table 250.66 says the grounding electrode conductor will be 3/0 AL.

Since I would be using ground rods I look at 250.66 (A) My question is I don't understand what the code is saying by "...that portion of the conductor that is the sole connection to the grounding electrode shall not be required to be larger than # 4 AL."

Is the code saying the whole conductor can be #4 AL or are they saying to give the 3/0 AL a "haircut" to #4 AL size. Neither seems to me to be right. I must be missing something.
 
It just means that any conductor that just runs to a ground rod only has to be 6 copper or 4 aluminum.

You could have a 4000 amp service out in woods and all it would need would be two rods connected to it by 4 AL or 6 CU
 
Unless the connection to the ground rod is more than 18" above the ground AL conductors can not be used as the GEC to a ground rod.
 
Wow, since the ground rods are below grade it looks like copper, and # 6 at that. I don't see why the NEC says to use 3/0 AL if it were going to building steel, but # 6 copper to rods but.. OK

Thanks
 
You think that's small. Most TVSS's for "whole house" surge and lightning protection are wired with #14 and rated at ~30 kA. I wouldn't worry about the #6 to the ground rod catching fire.

Mark
 
Made electrodes such as a 5/8" iron or steel can only provide a # 6 worth of protection whether you run a 4/0 copper conductor to it or a #6 the result will be the same.
 
MD that is a good way to put it. :)

Usually I say something about a ground rod not 'connecting to the dirt' well enough to need a larger conductor.
 
frankft,

Maybe I am missing something here but you said you are doing a 400A service...not sure where you get the GEC has to be 3/0 based on 250.66.

Are you looking at the LEFT column and assuming the "Over 350 through 600" is the column you are working in?

Chances are you are working with a 400A service that will have (2) 200A Panels and a single meter cab.....so chances are you will have 4/0 SE between the meter and to each panel for a combined 400A service....

So I am not sure where you get the 3/0 AL from......based on the chart the GEC could be 4 CU or 2 AL.....I venture to say you are not going to want to mess with the 2 AL.....BUT regardless the code allows for Ground Rods to not be larger than # 6 AWG as shown in 250.66(A)...

Point is...don't confuse the AMPS with the AWG and KCMILS listing on that table you are viewing....two different things...

Bob is correct.....(2) Rods and # 6 AWG is all you will need....Keep the #6 AWG Continuous to the FIRST rod and ACORN it..and then jump to the next ROD minimum 6' away....the GEC does not have to be continiuous from the first rod to the second rod....just for a FYI
 
radiopet said:
Chances are you are working with a 400A service that will have (2) 200A Panels and a single meter cab.....so chances are you will have 4/0 SE between the meter and to each panel for a combined 400A service
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It really depends on a lot of factors, if you only run one GEC from the electrode system to both panels the GEC will need to be sized for both panels...ie the size of the conductors feeding the meter.

But the GEC taps to each panel would be based on the service conductors for that particular panel.

Check 250.64(D)
 
lol...I guess I dont agree or maybe I am missing something.....The NEC allows any connection to the Ground Rod to not have to be larger than # 6 AWG regardless of the service size. ( edited: lol....Sorry I was refering to the Rods only...my Bad )

BUT again this is a "Supplimental " and I guess I was speaking on the Ground Rod Only issue....not the FACT it can be totally different if we are speaking of GEC's to the waterpipe and if their is parrallel conductors involved and so on.

I agree to the waterpipe....

The 4/0 conductor circular mil area can be found in Table 8 in Chapter 9 of the National Electrical Code?. The circular mil area for 4/0 is 211,600. Since there are two 4/0 conductors per panel the total or "equivalent" circular mil area is 2 x 211,600 or 413,200 circular mils or 413.2 kcmil. By Table 250-66 the required size of copper grounding electrode conductor is 1/0.

So I think I was actually trying to answer the Ground Rod Question...lol...but your right....guess we need to explain it all as well...:)
 
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radiopet said:
lol...I guess I dont agree or maybe I am missing something.....The NEC allows any connection to the Ground Rod to not have to be larger than # 6 AWG regardless of the service size.
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I wholeheartedly agree about the 6 AWG to rods.

it can be totally different if we are speaking of GEC's to the waterpipe and if their is parrallel conductors involved and so on.
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Again I agree.

The 4/0 conductor circular mil area can be found in Table 8 in Chapter 9 of the National Electrical Code?. The circular mil area for 4/0 is 211,600. Since there are two 4/0 conductors per phase the total or "equivalent" circular mil area is 2 x 211,600 or 413,200 circular mils or 413.2 kcmil. By Table 250-66 the required size of copper grounding electrode conductor is 1/0.
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Yes I agree.

But you had asked where he got a 3/0.

not sure where you get the GEC has to be 3/0 based on 250.66.
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He was using AL which happens to mean a 3/0 in this case.
 
iwire said:
But you had asked where he got a 3/0.



He was using AL which happens to mean a 3/0 in this case.
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AHHHH>..SNAP............man I always do CU when dealing with the GEC's....glad you cleared that up fella as I only GAVE thought to the original post in regards to the Ground Rod...not the OTHER aspects which is why 3/0 did not come into play with Ground Rods......lol

My bad....I do see the AL now......guess I am just a Copper man...:)

Interesting enough with so many homes now NOT having the WP option the UFER is the strongpoint and being # 4 AWG is allowed in this case and no additional suppliment is needed.

Bob I bet 9 or 10 homes I do now have no water pipe option....UFERS are the main option atleast here anyway.
 
AHHHH>..SNAP............man I always do CU when dealing with the GEC's....glad you cleared that up fella...lol

My bad....I do see the AL now......guess I am just a Copper man...:)
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Well when dealing with ground rods in dirt, we're all copper men. The AL can't be within 18" of the ground. Unless you want to use a 10' rod and only pound it in about 8.5'.
 
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