#6 Cu maximum required grounding electrode conductor?

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RUWired

Senior Member
Location
Pa.
Larry,Its possible that the reason for the up size to #4awg for concrete encased is physical strenght.The same for the up size to the #2 ground ring.The conditions are more harsh and need to be stronger.Its also possible that inorder to conduct the same amount of current to these electrodes as the rod ,pipe or plate, they need to be a bit larger.
Rick
 

ryan_618

Senior Member
I still think the reason for the larger condcutors for building steel and structural metal are actually intended for bonding more than for grounding. We just use the table to kill two birds with one stone. I think it does explain why a ring, CEE, and driven rod don't need to have a large GEC to them.
 
I agree with what Ryan posted in his last post.

The ground rod will very, very rarely have the chance of becoming energized by some circuit in the building.

The Steel and the water pipes do stand a greater risk of becoming energized within the building, so the GEC is really serving two functions... As a GEC and as a bonding conductor.
 

Gmack

Banned
Location
Michigan
"Without the code"

Ground rods are for lightning. Yes in theory they "try" to make it back to the source [grounded systems].

The "electrode" interior system is a different affair. Everything in there is
conductive and bonded. So it works on "ground faults".

One large EGC and 0% potential inside until/if you lose "the" system grounded conductor.

Then you have "floating" grounded/grounding conductor ON A MISSION!

But with multiple "derived systems" on a single premises [grounded] some problems. But the 0% potential card still holds.

On a single occupancy one system grounded. There are issues.

That ground rod with a # 6 wont win the day. Its a lightning rod for line surge to earth.

At 600 volts and below for sure.
 
I guess I'm guilty of referring to 250.66 when installing a ground rod. I've been using 1/0 for a 400amp service from the meter base to the 5/8 rod and then I always ground metal buildings. So what you guys are saying is that all I need is a number 6 to the ground rod, but use table 250.66 when determining the size to ground building structure? thanks for the advice.
 

Gmack

Banned
Location
Michigan
Rather than edit my first post I will just add here.

Interior systems use larger "electrode" conductors beyond "ground rods"
because they more conductive and bonded to piping systems forming an
electrode system that works.

That aside.

I "hate" corner grounded and straight delta systems [non wye] for their
hidden "potentials"

I once tried to speak on this but was told not to.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
b connection said:
So what you guys are saying is that all I need is a number 6 to the ground rod, but use table 250.66 when determining the size to ground building structure?
Correct. Just be sure to refer to 250.66(A), (B), & (C) when installing those electrodes.

Also, be sure to review 250.64(B) when sizing to electrodes as well.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Gmack said:
I "hate" corner grounded and straight delta systems [non wye] for their hidden "potentials"

I once tried to speak on this but was told not to.
What hidden potentials? By "straight" delta do you mean ungrounded?

Why/who told you not to discuss this?
Gmack said:
That ground rod with a # 6 wont win the day. Its a lightning rod for line surge to earth.
Can you clarify this statement, too?
 

Gmack

Banned
Location
Michigan
Sure George, yes I mean 3 wire delta / 3 phase. ie 440.

What do I mean by "hidden potential" on such a system?

Well if one leg [A] is ground faulted it floats because it has little or no potential to ground.

Should an electrician accidently touch phase [B/C] and conduit/equipment etc he can receive one hell of a shock at or near 440 volts.

This happened to me. But during another discussion early on I was told not to discuss such things by charlie b. So I wont give details.

I think it was Don who desribed this condition above as a corner grounded fault.

As others ,over time, I have concluded that though we treat a ground rod with much ado, it is much ado about "little" in respects to the interior grounding electrode portion of the system.

It was my mistake to refer to a ground rod as a lightning rod also because a single rod is not of much use in that capacity either IMO.

I have opened panels that were charred black powder and the guts/breakers crumbled out. Same thing for electric ranges and AC disconnects. Internal electronics "smoked" etc.

MO, a # 6 and a single rod wont win the day once the service grounded conductor is lost [seen that one too].

But during a "surge" on a entire city block from lightning, it wont protect
equipment/home/people. Its very humbling. I saw houses on both sides of the street for half a city block with "charred equipment .
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
I see. I wouldn't call that "hidden potential." I think this goes back to thinking that a 277V shock is more acceptable than a 480V one, so we'll leave that alone. The electrician shouldn't consider a 277V shock acceptable and get his feelings hurt when he gets 480V instead. We beat that horse to death, so I reckon there's no sense digging it up to get more licks in.

I concur with your opinion of grounding and lightning/surges, it fits with other information I've heard.
 

Glennw3

Member
Location
Augusta,GA
In my town we are required to install #6 for 150amp services and #4 for 200amp. Also one county requires us to install two ground rods 6 feet apart if the plumbing is not copper.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Glennw3 said:
In my town we are required to install #6 for 150amp services and #4 for 200amp. Also one county requires us to install two ground rods 6 feet apart if the plumbing is not copper.
How large must the service be before you're required to connect wire to those rods? :p

Actually, the wire sizes you quoted are required for water-pipe grounds, not earth, which never exceeds #6 cu.
 

Glennw3

Member
Location
Augusta,GA
We have probably 8 inspectors in our county only one of which is a master electrician so they all inspect everything. I've seen them turn down a job because it did not have #4 CU to the Ground Rod on a 200amp service but they are five with only #6 to the water pipe no matter the service size.
 
here in good'ol north florida (ya ya florida...) the local inspectors response to 250.66(a) was ..... i dont care what it says the table is what you go by.


truthfully i myself have a small argument with exception (a). i think the word "portion" needs a little clarification. if your only means of grounding is a ground rod or two does it mean the whole wire run to the electrode is the "portion" or only the actual physical section of wire that comes in contact with the electrode? way i could see it and correct me if im wrong here but it could be seen as i could run whatever size wire is required by the table for 250.66 then a millimeter before it contacts the ground rod use a splice that is irreversable to a piece of #6.

i dont know if that came out exactly how i wanted but im sure you all will get the point. personaly i believe the intent was the whole wire does not have to be larger then #6 but it really isnt about what i think now is it?
 

dnem

Senior Member
Location
Ohio
Re: #6 Cu maximum required grounding electrode conductor?

bburns said:
after looking at the referenced sections in the code, i have concluded that when 250.66(A) refers to "that portion of the conductor that is the sole connection to the grounding electrode...", it means that the part of the conductor that is in contact with the rod does not have to be larger than #6. the GEC itself must still comply with table 250.66.

how do you guys interpret this?
If you look at the picture on page 215 of the Handbook does it cause you to conclude differently ?

You're focusing on the "part of the conductor that is in contact with the ground rod" but the idea that I get from the picture is that the conductor between the ground rod and building steel is the one that would not have to be larger than #6 while the rest of the length that runs from the building steel to the service equipment would need to be sized according to Table250.66

Obviously, many installations have a unbroken conductor between the ground rod and service equipment but the wording of 250.66(A) "portion of the conductor" seems to be addressing the type of situation shown in the picture.

David
 

ryan_618

Senior Member
m73214 said:
infinity said:
A maximum of #4 is all that is required to a CEE. However, it can be smaller. A 100 amp service for example would require only a #8 to the CEE.

The way I read 250.52 (A) (3), #4 is the minimum sized CCE allowed

I agree if you are using the wire type of concrete encased electrode. If you are using the rebar type, you may use the Table values.
 

ryan_618

Senior Member
In 250.66. :) The wire type has to be 4 AWG, otherwise it isn't an electrode. If it is the rebar type, we would follow Table 250.66, except we don't have to have larger than 4 AWG because of the allowance in 250.66.
 
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