250.66 w/o water pipe

[Greg_E]

As an electrician and a certified inspector I see the grounding electrode undersized quite often on large sevices. Very frequently the water service is no longer metal but plastic. An example a profession engineer certified that an apt complex with 2 800amp services per building met code with a single #4 Ufer ground and a supplimental #6, 8' ground rod. The only way this service can meet code is with a 3/0 grounding ring, or better a 3/0 ufer, or a grounding plate, but this latter is not allowed in the Dallas area because of the corrosive soils. Note 250.52 (A) (3) concrete encased electrodes states "shall not be smaller than #4 AWG", it can be and should be equal to table 250.66 w/o a water pipe. What is going to happen if the transformer looses it's nuetral, or a large surge or lightning strikes the building? 250.66 clearly states that grounding conductor "shall not be less than table 250.66" My interpitation is that all other forms of the grounding electrode system would be supplimental and not subsitutable for. Any thoughts on this are welcomed ...Greg Eller

 

[don_resqcapt19]

Greg,
The engineer is correct. The GEC to the concrete encased electrode, ground ring or ground rod, is not required to be sized per Table 250.66. The rules in 250.66(A), (B) and (C) apply to the GEC to those electrodes no matter what size the service is or what other electrodes may or may not be available. The sizes in those sections are the maximum sizes required by the code for those electrodes. If you have a 10,000 amp service and the only grounding electrode is a ground rod the GEC is not required to be larger than #6.

What is going to happen if the transformer looses it's nuetral, or a large surge or lightning strikes the building?

In all of those cases the code minimum GEC will carry more current than the grounding electrode can disapate. About the only grounding electrode that can prevent damage in the case of an open neutral is a metal underground water piping system, but that is not because it is a good grounding electrode, it is because it is a metallic path back to the utility transformer via the bonding connections and grounded conductors of other services in the area that are connected to the common metal water piping system.
Don

 

[Bea]

Greg,
The engineer is correct. The GEC to the concrete encased electrode, ground ring or ground rod, is not required to be sized per Table 250.66. The rules in 250.66(A), (B) and (C) apply to the GEC to those electrodes no matter what size the service is or what other electrodes may or may not be available. The sizes in those sections are the maximum sizes required by the code for those electrodes. If you have a 10,000 amp service and the only grounding electrode is a ground rod the GEC is not required to be larger than #6.

I agree with one exception ground ring to be sized in accordance with 250.66 and not smaller than #2 copper 250.52.3

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[don_resqcapt19]

Bea,

I agree with one exception ground ring to be sized in accordance with 250.66 and not smaller than #2 copper 250.52.3

The minimum size of the ground ring conductor is #2 and in the cases where Table 250.66 requires a GEC smaller than #2 you can size the GEC from the table. In the cases where Table 250.66 requires a GEC larger than the size of the conductor used for the ground ring, you are permitted to use a GEC that is the same size as the ground ring.
Don

 

[iwire]

Greg I agree with Don.

250.66 clearly states that grounding conductor "shall not be less than table 250.66"

I think that explains the problem you are having.

250.66 does say that, but it also continues on.

I don't have my book in front of me but it says more or less...

'The size of the GEC shall not be less than given in Table 250.66 except as permitted by 250.66(A) through (C)'.

250.66(A) tells us that we never need more 6 CU or 4 AL to a ground rod.

 

[iwire]

An example a profession engineer certified that an apt complex with 2 800amp services per building met code with a single #4 Ufer ground and a supplimental #6, 8' ground rod.

Actually the engineer went beyond code.

There is no NEC requirement to supplement a concrete encased electrode.

It sounds like all they needed was the 'Ufer'.

Only water pipe electrodes need a supplemental electrode installed. 250.53(D)(2)

My interpitation is that all other forms of the grounding electrode system would be supplimental and not subsitutable for.

I do not understand that last part.

 

[brian john]

On Ufer electrodes does anyone know of any studies or personal EXPIERENCES where the service or structure took a direct hit, and the Ufer ground was damaged, popped or cracked due to the magnitude of the stroke and the moisture (steam) trying to escape the concrete?

 

[don_resqcapt19]

Brian,
I have never heard of any real world issues with building footings or foundations. One of the other moderators, Dereck, has posted about some issues with concrete bases for utility poles, but the problem went away if they double tie or welded the rebar in the concrete.
Don

 

[Bea]

Bea,

The minimum size of the ground ring conductor is #2 and in the cases where Table 250.66 requires a GEC smaller than #2 you can size the GEC from the table. In the cases where Table 250.66 requires a GEC larger than the size of the conductor used for the ground ring, you are permitted to use a GEC that is the same size as the ground ring.
Don

The minimum size a ground ring can be is # 2 250.52.4 if you have a service with service entrance conductors of 500 KCMILS for example you would have to have a ground ring sized in accordance with table 250.66 1/0 copper and GEC to the ground ring would have to be 1/0 as well based on 250.66 (c) No where in 250.52.4 does it use the words maximum size of ground ring it states not smaller than #2 copper. Please privide code reference that supports your responance
Thank You

 

[George Stolz]

Bea, sequentially speaking, in order for a GEC to become relevant it must first have a GE to connect to.

Therefore, the GE comes first. If this is so, then the ground ring is never required to be larger than #2. You can go larger if you choose, that's your design question.

Now that the GE exists, we are required to connect it to our GES with a GEC. The max size of the GEC is determined by the size of the ground ring it's connecting to.

JMO,

 

[iwire]

Bea, I agree with Don and George.

There is never a time when the NEC requires a ground ring, or the conductor running to it to be larger than 2 AWG.

The Code references are

250.52(4) and 250.66.

If you still believe it does need to be larger please provide a code reference stating so.

 

[iwire]

Here is an ROP for the 2008 NEC

5-210 Log #2253 NEC-P05 Final Action: Reject
(250.66 and Table 250.66)
____________________________________________________________
Submitter: Bryan P. Holland, Holland Electric
Recommendation: Delete Table 250.66 and revise 250.66 to state: ?The size
of the grounding electrode conductor of a grounded or ungrounded ac system
shall not be less than 4 AWG copper wire or 2 AWG aluminum wire, except as
permitted in 250.66(A). Delete 250.66(B).
Substantiation: The NEC is a minimum standard. If a structure or building is
compliant to the code and completely safe with only #4 AWG to a concreteencased
electrode, then there is no reason to require a different electrode type
to be connected with anything larger. It?s not logical nor should be a code
requirement to require anything above the minimum. Simply changing the
electrode type shouldn?t change the minimum safety requirement. If the table is
accurate, it could be assumed that systems connected to only ground rods or to
a concrete-encased electrode are less safe then a similar structure with a metal
underground water pipe system or metal frame. It is generally understood that
the concrtete-encased electrode is the most effective and low-impedance
electrode of choice yet it is only required to be connected with a #4 AWG
while other possibly less effective electrodes require such large conductors.
The requirement in 250.4(A)(1) and (2) can be satisfied with a grounding
electrode conductor no larger than #4 AWG regardless what electrode it is
connected to.
Panel Meeting Action: Reject
Panel Statement: Deleting Table 250.66 as proposed lessens the minimum
requirements of the NEC without substantiation. Sections 250.66(A), (B), and
(C) only apply where the grounding electrode conductor is a sole connection toany of the types of electrodes in those sections.
Number Eligible to Vote: 15
Ballot Results: Affirmative: 15

Notice that they do not dispute that a 4 AWG copper wire or 2 AWG aluminum wire is the largest needed to run to a concrete encased electrode.

 

[tom baker]

What is going to happen if the transformer looses it's nuetral, or a large surge or lightning strikes the building?

Surges don't go to ground.
For this and any building two ground rods meet code.
However, a CEE per 250.52(A)(3) is the most cost effective and provides the best ground....

 

[Jljohnson]

250.52(A)3 deals with "constructing" a Grounding Electrode. It clearly states the minumum size and length of conductor to be # 4 bare, 20' long. Now then, with that said, 250.66(B) states that the connection to the CCE shall not be required to be larger than # 4 AWG copper wire. Seems to me that, no matter what the service size, a # 4 connected to the UFER is satifacory to the 2005 NEC. The engineer referenced in the OP designed a code compliant GEC system.

 

[petersonra]

Surges don't go to ground.

agreed.

For this and any building two ground rods meet code.

don't agree. if a ufer exists, you do not have the option to put in two rods instead.

However, a CEE per 250.52(A)(3) is the most cost effective and provides the best ground....

define best.

 

[Bea]

Bea, I agree with Don and George.

There is never a time when the NEC requires a ground ring, or the conductor running to it to be larger than 2 AWG.

The Code references are

250.52(4) and 250.66.

That is what I have reference enlight of George's piont of view I will concede Thank You

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