Size of Equipment Grounding Conductor for 200A service

[jeff48356]

In the NEC, there appears to be two tables that contradict each other in regard to the minimum sized equipment grounding conductor.

In Table 250.66, it lists a 4 AWG copper grounding conductor for 2/0 copper or 4/0 aluminum service conductors, which are the sizes used for 200A services. However, in Table 250.122, it lists a 6 AWG copper grounding conductor for 200A service.

Could someone clarify this, or explain the differences?

 

[Smart $]

In the NEC, there appears to be two tables that contradict each other in regard to the minimum sized equipment grounding conductor.

In Table 250.66, it lists a 4 AWG copper grounding conductor for 2/0 copper or 4/0 aluminum service conductors, which are the sizes used for 200A services. However, in Table 250.122, it lists a 6 AWG copper grounding conductor for 200A service.

Could someone clarify this, or explain the differences?

Table 250.66 is for sizing GEC's and bonding jumpers.

Table 250.122 is for EGC's.

 

[augie47]

A simple method of determining which table is to look at the conductors accompanying the "ground". If they are protected by an overcurrent device then 250.122 applies.
If they are not protected by an overcurrent device such as with service conductors and separately derived system secondaries then 250.66 applies.

 

[infinity]

In the NEC, there appears to be two tables that contradict each other in regard to the minimum sized equipment grounding conductor.

In Table 250.66, it lists a 4 AWG copper grounding conductor for 2/0 copper or 4/0 aluminum service conductors, which are the sizes used for 200A services. However, in Table 250.122, it lists a 6 AWG copper grounding conductor for 200A service.

Could someone clarify this, or explain the differences?

Since this is a service there are no EGC's and table 250.122 does not apply. All grounding on the line side of the service disconnect is accomplished by the connection to the neutral.

 

[jtinge]

A simple method of determining which table is to look at the conductors accompanying the "ground". If they are protected by an overcurrent device then 250.122 applies.
If they are not protected by an overcurrent device such as with service conductors and separately derived system secondaries then 250.66 applies.

2014 NEC added Table 250.102(C)(1) for sizing bonding jumpers. Essentially the same as Table 250.66 except for conductors over 1100 Cu or 1750 Al.


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[tom baker]

The size of the EGC is based on the feeder overcurrent protection device
The size of the GEC and neutral is based on the size ungrounded service entrance conductors.

There are tables for each but what is more important is you understand the difference in sizing.

For example, what would the answer be to the following question:
"What size ground for a 200 amp commercial service"?

 

[charlie b]

For example, what would the answer be to the following question: "What size ground for a 200 amp commercial service"?

And the answer is, "the question does not provide enough information to determine the ground wire size." Tell me what you are using for service conductors (size and material), and I'll try again.

 

[infinity]

I agree with Charlie and the single word "ground" is so ambiguous it should never be used.

 

[texie]

You don't need to know the details. I'll just assume the only GEC available is 2 ground rods and use a #6.