EGC size for motor branch circuit

[philly]

I know when sizing equipment ground conductors (EGC's) you use table 250.122. However for a branch circuit run from a motor starter do you use the rating of the breaker in the motor starter for the breaker rating in the table?

Does it matter is its an mag only circuit breaker?

 

[LEO2854]

I know when sizing equipment ground conductors (EGC's) you use table 250.122. However for a branch circuit run from a motor starter do you use the rating of the breaker in the motor starter for the breaker rating in the table?

Does it matter is its an mag only circuit breaker?

Look at 430.81 on page 602 of The 2008 NEC HANDBOOK. I did not find any wording about (EGC's) But that is part VII.of Artcle 430 Motor controllers.

 

[david luchini]

Yes, the EGC for the motor branch circuit should be sized per T250.122, based on the size of the OCPD in the starter.

The egc for a mag only c/b can be sized using T250.122 based on the maximum permitted rated of a dual element time-delay fuse size for the motor horsepower. See 250.122(D).

 

[markstg]

I know when sizing equipment ground conductors (EGC's) you use table 250.122. However for a branch circuit run from a motor starter do you use the rating of the breaker in the motor starter for the breaker rating in the table?

Does it matter is its an mag only circuit breaker?

See NEC 250.122 (D) which allows the EGC to be sized based on the rating of the motor overload protective device where the OCP device is an MCP, but not less than table 250.122 allows, so use the MCP continuous current rating, not its instantaneous setting.

 

[david luchini]

See NEC 250.122 (D) which allows the EGC to be sized based on the rating of the motor overload protective device where the OCP device is an MCP, but not less than table 250.122 allows, so use the MCP continuous current rating, not its instantaneous setting.

Where does 250.122(D) allow the egc to be sized based on the rating of the motor overload protective device?:-?

250.122(D)(1) says "branch circuit short-circuit and ground fault protective device."

250.122(D)(2) says "dual element time-delay fuse selected for branch circuit short-circuit and ground fault protective device..."

 

[markstg]

Where does 250.122(D) allow the egc to be sized based on the rating of the motor overload protective device?:-?

250.122(D)(1) says "branch circuit short-circuit and ground fault protective device."

250.122(D)(2) says "dual element time-delay fuse selected for branch circuit short-circuit and ground fault protective device..."

I was looking at the 2005 Code. Never Mind.

 

[don_resqcapt19]

David,
It said that the EGC is to be based on the rating of the overload relay when the short circuit and ground fault protection is an instantaneous type device in the 2005 and earlier codes. That was changed in the 2008 code.

I type too slow

 

[david luchini]

I was looking at the 2005 Code. Never Mind.

That explains it. Perfectly valid point. Many jurisdictions (including mine) still use the 2005 Code (but I generally reach for the '08 Code when answering questions here, unless the OP mentions an older code.)