Grounded Conductor to Service

Status
Not open for further replies.
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
250.24(C) requires that with a grounded service supply, the grounded conductor be routed to the switchgear along with the ungrounded conductors. 250.24(C)(2) states the size shall be based on the size of the phase conductors and, when run in parallel, based sum of the sum of the total circular mil, however, it goes on to say "Where installed in two or more raceways, the size of the grounded conductor in each raceway shall be based on the size of the ungrounded service-entrance conductor in the raceway but not smaller than 1/0 AWG" (underline added).
Lets take the scenario of two conduits feeding an 600 amp service with
500kmil runs in each. The sum is 1000 kcmil thus requiring a 2/0 by 250.66
BUT each conduit has 500's and the underlined section makes me think that since the parallel service is in two conduits that only a 1/0 is required based on the 500 kcmil in each conduit.
What is the required size ?
 
I am confused Gus. What are you asking for. T. 250.66 is for the GEC but your discussion was about a grounded conductor...:-? What am I missing?
 
augie47 said:
...BUT each conduit has 500's and the underlined section makes me think that since the parallel service is in two conduits that only a 1/0 is required based on the 500 kcmil in each conduit.
What is the required size ?
Click to expand...

I agree with you, that we are allowed a smaller grounded conductor in each raceway, based on the size of the ungrounded in that raceway, and you need a total area equal at least to a 2/0, but allowed to be one 1/0 in each raceway, sized to 250.66.

It should probably be written as an exception:
Made Up Code 250.24(C) said:
Where the service-entrance phase conductors are installed in parallel, the size of the grounded conductor shall be based on the total circular mil area of the parallel conductors as indicated in this section.
Exception No. 1: Where installed in two or more raceways, the size of the grounded conductor in each raceway shall be based on the size of the ungrounded service-entrance conductor in the raceway but not smaller than 1/0 AWG.
Click to expand...
 
augie47 said:
250.24(C) requires that with a grounded service supply, the grounded conductor be routed to the switchgear along with the ungrounded conductors. 250.24(C)(2) states the size shall be based on the size of the phase conductors and, when run in parallel, based sum of the sum of the total circular mil, however, it goes on to say "Where installed in two or more raceways, the size of the grounded conductor in each raceway shall be based on the size of the ungrounded service-entrance conductor in the raceway but not smaller than 1/0 AWG" (underline added).
Lets take the scenario of two conduits feeding an 600 amp service with
500kmil runs in each. The sum is 1000 kcmil thus requiring a 2/0 by 250.66
BUT each conduit has 500's and the underlined section makes me think that since the parallel service is in two conduits that only a 1/0 is required based on the 500 kcmil in each conduit.
What is the required size ?
Click to expand...

1/0 is all that is required in each conduit.
 
Status
Not open for further replies.
Top