EGC sizing for tap conductors

Status
Not open for further replies.

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I'm sure that this has been discussed before but here's the situation:

400 amp feeder with a #3 EGC
Four sets of #3 tap conductors feeding (4)-100 amp fused disconnects
EGC tapped to disconnect switches based on 250.122-100 amps are #8


I say the EGC tap conductors should be #3 also since the feeder has an OCPD set at 400 amps? A fellow electrician disagrees. I cited 250.122(G). Opinions?
 
Last edited:

iwire

Moderator
Staff member
Location
Massachusetts
infinity said:
I say the EGC tap conductors should be #3 also since the feeder has an OCPD set at 400 amps? A fellow electrician disagrees. I cited 250.122(G). Opinions?

I agree for the reason Chris stated and the fact that sizing the EGC from the tap to the OCPD based on the 100 amp disconnect makes no electrical sense whatsoever.

We need to size the EGC based on the OCPD it will be expected to open.

Once you get to the load side of the new OCPD you can run 8 AWG.
 

chevyx92

Senior Member
Location
VA BCH, VA
infinity said:
I'm sure that this has been discussed before but here's the situation:

400 amp feeder with a #3 EGC
Four sets of #3 tap conductors feeding (4)-100 amp fused disconnects
EGC tapped to disconnect switches based on 250.122-100 amps are #8


I say the EGC tap conductors should be #3 also since the feeder has an OCPD set at 400 amps? A fellow electrician disagrees. I cited 250.122(G). Opinions?
I agree #3 EGC.
 

Smart $

Esteemed Member
Location
Ohio
iwire said:
I agree for the reason Chris stated and the fact that sizing the EGC from the tap to the OCPD based on the 100 amp disconnect makes no electrical sense whatsoever.

We need to size the EGC based on the OCPD it will be expected to open.

Once you get to the load side of the new OCPD you can run 8 AWG.
If we used the logic "we need to size the [conductors] based on the OCPD it will be expected to open", then we'd also have to maintain the size of the tapped CCC's to the disconnects.
 

iwire

Moderator
Staff member
Location
Massachusetts
Smart $ said:
If we used the logic "we need to size the [conductors] based on the OCPD it will be expected to open", then we'd also have to maintain the size of the tapped CCC's to the disconnects.

I disagree.

The tapped conductors are large enough and / or short enough that they are still capable of opening the OCPD in the case of a short or ground fault.
 

Smart $

Esteemed Member
Location
Ohio
iwire said:
I disagree.

The tapped conductors are large enough and / or short enough that they are still capable of opening the OCPD in the case of a short or ground fault.
I'll concede based simply on the facts that I always prefer the safer installation method and 250.122(G) is quite specific.
 
Status
Not open for further replies.
Top