Sized per the MCB of the panel (400A) or on the branch circuit sizes that are feeding the receptacles (20A)?It should be sized the same as any equipment grounding conductor in accordance with 250.122.
Chris
Sized per the MCB of the panel (400A) or on the branch circuit sizes that are feeding the receptacles (20A)?
Thanks
The main equipment ground should be sized to the 400 A OCPD. The branch circuit would in turn be sized per 20 amp cir.
Off topic. I'm talking about the isolated ground from the MDP to the 400A for connection to the isolated ground busbar. Not the equipment ground.
I concur.It is still an equipment ground it is just isolated so it must be sized to the breaker on the feeder.
250.146(D) has implications? It allows the IG run with circuit conductors to pass through panelboards without termination therein. Installing a IG bar will have those IG's terminating in the panelboard...and the IG run with the feeder is not run with circuit conductors. It also specifically calls the IG wire an equipment grounding conductor.Is there any mention in the NEC of sizing a single IG to accommodate a IG ground bar serving multiple devices or circuits? So far we have one vote for making it the same size as the EGC in the panel feeder. IMO if it supplies only 20 amp circuits then it can be sized for 20 amps but I can't find a decent reference either way.
Is there any mention in the NEC of sizing a single IG to accommodate a IG ground bar serving multiple devices or circuits? So far we have one vote for making it the same size as the EGC in the panel feeder. IMO if it supplies only 20 amp circuits then it can be sized for 20 amps but I can't find a decent reference either way.
This is what my supervisor and the signing engineer is telling me. I am serving 6 separete IG 20A-120V receptacle circuits from this IG busbar.
The way I see it the IG only needs to be sized to the 20 amp OCPD. The EGC in the feeder needs to open a 400 amp OCPD during a fault, the IG only needs to open a 20 amp OCPD. As I stated before the code isn't really clear on how to size this IG.
I would agree with you if each circuit IG ran through the panel without termination.The way I see it the IG only needs to be sized to the 20 amp OCPD. The EGC in the feeder needs to open a 400 amp OCPD during a fault, the IG only needs to open a 20 amp OCPD. As I stated before the code isn't really clear on how to size this IG.
As I replied to Trevor (infinity), that might be the case if you ran a #12 IG for each circuit back to the main panel.I think I agree with Trevor. The feeder egc is for the ground fault for the 400 amp but the isolated ground is really just a continuation of the #12 circuits back to the main panel.
I think you treat it just like the EGC in the panel. If you had a 400A feeder to a panel, but only had a few 20A circuits in it, that does not allow you to run a #12 EGC in the feeder. EGCs are sized by the overcurrent device supplying the ungrounded conductors in the circuit, doesn't matter whether the ground is isolated or not.
I would agree with you if each circuit IG ran through the panel without termination.
What if these six (6) 20A circuits were the only circuits in the panel? Still think the "feeder" IG only needs sized for 20A?
Yes, when run with the circuit conductors. The IG wire going back to the main is not bering run with the circuit conductors....
We're allowed to install one EGC in a raceway for multiple circuits based on the size of the largest OCDP protecting the mulitple circuits. I see this installation the same way regarding the singular IG back to MDP. I could install those 6 branch circuits and install only one IG sized for 20 amps so I'm ot sure why installing more branch circuit IG's would change anything.