Sizing an Isolated Ground conductor!!!

[sam34]

Hello every one, Could someone tell me what is the best approach to take to size an IGC (branch ckt's and feeders)? I have this situation where a multiple point of sale stations that required to have an Isolated ground.They are fed from 100A sub -panel back to MDP. I have been told to size it based on the same size of phase conductor?And also, can we daisy- chained the IG conductor?
Thank you,

Sam

 

[ryan_618]

Re: Sizing an Isolated Ground conductor!!!

Table 250.122

 

[petersonra]

Re: Sizing an Isolated Ground conductor!!!

Originally posted by sam34:
And also, can we daisy- chained the IG conductor?

The IG has to go with the branch circuit wiring, so as long as you do that you could justify daisy chaining the IGs together, at least from a code perspective.

Personally, I see no reason to install IG receptacles at all. It adds cost and serves no useful purpose (IMHO).

 

[sam34]

Re: Sizing an Isolated Ground conductor!!!

I agree with you, I don't see any use for IG but the owner have requested it because he thinks that will eliminate any noise for his equipment.

 

[dereckbc]

Re: Sizing an Isolated Ground conductor!!!

It is the same size as the EGC from 250.122

 

[iwire]

Re: Sizing an Isolated Ground conductor!!!

Originally posted by sam34:
Hello every one, Could someone tell me what is the best approach to take to size an IGC (branch ckt's and feeders)?

Sam there is no need to size the IGs based on the feeder size, as has been said you need to use Table 250.122 but the IG will only be protecting 20 amp circuits, not the the feeder.

So at minimum you could use 12 AWG all the way back to your MDP.

In the past when it has not been specified for me I have used an 8 or 6 AWG for the run back to the bonding point.

It just looks strange to install a 12 AWG in a 225 amp feeder raceway.

 

[hbiss]

Re: Sizing an Isolated Ground conductor!!!

Your question is irrelevant because in my opinion the IG from each receptacle should be run individually back to the MDP. Easy to do when you HR each receptacle from a main panel, not so easy from a sub panel.

I too see no reason IG's could make any difference here.

-Hal