Isolated Ground Required?

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ken44

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I have a tenant that wants to install some ATT equipment which requires a NEMA L5-30 receptacle but they are insisting that it be connect to an isolated ground receptacle. But we don't have any panels that are isolated ground in this 12 story commercial building? I am deciding to tell them if they need to purchase equipment that does not require the IG or is there another cost effective solution to provide the IG in this case. I have read a few of the posts concerning IG and the suggestions seem to lead to either installing an SDS or going back to the main.
 
ken44 said:
I have a tenant that wants to install some ATT equipment which requires a NEMA L5-30 receptacle but they are insisting that it be connect to an isolated ground receptacle. But we don't have any panels that are isolated ground in this 12 story commercial building? I am deciding to tell them if they need to purchase equipment that does not require the IG or is there another cost effective solution to provide the IG in this case. I have read a few of the posts concerning IG and the suggestions seem to lead to either installing an SDS or going back to the main.
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To be correct, you're right, it needs to be an SDS or go back to the service. I've run into this situation many times myself. Most of the people specifying these have no clue that it needs to be an SDS or back to the service and if you just run it to the nearest panel it is just a waste of money to do isolated grounds. When you tell 'em what it will take to correctly, most just say to run it to the nearest panel and all the explaining in the world why this is wrong usually goes nowhere. The good news is I don't think it violates code but rather defeats the purpose of the isolated recep. In any event, IMHO, even done when done correctly, in most cases it is still a waste of money to do isolated grounds. There have been numerous white papers debating this.
 
texie said:
To be correct, you're right, it needs to be an SDS or go back to the service. I've run into this situation many times myself. Most of the people specifying these have no clue that it needs to be an SDS or back to the service and if you just run it to the nearest panel it is just a waste of money to do isolated grounds. When you tell 'em what it will take to correctly, most just say to run it to the nearest panel and all the explaining in the world why this is wrong usually goes nowhere. The good news is I don't think it violates code but rather defeats the purpose of the isolated recep. In any event, IMHO, even done when done correctly, in most cases it is still a waste of money to do isolated grounds. There have been numerous white papers debating this.
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I agree for the most part... but a local SDS bonded locally to building steel electrode is likely no more ground isolated than a local panel.
 
petersonra said:
How would an SDS help? How would that be an IG unless you ran an EGC back to the service panel?
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It would be as isolated as the at the service and if the branch circuit was supplied from an SDS it would be a violation to run the IG back to the service.
 
Smart $ said:
I think that's debatable... but not something I care to debate given the topic. :p
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Picture one piece of utilization equipment at the end of a dedicated IG circuit.

Regardless if the IG runs back to XO of an SDS or the bond point of the service the only current that can flow on that IG is from the one piece of utilization equipment.

That is my understanding of the point of an IG.
 
iwire said:
Picture one piece of utilization equipment at the end of a dedicated IG circuit.

Regardless if the IG runs back to XO of an SDS or the bond point of the service the only current that can flow on that IG is from the one piece of utilization equipment.

That is my understanding of the point of an IG.
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I thought we wanted no current flow on any EGC. In any case, how is that helpful? Maybe that is kind of the issue with IG circuits in general.

What happens if the metal frame of the equipment is sitting on a metal shelf attached to the building structure?
 
iwire said:
Picture one piece of utilization equipment at the end of a dedicated IG circuit.

Regardless if the IG runs back to XO of an SDS or the bond point of the service the only current that can flow on that IG is from the one piece of utilization equipment.

That is my understanding of the point of an IG.
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I'll go with that... ;)
 
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