IG the Bus

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Coachmike

Coachmike

Senior Member
Location
Morris County, NJ
Occupation
Electrical Contractor
We installed 3- 100 amp buss duct feeders. They are isolated grounds. When bringing the IGs back to an IG buss bar in a sub panel. Does a separate IG have to go to the service? If so what size conductor is that? TIA
 
The IG should run back to the location of the main or system bonding jumper, which ever applies, without a connection to any other grounding path. It is a fault clearing path so must be sized per Table 250.122.
 
Normally (?) when IGs are used with wiring or cabling, there is also a separate non-isolated EGC. In your case, presumably the bus duct itself is still a valid EGC.
It seems to me that, depending on the equipment served and the job specs, you also have the option of simply ignoring the IG bus or of treating it as you would a non-isolated bus (as shown in the PDF.)
The IG must be sized as an EGC, but the more likely fault current path would be through the equipment case to the standard EGC.
 
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