supplemental ground rod

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wireday

Senior Member
Location
New England
Occupation
Master electrician
I have a 480 piece of equipment located in a indoor wet area, It was suggested by others that I should install a ground rod at the equipment. I have seen this done both inside and outdoors, the equipment has EGC from the feed circuit. does this offer further protection?
 
When I started my first job out of school as a plant engineer, the factory I worked in had a ground rod at every machine tool. I asked why and was told “we always do that.” I didn’t think it was in my interest to challenge the senior guy at that point, but I knew it was a waste.
 
wireday said:
I have a 480 piece of equipment located in a indoor wet area, It was suggested by others that I should install a ground rod at the equipment. I have seen this done both inside and outdoors, the equipment has EGC from the feed circuit. does this offer further protection?
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For the most part, all it offers is a commission to the guy selling ground rods, and maybe (I said maybe) a path for lightning to get into your equipment.
 
wireday said:
Yes that was there point
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Ok do the math. At 25 ohms, which is typically low for a ground rod, at 277 volts, in the event of a line to case fault, how much current will that be? Will that open the OCPD?
Or even at 480 V?
The NEC considers this ground rod to be a supplemental rod, it’s not required, so the GE rules do not apply - ie minimum size of GE conductor, etc
 
At 480V, due to the IR squared law, there is much more heat from a ground fault. Instead of a worthless ground rod, make sure all your joints are tight, use penetrox e on all joints, threads, use bonding bushings. Although 250.118 allows use of metal raceways as an EGC, pull a wire type EGC.
 
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