Driven ground at each machine

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Minuteman

Minuteman

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The Sooner Nation
Large industrial plant has a old 200HP air compressor and a air dryer. We are installing power to 3 new 50HP compressors and a new dryer. 480v using EMT. The manufacture of the new compressors sent out a guy yesterday to program the units. He notices that I am installing a EGC in each conduit (per local amendment) and says that it is customary for each unit to have a driven ground rod. What??? :confused: I have never heard of this.

The new machines are in a old metal building. There are under slab piping everywhere.
 
Not a violation

Not a violation

Minuteman said:
He said that it is standard practice in Texas. (Go figure).
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Unless he's the AHJ, he cannot enforce what he is stating. There is no code requirement for a driven ground rod at these locations. The EGC is sufficient.
 
No - he is not the AHJ, but he does have the ear of the Plant Manager. The PM acts as if WE missed something. I told the PM that we could install them with a change order, but I need to see a accurate marking of the piping locations first and that even then, we would not be responsible for any damage to what is beneath the slab.
 
Minuteman said:
He notices that I am installing a EGC in each conduit (per local amendment) and says that it is customary for each unit to have a driven ground rod.
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I love these customs :grin:. Since I'm a rabble rouser, I'd ask him when he's taking you to lunch, since 'round here, the mfg's rep always takes the electricians to lunch after the installation. Save some pie for me :D.
 
It used to be pretty common for machinery makers to specify a ground rod at the machine. Never could quite figure out why, but it was very common.
 
Supplementary ground rods for machinery are somewhat common. They are not required by the NEC but might be required by the manufacturer.


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infinity said:
Supplementary ground rods for machinery are somewhat common. They are not required by the NEC but might be required by the manufacturer.
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I'm very curious as to what a manufacture is trying to accomplish with this supplementary ground rod?
 
stickboy1375 said:
I'm very curious as to what a manufacture is trying to accomplish with this supplementary ground rod?
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I don't know but it's sometimes called, as Mike's graphic shows, a signal reference ground and they're not that uncommon. So IMO the guy making the request was not 100% wrong since supplementary electrodes do serve some purpose.
 
infinity said:
I don't know but it's sometimes called, as Mike's graphic shows, a signal reference ground and they're not that uncommon. So IMO the guy making the request was not 100% wrong since supplementary electrodes do serve some purpose.
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Whats a "signal reference ground"?
 
Okay, we finished today and the Plant Manager & the Plant Engineer dropped in to look things over. I asked the PE about the supplementary ground rods. He was didn't see the need, and thought it might set up a "floating ground" situation.
 
Only issue I see is IF HE IS THE MANUFACTURES rep and he request if it and DOES NOT violate code, machine goes bad for any reason he has a finger to point at YOU for not following their SPEC that was clearly explained to you.

Other than that I see no benefit.
 
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