Single ground rod for static discharge

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NoFluxGiven

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Location
Clearwater FL
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Service Manager
We have a customer that wants to drive a stand alone ground rod inside his business and connect to a metal cabinet. Should the cabinet not be bonded to building steel or the electrical service? Seems like having this stand alone rod and cabinet would be a hazard to the rest of his system.
 
Connecting a non-energized metal cabinet to a non-energized ground rod probably doesn't violate any code, but I agree this is probably a bad design choice.

If there is any voltage difference in the soil between the two grounding electrodes, this voltage will be present between the two components (the cabinet and the building steel). In particular the separate ground electrodes are essentially 'antennas for soil currents' from nearby lighting ground strikes.

I have personally seen lighting induced damage to phone wiring from having separate ground rods, with no evidence of a lightning strike to the building.
 
If there is no electric citcuit to the cabinet, a separate electrode may be ok. Is that cabinet sitting on a concrete floor? If so, that should be good enough for static.

If it has power, then the EGC in the circuit provides a path to an electrode system. You could certainly run a green #6 from somewhere near that is grounded, such as building steel, a panelboard ground bus, or even an electrical outlet.

You dont generally need a big wire for static, and 100K ohms of resistance would bleed off most static charges. If you run a separate rod, it would be prudent to tie it in with a #6 to the existing electrode system, and that would be required for most supplemental rods, as isolated ones can cause issues.
 
NoFluxGiven said:
We have a customer that wants to drive a stand alone ground rod inside his business and connect to a metal cabinet. Should the cabinet not be bonded to building steel or the electrical service? Seems like having this stand alone rod and cabinet would be a hazard to the rest of his system.
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There's no hazard without bonding it. The entire idea is a waste of time and energy because it will accomplish little to nothing. If it's likely to become energized it should be connected to an EGC.
 
I can see a hazard if the cabinet is holding flammable liquids or powders. I think our Hazmat people wanted the storage cabinets grounded, but they typically sat on concrete floors. If on some insulating floor covering, the cabinet could pick up charges and maybe discharge when you open the door.
 
I don't think it's a safety hazard to put it in, but I think you do technically have to bond it into your grounding electrode system per 250.50. Unless you can declare it as an "auxiliary electrode" - whatever that is.
 
I am pretty sure that metal cabinets containing flammable or explosive substances need to be grounded to the building grounding system.
 
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NEC Inspector said:
I don't think it's a safety hazard to put it in, but I think you do technically have to bond it into your grounding electrode system per 250.50. Unless you can declare it as an "auxiliary electrode" - whatever that is.
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It definitely could be called an auxiliary electrode although I think the code is a bit unclear on bonding requirements if there isn't already an EGC to the cabinet for other purposes.
 
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