New motor has EGC run to it - any requirement for a new ground well at the motor?

[MRKN]

I cannot find any requirement in the NEC for a grounding electrode at every piece of electrical equipment such as at a motor.

Yes, at every building or structure served per 250.32.

But in fact, it seems that it is specifically prohibited under 250.30(A):

(A) Grounded Systems. A separately derived ac system that is
grounded shall comply with 250.30(A)(1) through (A)(8).
Except as otherwise permitted in this article, a grounded
conductor shall not be connected to normally non–current carrying
metal parts of equipment, be connected to equipment
grounding conductors, or be reconnected to ground on the
load side of the system bonding jumper.

Informational Note: See 250.32 for connections at separate
buildings or structures and 250.142 for use of the grounded
circuit conductor for grounding equipment.

250.142(B) gives a few exceptions to this, but more importantly the handbook has two explanatory paragraphs as to why following this section. In the case of a 3-ph motor with no neutral wire it's not clear that their example is applicable as to the logic.

 

[LarryFine]

That says the same thing that every grounded system is supposed to conforms to. After the intentional bond at the SDS neutral point, the neutral is to remain insulated from any connection to non-current-carrying parts. In other words, the neutral is not to be used for the purpose of grounding equipment.

 

[MRKN]

Ok - so "grounded conductor" is equivalent to saying "neutral". I tried looking up "grounded conductor" in 100 - definitions - but it wasn't immediately clear to me. Both a neutral and an EGC are a grounded conductor?? Am I just not used to the jargon?

Regardless, are there any requirements beyond at every new building and structure, for additional ground electrodes?

E.g. if I had a 10,000 MVA system feeding 100 10 HP motors on skids scattered in every direction I could use just one electrode, say near the transformer.

 

[LarryFine]

Both a neutral and an EGC are a grounded conductor??

The neutral is the grounded conductor because we intentionally bond it to the GEC system, and the EGCs are intentionally bonded to the neutral. The EGC is the grounding conductor (although not always a wire) which must be bonded to the neutral for ground faults to trip breakers or blow fuses.

The premises EGC system actually begins at the main disconnect enclosure, which is the last point where the equipment enclosures are intentionally tied to the supply neutral, and is also the beginning of the neutral (grounded conductor) being intentionally insulated from grounded equipment.

Regardless, are there any requirements beyond at every new building and structure, for additional ground electrodes?

Nope. The main disconnect of every structure must have a GEC/EGC system, but the neutral remains insulated from that system everywhere except the first main disconnect enclosure at the incoming service. Every piece of distribution equipment beyond that point is treated as a sub-panel.

An isolation transformer (typical transformer) that has no direct connection between any primary and any secondary conductor creates an SDS, which requires its own bonding point. That means we designate one conductor to be that new system's neutral, which gets a GEC system like a service.

E.g. if I had a 10,000 MVA system feeding 100 10 HP motors on skids scattered in every direction I could use just one electrode, say near the transformer.

Yes, as long as they're in the same building; see above. Conductors that supply only a single (or a single multi-wire) circuit do not require a GEC system at a second building, but in all cases, neutrals do not get bonded to the EGC/GEC system again.

 

[don_resqcapt19]

The NEC only requires grounding electrodes at the service or at a separately derived source. Some industrial specifications require grounding electrodes at the equipment, and such electrodes are not prohibited by the code. The are called auxiliary grounding electrodes and are permitted by 250.54. There are no real requirements when you install an auxilliary grounding electrode.

 

[jaggedben]

Regardless, are there any requirements beyond at every new building and structure, for additional ground electrodes?

NO.

To elaborate...

- Depending on the electrodes you are using, more than one may be required to create the building grounding electrode system. But if so they are all tied together into one grounding electrode system for each building.
- Separate sytems (transformers, for example) may require additional grounding connections to the building grounding electrode system, which is not the same as additional electrodes.
- A bona-fide lightning protection system will have additional electrodes, but the criteria for those are not addressed in the NEC. NEC grounding requirements do not provide bona-fide lightning protection.
- Adding additional grounding electrodes just for random pieces of equipment is totally unnecessary, and generally stupid, but since various people can't absorb the message, 250.54 permits (but does not require) additional electrodes at equipment to allow for equipment instruction manuals that call for one.

 

[MRKN]

Larry,

Thank you for the clarification on grounding vs. grounded. Hopefully I will remember this nuance for the rest of my days...

And agreed that every transformer with galvanically isolated windings creates a SDS (I did know that one!), with it's own required GES.

My example of the many pumps was more along the lines of pumps outdoors on skids with piping everywhere (not contained within a building). As I understand, still only one ground electrode required.



Don,

The reference to 250.54 is perfect. Thank you.



Ben,

Agreed, all present electrodes must be tied together. Good comment on the lighting design going above and beyond NEC minimum requirements. However can you explain a little why you think additional ground electrodes at various pieces of equipment is "stupid"? There has to be a reason, e.g. prevention of static buildup, minimizing effects of galvanic corrosion of ground electrodes (no idea just guessing)




Overall this has answered my question about minimum NEC grounding electrode requirements. Thanks guys.

 

[jaggedben]

...

Ben,

Agreed, all present electrodes must be tied together. Good comment on the lighting design going above and beyond NEC minimum requirements. However can you explain a little why you think additional ground electrodes at various pieces of equipment is "stupid"? There has to be a reason, e.g. prevention of static buildup, minimizing effects of galvanic corrosion of ground electrodes (no idea just guessing)

Overall this has answered my question about minimum NEC grounding electrode requirements. Thanks guys.

https://www.youtube.com/watch?v=YuDqXFvRv94

This video was very formative in my understanding. It's long, and the code controversy has since been resolved in favor of what Mike argues - 690.47(D) was removed from the 2017 NEC. But the physical explanations are still totally relevant. I also think extra electrodes generally do rather little good and are a waste of material, and sometimes unsightly.

BTW, that was lightning, not lighting. Not sure if you misread the meaning or just mistyped your response. I misread those frequently myself.

 

[MRKN]

https://www.youtube.com/watch?v=YuDqXFvRv94

This video was very formative in my understanding. It's long, and the code controversy has since been resolved in favor of what Mike argues - 690.47(D) was removed from the 2017 NEC. But the physical explanations are still totally relevant. I also think extra electrodes generally do rather little good and are a waste of material, and sometimes unsightly.

BTW, that was lightning, not lighting. Not sure if you misread the meaning or just mistyped your response. I misread those frequently myself.

Typo - I meant lightning as you caught.

Point taken from the video. It's a concern in occupied buildings, when lightning strikes create voltage gradients. Out in fields, or industrial plants, it's more unclear to me. As Mike says, just a waste - but not a health and safety threat.