Consistent enforcement of 250.50

[dnem]

I think there?s something wrong with my departments enforcement of 250.50 that has been enforced from long before I came here and I?d like some opinions. . If I see a service on a building will no electrodes present, there needs to be an electrode installed, usually a ground rod. . If the service is on a pedestal, we consider it a structure served and need to see the ground rod at the pedestal. . The building supplied by the pedestal or a second building supplied from the first building can be supplied as a subpanel, with separated neutral and ground [250.32(B)(1)] or supplied like a main, with combined neutral and ground [250.32(B)(2)], but either way each structure must have its own electrode.

Now here?s where I see the inconsistency.
For a generator not in the building it powers, located either outside or in its own ?doghouse? that?s a separate structure from the building that it powers.
If a generator transfer switch breaks and transfers the grounded [neutral] along with the phase conductors, the generator is separately derived, has combined neutral and ground on the generator and, as a separate structure, has to have its own ground rod [electrode]. . But if the generator transfer switch does not break and transfer the neutral, the generator is not separately derived, needs to have separated neutral and ground but does not have to have its own ground rod.

When I ask why we don?t enforce a ground rod for a ?subpanel? generator, the answer I get is that it?s not separately derived. . When I ask how a ?subpanel? generator is different from a second building subpanel feed [250.32(B)(1)], I don?t get an explanation.

What do you think ?

David

 

[finhead]

Dave

I agree with you that the generator is a separately derived system if the neutral is also opened at the transfer switch and should be treated as such. Your building departments reluctance to enforcing the code could be that they are accustomed to transfer switches that do not open the neutral -- in my experience, the far more common type -- and want to be consistent with what they have been doing.

Brian

 

[RB1]

Dave,

I don't think it is prudent to always consider a generator located outdoors as a separate structure. Do you consider air-conditioning condensing units as separate structures? A structure is "that which is built" - built by whom? This is strictly an interpretive issue. As far as separate structures are concerned what difference does it make if the neutral is switched or not? How do you benefit from the standpoint of safety by considering the generators, or even the pedestals for that matter, as separate structures?

 

[mc5w]

250.50

250.50

However, a local ground rod for a generator or outbuilding provides a place for low energy lightning to go. Lets say lightning hits a tree and some of it sidestrikes to an outbuilding or generator. Without a local ground rod that sidestrike will tend to toast underground wiring. Same thing with bonding aluminum siding to a grounding electrode. You would not want Saint Elmo's Fire to turn aluminum siding into a great big light bulb.

Someone once told me about a house with a hip roof, metal gutters all around, and metal lath for the interior plaster. Lightning hit this building, used the gutter as a distribution bus, then jumped to the metal lath. All of the plaster looked like somebody went crazy with a ( expletive ) thompson submachine gun. Hence, nobody uses metal lath anymore except to plaster curves and arches.

Mike Cole

 

[iwire]

Dave,

I don't think it is prudent to always consider a generator located outdoors as a separate structure. Do you consider air-conditioning condensing units as separate structures? A structure is "that which is built" - built by whom?

There is no doubt in my mind at all the NEC considers simple light and sign poles as 'structures' (Check the exceptions 3 and 4 of 225.32 that allow the required disconnecting means for separate structures to be located remotely for these poles)

If a simple pole is a structure than IMO a generator or HVAC units are also structures.

Not saying it makes sense just that is how the code is written.

 

[tom baker]

Some of our confusion is due to the fact that the NEC defintion of structure is anything that is built or constructed. A luminare pole meets the definition of structure.

 

[tonyi]

State of FL job specs were demanding generators for toll booths on the FL Turnpike be hooked up as you described and NOT treated as SDS. Seemed retarded to me, but it was their job and they were their own AHJ, so they got what they wanted...

 

[RB1]

Bob,

Do you require a grounding electrode at the air-conditioning equipment? Is your air conditioner's disconnecting means marked "suitable for use as service equipment"? Is your disconnecting means mounted on the building or the equipment, or do you need a disconnecting means at both?

 

[George Stolz]

I'm confused. David, are you saying that these generators have panelboards on them?

FWIW, I fail to see the value of a ground rod driven at a generator, in any case.

 

[dnem]

I'm confused. David, are you saying that these generators have panelboards on them?

FWIW, I fail to see the value of a ground rod driven at a generator, in any case.

Every generator that I?ve ever seen has had a breaker built into it, but I can?t see that the presence of a panelboard or lack thereof makes any difference. . As far as a debate on the value of a ground rod at the generator, I imagine that pros and cons could be cited but right here I?m just focusing on what is required by code.

The requirement for a ground rod [or other electrode] in 250.50 is based on the words ?structure served?. . That pedestals and free standing outside generators are ?structures? can be questioned but that wouldn?t address why my department requires the ground on separately derived generators but not ?subpanel? wired generators. . Ground rod required on both or ground rod required on neither, but why yes on one and no on the other ? . If a separately derived generator is a structure then a subpanel wired generator is also a structure. . The definition of a structure isn?t dependent on the wiring method.

The word ?served? does refer to the electrical system of the structure. . A service is a electric utility supply but ?served? can also apply to the equivalent of a service [250.24(A)(5)FPN], transformer or generator [250.30(A)(1)] or separate building or structure [250.32(B)(2)]. . A pedestal with service equipment would qualify as a ?structure served? and a separately derived generator [neutral switched transfer switch generator] would qualify as a ?structure served? and a separate building with a main panel would qualify as a ?structure served?.

But how are an AC unit, pool equipment on a pedestal, a subpanel generator [neutral not switched transfer switch generator], and a separate building with a subpanel [250.32(B)(1)] different from each other ? . If the AC unit, the pedestal pool equipment, and the subpanel generator are all not a ?structure served? because the supply is only a feeder or branch circuit and not a service or service equivalent, then why does a subpanel separate building [250.32(B)(1)] need a ground rod ? . It isn?t any different. . It isn?t a ?structure served?. . It only has a feeder or branch circuit and not a service or service equivalent.

Am I missing something here or do I have a valid question ?

David

 

[don_resqcapt19]

David,

A pedestal with service equipment would qualify as a “structure served” and a separately derived generator [neutral switched transfer switch generator] would qualify as a “structure served” and a separate building with a main panel would qualify as a “structure served”.

In my opinion only the last item is a "structure served". There is no power uses at the service equipment pedestal and the generator is not served by a circuit from the first building...it supplies a circuit to the first building.

(A) Grounding Electrode Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with 250.50.

Don

 

[George Stolz]

Every generator that I?ve ever seen has had a breaker built into it, but I can?t see that the presence of a panelboard or lack thereof makes any difference.

I'm sorry, I was just confused by the term "subpanel generator". I was trying to get the significance of it.

The requirement for a ground rod [or other electrode] in 250.50 is based on the words ?structure served?.

I wonder if 250.50 is the true cause of what you're experiencing. I'd tend to believe that 250.30(A)(7), exception 1 is what's causing a ground rod to be installed at the doghouse.

Correct me if I'm mistaken, but is there any indication they wrote this with the prospect in mind that the SDS could be at a detached structure with no grounding electrodes present? It seems to be they expect the SDS to reside in the same structure, with the same electrodes as the source system.

Interesting twist on the "served" language, guys. That makes a lot of sense!

 

[dnem]

In my opinion only the last item is a "structure served". There is no power uses at the service equipment pedestal and the generator is not served by a circuit from the first building...it supplies a circuit to the first building.

OK, so let’s go with the definition of “served” as being
service or equivalent of a service [250.24(A)(5)FPN] plus usage at the structure itself.

So if we compare the following "structures" according to that definition:
Free standing outside “subpanel” wired generator [neutral not switched transfer switch generator]
Free standing outside separately derived generator [neutral switched transfer switch generator, 250.30(A)(1)]
A “main” panel wired building or structure supplied from another building or structure [250.32(B)(2)]
A subpanel wired building or structure supplied from another building or structure [250.32(B)(1)]
A pedestal with service equipment
A pedestal with pool equipment
An AC condensing unit

“Structure Served”, interpreted as both service or equivalent and usage
subpanel generator = . . . . . no equivalent, no usage, so no “structure served”
separately derived generator = . . . . . yes equivalent, no usage, so no “structure served”
main panel second building = . . . . . yes equivalent, yes usage, so yes “structure served”
subpanel second building = . . . . . no equivalent, yes usage, so no “structure served”
pedestal service = . . . . . yes service, no usage, so no “structure served”
pedestal pool equipment = . . . . . no equivalent, yes usage, so no “structure served”
AC condenser = . . . . . no equivalent, yes usage, so no “structure served”

So according to this logic, the only one that would need a ground rod would be “main” panel second building [250.32(B)(2)]. . A subpanel second building [250.32(B)(2)] would not require a ground rod.

Don, do you feel comfortable with these answers based on adding a usage specification ? . Do you think requiring a ground rod for a main panel wired second building but not for a subpanel wired second building is a good answer ?

My department ground rod requirement interpretations
subpanel generator = . . . . . no ground rod
separately derived generator = . . . . . yes ground rod
main panel second building = . . . . . yes ground rod
subpanel second building = . . . . . yes ground rod
pedestal service = . . . . . yes ground rod
pedestal pool equipment = . . . . . no ground rod
AC condenser = . . . . . no ground rod

I’m turning up alot more yes answers including both options for a second building [250.32(B)(1)&(2)].

I’m still not seeing a good answer to this situation.

David

 

[dnem]

Update

?Structure Served?, interpreted as both service or equivalent and usage
subpanel generator = . . . . . no equivalent, no usage, so no ?structure served?
separately derived generator = . . . . . yes equivalent, no usage, so no ?structure served?
main panel second building = . . . . . yes equivalent, yes usage, so yes ?structure served?
subpanel second building = . . . . . no equivalent, yes usage, so no ?structure served?
pedestal service = . . . . . yes service, no usage, so no ?structure served?
pedestal pool equipment = . . . . . no equivalent, yes usage, so no ?structure served?
AC condenser = . . . . . no equivalent, yes usage, so no ?structure served?

So according to this logic, the only one that would need a ground rod would be ?main? panel second building [250.32(B)(2)]. . A subpanel second building [250.32(B)(2)] would not require a ground rod.

Don, do you feel comfortable with these answers based on adding a usage specification ? . Do you think requiring a ground rod for a main panel wired second building but not for a subpanel wired second building is a good answer ?

I took a fresh look at it this morning and realized that I missed 250.32(A). . So the change would make it.

?Structure Served?, interpreted as both service or equivalent and usage
subpanel generator = . . . . . no equivalent, no usage, so no ?structure served?, no ground rod requirement
separately derived generator = . . . . . yes equivalent, no usage, so no ?structure served?, no ground rod requirement
main panel second building = . . . . . yes equivalent, yes usage, so yes ?structure served?, yes ground rod required
subpanel second building = . . . . . no equivalent, yes usage, so no ?structure served?, but still yes ground rod required by 250.32(A)
pedestal service = . . . . . yes service, no usage, so no ?structure served?, no ground rod requirement
pedestal pool equipment = . . . . . no equivalent, yes usage, so no ?structure served?, no ground rod requirement
AC condenser = . . . . . no equivalent, yes usage, so no ?structure served?, no ground rod requirement

My department ground rod requirement interpretations
subpanel generator = . . . . . no ground rod
separately derived generator = . . . . . yes ground rod
main panel second building = . . . . . yes ground rod
subpanel second building = . . . . . yes ground rod
pedestal service = . . . . . yes ground rod
pedestal pool equipment = . . . . . no ground rod
AC condenser = . . . . . no ground rod

So the only ones that don't seem to fit Dons interpretation of "structure served" are the free standing outside separately derived generator and the pedestal service.

So it comes back to the question of whether or not a usage specification should be added to the interpretation or not.

David

 

[iwire]

Bob,

Do you require a grounding electrode at the air-conditioning equipment?

First off I am not an inspector.

But no, I do not normally install electrodes at HVAC equipment.

IMO an inspector would be well within the code to require me to assuming it was supplied with a feeder or more than one branch circuit.

Is your air conditioner's disconnecting means marked "suitable for use as service equipment"?

As a matter of fact yes they are, I do commercial and the typical fused disconnect we use is suitable for service equipment.

This is just a coincidence, it is not that I ask specifically for service rated disconnects.

Is your disconnecting means mounted on the building or the equipment, or do you need a disconnecting means at both?

If you talking about equipment located directly beside the building either location is acceptable.

225.32 Location.
The disconnecting means shall be installed either inside or outside of the building or structure served or where the conductors pass through the building or structure. The disconnecting means shall be at a readily accessible location nearest the point of entrance of the conductors. For the purposes of this section, the requirements in 230.6 shall be permitted to be utilized.

If I bring a feeder to a building or structure I am not required to mount the disconnect to the building or structure.

Well... depending on the AHJs interpretation of nearest the point of entrance of the conductors is.

IMO given the fact that if the NEC provides a definition of a term that is the definition we must work with and the definition of 'structure' is so broad that virtually anything that is not a product of nature is a structure a HVAC unit is a structure.

We don't have to like it or agree with it but we are supposed to follow it.

 

[iwire]

pedestal pool equipment = . . . . . no equivalent, yes usage, so no ?structure served?, no ground rod requirement
AC condenser = . . . . . no equivalent, yes usage, so no ?structure served?, no ground rod requirement

Dave as I said I do not as a rule install electrodes at HVAC units.

That said I don't see how we can say an AC Condenser is not a structure and it is not served with electricity.

If the HVAC unit is supplied by a feeder or more than one branch circuit than you could require an electrode.

Same with the pool pedastal.

 

[don_resqcapt19]

David,

So it comes back to the question of whether or not a usage specification should be added to the interpretation or not.

I don't know how you can serve a structure with electricity unless that structure uses electricity.
Don

 

[RUWired]

David, Attached are two drawings i made for my reference on a job that is coming up. Would you agree with them?
Rick

 

[dnem]

David, Attached are two drawings i made for my reference on a job that is coming up. Would you agree with them?
Rick

Your drawings look great but the second one shows a ground rod on the "subpanel" [nonseperately derived] wired generator. . Whether or not that would be necessary is what is being discussed here and not answered definitively yet.

David

 

[dnem]

Dave as I said I do not as a rule install electrodes at HVAC units.

That said I don't see how we can say an AC Condenser is not a structure and it is not served with electricity.

If the HVAC unit is supplied by a feeder or more than one branch circuit than you could require an electrode.

Same with the pool pedastal.

According to that view of the word "structure", 250.32(A) says we need to start installing ground rods everywhere.

"Bar tender ! . Set up everyone on the whole web site with ground rods for all their pool, AC pedestal feeders, and every single light pole they've ever installed where they skipped the ground rod because it wasn't speced on the prints !"

I think we need to back off from that interpretation of the word "structure". . I don't think the Article 100 definition of "structure" is enforcable.

Just as the word "accessible" has different meanings depending on whether your talking about equipment or wiring methods. . I think the word "structure" has to have different definition when it's used in 250.32(A). . The alternative is to enforce it as written which doesn't make any sense at all.

David