Can two buildings share a service disconnect?

[tortuga]

On the general question as posed in the OP, 2023 NEC 230.70(A)(1) says that for a building supplied by a service, "The service disconnecting means shall be installed at a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the service conductors." This phrasing applies the "nearest the point of entrance" requirement only when the disconnecting means is inside.

In contrast, 2023 NEC 225.31(B) says that for a building supplied by a feeder the disconnecting means "shall be installed either inside or outside of the building" and "the disconnecting means shall be at a readily accessible location nearest the point of entrance of the conductors." The "nearest the point of entrance" requirement applies even to an outside disconnect. Apparently you can't put your disconnect on the outside of the building and then run the feeder conductors 100 ft along the outside of the building before they enter the building.

So if you put your service disconnect on a post 3 ft away from the building, does that satisfy 230.70(A)(1)? Seems like it does. Then if you have 2 buildings 6 feet apart, with a single service disconnect on a post that is 3 ft away from each building, does that satisfy 230.70(A)(1) for each building? Seems like it does.

To make the last question interesting, let's assume the feeder conductors run from the single service OCPD to each building run to panels within each building that are far enough inside that they are not "nearest the point of entrance" of the conductors. Either because the feeder conductors are full sized (not a tap), or because using the 25' tap rule we can get far enough into the building.

Cheers, Wayne

Yeah its a interesting slight difference in wording, the thing is as soon as you create an outdoor feeder you bring in the requirements of article 225, so 225.31 and 225.39 etc.

 

[wwhitney]

the thing is as soon as you create an outdoor feeder you bring in the requirements of article 225, so 225.31 and 225.39 etc.

Article 225 Part II only applies if the building is "supplied by" a feeder or branch circuit. I think most would interpret that if the service disconnect is on a post 3' away from the building, the building is "supplied by" a service. How far away the service disconnect needs to be before that changes to "supplied by" a feeder is undefined.

Cheers, Wayne

 

[tortuga]

Article 225 Part II only applies if the building is "supplied by" a feeder or branch circuit. I think most would interpret that if the service disconnect is on a post 3' away from the building, the building is "supplied by" a service. How far away the service disconnect needs to be before that changes to "supplied by" a feeder is undefined.

Cheers, Wayne

Here the convention is if your service equipment is on a different structure all circuit conductors after the service equipment (per article 100 definition) are feeders.

 

[wwhitney]

Here the convention is if your service equipment is on a different structure all circuit conductors after the service equipment (per article 100 definition) are feeders.

That is certainly defensible, since you have to draw the line somewhere. But the boundaries are still a bit fuzzy--if I run a single wood strut from the building to my post 3' away, is it now the same structure? Should the presence of such a strut really make a difference? So I think a bit more flexibility in distinguishing between building supplied by a feeder vs supplied by a service is reasonable.

Cheers, Wayne

 

[jaggedben]

...

In contrast, 2023 NEC 225.31(B) says that for a building supplied by a feeder the disconnecting means "shall be installed either inside or outside of the building" and "the disconnecting means shall be at a readily accessible location nearest the point of entrance of the conductors." The "nearest the point of entrance" requirement applies even to an outside disconnect. ...

I would never interpret it that way in the field and I doubt I'll run into an AHJ that does either. (I frequently run into recently inspected installations where the requirement for a main disconnect at the separate structure was missed entirely, so you're raising the bar well above where it already is in practice. ) Clearly the language in 225 was copied and pasted from 230 with the intent that the requirement be the same as applied to the *supply* conductors. And it was overlooked that in 230 the language implicitly does not apply to the load side because they become a feeder, while in 225 it could because they are still the feeder. Just another small thing we can nitpick on this forum but isn't worth the time to add words to the code to clarify, IMO. Also pretty irrelevant to the OP's question.

 

[tortuga]

Yeah if you look at the definitions of feeder and service equipment I dont think its even fuzzy that 225 applies.
Of relevance to the OP is if you omit your 400A disco and just have a meter CT can with doubble lugs and then you all would need is the service disconnects at buildings 1 and 2. Presuming the utility would allow that.

 

[wwhitney]

Yeah if you look at the definitions of feeder and service equipment I dont think its even fuzzy that 225 applies.

Depends on whether the service equipment on a post is a separate structure. If it is, I agree 225 applies for the conductors from the post to the building.

But you could either argue that (a) the equipment on the post is not a structure, as the post itself is also equipment or (b) at 3' away, it's the same structure for all practical purposes.

Now, change the post to a detached garage, and I'd probably be inclined to agree with you, even if it is only 3' away

Cheers, Wayne

 

[jaggedben]

Depends on whether the service equipment on a post is a separate structure. If it is, I agree 225 applies for the conductors from the post to the building.

But you could either argue that (a) the equipment on the post is not a structure, as the post itself is also equipment or (b) at 3' away, it's the same structure for all practical purposes.

Now, change the post to a detached garage, and I'd probably be inclined to agree with you, even if it is only 3' away

FWIW, 225 Part II is simply titled "Buildings of Other Structures Supplied by a Feeder(s) or Branch Circuit(s)." Doesn't use the word 'separate'; i.e. doesn’t imply anything about whether the service is on its own structure or not.

Seems like much more of a stretch to make the definition of 'Equipment' cover a post than it does for the definition of 'Structure'.

Requiring the disconnect to be 'outside on or within sight' instead of merely 'outside' would be a concise way to clarify limitations on disconnects not being on the building itself.

 

[wwhitney]

FWIW, 225 Part II is simply titled "Buildings of Other Structures Supplied by a Feeder(s) or Branch Circuit(s)." Doesn't use the word 'separate'; i.e. doesn’t imply anything about whether the service is on its own structure or not.

I guess you are right, that if the service equipment on the post is not a structure at all, then the structure is being supplied by a feeder, not a service. To say Article 225 doesn't apply, you need to say the structure is fed by a service, which means you need to say the post is part of the structure. Which still often seems plausible to me when the post is 3' away.

Cheers, Wayne