Thread: Seperate service to outbuilding serves circuits in main building with own service ...

New to me:

Apartment building has service, with load-side panels for each apartment.

Detached garage has separate service (different service drop from the same pole).

Per owner, common area circuits in apartment building are served by power from garage (!).

Can you do this?

If so, does it require a load side panel or other disconnect means in the main structure?

I understand the rules for a circuit from the service at a dwelling to a garage.

And I think I understand the rules for multiple services to a single structure.

But circuits from a building with one service to a building with another service?

For starters, how do you deal with the difference in ground potential?

Oh, and to make things even more fun: panel in the garage was obstructed, and I could not access, and I could not verify grounding method at either service.

I know the advice that’s coming: defer to an electrician…

But inquiring minds want to know….

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From the 2008 NEC (with no changes from the 2005 NEC). (underlining and bold are mine)
- 230.2 Number of Services.
- - A building or other structure served shall be supplied by only one service unless permitted in 230.2(A) through (D). For the purpose of 230.40, Exception No. 2 only, underground sets of conductors, 1/0 AWG and larger, running to the same location and connected together at their supply end but not connected together at their load end shall be considered to be supplying one service. (Jerry's note: This last sentence does not apply, so it can be ignored.)
- - - (A) Special Conditions. Additional services shall be permitted to supply the following: (Jerry's note: None of the following 6 Special Conditions apply.)
- - - - (1) Fire pumps
- - - - (2) Emergency systems
- - - - (3) Legally required standby systems
- - - - (4) Optional standby systems
- - - - (5) Parallel power production systems
- - - - (6) Systems designed for connection to multiple sources of supply for the purpose of enhanced reliability
- - - (B) Special Occupancies. By special permission, additional services shall be permitted for either of the following: (Jerry's note: None of the following 2 Special Occupancies apply.)
- - - - (1) Multiple-occupancy buildings where there is no available space for service equipment accessible to all occupants
- - - - (2) A single building or other structure sufficiently large to make two or more services necessary
- - - (C) Capacity Requirements. Additional services shall be permitted under any of the following: (Jerry's note: See (3), even though there is no "capacity requirement" or need, it does say "By special permission", and the AHJ 'can give' that 'special permission' even though this is for "capacity requirements".)
- - - - (1) Where the capacity requirements are in excess of 2000 amperes at a supply voltage of 600 volts or less
- - - - (2) Where the load requirements of a single-phase installation are greater than the serving agency normally supplies through one service
- - - - (3) By special permission
- - - (D) Different Characteristics. Additional services shall be permitted for different voltages, frequencies, or phases, or for different uses, such as for different rate schedules. (Jerry's note: This does not apply.)
- - - (E) Identification. Where a building or structure is supplied by more than one service, or any combination of branch circuits, feeders, and services, a permanent plaque or directory shall be installed at each service disconnect location denoting all other services, feeders, and branch circuits supplying that building or structure and the area served by each. See 225.37.

Regardless, those would be two (or more) services for one building or structure, not 'just running some circuits from one building to another'.

If not done "(3) By special permission ", then it is not allowed, and, if done "(3) By special permission ", even though for a different reason than allowed for by special permission, the AHJ may have (not likely though) allowed this "intentionally". I say "intentionally" because the AHJ probably did a plan review and 'just missed it', approving it "unintentionally", or, maybe it was changed from what was approved.

Either way, yeah, get a licensed electrical contractor to 'recommend appropriate repairs' and then consult with the local AHJ asking them about this ... they might 'just not know about it' and they could cause that condition to be corrected or they could accept it as it was built, either way makes it legal (correct or not) for the buyer and their in$urance company.

Thanks as always for your quick reply.

Great post Jerry. Long time no see.