How many service entrance conductor sets can you have? The short answer is that, normally, only one set can be supplied by each service drop (or set of overhead service conductors, set of underground service conductors, or service lateral) [230.40].
However, there are five exceptions to this rule. Do you know what they are?
The five exceptions are:
- The building has more than one occupancy, and the installation meets specific (and confusing) requirements.
- Where two to six service disconnects in separate enclosures are grouped at one location and supply separate loads from one service drop.
- A single-family dwelling unit with accessory structures (e.g., detached garage).
- Two-family dwelling units, multifamily dwellings, and multiple occupancy buildings.
- Systems covered by 230.82(5) and 230.82(6). These include fire pumps, standby power systems, and photovoltaic systems.
The exceptions lack clarity, so get a ruling from the AHJ before finalizing your design. For example, how does a multiple occupancy building (Exception No. 3) differ from a building that has more than one occupancy (Exception No. 1)? Exception No. 3 doesn’t have the same long passage of italicized requirements as Exception No. 1.
The NEC has been moving away from such negative framing of requirements (e.g., Exceptions) toward more comprehensible positive framing. The first of the five Exceptions to 230.40 is a good example of why the NEC should continue in this direction.
