4.2 Service Disconnecting Means

Why the Service Disconnect Appears on the Exam

The service disconnecting means is the single most-tested device in Area 2. The Knowledge part will quiz the six-disconnect rule, the minimum rating, the location requirement, and the marking of service equipment. The Calculations part occasionally tests the rating of the disconnect as the result of a service-load computation. Mastering 230.70 through 230.79 is mandatory.

Article 230 Part VI — Service Disconnecting Means

230.71 — Maximum Number of Disconnects (the Six-Handle Rule)

Each service is permitted a maximum of six service disconnecting means per 230.71(A). These six can be in:

1. A single enclosure (e.g., a six-position main lug load center with no main breaker), or
2. A group of separate enclosures grouped at one location.

Each disconnect must be capable of being opened independently. The rule is also called the "six movements of the hand" rule — it must take no more than six hand operations to disconnect all service conductors.

Key exception (230.71(A) Exception): A single disconnect with multiple handles (e.g., a 2-pole main breaker) counts as one disconnecting means, not two.

230.72 — Grouping of Disconnects

230.72(A) requires the two to six disconnects to be grouped in the same location. The only exceptions are:

• A separate disconnect for a fire pump (must be located to minimize fire hazard, per 695.5).
• A separate disconnect for an emergency system or standby generator (700.x, 702.x).
• Multiple-occupancy buildings where each occupant has access to their own service disconnect.

230.79 — Rating of Service Disconnect

The minimum rating depends on the occupancy type:

The 100-amp dwelling minimum in 230.79(C) is the most-tested value. Note that 230.79(D) for other installations sets a 60-amp floor, but the actual rating must always carry the calculated load.

230.70 — Location and Accessibility

230.70(A)(1): The service disconnect must be readily accessible — defined in Article 100 as capable of being reached quickly without obstacles, climbing, or portable ladders.

230.70(A)(2): It must be located outside the building or structure, or nearest the point of entrance of the service conductors if inside. This "outside or nearest the point of entry" rule prevents long unprotected runs of service-entrance conductors inside a building. Inside conductors are limited by 230.6 and 230.7 to essentially the minimum practical run.

230.70(B): Each disconnect must be legibly marked with a purpose (e.g., "Main," "Service Disconnect," or "House Panel — Service Entrance"). The marking must be sufficient to identify the disconnect from its purpose and location, and must be on the front of the enclosure or on the inside door.

230.66 — Service Equipment Short-Circuit Current Rating

230.66 requires all service equipment to be marked with its short-circuit current rating (SCCR), and the rating must be equal to or greater than the available fault current at the line terminals of the equipment. Available fault current is determined by the utility transformer impedance, conductor length, and conductor size (Annex D calculation or engineering analysis).

Worked Example

A single-family dwelling has a calculated service load of 92 amperes. What is the minimum service disconnect rating, and what size copper service-entrance conductor (75 °C column) is required?

1. Minimum disconnect rating: Per 230.79(C), a one-family dwelling requires a minimum 100 A disconnect. The calculated load of 92 A is below 100 A, but the 100 A floor governs.
2. Standard service size: Round up to the next standard rating (100 A).
3. Conductor ampacity (230.42): Must equal or exceed the disconnect rating. 100 A → Table 310.16, 75 °C column, copper:
   • 3 AWG Cu = 100 A — acceptable (equal to rating).

Result: 100 A service disconnect, 3 AWG copper THWN-2 service-entrance conductors in a raceway.

If the same dwelling had a 135 A calculated load:

1. Disconnect rating = 150 A (next standard size above 135 A).
2. Conductor = 1/0 AWG Cu (150 A at 75 °C).

Common Exam Pitfalls

• Counting handles: A 2-pole breaker counts as ONE disconnect, not two.
• "Six enclosures": The rule is six DISCONNECTS, not six enclosures. One enclosure can hold six disconnects, or six enclosures can hold one each.
• Interior location: "Nearest the point of entry" does NOT mean anywhere inside; the conductors must take the shortest practical route.
• Mobile home panel: A mobile home's panel inside the unit is NOT the service disconnect — the service disconnect for a mobile home park pedestal is outside per 550.23.