SFB-3 — Service Equipment and Disconnecting Means

Exam checkpoints

Locate the service boundary first

Article 100 defines service equipment as the necessary equipment, usually a circuit breaker or switch and fuses with their accessories, connected to the load end of service conductors and intended to constitute the main control and cutoff of the supply. The definition depends on function and location, not a casual label. A downstream panel with a “main” breaker is feeder-supplied equipment when service overcurrent protection is upstream.

The service disconnecting means disconnects the premises wiring from the service conductors. On the line side are service conductors and only the equipment permitted there; on the load side begins a feeder or, in some arrangements, branch circuits. This boundary affects neutral bonding, overcurrent protection, conductor names, and which equipment must be suitable for use as service equipment.

Under 230.66, service equipment rated 1,000 V or less must be listed and marked as suitable for use as service equipment. That suitability includes service-duty construction and bonding provisions. A panelboard listed only for use as service equipment when protected by a main device cannot be used as service equipment without satisfying that condition. Follow the listing and labeling instructions under 110.3(B).

Place the service disconnect correctly

Section 230.70(A)(1) requires the service disconnecting means to be readily accessible and located either outside the building or structure or inside nearest the point of entrance of the service conductors. The NEC does not publish one universal number of indoor feet that always qualifies as “nearest.” Routing, construction, protection, and the AHJ's application matter. Section 230.6 can treat conductors as outside the building when installed under specified conditions, which can change where the entrance point is evaluated.

Section 230.70(A)(2) prohibits installing service disconnects in bathrooms. Under 230.70(B), each service disconnect must be permanently marked to identify it as a service disconnect. Article 100 readily accessible criteria also apply: the disconnect must be reachable quickly without tools, climbing over or removing obstacles, or using a portable ladder. A locked electrical room can still be accessible to qualified persons under 110.26(F), but storage blocking the equipment is not cured by the lock.

Apply the 2017 six-disconnect rule

Under 2017 NEC 230.71(A), the service disconnecting means for each service permitted by 230.2, or for each permitted set of service-entrance conductors, may consist of not more than six switches or six circuit breakers. They may be mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. Later NEC editions changed service-equipment arrangements, so do not import a later rule into this 2017-reference exam.

Count disconnecting means, not branch-circuit poles. A common-trip two-pole breaker that simultaneously opens both ungrounded conductors is one disconnecting means. Six individual service disconnects do not permit a seventh because it serves a small load.

Section 230.72 requires the service disconnects for each service to be grouped and marked to indicate the load served. Permitted exceptions for fire pumps, emergency systems, legally required standby systems, and similar supplies must be evaluated from their own rules; they do not create a general permission to scatter ordinary service disconnects.

Example: assume one permitted set of service-entrance conductors supplies four service-rated circuit breakers in one enclosure and two service-rated fused switches immediately adjacent and grouped with them. The count is six and can fit 230.71(A), but the installation still must meet grouping, accessibility, rating, bonding, fault-current, and load requirements. Adding a seventh ordinary disconnect is not allowed by the 2017 six-disconnect rule.

Rate and operate the disconnects

Under 230.74, the service disconnect must simultaneously disconnect all ungrounded service conductors it controls. It must indicate whether it is open or closed under 230.77 and be manually or power operable under 230.76. Where the service disconnect does not disconnect the grounded conductor from the premises wiring, 230.75 requires another means in the service equipment for that purpose, such as the permitted terminal or bus arrangement.

Section 230.79 provides minimum service-disconnect ratings. For a one-family dwelling, the service disconnect must be at least 100 A, 3-wire. For other installations, the subsection matching the number and type of circuits applies; “60 A for every service” is not a safe shortcut. Where multiple service disconnects are used, their combined ratings must comply with 230.80 and be sufficient for the calculated load.

Coordinate service overcurrent protection

Section 230.90(A) generally requires each ungrounded service conductor to have overload protection. Under 230.91, the service overcurrent device must be integral with or immediately adjacent to the service disconnect. These provisions coordinate control and protection but do not make the disconnect and overcurrent device the same component in every installation.

The service protective device needs an interrupting rating sufficient for available fault current under 110.9, and assemblies need adequate short-circuit current ratings under 110.10. A correct normal ampere rating does not compensate for an inadequate fault rating. Solidly grounded wye services within the voltage and ampere conditions of 230.95 can require ground-fault protection of equipment; its exceptions must be checked rather than assumed.

Only equipment listed in 230.82 may be connected on the supply side of the service disconnect. Meter equipment, surge protection, fire-pump equipment, or control-power devices are not permission for an arbitrary load-side bypass. Finally, service grounding and the main bonding jumper are addressed by Article 250. At downstream feeder equipment, the grounded conductor is normally isolated from equipment grounding conductors; calling every disconnect a “main” does not authorize rebonding the neutral.