A long-standing requirement in the National Electrical Code (NEC) is to provide a service disconnecting means for each building or structure served by electricity. The concept is simple; the disconnecting means serves as a ready means for the occupant or other responder to remove all power from the building by operating the service disconnect. This article takes a closer look at the general requirements for service disconnects and the reasons behind the rules.
The rules for service disconnects are in Part VI of NEC Article 230. Three sections of Article 230 address the requirements for service disconnects. The first requirement is in 230.70 and indicates that a disconnecting means shall be provided to disconnect the building or structure from the service conductors, a term defined in Article 100. The location of the disconnecting means is addressed in 230.70(A), which requires it to be readily accessible (another defined term) and located either outside the building or inside at the nearest point where the service conductors enter the building. The reason is to limit the length of service conductors routed within a building because they have no overcurrent protection other than what the serving utility is providing.
The Code specifies no distance in this requirement because each service has different installation characteristics. For example, what could be accomplished relative to locating an indoor service disconnect for a 100-ampere (A) residential service is far different than what could be accomplished for a 3,000A service disconnect in a commercial building.
Section 230.70(B) also requires each service disconnecting means to be permanently marked to identify it as a service disconnect. This marking is field-applied and exists to readily direct the operators to the right switch or circuit breaker.
Product safety standards for service equipment also apply here. A disconnecting means used as a service disconnect is required to be listed as such. It will bear the marking “Suitable for Use as Service Equipment” or “Suitable for Use Only as Service Equipment.” Listed service equipment has to meet requirements such as short-circuit current rating marks, grounding and bonding provisions, and be constructed with a single main switch or circuit breaker or up to six disconnects installed in a single enclosure.
More than one disconnect
While 230.70(A) requires a service disconnecting means, the term “disconnecting means” is defined in Article 100 and addresses not only a single means, but also multiple means that serve together in a group arrangement as the building service disconnect. The long-standing NEC requirement places a limit on the quantity of disconnects permitted to serve as the required service disconnecting means; Section 230.71(A) clarifies that this quantity is not more than six switches or circuit breakers or any combination not exceeding six. The idea is not to have more than six motions of the hand or actions to remove all power from the building or structure being served. The service disconnecting means arrangement can be a single switch or circuit breaker. It can be up to six switches or circuit breakers in a single enclosure or up to six switches or circuit breakers in separate enclosures. Again, each of the service disconnects must be marked to identify it as such.
Grouping service disconnects
This is a gray area in the Code, but the objectives should be easy to achieve by applying common sense and a practical approach to the requirement. The Code falls short of specifying a distance in the grouping requirement because of the differences in physical characteristics between large and small service equipment. Ideally, each building should have a main or single means of disconnect. One action or hand motion should remove all the power in the building. Section 230.72(A) of the Code addresses the grouping requirements quite specifically and simply. The general rules are that the two to six service disconnects permitted in 230.71 must be grouped in the same location, either in a single enclosure or in separate enclosures located adjacent to each other. Obviously, the larger the service, the wider the grouping distance can become. This is where the service disconnect marking comes into play and is why it is so important. Where the service disconnecting means is provided in a multiple-occupancy building, generally, each of the building occupants must have access to their respective service disconnect.
Another important provision in the Code is to mark the service equipment to indicate if there is emergency power source, legally required standby power source, or optional standby power source and the location of such sources. This alerts occupants and responders that, while normal power is disconnected, the backup power system is functioning. See sections 700.8(A), 701.7(A) and 702.7(A)
Each building or structure must be provided with a service disconnecting means. It can be a single switch or circuit breaker or up to six in a single enclosure or in separate enclosures grouped in the same location. The service disconnect(s) must be marked as a service disconnect.