There are some issues involving installations in the National Electrical Code (NEC) that regularly generate considerable misunderstanding for installers, inspectors and engineers; recently, I was giving a workshop on the changes in the 2005 NEC, and as I was covering the change in Section 230.40, Exception No. 1, an attendee stated that a service drop or lateral could only supply one set of service-entrance conductors. He stated, furthermore, that the service could only have a maximum of six service disconnects, and all of these service disconnects must be grouped in one location. He now has a better understanding of the intricacies of the NEC on this issue, but I thought this subject was interesting enough to warrant another article and further explanation.
Before the number of service-entrance conductor sets and the number of installable service disconnects, a designer, plans reviewer or inspector must first determine the layout of the structure or building and whether there are any structural fire walls within the building. The source of this information is whatever building code is being enforced in that particular area. For example, a building with a four-hour fire wall built into the structure could be considered two separate buildings with a service for each building. It is interesting to note that each building can normally be supplied by only one service. However, Sections 230.2(A) through (D) permit the installation of additional services under certain conditions.
Section 230.40 states that each service drop or service lateral shall supply only one set of service-entrance conductors. However, a single service drop or lateral could supply more than one service on a single building where permission for multiple services are given in Section 230.2(A) through (D). Based on Section 230.71(A), each service is permitted to have up to six service-disconnecting means. For example, if three services are installed on a building, each service could have up to six disconnecting means for a total of 18 disconnects. If each service is supplied by the one set of service-entrance conductors, all 18 of these service disconnects could be at one location. Remember, Section 230.71(A) permits up to six service-disconnecting means for each service. It further states there shall be not more than six sets of disconnecting means per service grouped in any one location. Each service could be supplying power for a single occupant or for multiple occupants, but remember, permission for multiple services must be granted by one of the conditions provided in 230.2(A) through (D).
Now, let’s look at a situation where a building has multiple occupants. Based on 230.2(B), each occupant would be permitted to have their own service—if special permission is granted by written consent of the authority having jurisdiction (AHJ)—where there is no available space for the service equipment to be accessible to all occupants. Section 230.40, Exception No. 1, would also permit one service to be installed with a set of service-entrance conductors run to each occupancy or group of occupancies. Multiple meters could be installed at the service drop or lateral location with the service-entrance conductors run on the outside of the building and supplying each different occupant. Now the number of service-disconnecting means for this installation becomes an issue. If the disconnects are mounted on the outside of the building, then Section 230.72 requires the two to six disconnects permitted in 230.71 to be grouped in one location.
Where the service-entrance conductors enter into each occupancy before terminating at the service-disconnecting means, then Section 230.71(A) permits the service-disconnecting means for each set of service-entrance conductors permitted by 230.40, Exception No. 1, to consist of not more than six switches or sets of circuit breakers. Section 230.72 would then require each of these six sets of service-disconnecting means to be grouped at one location within that occupancy.
This particular exception has been in the NEC since at least the 1946 NEC. Section 1807 of the 1946 NEC permitted, by special permission, more than one set of service-drop conductors in a multi-occupancy building where there was no available space for service equipment accessible to all occupants. This exception permitted the occupant to have access to their own service-disconnecting means. However, any multiple-occupancy building that did not have an individual occupancy above the second floor could have the service-entrance conductors run to each occupancy and have up to six switches or circuit breakers at that location.
Permission for installations for service-entrance conductors to each occupant is a long-standing rule, but check with the utility company and the local AHJ before designing and installing a service under these conditions.