The What and Where of Service Point Locations

The What and Where of Service Point Locations

Different interpretations of the Code have led to confusion when determining the service point for a premises. Clearing up some definitions is the first step to mastering this complicated issue.

Ever since the National Electrical Code (NEC) introduced the phrase "service point locations" in 1993, varying interpretations of this phrase have left the industry perplexed. Acquiring a clear interpretation of certain definitions in Art. 100 is the first step toward understanding the procedure for determining the service point for a facility. Applying such definitions to the supply and load side of the service equipment and premises wiring system is next. Let's look at some of the most important definitions pertaining to the classification of the service point for a facility.

Premises wiring. A premise wiring system covers interior and exterior wiring that extends from the service point (of utility conductors) or source of power (e.g., battery) to the outlet(s). Understand that the Code defines an outlet as a point on the wiring system where current supplies equipment - an outlet isn't necessarily a receptacle. This wiring includes power, lighting, control and signal circuits along with their hardware, fittings, and wiring devices. Such wiring does not include wiring internal to appliances, fixtures, motors, controllers, motor control centers, and similar equipment.

In 1999, the NEC revised this definition by removing the term separately derived system and expanding the definition. The updated definition includes sources of power such as batteries, solar photovoltaic systems, generators, transformers, and converter windings.

Service equipment. This is the necessary equipment connected to the load end of the service conductors, which serve a building, other structure, or an otherwise designated area. The equipment is intended to constitute the main control and cutoff of the supply of power.

Revised in the 1999 NEC, the phrase "connected to the load end of service conductors" substitutes the phrase "located near the point of entrance." This change coincides with other changes to the definitions of "service" and "service conductors."

Service equipment may consist of circuit breakers or fused switches provided to disconnect all ungrounded conductors in a building or other structure from the service-entrance conductors.

Service lateral. A service lateral consists of the underground service conductors between the street main - including risers - and the first point of connection to the service-entrance conductors in a terminal box, meter, or other enclosure. Where there is no terminal box, meter, or other enclosure, the point of connection shall be the point of entrance of the service conductors.

The 1999 NEC revision of this definition removes references to adequate space. You can run the underground service laterals from poles or from transformers (with or without terminal boxes) - provided they begin at the service point. The NEC does not cover conductors on the utility side of the service point.

Service-entrance conductors/underground system. These are the service conductors between the terminals of the service equipment and the point of connection of the service lateral.

Service drop. A service drop consists of the overhead service conductors from the last pole or any other aerial support to and including the splices, if any, connecting to the service-entrance conductors at the building or other structure.

Service-entrance conductors/overhead system. The Code defines this system as the service conductors between the terminals of the service equipment and a point usually outside the building (clear of walls) where joined by tap or splice to the service drop (Fig. 2).

Service conductors. Service conductors are the conductors from the service point to the service disconnecting means.

Note that these service conductors only originate from the supplying utility side. "Service conductors" is a generic term and may include service drops, service laterals, and service-entrance conductors. This definition excludes wiring on the supply side of the service point.

The 1999 NEC omits the phrase "or other source of power." The service conductors originate at the service point where the supplying utility ends, and they also end at the service disconnecting means.

Service point. This term helped create the confusion because designers, installers, and inspectors had to make an interpretation and apply such rules. Service point is the point of connection between the facilities of the serving utility and the premises wiring. In other words, the "service point" is the point of demarcation between the utility supply and the premises wiring system.

Feeder-circuit conductors. The Code defines feeders as all circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent protective device.

In summary. The supplying utility and local codes usually specify the location of the service point. However, you should always check such codes when determining service point. Therefore, the service-drop conductors and the service-lateral conductors may or may not be part of the service, as the NEC outlines.

Where the service point is at the utility pole, the service conductors from an overhead distribution system will originate at the utility pole and connect at the service disconnecting means. When the service point exists at the utility manhole, then the service conductors originate at the utility manhole and connect at the service disconnecting means.

The NEC considers conductors that extend to an outdoor pad-mounted transformer located on private property to be service conductors - if the installer specifies the service point is at the secondary connections of the transformer's terminals.

If you encounter confusion or difficulty when determining a service point, refer to the definitions in Art. 100.