Service Conductors and Service Equipment

Sept. 1, 2001
Knowing where the service ends can put an end to some typical problems. The National Electrical Code refers to the phrase service equipment in almost 50 Code sections. Understanding where the service begins and ends is critical in the proper application of many Code rules particularly those for grounding, bonding, and disconnecting means. To understand how to apply these rules, review the following

Knowing where the service ends can put an end to some typical problems.

The National Electrical Code refers to the phrase “service equipment” in almost 50 Code sections. Understanding where the service begins and ends is critical in the proper application of many Code rules — particularly those for grounding, bonding, and disconnecting means. To understand how to apply these rules, review the following definitions in Art. 100.

Service point. This is the connection point between the serving utility facilities and the premises wiring.

Service conductors. These run from the service point to the service disconnecting means (the service equipment, not the meter). Service-entrance conductors can enter an installation from overhead (service drop) or underground (service lateral).

Service equipment. This necessary equipment, which usually consists of circuit breakers or switches and fuses and their accessories, is connected to the load end of service conductors that serve a structure and constitutes the main control and cutoff of the supply. Service equipment does not include the metering equipment, such as the meter and/or meter enclosures (Sec. 230-66).

Reviewing these definitions should help you understand that service conductors originate at the serving utility (service point) and terminate on the line side of the service disconnecting means (service equipment). The following conductors and equipment on the load side of service equipment are considered feeder conductors:

  • Secondary conductors from customer-owned transformers.

  • Feeder conductors from generators, UPS systems, or photovoltaic systems.

  • Feeder conductors serving remote structures.

You must install feeder conductors in accordance with the requirements in Arts. 215 (feeders) and 225 (outside wiring). In addition, Sec. 250-30 contains the grounding requirements for separately derived systems, and Sec. 250-32 outlines the grounding requirements for separate structures. Do not apply the grounding requirements for services (Sec. 250-24) to feeder conductors and equipment.

Neutral-to-case connections in violation of Secs. 250-6 and 250-142(b) create a condition where neutral current has multiple return paths to the grounded (neutral) conductor of a power supply. This allows objectionable neutral current to flow on the metal parts of the electrical system and building, which can lead to fire, shock hazard, and power quality issues with digital equipment.

Too many electrical workers (and inspectors) think service conductors include the secondary conductors of transformers and supply conductors to a remote building. This misunderstanding has led to several improper and unsafe neutral-to-case connections at disconnects and panelboards. To ensure a safe electrical installation, know where the service begins and ends. You must ground service equipment, separately derived systems, and separate buildings and structures in accordance with Secs. 250-24, 250-30, and 250-32, respectively.

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.

Voice your opinion!

To join the conversation, and become an exclusive member of EC&M, create an account today!

Sponsored Recommendations

Electrical Conduit Comparison Chart

CHAMPION FIBERGLASS electrical conduit is a lightweight, durable option that provides lasting savings when compared to other materials. Compare electrical conduit types including...

Fiberglass Electrical Conduit Chemical Resistance Chart

This information is provided solely as a guide since it is impossible to anticipate all individual site conditions. For specific applications which are not covered in this guide...

Considerations for Direct Burial Conduit

Installation type plays a key role in the type of conduit selected for electrical systems in industrial construction projects. Above ground, below ground, direct buried, encased...

How to Calculate Labor Costs

Most important to accurately estimating labor costs is knowing the approximate hours required for project completion. Learn how to calculate electrical labor cost.