The Apprentice’s Guide to Electrical Services


This article will give apprentice electricians quick tips on industry recommended practices, electrical service installation tips, and instructions for navigating an essential article in Chapter 2 (Wiring and Protection) effectively. As you begin your journey to understand the layout, purpose, and structure of the NEC, you will begin to rely on its well-organized guidelines for all your daily tasks. Remember that the local authority having jurisdiction (AHJ) will enforce these guidelines nationally; use these practices wherever you work. Moreover, art. 230 (Services) sets minimum installation standards, so be prepared to do more if local jurisdictions require it.

Understanding Figure 230.1

At the beginning of art. 230, you will find a directory (Figure 230.1) that illustrates a main electrical service/system that supplies homes, commercial buildings, and industrial facilities from the utility connection (hook-off), down to the branch circuits supplying the building. Figure 230.1 is a time-saving directory/illustration that makes navigating through the entire article simple and efficient.

Electricians looking for installation guidelines for overhead service with overhead wires called triplexes can find guidelines at the top left of the directory/illustration. Electricians looking for guidelines for installing, repairing or modifying underground electrical service wires called service drops can find the guidelines at the top right of the directory/illustration.

The next stop for electrical service is metering. Typically, you can find these guidelines from the local power company or local AHJ. For example, in Philadelphia, I use a set of electrical building guidelines for metering and electrical service from the “Blue Book”. This publication is designed specifically for contractors and builders who request electricity and meters from the utility company. This manual explains:

  • The type, model and manufacturer of the meter outlet(s) needed to receive electrical service.
  • The method, type and value of the electricity meter used to bill the customer (for example, watt-hour meter or current transformers). Typically, the power company provides this equipment and remains responsible for its maintenance.
  • The location of metering equipment for access by the power company.

Remember that these installation guidelines should be used in conjunction with any permits or conditions set by the local power company or AHJ requirements.

Standard (US) voltage systems for electrical services

Here in North America, our standard voltage systems supplied by power companies on the secondary side of their transformers are:

  • 120/240V single-phase service (three-wire system): residential homes, multi-family dwellings, small commercial buildings
  • 208/120 V three-phase wye system (four-wire system): multi-family dwellings, commercial buildings, light industrial buildings
  • 480/277 V three-phase wye system (four-wire system): multi-family dwellings, commercial buildings, industrial buildings and factories
  • 600/480 V three-phase delta system (four-wire system): industrial buildings and plants (manufacturing facilities)

Additional older systems still in use in some regions:

  • 240/208/120 V 3-phase (high-legged four-wire wye system): commercial buildings, light industrial buildings
  • 120/240 V two-phase (four-wire system): commercial buildings, industrial buildings and factories

A building can have more than one service

In special conditions, an additional service can be installed: supplying a fire pump [Sec. 230.2(A)(1)] or increase reliability [Sec. 230.2(A)(6)]; for ventilation systems or legally required backup systems; and where it may be essential to maintain life, alarm systems, elevators, public safety communication systems and industrial processes where interruption of power would cause serious risk to life safety or health [230.2(A)(3)]. Additional electrical service may be installed under special permission for Chapter 5 Specific occupations where:

  • There is no space available for service equipment accessible to all occupants; or where a single building or other structure is large enough to make two or more services necessary.
  • If the load or capacity requirements are greater than 2000 A at a supply voltage of 1000 V or less.
  • When the load requirements of a single phase 120/240V installation are greater than the service agency (electric company) typically provides through a service.
  • Additional services may also be authorized if a building requires different voltages, frequencies or phases, or for various uses, such as different rate schedules; it can be granted under “different characteristics”.

Run service conductors through a building

An electrical contractor may need to move a main electrical service to a more suitable location for a variety of reasons. Sometimes this is necessary to avoid installing service equipment in a flood prone area or simply placed in a location where it is more accessible for all tenants. This situation is typical in new residential construction to conceal service equipment away from the facade of the building. This situation may require the electrical contractor to run service conductors through a building. This type of installation is authorized under the following conditions. The conductors must be protected in a reinforced manner; they must be considered outside the building. Conductors must be installed in at least 2 inches of concrete under a building or other structure; additional guidelines may apply to any type of cable tray or conductor insulation used. Conductors must be installed in raceway embedded in concrete or brick at least 2” thick.

Clearances for Service Conductors on Buildings

Live service conductors can be very dangerous; they carry the unlimited potential to cause harm and damage if not installed correctly. The NEC establishes guidelines for the installation of service conductors that ensure the safety of personnel, building owners and the properties to which we provide electrical services.

An important aspect of art. 230 follows the strict guidelines that keep energized service conductors away from unintended contact with trucks, moving equipment, or construction personnel working around them. Overhead service conductors such as multi-conductor cables without an overall outer jacket should not be easily accessible.

Article 100 explains that it means “without the aid of a portable ladder” or lifts, they must not be within easy reach; keep them at least 3 feet away from windows designed to be opened, doors, porches, balconies, ladders, stairs, fire escapes, or similar locations. The exception is that conductors passing above the upper level of a window must be allowed to be less than 3 feet. requirement.

Note to remember

The guidelines of art. 230 do not concern installations under the exclusive control of the local electricity company, the communication company and their structures; this includes buildings, equipment and conductors that these companies own, control and maintain (for example, service outlets or service branches, or any associated meters). The NEC does not cover their equipment or conductors on property owned or leased by the electric utility for the communications, metering, generation, control, transformation, transmission, or distribution of electric power.

The NEC does not cover the facilities of companies that control communications systems (eg, telephone, CATV, Internet, satellite, or data services). So, in simpler terms, companies with exclusive control over such conductors, equipment, or production systems are subject to the codes and standards established by utility/utility commissions or their regulated industry.

Here’s how I like to simplify what the NEC covers – the electrical contractor’s installation or installations, from the basement to where service conductors connect to utility wires or transformers. electricity. However, the Code does not cover equipment or conductors beyond our connection to the utility company.

Harold DeLoach, master electrician and electrical trainer/instructor, is the founder of the Academy of Industrial Arts ( in Philadelphia. With over 30 years of experience in the field, he will regularly write exclusive content for E-Train and can be reached at [email protected].


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