Rules for Electrical Utility Supply

The Canadian Electrical Code, Section 6 provides us with some important rules for installing service equipment, wiring methods and metering. The following rules apply to electrical utilities and their customers at the service entrance, the point where an electrical utility connects to a customer’s electrical installation. This article covers some of the main requirements on the number and locations of electrical services and defines the terms used in the code.

To avoid undue hazards to people working on electrical systems and to ensure that electrical services can be readily disconnected in an emergency, Rule 6-102 requires that the number of “supply services” be limited. There must not be more than one to a building except for special
situations including:

  • Fire pumps
  • Industrial or complex buildings; or
  • Buildings divided into a number of units where all units are at grade level with separate entrances

To jog your memory, the term “supply service” refers to an electrical utility’s wiring from its power distribution system to the point of connection at a customer’s premises.

For the same reasons, Rule 6-102 also says that when a customer needs to have more than one “service box,” the “service boxes” should be grouped in one location. If that’s not possible for valid reasons, a diagram must be posted at each “service box” showing the locations of all other main disconnection points. This is so that people can be assured that all sources of supply are disconnected when that becomes necessary.

The term “service box” refers to the main service equipment containing the main circuit-breaker or switch and fuses for an electrical utility customer’s electrical system, and approved for use as service entrance equipment.

For some very practical reasons, emergency and life safety systems belong in an independent category with some different rules. Going back to the CEC exception for fire pumps, Rule 32-204 that tells us they can have a separate “service box,” and that despite Rule 6-102, this equipment may be located apart from the building’s main service. However, each fire pump service must be well marked and identified. For a more secure supply in an emergency, fire pumps alternatively fed from a building’s standby power, are required by Rule 32-206 to have a nearby transfer switch for each fire pump, or within each fire pump controller.

Rule 6-104 limits the number of services from one supply by specifying that: The number of “consumer’s services” of the same voltage and characteristic, terminating at one “supply service,” run to, on, or in any building, shall not exceed four, unless a deviation is allowed in accordance with Rule 2-030. A typical example installation would be electrical utility conductors to a multiple metering arrangement supplying several different units within a building. The electrical code reference to Rule 2-030 means you need the permission of an inspector if you wish to exceed that number.

To avoid having to look it up, a “consumer’s service” is all of the wiring and equipment within the customer’s premises past the point where the electrical utility makes its connections. An electrical utility’s connections are usually made either at the customer’s overhead service mast, the top side of the metering equipment or at the main “service box” depending on the size and type of supply.

To facilitate disconnecting the electrical supply, Rule 6-200 says each “consumer’s service” should have its own “service box” except when the main service is subdivided in an outdoor multiple or dual lug meter base, up to 600 amperes and 150-volts to ground. For the purposes of Rule 6-104, each metering point can be considered a “consumer’s service.” You can have several “service boxes” in a building supplied from the same metering arrangement.

Rule 6-106 tells us that an electrical installation or part of an installation must not at any time be supplied by more than one source. If an installation has several “supply services” or other sources of supply such as standby power, there must be transfer switching or key interlocking among the supplies to prevent connection to more than one supply system at a time.

Rule 6-206 tells us where we may locate the main electrical service equipment and limits it to the following:

  • The location must meet the electrical utility’s requirement.
  • The service equipment must be “readily accessible.”
  • The service equipment must be as close as possible to the point where the service conductors enter the building.
  • Not in any location where it would be dangerous to enter or without sufficient working space, such as where the ambient temperature exceeds 30C or where there is less than 2m headroom
  • Inside the building unless there are valid reasons to locate the service equipment outdoors, such as when buildings have high humidity, a corrosive or hazardous, explosive atmosphere, when permitted by an electrical inspector
  • When outdoors, equipment must be weatherproof or protected from the weather and protected from damage when less that 2 m above the ground.

“Readily accessible” means capable of being reached quickly without having to climb over anything or using a ladder.

As you can appreciate, the Canadian Electrical Code, Section 6 contains important rules governing interconnections between an electrical utility system and its customers. As with previous articles, you should check with the electrical inspection authority in each province or territory as applicable for a more precise interpretation of the above.

Leslie Stoch
Leslie Stoch, P. Eng, is principal of L. Stoch & Associates, providing electrical engineering and ISO 9000 quality systems consulting. Prior to that, he spent over 20 years with Ontario Hydro as an electrical inspection manager and engineer. Les holds a B. S. in electrical engineering from Concordia University in Montreal.