Determining minimum service or feeder conductor size for single dwellings and single dwelling units of row housing or apartment and similar buildings

This bulletin provides guidance on the application of rules in the 2018 BC Electrical Code Regulation. The requirements of local municipal authorities having jurisdiction may vary. Installers should consult with local authorities having jurisdiction before starting work to determine their requirements.

Rule 4-004 Ampacity of wires and cables (see Appendix B)

When determining the size of service and feeder conductors for single dwellings and feeder conductors supplying single dwelling units of row housing, apartments, and similar buildings, several rules throughout the code provide guidance in selecting the appropriate size - specifically rules 4-004, 4-006, 8-104 1, 8-106, 8-200 1, and 8-202 1  

Example 1– Single family dwelling with 105m2 total floor area supplied with aluminum service conductors, and equipment marked as 75 degrees.

Minimum ampacity of service conductors shall be the greater of 8-200 1) a) or 1) b). A load calculation determines the load as being 95A. In this example, the total floor area (>80m2) and based on area will require the minimum 100-amp service. When selecting the service conductors from the 75 degree column of Table 4, a #1 AWG service conductor is to be used to supply this installation.

Example 2– Single family dwelling with 105m2 total floor area supplied with copper conductors and equipment marked as 75 degrees.

Minimum ampacity of service conductors shall be the greater of 8-200 1) a) or 1) b). A load calculation determines the load as being 180 A. Table 2 requires a #3/0 AWG Cu service conductor to be used to supply this installation.

Rationale

Insulated conductors available in Canada are primarily supplied with a 90C insulation rating.

Rule 4-006 requires conductors to be sized using temperature columns in tables 1-4 which correspond with the termination temperature rating marked on equipment. This prevents the conductor’s operating temperature from adversely affecting the overcurrent device.

Provincial Safety Manager

References: 

Safety Standards Act 
Electrical Safety Regulation 
Safety Standards General Regulation