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

Persona

Technologies

Technologies
Reference number
IB-EL 2016-07
Revision Number
Rev 1

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.

Use of Table 39

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

22) Notwithstanding rule 4-006, 3-wire 120/240 V and 120/208 V service conductors for single dwellings are permitted to be sized in accordance with table 39. Feeder conductors supplying single dwelling units of row housing, apartments, and similar buildings that terminate on equipment having a conductor termination temperature of not less than 75 °C are also permitted to be sized in accordance with table 39.

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 8-104 1), 8-200 1), and 8-202 1), 4-006 and 4-004 22).

In accordance with 4-004 22), installers wishing to select conductors using the values in table 39 must provide a load calculation. If the calculated load (A*) exceeds the limit shown in the table, the next larger size conductor shall be used as indicated in Note (2) of the table.

Example 1– Single family dwelling with 105m2 total floor area supplied with aluminum service conductors.

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) will require the minimum ampacity of the service to be 100A. When selecting the service conductor from table 39, the table permits a #2 AWG Al service conductor to be used to supply this installation.

A load calculation which exceeds the 95A threshold will require the next larger size conductor to be used in accordance with note (2).

Example 2– Single family dwelling with 105m2 total floor area supplied with copper conductors.

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. In this example, the minimum service or feeder rating, (A), is 200A based on the load calculation.

Table 39 permits a #2/0 AWG Cu service conductor to be used to supply this installation. If the load calculation had exceeded the 184 A threshold, the next larger size conductor must be used in accordance with note (2).

Table 39
Minimum permitted size for 3-wire 120/240 V and 120/208 V service conductors for single dwellings and feeder conductors or cables supplying single dwelling units  
of row housing, apartment, or similar buildings and terminating on equipment having a conductor termination temperature of not less than 75 °C.

[See Rule 4-004 22).]

  Copper [See Note 2)] Aluminum [See Note 3)]

Overcurrent device rating. A

For calculated loads up to, A*

Conductor size, AWG or kcmil

For calculated loads up to, A*

Conductor size. AWG or kcmil

60

60

6

53

6

100

89

4

95

2

125

121

2

125

1/0

200

184

2/0

189

4/0

225

210

3/0

215

250

400

352

400

357

600

  • These ampacities are the ampacities given in Tables 2 and 4 for 75°C increased by 5%

Notes:

  1. This Table applies only to conductors sized for loads calculated in accordance with Rules 8-200 1)a), 8-2002), or 8-2021).
  2. If the calculated load exceeds the limit shown in this Table, the next larger size insulated conductor or cable shall be used.

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.

Subrule 4-004 22) amends the requirements of rule 4-006, and the size of the service conductor to be selected from table 39. The calculated loads provided in table 39 are within the maximum values where the operating temperatures of the conductors will not affect an overcurrent (O/C) device. Conductors with a 90C insulation rating and used in table 39 have an ampacity that closely aligns with the rating of the overcurrent device.

Example

A #2 RW90 Al conductor has an allowable ampacity of 100A, as listed in table 4. In table 39, for calculated loads up 95A, a #2 RW90 Al conductor may be used for service or feeders with a 100A rating. 95A is the ampacity provided in the 75C column of table 4 increased by 5% in accordance with rule 8-106 1). This current rating will result in the operating temperature not exceeding the 75C TTR rating of the O/C device.

 

Provincial Safety Manager

References:
Safety Standards Act
Electrical Safety Regulation
Safety Standards General Regulation