Information Bulletin: Section 4 - Conductors

Persona

Technologies

Technologies
Reference number
IB-EL 2016-06
Revision Number
Rev 1

Topic: Conductors

The following bulletin provides guidance on the applying the rules from 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.

Ampacities of underground conductors - General

Rule 4-004, subrule 1) f) and subrule 2) f) are interpreted as follows:
When the ampacity of a conductor is selected in accordance with item f) and subsequently increased in size due to voltage drop requirements to #1/0 and larger, the conductor may be installed in compliance with rule 12-012.

Ampacities of underground conductors – residential installations.

Rule 4-004 22) has introduced a new table, table 39.

22) Notwithstanding rule 4-006, and 8-200 1) b), 3-wire 120/240 V and 120/208 V service conductors for single dwellings and feeder conductors 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 shall be permitted to be sized in accordance with Table 39...

Rule 4-004 22) applies to service and feeder conductors supplying single family dwellings and feeders for single dwelling units in townhomes, apartments, and similar buildings.

A load calculation is required confirming the conductor selected from table 39 is acceptable for the proposed service or feeder rating.

Users should note that a load calculation exceeding that shown in table 39 requires the next larger size conductor to be used.

Service conductors and feeder conductors selected in accordance with this subrule are permitted to be installed in accordance with rule 12-012.

Examples;

New construction : Single family dwelling with suite or duplex

New construction : Single family dwelling with suite or duplex


Load calculation is required to use table 39
A dual lug meter base may be used.

 

Existing Construction : Single dwelling with suite added

Existing Construction : Single dwelling with suite added


Load calculation is required to use table 39
If main service requires upgrading, tables 2 or 4 will be used for service conductors.

 

Duplex home with two separate service

Duplex home with two separate service

 

Single dwelling with 400A (or larger) service

Single dwelling with 400A (or larger) service

 

Building with one main service and multiple residential feeders

Building with one main service and multiple residential feeders


Sizing of neutral conductors

  1. Rule 4-018 permits the service neutral to be reduced in size provided it has sufficient ampacity to carry the unbalanced load subject to the requirements of rule 10-210 b) and table 16.
     
  2. Rule 4-0182) a) requires that there be no reduction in size for that portion of the load consisting of electric discharge lighting. Because the third harmonic current that flows in electric discharge lighting circuits feeding ballast or transformers is of considerable size, the neutral conductor will carry a current even when the load has been carefully balanced. This current may be as large as the current in the phase conductors. Electric discharge lighting includes fluorescent, mercury, metal halide, and sodium lighting systems. For this reason, rule 4-018 2) a) does not allow any reduction in size of the neutral conductor for that portion of the load which is made up of electric discharge lighting. Consideration should also be given to other loads which may contribute to third harmonic current.
     
  3. In the application of rule 4-018, it is necessary to subtract the electric discharge lighting load and the balanced portion of the load from the total load, then subtract the 200 amps noted in paragraph 2) b) of rule 4-018 to arrive at a figure to which you may apply the 70% demand. The result must then be added to the sum of, the discharge lighting load and the 200 amps noted in paragraph 2) b) of rule 4-018.

    Example calculation:
    1000 amp service, 400 amps of unbalanced load including 50 amps of discharge lighting.
    1000 A – 50 A discharge lighting = 950 A
    950 A – 600 A balanced portion of load = 350 A
    350A – 200 A from 4-018(2) (b) = 150 A
    150 A multiplied by 70% derating factor = 105 A

    105 A + 50 A (discharge lighting) + 200 A (from 4-018(2) (b) = 355 A
     
  4. A three-phase, four-wire circuit feeding electric discharge lighting equipment must be treated as four fully loaded conductors for the purpose of rule 4-004, and be de-rated as required by the rule.
     
  5. For 120/240 V, single-phase services to residential occupancies, sized under the provisions of rules 8-200 or 8-202:
    1. The reduction should be calculated by subtraction of the “240 V permanently connected loads” (with appropriate demand factors), from the service ampacity. Cord-connected electric dryers and ranges operating at 240 volts are considered to be “240 V permanently connected loads.”
    2. Paragraphs 1(b) of rules 8-200 and 8-202 are not interpreted to limit the reduction in size of the service neutral.

Refer to the following example.
Calculation of Neutral Conductor Ampacity

Example:

120 m2 house with:
8 kW of electric heat, at 240 V 1 - 12 kW range
1 - 4 kW water heater Calculation:

Service size using appropriate demand factors from Rule 8-200
120 m2 (5kW + 1kW) = 6kW
Electrical Heat    = 8kW
Range =    6kW
Water heater = 1kW

Total = 21 kW

21 kW / 240 V = 87.5 A

Paragraph (1) (b) requires the service size to be 100 amps. The minimum neutral size is calculated by subtracting the 240-volt loads with appropriate demand factors from 100 amperes.

i.e.
Heat = 8 kW
Water Heater = 1kW
Range = 6kW
Total =    15kW
15 kW / 240 V =    62.5 A

The calculated size for the neutral:
100 A – 62.5 A = 37.5 amperes

Rule 4-018 3) b) requires that the neutral be sized no smaller than required by table 16.

Minimum size neutral conductor: # 8 AWG copper or # 6 AWG aluminum.

 

Provincial Safety Manager

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