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Wiring Methods

Posted By Steve Douglas, Tuesday, May 01, 2012
Updated: Friday, September 07, 2012

Section 4 of the Canadian Electrical Code covering conductors has seen ten revised subrules, eleven new subrules and one new rule for the 2012 CE Code. The most significant change to Section 4 is the addition of new Rule 4-006. Similar to Article 110.14 of the National Electrical Code, Rule 4-006 limits the maximum allowable ampacity of a conductor to be based on the lesser of the temperature rating of the conductor or the maximum termination temperature marked on equipment. By default, equipment without a termination temperature marking is considered 90°C. As an example, an installation with three current-carrying 500 kcm RW90 copper conductors in a raceway terminating on a breaker with a maximum termination temperature of 75⁰C would have an allowable ampacity based on the 75⁰C column in Table 2, resulting in an allowable ampacity of 380 amp. The reason for this change was to recognise the size of conductor used during temperature testing of the equipment, and to harmonise with the requirements in the National Electrical Code. In conjunction with this change, Rules 6-310 and 12-108 have been modified to allow splicing of conductors to satisfy Rule 4-006. The next question is, what is the minimum length of conductor required to satisfy the requirements of Rule 4-006? The answer can be found in CSA Standards C22.2 No 4 Enclosed and Dead-Front Switches, C22.2 No 29 Panelboards and Enclosed Panelboards, and C22.2 No 244 Switchboards. All three of these standards have the same requirement of 1.2 m.

Subrules (1) and (2) of Rule 4-004 have been revised, making the underground allowable ampacities for conductors of 1/0 or larger in the Appendix D tables mandatory for installations matching the configuration drawings in Appendix B. For installations not matching the configurations in Appendix B, the requirements for IEEE 835 calculations have been assigned to Item (e).

New Subrules (9) and (10) have been added to Rule 4-004 to address allowable ampacities of single conductor cable with cable spacing less than 100%. Where more than four single-conductor cables in free air, with spacing less than 25%, are installed, new Subrule (12) directs code users to Tables 2 or 4, and to the correction factors in Table 5C for the allowable ampacity.

New Table 66 for the maximum allowable ampacity of bare or covered conductors in free air has been added; a new Subrule (21) to Rule 4-004 states the allowable ampacity shall be as specified in Table 66.

Rules 4-010, 4-012, 4-020, and 4-040 have been reworded as part of a series of proposals to direct code users to Section 4 when determining the specific conditions of use of conductors and cables found in Tables 11 and 19 with respect to moisture, corrosive action, temperature, degree of enclosure, and exposure to mechanical injury.

The induced voltages and currents in metal armour or sheath of single conductor cable requirements from Rule 12-3022 from the 2009 CE Code, along with the note from Appendix B, have been moved to Rule 4-010. The intent of this move was to have all these similar requirements in the same rule of the code.

Additional limitations to the allowable reductions for the size of neutral conductors found in Item (2)(a) of Rule 4-024 now include the portion of the load that consists of non-linear loads supplied from a 3-phase, 4-wire system such as dimmers, computers, microprocessors, and most other electronic loads.

The last change in Section 4 adds requirements for diesel locomotive (DLO) cable. DLO cable is an extra flexible cable that can have conductor sizes not seen in the CE Code until now, such as 535 kcm, 777 kcm, etc. Rules 4-040 and 4-042 now allow DLO cable 1/0 and larger marked as a TC cable to be installed in cable tray. Precautions do need to be made when terminating the DLO cable. Due to the fine stranding of the cable, it must terminate in connectors specifically approved for these cables. Allowable ampacity for the cable can be found in new Table 12E.

Read more by Steve Douglas

Tags:  Featured  May-June 2012 

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