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## Another Look at Appendix B

Posted By Leslie Stoch, Tuesday, January 01, 2013
Updated: Thursday, December 13, 2012

In an earlier article, I suggested checking for an Appendix B interpretation when applying any of the Canadian Electrical Code rules for the first time.  Appendix B is there to help us better understand the intent of the CEC rules and to provide important supporting information. Here are a few more examples.

Rules 4-004 (1) (d) and 4-004(2) (d) provide allowable ampacities for underground wiring. Conductor configuration Diagrams B4-1 to B4-4 for underground conductor installations are located in Appendix B and the allowable ampacity Tables D8A to D15B associated with these   diagrams for copper and aluminum underground conductors in Appendix D. The ampacity tables are based on 90 C rated conductors.

However as you know, the new Rule 4-006 requires that when equipment is marked with maximum connection temperatures, the conductor ampacities must be based on the applicable columns in Tables 1 to 4. To convert the 90° C conductor ampacities, Appendix B  explains that underground ampacities for conductor temperatures of 75° C to 60° C respectively may be obtained by multiplying the 90° C temperature ampacities by the derating factor 0.886 (for 75° C) or 0.756 (for 60° C). These conversion factors help us meet the requirements of Rule 4-006.

Rule 2-320 requires that adequate ventilation be provided to prevent overheating of heat-producing electrical equipment. Appendix B helps us by specifying that approximately 3.5 to 4.3 cubic metres of air per minute is normally provided for each kilowatt of loss for ventilating 40° C rise equipment.

Rule 10-500 defines effective grounding as a ground-fault path of sufficiently low impedance so as to facilitate operation of overcurrent devices (fuses and circuit-breakers). Appendix B explains that an effective ground-fault path will have impedance sufficiently low enough to permit at least five times rated current to flow during a ground fault. This definition explains various rules that call for effective grounding.

Rule 10-814(1) specifies that bonding conductor sizes must not be smaller that specified in Table 16. Appendix B makes two important exceptions to the rule:

1. When correctly sized raceways (conduit or tubing) and metallic cable sheaths are permitted for use as bonding conductors, they are considered to be adequate for the purpose.
2. Bonding conductors in cable assemblies are sized in accordance with the applicable Part II standards – although bonding conductor sizes may differ from Table 16, they are considered adequate for the purpose.

Rules 18-050 and 18-066 provide requirements for selection of equipment when employing the Zone system of classifying locations for flammable and explosive gases and vapours. To assist us in identifying hazardous location equipment, Appendix B supports the rules with detailed specifications for the hazardous gas groups.

Rule 32-202 specifies permissible wiring methods for fire pumps, (metal raceways, cables with metal armour or sheaths and non-metallic conduit and tubing in minimum 50 mm concrete). Appendix B takes the requirements for fire pump wiring a step further with this recommendation "Consideration should be given to the location, routing and design of wiring to minimize hazards that might cause failure due to explosions, floods, fires, icing vandalism and other adverse conditions that might impair the function of a fire pump”. This extra step is taken to help ensure that power will be available when fire pumps are called upon to perform in an emergency.

With the examples given in these two articles, I hope I have convinced you of the value that you can find in Appendix B.

As with previous articles, you should always check with the electrical inspection authority in each province or territory for a more precise interpretation of any of the above.

Read more by Leslie Stoch, P. Eng