Many of the Canadian Electrical Code rules display a note, “See Appendix B.” Appendix B provides important information on interpreting and applying the rules. To be sure you’re on the right track it’s always a good idea to find out what Appendix B has to say. This article reviews a sample of excerpts from this valuable information source.
Rule 10-700 defines an in-situ grounding electrode as a part of the existing infrastructure, buried a minimum 600 mm below grade and having a surface area equivalent to a manufactured grounding electrode (two rod electrodes or a plate electrode).
Appendix B provides a list of acceptable in-situ grounding electrodes such as three metres of metal water piping, concrete reinforcing rods and iron pilings. It also provides a cautionary note – metal treated with a non-conducting corrosion protection does not satisfy the requirements for an in-situ grounding electrode.
Rule 12-120(4) now requires that the internal conductors of long vertical runs of armoured or sheathed cable must be supported at intervals not exceeding the distances specified in Table 21. Alternative methods of support include a 90-degree bend or several bends totaling 90 degrees at intervals not exceeding the Table 21 intervals, a horizontal run not shorter than the vertical run or a cable designed for vertical runs.
Appendix B explains that a horizontal run that equals or exceeds the vertical length or incorporates a 90-degree bend or several bends equal to 90 degrees reduces the strain on the conductor terminations.
Rule 12-902 permits pulling armoured cables into raceways with a number of conditions.
Appendix B warns that armoured cables may be damaged when pulled into conduit or tubing. Calculations and specifications are required to determine maximum cable lengths. Cable manufacturers should also be consulted for minimum bending radii.
Rules 12-1104, 1154 and 1508 refer to temperature limitations for PVC conduit, duct and tubing and specify that PVC must not be subjected to temperatures in excess of 75°C. However, 90°C rated conductors may be installed at their assigned ampacity ratings.
Appendix B explains that continuously loaded 90°C conductors under conditions of 50% fill and 30°C ambient do not result in temperatures above 75°C. Conductors with insulation temperature ratings above 90°C are also acceptable as long as their ampacities are derated to 90°C.
Rule 12-714 requires that mineral insulated box connectors must be used for mineral insulated cables.
Appendix B explains that mineral insulated cables may have copper, aluminum or stainless steel sheaths. Therefore box connectors must be suitable for use with each sheath material.
Rule 12-012 requires that allowance must be made for expansion and contraction of PVC conduit due to changes in temperature by using approved expansion joints.
Appendix B identifies the PVC coefficient of expansion as .0520 and provides a sample calculation. For a 20-metre run of rigid PVC conduit where temperatures range from minus 40 C to plus 30 C, the change in conduit length is 20 x (40 + 30) x .0520 = 73 mm.
Rule 14-510 specifies that manually operated general-use switches must be approved and marked for each purpose.
Appendix B the required switch markings as follows:
“T” – A switch for control of tungsten AC or DC filament lamps up to 125 volts
“L” – An AC/DC switch for control of AC lamps up to 125 volts
“AC, frequency or phase markings” – A general-use switch for use only on AC circuits
Rules 18-108 and 18-154 specify that cable seals must be provided where cables enter an explosion-proof or flame-proof enclosure or where first terminating in a Zone 1 explosive gas atmosphere.
Appendix B explains that cables are not tested for their ability to withstand an internal explosion and therefore must be sealed. Seals are also necessary to prevent passage through the cables of gases, vapours or flames.
I hope I have convinced you that Appendix B holds a wealth of invaluable information. Spending a few moments to find out what it has to say can provide big dividends.
As with earlier articles, you should always consult with the electrical inspection authority in each province or territory for a more precise interpretation of any of the above.