CEC Rule 14-100(d) permits the secondary conductors supplied by a high voltage power transformer to be protected by the transformer’s primary overcurrent protection (with no restriction in conductor length through the building). The rule requires that the wiring be mechanically protected and terminates at a single circuit-breaker or set of fuses set to protect the tap conductors against overloading.
The NEC wisely restricts this application by permitting high-voltage primary overcurrent protection for secondary conductors only for single-phase or delta-delta wound transformers. (We can assume the delta-delta restriction applies so as to reduce the possibility of arcing ground faults.)
CEC Rules 10-700 to 10-710 provide a list of permissible electrical system grounding electrodes. The list includes metal water piping systems, metal well casings, ground rods, concrete-encased conductors, concrete-encased metal plates and buried metal plates.
The NEC expands the CEC list considerably to include an effectively grounded metal building frame, a ground ring around a building, concrete-encased reinforcing bars, underground metallic objects such as piping and storage tanks.
CEC Rules 4-004(3) and (4) allow us to consider the neutrals of normally balanced three-phase, four-wire circuits as non-current-carrying conductors when determining the ampacities of cables or conductors in raceways.
The NEC takes this to a different level, considering the neutral conductor to be current-carrying when a major portion of the load is non-linear (contains harmonics).
CEC Rule 14-014 permits series rated electrical equipment in locations where the fault level exceeds the equipment rating, when installed as a component of a tested and approved series combination. Appendix B – Notes on the Rules tells us that motor loads connected between the upstream and downstream protective devices of series rated overcurrent protection must be restricted to no greater than 1% of the interrupting rating of the downstream devices. Here the intention is to ensure that the motor contribution during a fault does not affect the ability of the downstream protection to safely isolate the fault. Since this note is located in Appendix B, it becomes a “”good installation practice”” rather than a code requirement.
The NEC makes this an electrical code requirement by writing it as a rule.
CEC Rule 18-000 requires our using the Zone method of classifying all new locations containing flammable gases and vapours in quantities sufficient to produce an explosive gas atmosphere. The CEC permits the Division system of classification only for additions, modifications, renovations, operation and maintenance of existing facilities.
The NEC takes a more laissez-faire view, permitting either classification method to be used in any situation.
CEC Rules 28-100 to 28-210 provide requirements for determining minimum motor conductor ampacities and maximum overcurrent protection. Although the CEC provides Tables 44 and 45, listing motor currents for single-phase and three-phase motors, it is silent on whether the tables or actual motor nameplate ratings are to be used for these purposes.
The NEC also provides motor current tables, but specifically requires they be used for determining motor conductor sizes and overcurrent protection. However, this does not apply to motor overload protection, where the NEC requires that actual nameplate data be used.
CEC Rule 14-100(c) permits reduced size feeder taps up to 7.5 m as long as each tap conductor:
- Has an ampacity not less than 1/3 of the ampacity of the feeder
- Is protected against damage
- Terminates in a single set of fuses or circuit breaker, set at a value not exceeding the ampacity of the tap conductor
The NEC has an identical rule but goes on to expand this practice even further, to permit 1/3 size taps up to 30 m in length, but with an abundance of conditions:
- The feeder is located in a high bay manufacturing building minimum 11 m high
- Qualified persons service the electrical system
- Tap conductors are not over 7.5 m long horizontally, not over 30 m in total length and terminate in a single set of fuses or circuit-breaker set at a value not exceeding the ampacity of the tap
- The tap is protected against mechanical damage and without splices
- Minimum tap conductor size is 6 AWG copper or 4 AWG aluminum
- Taps are made not less than 9 m above the floor and do not penetrate through any floors, walls or ceilings
As with earlier articles, you should always consult the electrical inspection authority in each province or territory as applicable to obtain a more specific interpretation of any of the above.