Question 1
According to CSA C22.1:24, when armoured cable (AC90) is installed in a dry indoor location and run along the side of a wood joist at a height of 1.8 m above the floor, which of the following is correct regarding physical protection?
- A. No additional protection is required because AC90 armour provides sufficient mechanical protection at that height. ✓ Answer
- B. A steel plate at least 1.6 mm thick must be installed wherever the cable is within 32 mm of the edge of a framing member.
- C. A non-metallic sleeve must enclose the cable wherever it is exposed and within 2.5 m of the floor.
- D. The cable must be enclosed in EMT conduit for the entire exposed run if accessible to physical damage.
Explanation: CEC Rule 12-010 requires mechanical protection (e.g., a steel plate) only where cables are subject to physical damage. AC90 armoured cable, by virtue of its interlocked steel or aluminum armour, is recognised as providing adequate mechanical protection for general indoor dry locations. The 32 mm steel-plate rule (Rule 12-516(2)) applies to NMD90 and similar non-armoured cables running through or notched into wood framing members, not to armoured cable running along the side of a joist at working height where it is not subject to physical damage. No additional protection is required for AC90 in that scenario.
Question 2
According to CEC Rule 28-604, when a motor controller is required to open all ungrounded supply conductors simultaneously, which of the following motor installations specifically requires this simultaneous disconnection by the controller?
- A. Any 3-phase motor rated over 10 hp at 600 V
- B. A motor where the stop of the motor could create a hazard, such as in a reversing application with dynamic braking
- C. A motor installed in a Class I, Division 1 hazardous location
- D. A single-phase motor where the controller is also used as the branch circuit disconnecting means ✓ Answer
Explanation: CEC Rule 28-604 generally does not require a motor controller to open all conductors to the motor. However, when the controller is also used as the motor branch-circuit disconnecting means, it must open all ungrounded supply conductors simultaneously. A hazardous location installation may impose other equipment and wiring requirements, but Rule 28-604 is not a specific Class I, Division 1 motor rule.
Question 3
Under CEC Section 28, which of the following statements correctly describes the requirement for motor overload protection on a single-phase motor connected to a 120 V branch circuit?
- A. Overload protection must be provided in both the ungrounded and grounded conductors
- B. Overload protection is required only in the ungrounded conductor ✓ Answer
- C. No overload protection is required for single-phase motors under 1 hp on a 120 V circuit
- D. Overload protection must be provided in all conductors including the equipment grounding conductor
Explanation: CEC Rule 28-700 requires overload protection in each ungrounded conductor. For a single-phase 120 V motor, there is only one ungrounded (hot) conductor, so only one overload device is required. Installing an overload in the grounded (neutral) conductor is not required and would create a hazard by potentially interrupting the neutral while leaving the ungrounded conductor energized. The equipment grounding conductor must never be interrupted by an overload device.
Question 4
A 3-phase, 600 V, 75 hp Design B squirrel cage motor has a full-load current of 72 A per CEC Table 44. Using a time-delay (dual-element) fuse as the branch circuit short-circuit and ground-fault protective device, and applying CEC Table 29D (maximum 175% of FLC for time-delay fuses), what is the maximum standard fuse size permitted?
- A. 110 A
- B. 125 A
- C. 150 A ✓ Answer
- D. 175 A
Explanation: CEC Table 29D limits a time-delay dual-element fuse for this Design B squirrel-cage motor branch-circuit short-circuit and ground-fault protection to 175% of the Table 44 full-load current. 72 A x 1.75 = 126 A. Because 126 A is not a standard fuse rating, the CEC motor branch-circuit rule permits the next higher standard rating to be used. The next standard size above 126 A is 150 A, so the maximum permitted standard fuse size is 150 A.
Question 5
According to CEC Rule 28-200, a manually operated air-break switch is listed as an acceptable motor disconnecting means. Which of the following conditions must this switch satisfy to be used as the disconnecting means for a 600 V, 3-phase, 20 hp motor?
- A. It must be rated at least 20 hp and have a continuous current rating of not less than 115% of the motor full-load current ✓ Answer
- B. It must be a motor-circuit switch rated in horsepower at not less than the horsepower rating of the motor
- C. It must be rated at 125% of the motor full-load current and be lockable in the open position
- D. It must be a fused switch with a minimum interrupting rating equal to the available fault current at that point
Explanation: For a manually operated air-break switch used as a motor disconnecting means under CEC Rule 28-200, the switch must be suitably rated for the motor load. For this 600 V, 3-phase, 20 hp motor, the relevant requirement is that the disconnecting means have an adequate horsepower rating for the motor and a continuous current rating of not less than 115% of the motor full-load current. Option B describes the horsepower-rating rule for a motor-circuit switch, but the question specifically asks about a manually operated air-break switch.
Question 6
An inspector is reviewing several motor installations for compliance with CEC Section 28 overload requirements. Which ONE of the following motors may be installed WITHOUT its own overload device under the exemption in Rule 28-308?
- A. A 1/2 hp roof-mounted exhaust fan motor that is difficult to reach and is fed from a 15 A branch circuit with no starter
- B. The burner motor of a domestic oil-burner furnace supplied as an approved assembly that is not normally subject to overloading and whose combustion safety controls also protect the motor against overload ✓ Answer
- C. A 5 hp three-phase pump motor mounted on a factory-built skid and controlled by a standard across-the-line magnetic starter
- D. A 2 hp air compressor motor wired by the contractor to an approved fusible disconnect switch located within sight of the motor
Explanation: CEC Rule 28-300 requires overload protection for motors in general, but Rule 28-308 states that overload protection is not required for a motor that is part of an approved assembly that is not normally subject to overloading and that is equipped with other safety controls (the Code cites the safety combustion controls on a domestic oil burner as the example) which also protect the motor against overload. The oil-burner motor in option B meets both conditions. Option A is wrong because being hard to reach is not an exemption; a 1/2 hp fan motor still needs overload protection (only the separate small-motor exemption in 28-308 for 1/8 hp or less manually started portable motors applies to tiny motors). Option C is a conventional motor whose starter must contain properly rated overload devices per Rules 28-304 and 28-306; the skid does not make it an approved assembly with alternate overload safeguards. Option D describes only a disconnecting means (Rule 28-600 series) and fuses sized for branch-circuit overcurrent protection (Rule 28-200), which do not replace running overload protection.