A 230V single-phase refrigeration compressor motor has a rated full load current (FLA) of 15.0 A and a locked rotor current (LRA) of 90.0 A. What is the minimum fuse size required for motor branch circuit short-circuit and ground-fault protection, based on allowing up to 175% of FLA as per typical Canadian electrical code guidelines for non-time delay fuses, or 250% for dual-element time delay fuses, whichever is applicable and lowest standard rating below LRA?

Question: A 230V single-phase refrigeration compressor motor has a rated full load current (FLA) of 15.0 A and a locked rotor current (LRA) of 90.0 A. What is the minimum fuse size required for motor branch circuit short-circuit and ground-fault protection, based on allowing up to 175% of FLA as per typical Canadian electrical code guidelines for non-time delay fuses, or 250% for dual-element time delay fuses, whichever is applicable and lowest standard rating below LRA?

Answer options:

• 25 A (non-time delay fuse).
• 30 A (non-time delay fuse). ✅ 40 A (time delay fuse).
• 60 A (non-time delay fuse).

Correct answer: 40 A (time delay fuse).

Explanation: For motor branch circuit protection, the maximum rating for a non-time delay fuse is 175% of FLA (1.75 * 15A = 26.25A which rounds to a 25A standard fuse). For a time-delay fuse, it's 250% of FLA (2.5 * 15A = 37.5A which rounds up to a 40A standard fuse). The selected fuse must also be less than the LRA (90A). So 40A time delay is the appropriate choice as it allows for starting current while offering protection, and is lower than the 60A potential for a standard non-time delay fuse if selected by the wrong percentage.