An electrician is mounting a light fixture directly to the ceiling of a dwelling unit. The fixture weighs 15 kg (33 lbs). What is the minimum standard outlet box size required to support this fixture, assuming the box is secured to building joists or blocking?

Question: An electrician is mounting a light fixture directly to the ceiling of a dwelling unit. The fixture weighs 15 kg (33 lbs). What is the minimum standard outlet box size required to support this fixture, assuming the box is secured to building joists or blocking?

Answer options:

• A standard 100 mm (4 in.) octagonal box. ✅ A box listed for the weight, typically a heavy-duty box.
• Any box rated for conductors, regardless of weight rating.
• A 50 mm (2 in.) deep box, minimum.

Correct answer: A box listed for the weight, typically a heavy-duty box.

Explanation: Rule 12-3012(1) of the CEC states that outlet boxes must be strongly mounted and securely fastened in place. Rule 12-3012(3) specifies that where a luminaire weighing more than 9 kg (20 lbs) is supported, the outlet box must be suitably marked by a recognized testing laboratory for the weight to be supported. A standard octagonal box is typically rated for 9 kg (20 lbs), so a heavier-duty box specifically listed for weights above 9 kg (20 lbs) is required.