Electrician Red Seal · Question
An electrician is sizing overcurrent protection for a 15 kW, 208 V, 3-phase resistive heating load. The heaters are continuous duty. What is the minimum standard-rated circuit breaker size required, assuming the conductors are sized correctly for the load?
First, calculate the full-load current: I = P / (√3 × V) = 15000 W / (1.732 × 208 V) ≈ 41.6 A. For continuous loads, CEC Rule 8-104(2) requires overcurrent prot
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Question: An electrician is sizing overcurrent protection for a 15 kW, 208 V, 3-phase resistive heating load. The heaters are continuous duty. What is the minimum standard-rated circuit breaker size required, assuming the conductors are sized correctly for the load?
Answer options:
- 40 A ✅ 50 A
- 60 A
- 70 A
Correct answer: 50 A
Explanation: First, calculate the full-load current: I = P / (√3 × V) = 15000 W / (1.732 × 208 V) ≈ 41.6 A. For continuous loads, CEC Rule 8-104(2) requires overcurrent protection to be sized at 125% of the calculated current. So, 41.6 A × 1.25 = 52 A. The next standard fuse or circuit breaker size above 52 A is 50 A, as per CEC Rule 14-106(1) and Table 13.
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