NASCLA Accredited Commercial General ContractorMechanical, Electrical, Plumbing (MEP)Hard
A general contractor is reviewing the electrical plans for a new commercial kitchen. The plans specify a 208V, three-phase circuit for a heavy-duty commercial oven. The overcurrent protection device (OCPD) for this circuit is rated at 60A. What is the maximum continuous current that this circuit can safely carry, according to NEC regulations for continuous loads?
- A75 Amperes
- B80 Amperes
- C60 Amperes
- D48 Amperes
Show answer & explanationAnswer & explanation
Correct answer: D. 48 Amperes
For continuous loads (operating for 3 hours or more), the overcurrent protection device must be sized at 125% of the continuous load. Conversely, the continuous load itself cannot exceed 80% of the OCPD rating. Therefore, 60A * 0.80 = 48A.
Why the other options are wrong
- A. Incorrect. This would imply the OCPD is undersized for a 60A continuous load.
- B. Incorrect. This value is significantly higher than the allowed continuous current for a 60A OCPD.
- C. Incorrect. 60A is the OCPD rating, not the maximum continuous current it can safely carry.
NEC Continuous Load Rule
For continuous loads (expected to operate for 3 hours or more), the overcurrent protection device must be sized at least 125% of the continuous load, or the continuous load must not exceed 80% of the OCPD rating.
- Applies to loads operating for 3+ hours.
- OCPD must be 125% of continuous load.
- Continuous load must be 80% or less of OCPD rating.
- Prevents overheating and ensures safety.
Memory trick: Continuous Current Cuts Circuit Capacity by 20% for Safety.