CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A client requests a material takeoff for a new residential kitchen. The plans specify a 20A, 120V dedicated branch circuit for a wall-mounted microwave oven rated at 1500W. What is the minimum continuous load current that must be used for sizing the overcurrent protective device (OCPD) for this circuit, assuming the microwave is considered a non-continuous load for this context?
- A20.0 A
- B12.5 A
- C18.75 A
- D15.0 A
Show answer & explanationAnswer & explanation
Correct answer: B. 12.5 A
Even though a microwave oven can operate for extended periods, for residential kitchen appliance branch circuits, the NEC typically considers them as non-continuous for load calculations unless explicitly stated otherwise or part of a defined continuous operation. The current is calculated as Power (W) / Voltage (V) = 1500W / 120V = 12.5 Amps. No 125% factor is applied for non-continuous loads.
Why the other options are wrong
- A. Incorrect. This is the circuit rating, not the load current.
- C. Incorrect. This would be the current if it were a continuous load, but the question specifies non-continuous.
- D. Incorrect. This value is not derived from the given power and voltage.
Non-Continuous Load Sizing for OCPD
The process of sizing an overcurrent protective device (OCPD) for a load that does not operate for 3 hours or more, where the OCPD rating can be equal to or greater than the calculated load current.
- A non-continuous load operates for less than 3 hours.
- OCPD rating can be 100% of the calculated load current.
- No 125% multiplier is applied for non-continuous loads.
Memory trick: Non-continuous: 'NO' extra 'PERCENT' for the OCPD.