CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A material takeoff for a new commercial office space includes several lighting branch circuits. Each circuit is 120V and serves 10 LED luminaires, with each luminaire rated at 100 VA. The luminaires are expected to operate continuously for more than 3 hours daily. What is the minimum continuous load current that must be used for sizing the overcurrent protective device (OCPD) for one of these branch circuits?
- A10.41 A
- B12.50 A
- C8.33 A
- D15.00 A
Show answer & explanationAnswer & explanation
Correct answer: A. 10.41 A
The total load for one circuit is 10 luminaires * 100 VA/luminaire = 1000 VA. Since the load is continuous, the current must be multiplied by 125%. So, (1000 VA / 120V) * 1.25 = 8.33 A * 1.25 = 10.41 A.
Why the other options are wrong
- B. Incorrect. Calculation error in applying the 125% factor.
- C. Incorrect. This is the non-continuous load current.
- D. Incorrect. This is an overestimation of the continuous load current.
Continuous Load Sizing for OCPD
The requirement in the NEC (210.20(A), 215.2(A)(1)) to size overcurrent protective devices (OCPDs) for continuous loads at not less than 125% of the continuous load current.
- A continuous load operates for 3 hours or more.
- OCPDs must be sized at 125% of the continuous load current.
- This factor accounts for heat buildup in the OCPD.
Memory trick: Continuous loads need an 'OCPD' that's '125' percent strong to avoid 'OVER'heating.