CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A lighting layout on a blueprint shows a linear array of LED strip lights, with each section requiring 50 VA. The entire run consists of 10 sections. The circuit is 120V. When performing a material takeoff for the overcurrent protection, what is the minimum required amperage for the branch circuit overcurrent protective device if these lights are considered a continuous load?
- A20A
- B15A
- C10A
- D5A
Show answer & explanationAnswer & explanation
Correct answer: B. 15A
Total connected load = 10 sections * 50 VA/section = 500 VA. Current = Power / Voltage = 500 VA / 120V = 4.167A. Since these are continuous loads (lighting), the OCPD must be sized at 125% of the continuous load current (CEC 210.20(A)). Required OCPD current = 4.167A * 1.25 = 5.209A. The next standard OCPD size is 15A (CEC 240.6(A)).
Why the other options are wrong
- A. Incorrect. 20A is a standard size but is significantly larger than the minimum required.
- C. Incorrect. 10A is a standard size but is larger than the minimum required.
- D. Incorrect. 5A is less than the calculated 5.209A needed after the 125% adjustment.
Continuous Load OCPD Sizing
Overcurrent protective devices (OCPDs) for continuous loads (operating for 3 hours or more) must be sized at not less than 125% of the maximum continuous load current.
- Applies to feeders and branch circuits (CEC 210.20(A), 215.2(A)(1)).
- Ensures the OCPD does not trip prematurely due to heating effects.
- The calculated value is then matched to the next standard OCPD size (CEC 240.6(A)).
Memory trick: Long run, add a quarter, then pick the next fuse.