CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A material takeoff for a new commercial office space includes several lighting branch circuits. Each circuit serves 10 fluorescent fixtures, with each fixture rated at 0.5A at 120V. If these circuits are expected to operate for more than 3 hours at a time, what is the minimum calculated load in VA for each circuit to correctly size the overcurrent protective device (OCPD)?
- A600 VA
- B750 VA
- C1200 VA
- D900 VA
Show answer & explanationAnswer & explanation
Correct answer: B. 750 VA
Each fixture draws 0.5A at 120V, so 10 fixtures draw 10 * 0.5A = 5A. Since the load is continuous (operates for more than 3 hours), the calculated load for OCPD sizing must be 125% of the actual load. Therefore, 5A * 125% = 6.25A. The minimum calculated load in VA is 6.25A * 120V = 750 VA.
Why the other options are wrong
- A. 600 VA is incorrect; this represents the actual load (5A * 120V) without applying the continuous load factor.
- C. 1200 VA is incorrect; this calculation is not derived from the standard continuous load rules.
- D. 900 VA is incorrect; this would result from applying a 150% factor, which is not the standard for continuous loads.
Continuous Load VA Calculation
When determining the VA for continuous loads (operating for 3+ hours) to size an OCPD, the actual VA load must be multiplied by 125%.
- Continuous load: max current for 3+ hours
- OCPD must be sized at 125% of continuous current
- Calculated VA = actual VA * 1.25
Memory trick: VA for continuous loads needs a 'quarter-more' for safety.