CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A contractor is estimating the cost for a new branch circuit in a retail store. The circuit will be 120V and serve six display lights, each with a total load of 75 VA. The circuit breaker is 20A. What is the total estimated continuous load VA for these display lights, requiring the 125% adjustment for the OCPD?
- A562.5 VA
- B450 VA
- C600 VA
- D375 VA
Show answer & explanationAnswer & explanation
Correct answer: B. 450 VA
Total connected load = 6 lights * 75 VA/light = 450 VA. The question asks for the 'total estimated continuous load VA' for the lights. The 125% factor is applied to the calculated continuous load *current* to size the OCPD, not to the VA of the load itself. The continuous load VA remains 450 VA.
Why the other options are wrong
- A. Incorrect. This is 450 VA * 1.25, which is the adjusted load for OCPD sizing (in VA equivalent), but the question asks for the 'continuous load VA' of the lights.
- C. Incorrect. This is higher than the actual connected load.
- D. Incorrect. This is 5 lights * 75 VA.
Continuous Load VA vs. OCPD Sizing
The VA of a continuous load is its actual connected power. The 125% rule (CEC 210.20(A)) applies to the *current* of this continuous load when sizing the overcurrent protective device, not to the VA of the load itself.
- Continuous load: operating for 3 hours or more.
- Load VA is actual power consumed.
- OCPD is sized based on 125% of continuous load current (or equivalent VA for calculation purposes, but the load itself doesn't 'become' 125% larger).
- The conductor ampacity must also be rated for the 125% adjusted current.
Memory trick: Load's VA is actual, Breaker's VA is adjusted.