A residential client requests an electrical service upgrade. The existing service is 100A, 120/240V. The new load calculation, per Article 220 of the CEC, includes 2500 sq ft of living space, a 12 kW electric range, a 4.5 kW water heater, and a 5 kW dryer. What is the minimum standard service size required for this dwelling?
- A125A
- B100A
- C150A
- D200A
Show answer & explanationAnswer & explanation
Correct answer: D. 200A
Applying the Optional Method for Dwelling Units (CEC 220.82): 1. General lighting/receptacle load: 2500 sq ft * 3 VA/sq ft = 7500 VA. 2. Small appliance and laundry branch circuits: 3000 VA * 2 (small appliance) + 1500 VA (laundry) = 7500 VA. 3. Total initial load (7500 + 7500) = 15000 VA. Apply demand factors: First 10,000 VA at 100% = 10,000 VA. Remainder (15000 - 10000 = 5000 VA) at 40% = 2000 VA. Total general load = 12,000 VA. 4. Fixed appliances: Range (12000 VA), Water Heater (4500 VA), Dryer (5000 VA). Total = 21500 VA. Apply demand factor for 3 appliances: 75% of 21500 VA = 16125 VA. 5. Total calculated load = 12000 VA (general) + 16125 VA (fixed appliances) = 28125 VA. 6. Service Amperage: 28125 VA / 240V = 117.1875A. The next standard service size is 200A.
Why the other options are wrong
- A. Incorrect. A 125A service is not typically a standard residential service size for this load (117.1875A).
- B. Incorrect. This is the existing service and would be insufficient for the calculated new load.
- C. Incorrect. While 150A is a standard size, it is slightly below the calculated 117.1875A when considering continuous loads and future expansion, and 200A is the more common next step up.
Optional Method Dwelling Unit Load Calculation
A simplified method for calculating the feeder and service loads for dwelling units based on the total connected load, applying specific demand factors.
- Used for single-family dwellings or individual dwelling units.
- Combines general lighting, small appliance, laundry, and fixed appliance loads.
- Applies specific demand factors found in CEC Article 220.82.
Memory trick: CEC's Optional path for Dwellings guides the current flow.