An electrical schedule shows a panel with a 200-amp main breaker and lists 40 circuits. If each circuit breaker is rated at 20 amps, what is the demand factor being applied?
Correct Answer
A) 25%
Total circuit capacity = 40 circuits × 20 amps = 800 amps. Panel capacity = 200 amps. Demand factor = 200/800 = 0.25 or 25%.
Why This Is the Correct Answer
The demand factor is calculated by dividing the actual panel capacity by the total connected load capacity. With 40 circuits at 20 amps each, the total connected load is 800 amps, but the panel only has a 200-amp main breaker capacity. This gives us 200 ÷ 800 = 0.25 or 25%, which reflects the realistic expectation that not all circuits will operate at full capacity simultaneously.
Why the Other Options Are Wrong
Option B: 50%
50% would result from incorrectly calculating the demand factor, possibly by confusing the relationship between panel capacity and circuit capacity or using wrong values in the calculation.
Option C: 75%
75% represents a much higher demand factor that would require a 600-amp main breaker (75% of 800 amps), which doesn't match the given 200-amp panel capacity.
Option D: 100%
100% would mean no demand factor is applied, requiring the panel capacity to equal the total circuit capacity (800 amps), which clearly doesn't match the 200-amp main breaker shown.
Memory Technique
Think 'Demand = Delivered ÷ Designed' - the actual delivered capacity (panel) divided by the designed total capacity (all circuits)
Reference Hint
NEC Article 220 - Branch-Circuit, Feeder, and Service Load Calculations, specifically sections on demand factors and load calculations
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