An electrical panel schedule shows a 40-amp, 240-volt circuit for an electric water heater. What is the maximum wattage this circuit can safely supply?
Correct Answer
C) 9,600 watts
Power (watts) = Voltage × Amperage. For a 40-amp, 240-volt circuit: 240V × 40A = 9,600 watts. This calculation helps verify that the circuit capacity matches the equipment requirements.
Why This Is the Correct Answer
Option B is correct because electrical power is calculated using the fundamental formula P = V × I (Power = Voltage × Current). For a 40-amp, 240-volt circuit, the maximum wattage is 240V × 40A = 9,600 watts. This represents the theoretical maximum power the circuit can safely supply under continuous load conditions. Understanding this calculation is essential for verifying that electrical circuits are properly sized for their intended equipment loads.
Why the Other Options Are Wrong
Option A: 10,200 watts
8,000 watts is too low and would result from an incorrect calculation, possibly using 200 volts instead of 240 volts (200V × 40A = 8,000W) or miscalculating the amperage.
Option D: 8,000 watts
12,000 watts significantly exceeds the circuit capacity and would require a 50-amp circuit at 240 volts (240V × 50A = 12,000W) rather than the 40-amp circuit specified.
Memory Technique
Remember 'VIP' - Voltage × Amps = Power. For 240V circuits, think '240 × amps = watts' - it's a straight multiplication with no tricks.
Reference Hint
NEC Article 220 - Branch Circuit, Feeder, and Service Load Calculations, or basic electrical theory sections in contractor reference materials
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