Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingEasy
A technician is installing a new 240V, 10kW electric water heater. The circuit is protected by a 50A overcurrent device. What is the approximate operating current of the water heater at its rated power?
- A20.8 A
- B50.0 A
- C24.0 A
- D41.7 A
Show answer & explanationAnswer & explanation
Correct answer: D. 41.7 A
To find the operating current, use the formula P = V × I, where P is power, V is voltage, and I is current. Rearranging for current, I = P / V. So, I = 10,000 W / 240 V = 41.66 A, which is approximately 41.7 A.
Why the other options are wrong
- A. This would be the current if the voltage was 480V or if the power was 5kW at 240V.
- B. This is the rating of the overcurrent device, not the operating current of the appliance.
- C. This would be the current if the power was 5.76 kW at 240V.
Ohm's Law for Power
Ohm's Law for Power relates power (P), voltage (V), and current (I) in an electrical circuit.
- P = V × I (Power = Voltage × Current)
- P = I² × R (Power = Current squared × Resistance)
- P = V² / R (Power = Voltage squared / Resistance)
Memory trick: P-IV, Power is IV, as in intravenous, a direct line.