Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingMedium
A client's single-phase heating element draws 50A at 240V. If the circuit conductors are sized for this load and the voltage drop is calculated to be 3% of the supply voltage, what is the actual voltage at the heating element?
- A232.8V
- B240V
- C237.6V
- D235.2V
Show answer & explanationAnswer & explanation
Correct answer: A. 232.8V
Voltage drop (VD) is 3% of 240V. So, VD = 0.03 * 240V = 7.2V. The actual voltage at the load is the supply voltage minus the voltage drop: V_load = 240V - 7.2V = 232.8V.
Why the other options are wrong
- B. This would be the voltage if there was no voltage drop, which is not the case.
- C. Incorrect calculation.
- D. Incorrect calculation.
Voltage at Load with Voltage Drop
The actual voltage available at a load is the supply voltage minus the voltage drop that occurs along the circuit conductors.
- Voltage drop reduces the voltage supplied to the load.
- Excessive voltage drop can impair equipment performance and efficiency.
- VD is often expressed as a percentage of the supply voltage.
- V_load = V_supply - V_drop.
Memory trick: Drop means less; supply minus drop is load.