CSLB C-10 Electrical ContractorElectrical Theory and CalculationsMedium
A 240V single-phase circuit supplies a load with 20 amps. What is the maximum voltage drop allowed for a branch circuit that is 100 feet long, if the NEC limits voltage drop to 3% for branch circuits?
- A12 volts
- B7.2 volts
- C3.6 volts
- D2.4 volts
Show answer & explanationAnswer & explanation
Correct answer: B. 7.2 volts
The maximum allowed voltage drop for a branch circuit is 3% of the nominal voltage. 3% of 240V is 0.03 * 240V = 7.2 volts. The current and length are distractors for this specific question.
Why the other options are wrong
- A. This would be 5% of the voltage, exceeding the 3% limit for branch circuits.
- C. This is 1.5% of the voltage, or possibly a calculation error.
- D. This would be 1% of the voltage, not 3%.
NEC Voltage Drop Limits
The National Electrical Code (NEC) recommends maximum voltage drops of 3% for feeders and 3% for branch circuits (total 5% from service to farthest outlet) to ensure efficient operation and prevent equipment damage.
- 3% maximum for feeders.
- 3% maximum for branch circuits.
- Total maximum of 5% from service entrance to the farthest outlet.
- Recommendations are not mandatory unless adopted by local jurisdiction or specified by equipment manufacturer.
Memory trick: Three for Branch, Three for Feed, Five for Total, a good electrical deed.