Electrical Power Testing Flashcards

In the fall-of-potential ground resistance test, the potential probe is typically placed at what percentage of the distance to the current probe?

Answer: 62%

The 62% rule places the potential probe at 62% of the electrode-to-current-probe distance for accurate readings.

Which standard covers electrical safety in the workplace, including arc flash requirements?

Answer: NFPA 70E

NFPA 70E is the Standard for Electrical Safety in the Workplace.

Very low frequency (VLF) withstand testing of medium-voltage cables commonly uses a frequency of:

Answer: 0.1 Hz

VLF testing typically uses 0.1 Hz to reduce the charging power needed for long cable lengths.

Per NETA thermography guidelines, a temperature difference greater than 15°C between similar components under similar load indicates:

Answer: A major discrepancy requiring immediate repair

NETA classifies a >15°C rise between similar components as a major discrepancy requiring immediate repair.

Under the NEC, a single ground rod with resistance above what value requires a supplemental electrode?

Answer: 25 ohms

NEC 250.53(A)(2) requires a supplemental electrode unless a single rod is 25 ohms or less.

During a DC high-potential test on a cable, which leakage current behavior indicates a potential insulation problem?

Answer: Current increasing at constant test voltage

Rising leakage current at a constant voltage suggests insulation deterioration or impending breakdown.

The arc flash boundary is defined as the distance at which incident energy equals:

Answer: 1.2 cal/cm²

NFPA 70E defines the arc flash boundary at 1.2 cal/cm², the onset of a second-degree burn.