What is a sag test in electrical systems and when is it performed?

• A. A test of voltage drop under load to assess conductor adequacy; performed at commissioning or after major load changes.
• B. A test of insulation resistance under no load.
• C. A test of current carrying capacity at ambient temperature.
• D. A test of circuit breaker trip times.

Answer: (A)

The main idea is to assess how much voltage drops along distribution conductors when the system is actually under load. A sag test checks whether the conductor sizing and wiring arrangement can keep voltages within acceptable limits across the network, especially at points that are farthest from the source or that carry the heaviest load. This is about ensuring voltage regulation under real operating conditions, not about measuring insulation, carrying capacity at a specific ambient temperature, or the timing of circuit breaker trips.

That’s why this option is the best fit: it describes testing voltage drop under load to gauge conductor adequacy. It’s typically done at commissioning to establish a baseline and again after major changes to the load profile or configuration (such as adding feeders or rerouting circuits) to confirm the system still meets voltage requirements.