What does a polarity tester primarily check?

A polarity tester is specifically designed to determine whether an electrical receptacle is wired correctly, ensuring that live, neutral, and ground wires are properly configured in the circuit. This is crucial for safety, as incorrect wiring can lead to electric shock hazards and malfunctioning devices.

When using a polarity tester, it typically confirms that the hot wire is connected to the correct terminal, the neutral wire is appropriately grounded, and that the receptacle is functioning as intended. This verification helps prevent accidents and ensures that electrical equipment will operate safely and effectively.

The other options focus on different aspects of electrical systems. For instance, checking the efficiency of a power supply and measuring the voltage of a circuit may require different tools, such as a multimeter, rather than a polarity tester. Additionally, determining the length of wiring is a task that involves physical measurement rather than evaluating the electrical properties of a circuit. Thus, the primary function of a polarity tester is indeed to verify proper wiring in electrical receptacles.