What is the most important safety measure before working on electrical circuits?

Before commencing work on electrical circuits, the most crucial safety measure is disconnecting power. This action ensures that there is no live electrical current flowing through the circuits you are about to work on, reducing the risk of electric shock, burns, or other hazards associated with working on energized circuits. Properly isolating energy sources not only protects the individual performing the work but also safeguards others who may inadvertently come into contact with the circuit during maintenance or repairs.

In contrast, using non-insulated tools does not address the primary concern of live current. Similarly, wearing shorts and a t-shirt does not provide adequate protection from electrical hazards, as appropriate personal protective equipment and clothing should always be used. Additionally, using tools designed for a variety of voltage ratings without ensuring they are appropriate for the specific job can lead to dangerous situations, as not all tools are suitable for every electrical application.