What is the first step to take before working on existing circuits?

The first step to take before working on existing circuits is to turn off the power to the circuits. This is crucial for safety reasons. Working on live circuits can pose serious risks, including electric shock or electrical fires. By ensuring that the power is turned off, you create a safe environment to conduct work, reducing the risk of injury.

When you turn off the power, it is also advisable to verify that the power is indeed off by using a voltage tester. This additional step ensures that there is no residual voltage present that could be hazardous.

While checking voltage levels, inspecting the wiring, and labeling the circuits can be important tasks, they should only be done after ensuring that the power is completely turned off. Such practices help maintain safety and should always follow the initial step of cutting power to the circuit in question.