What is the first step to take when diagnosing any electrical issue on a SEPTA bus to ensure safety?

• A. Secure the vehicle (parking brake applied, wheels chocked) and de-energize the circuit using Lockout/Tagout before touching conductors.
• B. Check tire pressure.
• C. Remove battery terminals immediately.
• D. Start diagnostic with power on.

Answer: (A)

The main safety idea is that you must remove all energy and prevent any accidental re-energization before you touch electrical components. In practice on a SEPTA bus, that means securing the vehicle so it cannot move (parking brake applied and wheels chocked) and isolating the electrical system with Lockout/Tagout. Lockout/Tagout involves locking out power sources and tagging them so no one can restore energy while you’re diagnosing or servicing conductors. This eliminates shock hazards, arc flash risks, and the danger of moving parts while you work, and it covers not just the main battery but all potential energy sources and stored energy in capacitors or circuits.

Starting with power on or simply removing battery terminals would miss other energy sources and stored energy that could still pose a threat. Checking tire pressure is unrelated to electrical safety in this context, and beginning diagnostics with power on directly exposes you to shock, arc flash, and unintended device start-up.