When using the 3rd rail tester, always attach to the __ first.

Attaching the 3rd rail tester to the lower running rail first is essential for safety and accuracy during testing. The lower running rail serves as a ground reference point, which helps ensure that any potential electrical faults or abnormalities are safely managed. By establishing a connection with the lower running rail first, testers can effectively measure the voltage or current in the third rail while minimizing the risk of electrical shock or equipment damage.

Establishing the lower running rail as a reference point also allows for a more accurate assessment of the circuit's continuity and helps in identifying any issues with the third rail's functionality without exposing the technician to unnecessary risks. This approach is consistent with safety protocols in railway operations, emphasizing the importance of grounding before engaging with potentially live components.