RCO Training – Mechanical Practice Test

In GE locomotive panels, circuits are presented as two rows with a Lead (supply) side and a Trailing (return) side. The intended way to energize a circuit is to have the top row connect the Lead while the Trailing is kept OFF, and then have the bottom row ON to complete the path. This sequencing prevents backfeed and ensures the load is energized in a controlled, safe order. When the top row shows Lead ON and Trailing OFF, and the bottom row is ON, power flows through the circuit properly from the Lead through the load back to the return path. If the top row were to have both paths ON or the bottom row were OFF, the circuit could short or fail to energize correctly.