Train order home control relay?

• A. Tb
• B. Toh
• C. Te
• D. T

Answer: (B)

The key idea is identifying the relay that explicitly represents the Train Order Home function. In signaling practice, relay names are built from the function they serve, with a suffix that tweaks the role. The Train Order Home control relay is labeled Toh, which breaks down to Train Order (To) plus home (h). That naming makes it the relay that governs the “home” point of the train order circuit, essentially gating the train-order flow at the home position so orders are issued or accepted only when the equipment is properly ready. If the home point isn’t in the correct state, the Toh relay won’t allow the train-order circuit to operate, helping prevent misrouted or unsafe orders.

The other names correspond to different functions in the same system and don’t carry the specific home designation, so they don’t indicate the home-control role.