If the relay STR has voltage, TRU has voltage, but RU has no voltage, what could be causing this?

In this scenario, the observed condition is that while the relay STR and TRU both have voltage, RU does not. This suggests that there may be an issue in the circuit or system specifically related to the connections or signaling associated with the TRU pathways leading to RU.

Option indicating TRU 9/8 likely refers to a particular configuration or connection in the TRU circuit that should provide voltage to RU. If this specific connection is not allowing voltage to pass through effectively, it might mean that there's an interruption or fault in that pathway, which would explain the lack of voltage at RU.

Understanding the function of each component is crucial: the relay is capable of switching voltage based on signals it receives, while TRU likely serves as a transformer or control unit facilitating power distribution. The failure of RU to receive voltage confirms that an issue exists downstream of the TRU circuit where TRU 9/8 is responsible.

Therefore, by identifying the specific TRU connection in question—designated as 9/8—it's clearer that restoring or addressing the potential fault in this area may rectify the absence of voltage at RU, ensuring proper operation of the system.