Which circuit breaker on the SIU power distribution unit must be set to OFF when working on top of the ATG?

The correct choice is to set the AZIMUTH DRIVE circuit breaker to OFF when working on top of the ATG (Air Target Generator). This is essential for safety reasons; the AZIMUTH DRIVE is responsible for controlling the movement of the radar and antenna systems. Ensuring that this circuit breaker is turned off eliminates any risk of unexpected movement or electrical hazards while personnel are on or near the equipment.

This precaution is crucial to prevent accidents that could occur during maintenance or inspections. By isolating this part of the power distribution unit, technicians can work with a reduced risk of injury or damage to equipment. The other circuit breakers, while important for various functionalities of the system, do not directly control the physical movement that poses a risk in this scenario.