Custodian Engineer Book Practice Test

An electric hot water heater controlled by an aquastat requires a magnetic contactor to manage the electrical power supplied to the heating elements. The aquastat itself monitors the water temperature and can signal when the heater should be on or off; however, the actual control of high voltage power to the heating elements demands a magnetic contactor.

The magnetic contactor serves as an intermediary that allows the low voltage signal from the aquastat to safely control a higher voltage circuit. By doing so, it ensures that the electric hot water heater operates effectively without risking damage or safety hazards from direct handling of high voltage.

In contrast, the other options do not serve this essential function. A fuse box primarily protects against overloads and short circuits but doesn’t directly control the operation of the heater. A pressure gauge measures water pressure and wouldn’t influence heating operation or temperature regulation. A thermostat, while important in traditional heating systems, does not apply in the same direct control manner as an aquastat does for electric hot water heaters, especially since the aquastat itself already performs the temperature regulation required in this context.