A controller's output interface is often provided by a device with no moving parts to control a higher-power load.

• A. Solid-state relay
• B. Mechanical relay
• C. Thermal switch
• D. Magnetic contactor

Answer: (A)

Switching a higher-power load with no moving parts is what a solid-state relay provides. A solid-state relay uses semiconductor switches controlled by a low-power input, often with opto-isolation between the control side and the load side. Because there are no mechanical contacts to move, there’s no wear from arcing, and switching is fast and quiet, giving long life and reliable control from a controller output.

Mechanical relays and magnetic contactors rely on coils pulling contacts together, which involve moving parts and wear over time. Thermal switches rely on a temperature-sensitive element that changes state, which also involves mechanical action. These options don’t match the “no moving parts” advantage as well as a solid-state relay.