The main components in HVAC equipment are fan motors, compressors and devices like expansion valves and solenoid valves. All of these are electrical loads. A load is a component in a circuit that converts electricity into light, heat, or mechanical motion. HVAC control systems also contain switches and other control devices. Some switching devices have load electrical components such as the coils in a contactor or relay.
Circuits are controlled by a switchgear / electrical components which are assembled so that the circuit may be operated safely under normal conditions, isolated automatically under fault conditions, or isolated manually for safe maintenance. These requirements are met by good workmanship and the installation of proper materials such as: