NOTE 1 Examples for electrical relays in the sense of this document include electromechanical relays, reed relays, reed contacts, reed switches, solid state relays, time relays and technology combinations of these.

NOTE 2 If different metals are attached at both ends and the temperatures where the metals are connected are different, then a current will flow in one direction in the circuit. The electromotive force that causes this current is called thermoelectromotive force.