This International Standard specifies principles for the design and selection – independent of the nature of the energy source – of interlocking devices associated with guards. It also provides requirements specifically intended for electrical interlocking devices. This International Standard covers the parts of guards which actuate interlocking devices. NOTE – Requirements for guards are given in ISO 14120. The processing of the signal from the interlocking device to stop and immobilize the machine is dealt with in ISO 13849-1. This International standard is intended to provide measures to minimize defeat of interlocking devices in a reasonably foreseeable manner.