This standard specifies principles for the design and selection - independent of the nature of the energy source - of interlocking devices associated with guards (as defined in 3.23.1 ' interlocking device [interlock]' , 3.22.4 ' interlocking guard' and 3.22.5 ' interlocking guard with guard locking' of EN 292-1). It also provides requirements specifically intended for electrical interlocking devices (see clause 6). This standard covers the parts of guards which actuate interlocking devices. Requirements for guards are given in prEN 953. The processing of the signal from the interlocking device to stop and immobilize the machine is dealt with in prEN 954-1.