Designing a risk reduction strategy where inertia plays a critical role in the risk assessment, such as rotating equipment and high pressure pneumatic valves, is challenging. The D4NL series is a flexible and cost effective guard-locking door switch designed to prevent access to hazards in this situations. With the various combinations of mechanical lock/solenoid release, the D4L has a key holding force of up to 1300N, reducing the risk of access to the hazard. The D4L simplifies installation and maintenance with a plastic housing, availability with four or five built-in contacts, compatibility various conduit types and sharing a common key set with D4GL and D4NS series