440G-MZS20UNRJ — MZS Series Guard Locking Safety Interlock Switch, 24V DC

The 440G-MZS20UNRJ is a guard locking safety interlock switch from the MZS series. It combines the position monitoring function of a safety interlock switch with an electromechanical locking mechanism that physically holds a guard door closed until an electrical unlock signal is applied. The device serves two safety functions simultaneously: detecting guard position (is the door closed?) and preventing guard opening (can the door be opened?) based on the machine's safety state.

Where a standard safety interlock detects guard position and initiates a stop when the guard opens, a locking switch prevents the guard from opening at all until a safe condition is confirmed — motor stopped, hazardous energy dissipated, safe speed verified. This is mandatory for hazards with run-down times longer than the operator's reach time, or where energy stored in the process (pressure, elevated temperature, rotating inertia) persists after motor stop.

Specifications

Parameter	Value
Part Number	440G-MZS20UNRJ
Series	MZS
Locking Mechanism	Solenoid-actuated, spring-locked (power to unlock)
Lock Voltage	24V DC
Lock Force (holding)	Up to 2000 N
Guard Monitoring Contacts	2 × NC (safety) + 1 × NO (auxiliary)
Lock Status Contacts	1 × NC (lock monitoring)
Safety Rating	SIL 2 / PLe Category 4 (ISO 13849-1)
Actuator Type	Tongue-style, separate from switch body
Emergency Release	Internal manual release (via tool) + external cable release option
Enclosure	IP67
Operating Temperature	−25°C to 70°C
Standards	IEC 60947-5-1, EN ISO 14119, UL 508, CE

Safety Circuit Integration

The 440G-MZS20UNRJ integrates into the safety circuit at two levels. The guard monitoring NC contacts (two) wire to a dual-channel safety relay or safety controller input — confirming guard is closed. The lock status NC contact provides feedback that the mechanical lock is engaged, which the safety controller uses to confirm the machine can operate. The unlock coil (solenoid) connects to the safety controller's output: when a safe condition is confirmed, the safety controller energizes the coil to release the lock and allow access.

The sequence in a well-designed implementation:

Operator requests access → safety controller confirms hazard is resolved (speed, temperature, pressure within safe limits).
Safety controller energizes unlock coil → solenoid releases → guard can be opened.
Guard opens → guard monitoring contacts open → safety controller confirms machine is safe-stopped.
Guard closes → tongue inserts → monitoring contacts close → lock re-engages (spring) → lock status contact confirms locked.
Safety controller confirms locked state → machine can restart.

FAQ

Q: What happens if power is lost while the guard is unlocked?

Spring lock engages immediately on power loss — the guard locks. Operators inside the guarded area may be temporarily locked in. The emergency release (internal manual actuator or external cable release) provides egress in this scenario — verify its accessibility before installation and train operators on its location and use.

Q: Can the lock be bypassed in an emergency without tools?

The 440G-MZS20UNRJ includes a tool-operated internal manual release as standard. An external cable release option provides tool-free release from outside the guarded area. At least one release mechanism must be accessible from inside the guarded zone to satisfy EN ISO 14119's requirement that trapped persons can always exit.

Q: Does guard locking eliminate the need for a separate door position sensor?

No separate sensor is needed — the two NC guard monitoring contacts in the switch body confirm door closed and tongue fully inserted. The lock status contact additionally confirms the mechanical latch is engaged. All three functions are integrated in one device.

Q: What defines when the machine can unlock the guard — is this set in the switch itself?

The unlock condition is defined in the safety controller logic, not the switch. The switch provides the lock/unlock interface (solenoid input) and the feedback contacts. The decision of when safe conditions have been met — based on speed monitoring, temperature sensors, process pressure, or other hazard-specific parameters — is the safety controller's responsibility.

440G-MZS20UNRJ Brand New 440GMZS20UNRJ Guardmaster Switch