EUCHNER STP-TW-3A-2131AC024M Twin Guard Locking Switch

One guard locking switch for two doors

The EUCHNER STP-TW-3A-2131AC024M (order no. 099973) is a plastic-housing safety switch with guard locking and a TWIN function: it has two actuating heads, so a single switch secures two movable guards at the same time, for example the two leaves of a double door or two adjacent guards. Guard locking follows the closed-circuit current principle, so a spring keeps the guard locked until the 24 V solenoid is energised and a power failure leaves the guards locked.

The switching element 2131 provides one NC contact for door monitoring and, for guard-lock monitoring, two positively driven contacts plus one NO contact. The device is wired through three M20 x 1.5 cable entries, has an auxiliary release on the front for use during faults, and the actuating heads accept horizontal or vertical approach in 90 degree steps (approach directions A and C for the two heads).

Technical specifications

Actuators and release options

The actuators are not included. EUCHNER lists actuators for the SGA/SGP/STA/STP/STM family, for example BETAETIGER-S-G-SN-C2115 (097861), the bent actuators BETAETIGER-S-W-SN-C2115 (115073) and BETAETIGER-S-WT-SN-C2115 (105808) for a minimum door radius of 300 mm, and hinged stainless steel actuators A-S-RLR-SS-175747 (left/right) and A-S-ROU-SS-176045 (top/bottom). With the actuator BETAETIGER-S-GT-SN the overtravel is 5 mm, which relieves the switch head when a door closes against a rubber end stop.

Because the guard locking control is external, the performance level for the locking function depends on how the solenoid is switched. The auxiliary release must be protected against misuse, for example by sealing or lacquer. Evaluate the door and guard-lock contacts in a safety relay or controller, and protect against inductive loads according to the operating instructions.

How the EUCHNER STP-TW-3A-2131AC024M guard locking switch works

A guard locking switch keeps a safety door closed and locked while a machine is in a dangerous state. A coded actuator is fixed to the door, and when the door closes the actuator enters the head of the switch. The switch then confirms that the door is closed and, with its locking pin, holds the door locked. In the STP-TW-3A-2131AC024M the guard locking works on the closed-circuit current principle. A spring locks the guard, and the 24 V solenoid must be energised to unlock it. If the power fails, the guard stays locked. The TWIN version has two actuating heads, so one switch monitors and locks two doors.

Where the STP-TW-3A-2131AC024M is used

• Double doors on machine guards.
• Two adjacent guards that open at the same time.
• Machines with a run-down time, where the door must stay locked until motion has stopped.
• Process machines where an open door would expose hot or moving parts.
• Packaging, assembly and handling cells.

Selection checklist for the STP-TW-3A-2131AC024M

• Guard locking principle: closed-circuit current, power to unlock.
• Solenoid voltage of 24 V AC or DC and power of 8 W.
• Contacts: one NC for door monitoring, and two positively driven contacts plus one NO for lock monitoring.
• Locking force of 2500 N maximum.
• Protection class IP67 and ambient temperature of -20 to +55 degrees C.
• Cable entries: three M20 x 1.5.
• Actuators, which are ordered separately, in the right shape for the door.
• Approach direction of the actuator at each head.
• Safety level required by the risk assessment, and the B10D value for the calculation.

Installation, commissioning and maintenance notes

Fix the switch on the frame and the actuators on the doors, so that each actuator enters its head squarely. Do not use the switch as a mechanical stop. Wire the contacts into the safety circuit as the risk assessment requires, and check the lock monitoring contacts. The auxiliary release on the front is for use during faults, and it should be sealed or protected against misuse. After installation, test each door for locking, unlocking and monitoring, and repeat the test at regular intervals.

Requesting a quotation for the EUCHNER STP-TW-3A-2131AC024M

Send the quantity and the actuators that you need. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

Why the actuator is ordered separately

The shape of the door and its hinge decide the best actuator. Straight and bent versions are available for the switch family, so choose them for the door movement.

Closed-circuit current and process safety

With this principle the door stays locked when the power is off. This suits machines that keep moving after the supply is cut, but a person inside a guarded area then needs a way to escape, so check the rules for the machine.

Records for safety devices

Keep the type, the order number and the test results of each safety switch with the machine file.

Documents and quotation

The attached EUCHNER operating instructions for the STP-TW (Twin) safety switch (14, 04/2025) cover mounting, wiring and releases. For a quotation, give the order number 099973, the actuator types for both doors and the quantity. Related interlocks are under Safety Switches and Guard Locking.