Trapped Key Interlock Switches

A trapped key system uses a series of mechanical locks and keys to control the access to running equipment or machines, ensuring safe access to those machines. These systems rely on the transfer of keys between a power isolation switch (or control switch) and a mechanical locking mechanism fixed on a guard.

The essential feature of the system is that a removable key is literally trapped either in the guard lock or in the control switch. The lock on the guard is arranged so that the key can be released only when the guard has been closed and locked.

Where there is more than one guard on a machine, an exchange box will accommodate the equivalent number of access keys. A series of operations has to be carried out in a pre-determined sequence for the current key to be exchanged for the next key in the sequence. Human operation of locking/unlocking provides first hand, observable safety.

• Trapped key interlock systems are available in push-pull and rotary key styles (with and without solenoid locking).
• A trapped key system is cost-effective for multiple locks over a large area and eliminates the cost of running electrical wiring over long distances.
• Note: Ordering a larger gate set than needed for the number of gates in a system compromises the safety integrity of that system. Spare keys are not available.

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