Automation NotebookIssue 30 - 2014Learning ResourcesNotebook IssueProductSafety

Control Access to Equipment with Dold Trapped Keys

AutomationDirect has added Dold trapped key systems to its line of safety products. A trapped key system uses a series of mechanical locks and keys to control the access of gates or doors to running equipment or machines, ensuring safe access to those machines.

Since multiple doors are connected via uniquely coded keys, you can manage access and safety control on doors that are spaced far apart without having to run expensive wiring.

For example, let’s say you have a production line composed of several machines from various manufacturers.  You want to centrally guard control to the access panels on all the machines which would require safety devices mounted and wired in series throughout the production line. SafetyTrapKeys 5x7Depending on spacing and conduit accessibility, this could be expensive.  Installing a trapped key would allow you to wire one safety circuit to the main contact and only mount mechanical locks on the doors, no wires. Once your machine is safely shut down, four keys are released and can be used to access the four locked doors on each machine. Only after all four keys are returned, can the machine be re-energized.

If you are currently using lock-out tag-out procedures, this system is designed to work in conjunction with lock-out tag-out, instead of replace it. You can apply locks to the trapped keys or the door access gate themselves providing safety sequencing and manual lock-out procedures.

Constructed of solid stainless steel, these parts are ideal for the harshest conditions. Except for the relay unit with your electrical contacts, all the door gate components are purely mechanical and can handle temperatures from -75 to 140C in addition to extreme washdown environments.

Dold trapped key system gate sets provide a full trapped key safety system, in one- to five-gate sets. Available in standard (SX) or solenoid-locking (ZRH) versions, all keys and their corresponding receivers and modules are unique within a set.

trapped_key_lock_300The SX-series of standard gate sets are 316L stainless steel body interlock safety switches with one
normally-closed and two forced opening normally-open/normally-closed changeover contacts.

The ZRH-series solenoid gate sets are 24 VAC/DC solenoid interlocking safety switches. These gate sets are designed with one NC and two forced opening NO/NC changeover contacts for actuator tongue (key) status, and two NC and one forced opening NO/NC changeover contacts for solenoid status.

Accessories available include door actuators, captive safety key sets, key modules for key exchange box setup and tongue key actuators (purchased separately from the gate sets). Steel mounting plates are offered in eight pre-fabricated sizes for easy mounting of various configured trapped key stations; mounting plate size needed depends on size and number of modules in your application.

Prices start at $1,019 for the standard one-gate set; solenoid gate sets start at $1,239. [hozbreak]

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Originally Posted: Sept. 10, 2014