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Trapped Key Interlocking

mGard is a modular range of trapped key interlocks from Fortress. Mechanical interlocking is a tried and test method of safeguaridng hazardous machines and dangerous processes which virtually elimiantes the need for electrical wiring, making these systems cost-effective to install and maintain. 

What is Trapped Key Interlocking?

Often referred to as Castell or Castle Key Locks; Trapped Key interlocking is the sequential control of dangerous machinery and hazardous processes for industrial safety applications. mGard is the only modular range of mechanical Trapped Key interlocks that have been independently certified to PLe; the highest safety rating on the market.

It is called 'Trapped Key' as it works by releasing and trapping keys in a predetermined sequence that cannot be intentionally defeated or circumvented by unauthorised means. Therefore, Trapped Key interlocks have been designed to minimise the motivation for defeating the interlocking device in accordance ISO 14119: Safety of Machinery - Interlocking devices associated with guards. 

The principles of Trapped Key interlocking apply to all industries where it is essential to isolate all energy sources before safe access into machinery or protected areas can be achieved. As an example, after a machine's control circuit has been isolated by means of a 'Key Switch,' a key is released that can be used to grant access to the guard doors around the perimeter of a dangerous machine.

Purely Mechanical Interlocking

The mGard range of Trapped Key interlocks is a tried and tested method of mechanically safeguarding dangerous machines and hazardous processes which eliminates most of the electrical wiring associated with other types of interlock devices, making it cost effective to install and maintain.

How to design a Trapped Key system?

Trapped Key interlocking systems can be as simple as safeguarding a single access point or as complex as protecting a series of machines that each have multiple guard doors. However, all Trapped Key systems can be designed by following three simple principles. 

1) Identify the energy sources to be isolated

Most machinery safety applications require that the machine's electrical supply should be isolated to mitigate the risk of serious/fatal injury but in some applications, the pneumatic and hydraulic supply may also need to be isolated to ensure safe access.

2) Identify the number of access points

The second step is to identify the number of access points that will need safeguarding around the perimeter of the machine. All moveable guards or enclosure doors should be fitted with an appropriate safety interlocking device. 

3) Determine the type of access required

The type of access that is required will determine what type of safety interlock will be suitable. For example, is there a risk that an operator could enter the machine and remain hidden from view. In these scenarios, providing the user with a safety key to prevent unexpected machine restart. 

mGard Product Builder

Seamlessly configure all standard mechanical interlocks within  the Fortress trapped key range using the mGard product builder and download all relevant product files inclduing 3D CAD data and dimensional drawings. 

Configure your interlock

Common Trapped Key Applications

Developing a trapped key interlocking system isn't as difficult as you might think. Check out these application examples for some safety-inspiration

Achieving Maximum Safety

The mGard range of Trapped Key interlocks are suitable for use in safety applications up to SIL 3 (EN/IEC 62061), Category 4 and PLe (EN/ISO 13849-1), as approved by independent test house TUV SUD. Download a copy of the certificate here for your documentation.