Switchgear Control

with Trapped Key Interlock Solutions

In this article, we will discuss how trapped key interlocking is implemented within switchgear controls while maintaining system integrity. Factors such as aging infrastructure, technological advancements, lack of investment, and demands for cleaner more reliable ever-present energy have significantly altered the energy sector with switchgear systems becoming increasingly complex. Switchgear systems can involve several power sources, making the integration of HV (High Voltage), MV (Medium Voltage, and LV (Low Voltage) and switching of loads potentially complicated and hazardous. This complexity and risk require the need for a reliable safety solution that ensures personnel safety and protects electrical equipment from hazards during maintenance operations.

A safe process of switchgear maintenance operations requires determining the sequential steps to follow each time the procedure is necessary.  Implementing a trapped key interlocking solution, fixed mounted on the equipment, releasing applicable keys in a pre-determined sequence, removes the sole reliance from work instructions alone and mitigates human error.  A trapped key interlocking solution ensures that the process cannot be circumvented and that wherever personnel find themselves, either starting or shutting down operations, can be assured power has been safely isolated.


The prevention of the paralleling of power sources is critical when performing switchgear maintenance while needing to maintain one source of power.  In the example below, Scheme 16 from the KIRK Scheme Book there are three power loads with two tie breakers to ensure that only one load is closed and in operation at any given time.  This video represents the trapped key interlock logic that would be implemented into this application to ensure the sequence of safety operations and protecting employees and assets.



Designing an interlocking system 

The design of an interlocking system is a process that must be carefully undertaken. A good interlocking scheme requires all risks and operational procedures to be considered to maintain the integrity of the safety solution. This can proactively address how the system will respond in both operational and failure modes along with routine maintenance. An interlocking system will set out the process and steps that must be followed to ensure personnel cannot access potentially dangerous areas. When maintenance activities are being performed, trapped key interlocking systems can ensure that the switchgear system is always in a safe isolated state.


Complicated switchgear systems need to have a robust management system to protect personnel and machinery. Designed correctly, an interlocking scheme can contribute by eliminating human error on site while permitting safe access to electrical equipment. Integration of older equipment with new switchgear can be a challenge, trapped key interlocking allows for the safe integration of OEM switchgear, ensuring safe site operations and negating the need for complicated controls.

KIRK has been delivering safety solutions for switchgear since 1932. Working closely with original equipment manufacturers (OEMs) has enabled KIRK to produce interlocks designed specifically for use on the leading manufacturers own breakers, isolators, and disconnects. KIRK’s comprehensive product offering of isolation and access interlock products for switchgear applications ensures the right solution can be implemented for any application. Mounting provisions often supplied by OEMs enable the interlocks to be easily incorporated however, if a unique mounting provision is required, KIRK’s Applied Engineering Services team can design a customized interlock or provision to meet the requirements.

To discuss any switchgear application requirements please contact our team of technical experts: sales@kirkkey.com