What is a Kirk Key?
A Kirk Key is a safety device that controls access to electrical equipment. They are a type of mechanical interlock. While Kirk Keys aren't necessary to have on your transformer, they do add an extra layer of safety.
What does “Kirk” mean?
The technical name for Kirk Key interlocks is “trapped-key interlocking systems.” Kirk is a company that designs and manufactures these locks. So, today, it’s common to refer to all such mechanical interlocking systems as “Kirk Key Interlocks.”
Parts of a Kirk Key Systems
There are a few different types of Kirk Key Interlocks, but the basic parts are the same. Here are the main components of a Kirk Key setup:
- Kirk keys
- Mounting provisions
- Interlock scheme
Kirk Key Mounting Provisions
It’s important to distinguish between the actual kirk key and its mounting provision. Electrical manufacturers usually provide the kirk key mounting provisions. But not the key and lock. This allows the end user some liberty in choosing the interlocking system.
Here’s an example of a Kirk Key mounting provision installed inside a padmount on the load break switch:
Kirk Key Interlock
The device itself is called an “interlock.” Two or more of these devices work together–hence the name interlock. There are many versions of kirk interlocks. The one pictured below is a bolt style interlock. It is made up of a housing, cylinder, bolt, and key.
Lock Housing
The housing contains the lock cylinder and attaches to the mounting provision. It also furnishes the bolt which the lock cylinder controls.
Bolt
The interlock itself locks like any standard deadbolt. The length of that bolt will depend on the specific type of interlock.
As mentioned before, there are different style kirk interlocks. The one pictured above locks a device with an extended bolt. It retracts the bolt to unlock it.
Key
Most kirk interlocks operate with a key. Two separate interlocks sequentially trap and release a single key to control a device’s operation. Let's go into this in more detail.
What Does a Kirk Key Interlock Do?
Put simply, Kirk Keys keep people from opening or closing something they shouldn’t. You can use them to prevent access to live components before it’s safe.
How Does a Kirk Key Interlock Work?
Kirk Key interlocks work in a sequential locking system. The interlocks use one key between them. That key can only be removed when certain conditions are met (this will depend on the interlock design).
Let’s look at how this works with Kirk Keys on a switchgear and a padmount transformer.
- A lock is installed on both the switchgear and the transformer cabinet.
- One key operates both locks.
- To access the transformer, the switch must be opened. Once this is done, the key can be removed to open the transformer.
- After the key opens the transformer door interlock, it remains trapped until the door of the transformer is closed.
- With the transformer cabinet door closed, the key can be returned to the switch
- The switch is closed to energize the transformer
This idea of catch and release with a single key between multiple locks is called a trapped-key interlock system. This trapped-key system is used on many electrical devices to control operation and keep personnel safe.
Common Kirk Key Applications
Here are the most common applications where we see customers using Kirk Keys:
Padmount Cabinet
As shown in the example above, interlocks can control access to a padmount cabinet. The transformer cabinet can only be opened once the key is released from the upstream equipment.
Load Break Switches
Kirk key interlocks also work between two or more loadbreak switches inside a padmount cabinet, as pictured here:
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Loop Feed Systems
In certain loop feed systems, it may be necessary to prevent parallel operation between the A and B loadbreak switches. Interlocks prevent closing both switches simultaneously.
The interlock allows only one switch to be closed at a time. To close the A switch, you must open the B switch, and vice versa. Opening the A switch releases the key to close the B switch.
Is a Kirk Key Right for Your Equipment?
Mechanical interlocks control the opening and closing of two or more devices. If you are simply looking to lock your transformer’s cabinet door, a simple padlock works best. If you are looking to control how that cabinet door is opened and closed in relation to something else (like a switch), an interlock system may be your best choice. In the right situations, Kirk keys add an extra level of control and safety to your system.
Maddox typically offers Kirk Key provisions, not the interlocks themselves. How each interlock is coded and installed will vary from system to system. If you need Kirk Key provisions on your transformer, we’re ready to help. Fill out the form below for a quote today!
