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Understanding the “Keylock Push On/Off” Switch in Building Automation Systems

October 28, 2025

In Building Automation and HVAC Control Panels, security and operational safety are just as important as performance. One often overlooked yet powerful device that ensures this is the Keylock Push On/Off Switch.

What Is a Keylock Switch?

A keylock switch is a control device that can be operated only with a key, making it ideal for restricted access functions. It’s commonly used by maintenance engineers, supervisors, or authorized personnel to prevent accidental or unauthorized operation. Think of it as the “master permission control” inside your panel the system responds only when the keyholder decides.

How It Works: “Push On/Off” Action

Unlike a momentary pushbutton that activates only when pressed, a Push On/Off (latching) type switch changes state and stays there until operated again.
Push ON = circuit closes = power or signal flows
Push OFF = circuit opens = power cuts off
Combine this with a keylock mechanism, and you have both control and security.

Where It’s Used in BMS Panels

Application Purpose
1. System Enable / Disable = To allow only authorized activation of
control systems
2. Mode Selection = Switching between Hand / Off / Auto with
restricted access
3. Alarm Reset = Prevents unauthorized reset of alarms
4. Manual Override = Allows service engineers to override
automatic control safely

Real-World Example

In a chiller plant control panel, a keylock switch is often used to enable or disable system power. Only the facility engineer can turn the system ON before scheduled operation or maintenance, ensuring no accidental start occurs during servicing. In the world of Building Automation, small components make a big difference. The humble Keylock Push On/Off switch is more than a button, it’s a safeguard for human safety, system reliability, and operational discipline.

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