All About Metasys Interlocks - Complete Tutorial

Interlocks in Metasys provide safety and coordination between equipment, ensuring proper sequencing and protection against unsafe operating conditions.

What Are Interlocks?

Interlocks are logical connections between equipment that:

• Prevent unsafe operation
• Coordinate equipment sequencing
• Protect mechanical systems
• Enforce operational dependencies

Types of Interlocks

Safety Interlocks

Protect equipment and personnel:

Interlock	Purpose
Freeze protection	Stops fan if coil temp drops too low
Fire/smoke	Shuts down AHU on fire alarm
High static	Limits fan speed on high duct pressure
Motor overload	Disables equipment on electrical fault

Operational Interlocks

Ensure proper sequence of operations:

Interlock	Purpose
Chiller flow proof	Requires pump flow before starting chiller
AHU enable	Requires OA damper open before fan start
Exhaust/supply coordination	Balance supply and exhaust fans
Lead/lag	Coordinate multiple equipment staging

Configuring Interlocks in Metasys

Using CCT (Controller Configuration Tool)

1. Open equipment module in CCT
2. Navigate to Interlocks section
3. Define input source (the triggering condition)
4. Set action (what happens when triggered)
5. Configure delay timers if needed
6. Download to controller

Common Interlock Parameters

Parameter	Description
Source Point	The monitored condition
Condition	Equal, Not Equal, Greater Than, etc.
Action	Disable, Enable, Shutdown, etc.
On Delay	Time before interlock activates
Off Delay	Time before interlock releases
Priority	Override level (higher = stronger)

Interlock Logic Examples

AHU Freeze Protection

IF Coil_Temp < 38°F
AND Condition persists > 30 seconds
THEN:
  - Close OA damper to minimum
  - Open heating valve to 100%
  - If temp continues dropping, stop supply fan

Chiller Safety Interlock

IF Chilled_Water_Flow < Minimum_Flow
AND Chiller is RUNNING
THEN:
  - Alarm: Low flow condition
  - After 60 seconds: Stop compressor
  - Lock out until flow proven

VAV Minimum Airflow

IF Occupancy = UNOCCUPIED
THEN:
  - Reduce minimum airflow to 0 CFM
ELSE:
  - Maintain ventilation minimum per ASHRAE 62.1

Testing Interlocks

Pre-Commissioning Checklist

1. Verify point connections - Ensure all interlock inputs are wired correctly
2. Simulate conditions - Force input values to test logic
3. Check timing - Verify delays operate as designed
4. Document results - Record all test conditions and responses

Safe Testing Procedures

• Test during unoccupied periods when possible
• Have manual overrides ready
• Coordinate with operations staff
• Start with less critical interlocks first
• Never bypass safety interlocks without proper lockout

Troubleshooting Interlocks

Equipment Won't Start

1. Check for active interlocks in point status
2. Review interlock conditions in CCT
3. Verify input point values
4. Check for latched fault conditions
5. Look for priority command overrides

Interlock Keeps Tripping

1. Verify sensor calibration
2. Check for intermittent wiring issues
3. Review setpoints (may be too sensitive)
4. Examine timing parameters
5. Look for environmental causes

Best Practices

Design

• Document all interlock logic in sequence of operations
• Use consistent naming conventions
• Include appropriate time delays to prevent nuisance trips
• Consider failure modes (what if sensor fails?)

Implementation

• Test each interlock individually during commissioning
• Verify all hardwired safety interlocks first
• Train operators on interlock behavior
• Provide clear alarm messages

Maintenance

• Periodically test critical safety interlocks
• Document any changes to interlock logic
• Review interlock performance after system modifications

Video Tutorial

For a complete visual demonstration of Metasys interlock configuration:

Video Tutorial: