BAS Point-to-Point Checkout Procedures

Point-to-point (P2P) checkout is a systematic verification process that confirms every input and output in a building automation system is correctly wired, addressed, and functioning. This critical commissioning step catches wiring errors before they cause operational problems.

What is Point-to-Point Checkout?

Point-to-point verification confirms that:

• Physical sensors/actuators are wired to correct controller terminals
• Controller I/O addressing matches design documents
• Signal types match (voltage, current, resistance)
• Measured values are reasonable and accurate
• Actuators respond correctly to commands

Why P2P is Essential

• Catches wiring errors early: Easier to fix during construction
• Validates documentation: Confirms as-builts match reality
• Prevents equipment damage: Wrong signals can damage sensors or actuators
• Establishes baseline: Documents initial calibration state
• Required by specs: Most commissioning specs mandate P2P

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Preparation

Documentation Required

1. Control drawings: I/O schedules, wiring diagrams
2. Submittal data: Sensor ranges, actuator specifications
3. Points list: Complete BAS points with addresses
4. Sequence of operations: Expected behavior reference
5. P2P forms: Standardized checkout sheets

Tools Needed

• Digital multimeter (DMM)
• Temperature reference (ice bath, calibrated thermometer)
• Pressure reference (manometer, calibrated gauge)
• Current source/simulator (4-20mA)
• Laptop with BAS software access
• Two-way radios for coordination

Pre-Checkout Verification

Before starting P2P:

• All wiring complete and terminated
• Controllers powered and communicating
• BAS graphics accessible
• Safety systems verified separately
• Coordination with other trades complete

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Input Point Verification

Temperature Sensors (Thermistors/RTDs)

Procedure:

1. Identify sensor location and type from drawings
2. Access BAS point value on workstation
3. Compare displayed value to reference thermometer at sensor
4. Document deviation

Acceptance Criteria (typical):

• Space temperature: ±1°F (±0.5°C)
• Duct temperature: ±1°F (±0.5°C)
• Water temperature: ±1°F (±0.5°C)
• Outside air temperature: ±2°F (±1°C)

Common Issues:

• Wrong thermistor type selected in software
• Sensor in poor location (direct sunlight, near heat source)
• Wiring reversed (if using RTDs)

Pressure Sensors

Procedure:

1. Verify sensor range matches application
2. Zero sensor at atmospheric pressure (if applicable)
3. Apply known pressure using manometer
4. Compare BAS reading to reference

Acceptance Criteria:

• ±2% of full scale (typical)
• Zero offset: ±0.05" w.c. for duct pressure

Common Issues:

• Tubing connected to wrong port (high/low reversed)
• Units mismatch (inches w.c. vs. Pa)
• Calibration offset not set

Current Inputs (4-20mA)

Procedure:

1. Disconnect sensor
2. Connect current source to input terminals
3. Apply 4mA, verify 0% reading
4. Apply 12mA, verify 50% reading
5. Apply 20mA, verify 100% reading
6. Reconnect sensor and verify live reading

Acceptance Criteria:

• ±1% of span at each test point

Binary/Digital Inputs

Procedure:

1. Identify normal state (NO/NC)
2. Actuate switch/contact manually
3. Verify BAS state change matches physical state
4. Verify alarm generation if applicable

Common Issues:

• NO/NC configured backwards
• Supervision resistors not installed
• Contact bounce causing false triggers

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Output Point Verification

Analog Outputs (AO)

Procedure:

1. Command output to 0%
2. Measure voltage or current at terminals
3. Command to 50%, measure again
4. Command to 100%, measure again
5. Verify actuator responds proportionally

Acceptance Criteria:

• 0-10V outputs: ±0.2V at each point
• 4-20mA outputs: ±0.4mA at each point

Actuator Stroke Verification:

• Command 0%: Actuator fully closed/minimum
• Command 50%: Actuator at midpoint
• Command 100%: Actuator fully open/maximum
• Verify stroke direction matches sequence

Binary/Digital Outputs (DO)

Procedure:

1. Command output ON
2. Verify relay energizes (listen for click or measure coil)
3. Verify controlled device operates
4. Command output OFF
5. Verify relay de-energizes and device stops

Safety Verification:

• Test with equipment safeties active
• Verify interlock operation
• Document hand-off-auto switch positions

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Documentation

P2P Checkout Form Contents

Each point should document:

• Point name and address
• Design value/range
• Measured/commanded value
• Reference instrument used
• Pass/fail status
• Technician initials and date
• Notes on corrections made

Sample Form Structure

| Point ID | Description | Design Range | Measured | Reference | Pass/Fail | Notes |
|----------|-------------|--------------|----------|-----------|-----------|-------|
| AHU1-SAT | Supply Air Temp | 55-85°F | 72.3°F | Fluke 54II | Pass | Cal OK |
| AHU1-SF-CMD | Supply Fan Start | On/Off | On | Visual | Pass | - |

Issue Tracking

Document all issues found:

• Point identification
• Issue description
• Root cause
• Corrective action taken
• Retest result

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Common Issues and Solutions

Wiring Problems

Symptom	Likely Cause	Solution
Reading stuck at min/max	Open wire or short	Check continuity, repair
Erratic readings	Loose termination	Re-terminate, torque to spec
Wrong polarity	Wires reversed	Swap at terminals
Interference/noise	Poor shielding	Verify shield grounding

Configuration Problems

Symptom	Likely Cause	Solution
Wrong units displayed	Scaling incorrect	Adjust I/O configuration
Value offset	Calibration needed	Apply offset in software
Wrong point addressed	Database error	Correct address mapping
Inverted operation	NO/NC or direction wrong	Change configuration

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Best Practices

Efficiency Tips

1. Work systematically: Go panel by panel, not random
2. Two-person team: One at field device, one at workstation
3. Use radios: Clear communication prevents errors
4. Pre-fill forms: Enter design data before field work
5. Fix issues immediately: Don't defer "minor" problems

Quality Assurance

• Independent verification of critical points
• Supervisor spot-checks of completed P2P
• Complete documentation before system turnover
• Archive all P2P records with O&M manuals

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References

• ASHRAE Guideline 1.1: HVAC&R Technical Requirements for the Commissioning Process
• NEBB Procedural Standards for Building Systems Commissioning
• AABC Commissioning Guideline

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Point-to-point checkout is tedious but essential. Time invested during P2P prevents countless hours of troubleshooting later.