Point-to-point (P2P) commissioning verifies that every physical input and output is wired correctly, scaled properly, and communicates to the front-end. Skipping this step is the most common source of chronic building problems that persist for years.
Before starting P2P checkout:
Prerequisites Checklist:
[ ] Control submittals approved
[ ] As-built wiring diagrams available
[ ] Controllers powered and online
[ ] Network communication verified
[ ] Mechanical systems ready for testing
[ ] Lockout/tagout procedures reviewed
[ ] Test equipment calibrated
| Equipment | Purpose |
|---|---|
| Digital multimeter | Voltage, current, resistance measurements |
| 4-20mA simulator | Simulate analog sensor inputs |
| Decade resistance box | Simulate RTD/thermistor inputs |
| Laptop with front-end access | Verify point values at supervisor |
| Two-way radio | Coordination between field and front-end |
| Calibrated thermometer | Temperature sensor verification |
| Manometer | Pressure sensor verification |
For each analog input point:
AI Checkout Procedure:
1. Identify the sensor and controller terminal
2. Disconnect the sensor
3. Apply a known signal (simulator or decade box)
4. Verify the raw value at the controller
5. Verify the scaled value at the front-end
6. Check engineering units are correct
7. Reconnect the sensor
8. Compare reading to reference instrument
9. Document results
| Signal | Low End | High End | Expected Range |
|---|---|---|---|
| 4-20mA temperature | 4mA = 0degF | 20mA = 100degF | Linear |
| 0-10V pressure | 0V = 0"WC | 10V = 5"WC | Linear |
| 10K thermistor | 10K ohm @ 77degF | Per NTC curve | Non-linear |
| 1K RTD | 1000 ohm @ 32degF | Per PT1000 curve | Non-linear |
| Sensor Type | Tolerance |
|---|---|
| Temperature (space) | +/- 1degF |
| Temperature (duct) | +/- 1degF |
| Temperature (pipe) | +/- 0.5degF |
| Pressure (duct) | +/- 0.05"WC |
| Humidity | +/- 3% RH |
| CO2 | +/- 75 ppm |
| Airflow | +/- 10% of reading |
For each analog output point:
AO Checkout Procedure:
1. Identify the actuator and controller terminal
2. Command output to 0% from front-end
3. Verify actuator at minimum position
4. Measure output signal (should be 0V or 4mA)
5. Command output to 50%
6. Verify actuator at mid-position
7. Measure output signal (should be 5V or 12mA)
8. Command output to 100%
9. Verify actuator at maximum position
10. Measure output signal (should be 10V or 20mA)
11. Check feedback signal matches command
12. Document stroke time and direction
| Actuator Type | Typical Stroke Time | Check |
|---|---|---|
| Valve (small) | 30-60 seconds | Full open to full closed |
| Valve (large) | 60-120 seconds | Full open to full closed |
| Damper | 30-90 seconds | Full open to full closed |
| VFD | Instantaneous | Ramp rate settings |
For each digital input:
DI Checkout Procedure:
1. Identify the contact type (NO/NC)
2. Verify normal state reading at front-end
3. Force the contact to opposite state
4. Verify state change at front-end
5. Check that status text is correct (Running/Stopped, Open/Closed)
6. Verify contact type matches design documents
7. Document results
| Equipment | Status Point | Normal State |
|---|---|---|
| Fan status | Proof of flow | NO (closed when running) |
| Filter status | Differential pressure switch | NO (closed when dirty) |
| Freeze stat | Low temperature | NC (opens on freeze) |
| Smoke detector | Duct smoke | NC (opens on smoke) |
For each digital output:
DO Checkout Procedure:
1. Verify equipment can be safely started
2. Command ON from front-end
3. Verify equipment starts
4. Verify status feedback changes
5. Command OFF from front-end
6. Verify equipment stops
7. Verify status feedback changes
8. Check HOA switch operation (Hand/Off/Auto)
9. Document results
For integrated BACnet devices:
BACnet Checkout:
[ ] Device instance ID matches documentation
[ ] All expected objects present
[ ] Object names match point naming standard
[ ] Engineering units correct on all points
[ ] COV subscriptions functioning
[ ] Priority array writeable at correct levels
[ ] Alarms generating and routing correctly
[ ] Trends collecting at specified intervals
After P2P checkout, test sequences of operation:
FPT Procedure:
1. Review sequence of operation
2. Set up trend logging on all related points
3. Walk through each operating mode:
- Occupied heating
- Occupied cooling
- Unoccupied
- Morning warmup/cooldown
- Emergency/safety modes
4. Verify setpoint response
5. Test safety interlocks
6. Verify alarm generation
7. Document results with trend data
Record results for each point:
| Field | Value |
|---|---|
| Point Name | AHU-1.SAT |
| Controller | NAE-1, Terminal AI-3 |
| Description | Supply Air Temperature |
| Sensor Type | 10K Thermistor |
| Range | 0-150degF |
| Reference Reading | 72.3degF |
| BAS Reading | 72.5degF |
| Error | 0.2degF |
| Pass/Fail | Pass |
| Technician | J. Smith |
| Date | 2026-01-15 |
| Issue | Frequency | Impact |
|---|---|---|
| Reversed wiring (NO vs NC) | Very Common | False alarms, wrong status |
| Wrong scaling factor | Common | Incorrect readings |
| Missing end-of-line resistor | Common | Supervision faults |
| Sensor in wrong location | Occasional | Poor control |
| Actuator installed backwards | Occasional | Reverse operation |
| Wrong voltage signal type | Occasional | No control or damage |
Every hour spent on thorough P2P commissioning saves ten hours of troubleshooting after occupancy. There are no shortcuts worth taking.