Purpose
This article explains how to correctly wire dry contact alarm outputs from South-Tek FPS-series nitrogen generators to an external fire alarm panel, BMS, or control panel, including when to use Normally Open (NO) versus Normally Closed (NC) contacts.
Overview: Dry Contacts on FPS Generators
FPS-series generators provide voltage-free (dry) relay contacts for alarm and status signaling. These contacts do not supply voltage. The receiving system (fire alarm panel or BMS) must provide its own control voltage.
Each alarm relay provides three terminals: - COM – Common - NO – Normally Open - NC – Normally Closed
Understanding NO vs NC
Normally Open (NO)
- Circuit is open during normal operation
- Circuit closes when an alarm occurs
Use NO when: - Connecting to a BMS / BAS - Using a non-supervised input - Alarm should trigger only on an active fault
Wiring: - COM → Panel input common - NO → Panel alarm input
State logic: - Normal: Open - Alarm: Closed
Normally Closed (NC)
- Circuit is closed during normal operation
- Circuit opens on alarm or loss of power
Use NC when: - Connecting to a fire alarm panel (FACP) - Using supervised or fail-safe inputs - Loss of power or broken wire must signal a trouble/alarm
Wiring: - COM → Panel input common - NC → Panel alarm input
State logic: - Normal: Closed - Alarm or power loss: Open
Note: NC is the preferred method for fire protection systems due to fail-safe behavior.
Recommended Usage Summary
| Application | Recommended Pins |
|---|---|
| Fire alarm panel (FACP) | COM + NC |
| Supervised alarm input | COM + NC |
| BMS / BAS monitoring | COM + NO |
| Fail-safe design | COM + NC |
Commissioning & Verification
After wiring is complete, always verify alarm signaling:
- On the generator touchscreen, navigate to: Maintenance → Alarm Contacts
- Toggle each alarm contact ON/OFF
- Confirm at the external panel that:
- NO contacts close on alarm
- NC contacts open on alarm
This step ensures correct wiring and correct point mapping before system turnover.
Important Notes
- Do not apply external voltage directly to FPS alarm terminals.
- All wiring must comply with local electrical and fire codes.
- Alarm logic (NO vs NC) must be coordinated with the fire alarm or BMS contractor and AHJ.
Need Help?
If you need confirmation of alarm point assignments, wiring diagrams, or assistance coordinating with a fire alarm contractor, contact South-Tek Systems Support via Zendesk.