**Device Type:** Binary Input - Digital Status Monitoring

**Signal:** Dry contact (NO/NC) or voltage input

**Power:** 24VAC/VDC (for controller input) or dry contact

**Version:** 1.0 | **Date:** Dec 2025

---

**Common Models:**

- Standalone binary input modules (part of controller), Functional Devices RIB relay with status, Dry contact monitors

**Used For:**

Proof of operation (fans, pumps, dampers), status monitoring (filter status, flow switches, door contacts), alarm monitoring (fire alarm, freeze stat, high temp), end switches, limit switches

* Dry contact (most common) - voltage-free switch closure

* Wet contact - voltage present on input

* Voltage sensing - monitors presence of voltage (24V-277V)

* NO (Normally Open) - closes when activated

* NC (Normally Closed) - opens when activated

- **Wire Type:** 18AWG minimum

- **Wiring:** 2-wire typical (digital input + common)

**Environment:** Varies by monitored device

---

- ☑ Safety glasses (ANSI Z87.1)

- ☑ Work gloves

- ☑ **Insulated gloves if monitoring voltage >50V**

- ☑ Hard hat (if in mechanical room)

- ⚠️ **VOLTAGE SENSING APPLICATIONS** - May involve line voltage (120V-277V)

- ⚠️ **MECHANICAL EQUIPMENT** - Monitored devices may have moving parts

- ⚠️ **Warning:** Binary input indicates electrical status, not mechanical safety

- [ ] **Required if wiring to energized equipment**

- [ ] **Required if accessing equipment with moving parts**

- [ ] NOT required for low-voltage dry contacts

- [ ] Verify voltage type before working

---

- Wire strippers (18AWG)

- Screwdrivers

- Multimeter (DMM)

- Continuity tester

- Label maker

- Wire (18AWG)

- Wire nuts or terminal blocks

- Binary input device (if external module)

- Status switch/relay (if monitoring equipment without built-in contacts)

- [ ] Identify device/equipment to monitor

- [ ] Determine contact type available (NO or NC)

- [ ] Verify contact rating if switching current

- [ ] Confirm controller has available binary input point

- [ ] Review wiring diagram

1. **Identify source contacts:**

- Pump/fan starter: Auxiliary contacts (typically NO)

- Motor starter: Status contacts

- Relay: Extra contacts if available

- End switch: Mechanical position switch

- Flow switch: Paddle or differential pressure switch

- Pressure switch: High/low pressure cutout

- Thermostat: Heat/cool status contacts

2. **Determine contact state:**

- **NO (Normally Open):** Open when off, closes when on

* Use for: Proof of operation (pump running = closed contact)

- **NC (Normally Closed):** Closed when off, opens when on

* Use for: Alarm monitoring (fire alarm = opens when tripped)

3. **Connect to controller binary input:**

* Wire 1: From contact terminal 1 → Controller BI terminal

* Wire 2: From contact terminal 2 → Controller common

- **Polarity doesn't matter** for dry contacts

- Tighten terminals: 7-9 in-lbs

- Route wiring away from high-voltage cables

4. **Configure controller input:**

- Set as NO (normal state = open) or NC (normal state = closed)

- Example: Motor status NO contact:

* Motor OFF: Contact open = Binary input FALSE/0

* Motor ON: Contact closed = Binary input TRUE/1

5. **Label wiring:**

- Example: "PUMP-1-STATUS" or "FILTER-ALARM"

- Label at both controller and device ends

1. **Select voltage sensing module:**

- Must be rated for monitored voltage (24V, 120V, 208V, 277V)

- Example: Functional Devices RIBS voltage sensing relay

2. **Connect to monitored circuit:**

* Connect voltage sensing module to circuit being monitored

* Follow module wiring diagram

* Connect module output contacts to controller binary input

* Typically NO contacts (closed when voltage present)

3. **Configuration:**

- Controller sees dry contact status

- Voltage present = contact closed = TRUE

- Voltage absent = contact open = FALSE

- [ ] Wiring connections tight

- [ ] Correct contact type confirmed (NO vs NC)

- [ ] Labels applied at both ends

- [ ] Controller input configured correctly

- [ ] Work area cleaned

- [ ] Photos taken

---

- **Continuity:** Open circuit (infinite resistance)

- **Controller Reading:** FALSE / 0 / OFF / Inactive

- **Continuity:** Closed (<1 ohm)

- **Controller Reading:** TRUE / 1 / ON / Active

| Equipment State | Contact State | Controller Reading |

|----------------|---------------|-------------------|

| OFF | Open | FALSE / 0 |

| ON | Closed | TRUE / 1 |

| Equipment State | Contact State | Controller Reading |

|----------------|---------------|-------------------|

| Normal | Closed | TRUE / 1 |

| Alarm | Open | FALSE / 0 |

- Set controller to expect NO or NC

- **Alarm on Change:** Trigger alarm when state changes

- **Alarm on State:** Trigger alarm when specific state (TRUE or FALSE)

---

- **Do:** Measure continuity across contact with multimeter

* NO contact: Open (infinite ohms) when de-energized

* NC contact: Closed (<1 ohm) when de-energized

- **Pass If:** Contact state matches specification

- **Do:** Activate equipment (turn pump/fan ON)

* NO contact: Changes from open to closed

* NC contact: Changes from closed to open

* Controller binary input changes state

- **Pass If:** State changes when equipment operates

- **Do:** Manually operate contact (close/open by hand if possible)

- **Expect:** Controller input responds immediately

- **Pass If:** Controller sees state change

- **Do:** Observe controller graphics or display

- **Expect:** Binary input status updates in real-time

- **Pass If:** Display matches actual equipment state

- **Do:** Trigger alarm condition (if monitoring alarm)

- **Expect:** Controller alarm activates

- **Pass If:** Alarm notification works correctly

- **Do:** Verify contact rating adequate for load

- **Measure:** Current through contact (if switching power)

- **Pass If:** Contact operates without chattering or overheating

---

1. **Check equipment:** Is device actually running?

2. **Test contact:** Measure continuity across contact

- **If open when should be closed:** Contact not closing - device issue

3. **Check wiring:** Verify connections at both ends

4. **Test continuity end-to-end:** Should be <5 ohms when closed

5. **Verify controller config:** Input set to correct contact type (NO vs NC)?

6. **If wiring OK but no response:** Controller input may be failed

1. **Check equipment:** Is device actually off?

2. **Test contact:** Should be open when equipment off

- **If closed when should be open:** Contact stuck - device issue

3. **Check for short circuit:** Wires touching somewhere

4. **Verify controller config:** May be configured backwards (NO vs NC)

5. **If persistently closed:** Contact welded shut or wiring short

1. **Mechanical chatter:** Contact bouncing during switching

- Solution: Add time delay in controller (0.5-1 sec)

2. **Loose wiring:** Check all connections tight

3. **EMI/RFI interference:** Route wiring away from power cables

4. **Contact arcing:** Contact switching too much current - add relay

5. **Vibration:** Secure device and wiring to prevent movement

1. **Controller config:** Input configured as NO when should be NC (or vice versa)

2. **Solution:** Change controller configuration to opposite type

3. **Verify logic:** Some controllers use "Active High" or "Active Low"

1. **Verify binary input changing state:** Check controller display

2. **Check alarm configuration:**

- Alarm enabled?

- Correct trigger condition (state change vs specific state)?

- Time delay too long?

3. **Check notification routing:** Email, text, or on-screen only?

1. **Check voltage present:** Measure with multimeter at monitored circuit

2. **Verify voltage sensing module powered:** Some require separate power

3. **Check voltage rating:** Module rated for monitored voltage?

4. **Test module output contacts:** Should close when voltage present

5. **If voltage present but module no output:** Module failed - replace

---

- [ ] Verified equipment actually operating (visual/audible)

- [ ] Tested contact continuity (open vs closed)

- [ ] Verified all wiring connections tight

- [ ] Tested continuity end-to-end (<5 ohms when closed)

- [ ] Checked controller configuration (NO vs NC)

- [ ] Verified binary input point configured in controller

- [ ] Documented actual equipment state vs controller reading

- [ ] Taken photos of wiring

- **Monitored Device:** [Type / Location]

- **Contact Type:** NO / NC / Voltage sensing

- **Equipment State:** ON / OFF / Cycling

- **Contact Continuity:** Open / Closed / _____ ohms

- **Controller Reading:** TRUE/1 / FALSE/0 / Erratic

- **Controller Config:** NO / NC / Unknown

- **Symptoms:** [Always false, always true, erratic, reversed]

- **Steps Taken:** [Troubleshooting completed]

- **Field Specialist:** [Phone]

- **Programmer:** [Phone] (if alarm/logic issue)

- **Electrician:** [Phone] (if device repair needed)

- **Dispatch:** [Phone]

---

- Source: Auxiliary contacts from motor starter (NO)

- Wiring: NO contact → Controller BI

- Logic: Closed when running = TRUE = Equipment ON

- Alarm: If FALSE for >60 seconds = Failed to start

- Source: VFD auxiliary relay output (NO)

- Wiring: Relay NO contact → Controller BI

- Logic: Closed when VFD running = TRUE

- Alarm: Command ON but status FALSE = VFD fault

- Source: Mechanical limit switch at actuator (NO or NC)

- Wiring: Switch contact → Controller BI

- Logic: Closed when fully open (or closed) = TRUE

- Alarm: Position doesn't match command = Stuck actuator

- Source: Fire alarm panel relay (NC typical)

- Wiring: NC contact → Controller BI

- Normal: Closed = TRUE = No alarm

- Alarm: Opens = FALSE = Fire alarm active

- **Critical:** Fail-safe design (wire break = alarm condition)

- Source: Capillary tube thermostat (NC)

- Wiring: NC contact → Controller BI

- Normal: Closed = TRUE = Temp OK

- Alarm: Opens = FALSE = Freeze condition

- Action: Shut down system, notify operator

- Source: Pressure switch (NC typical)

- Wiring: NC contact → Controller BI

- Normal: Closed = TRUE = Pressure normal

- Alarm: Opens = FALSE = High pressure

- Action: Shut down fan, check filter

- Source: Paddle-type flow switch (NO)

- Wiring: NO contact → Controller BI

- Normal (flow): Closed = TRUE = Flow proven

- Alarm: Open = FALSE = No flow detected

- Action: Check pump operation, strainer, valves

- Source: Duct smoke detector relay (NC)

- Wiring: NC contact → Controller BI

- Normal: Closed = TRUE = No smoke

- Alarm: Opens = FALSE = Smoke detected

- Action: Shut down air handler, activate smoke control

- Source: Differential pressure switch (NO)

- Wiring: NO contact → Controller BI

- Normal: Open = FALSE = Filter clean

- Alarm: Closed = TRUE = Filter dirty (high ΔP)

- Action: Schedule filter change

- Source: Water detection sensor (NO)

- Wiring: NO contact → Controller BI

- Normal: Open = FALSE = No water

- Alarm: Closed = TRUE = Water detected

- Action: Shut down equipment, investigate leak

- Source: Magnetic reed switch (NC)

- Wiring: NC contact → Controller BI

- Normal: Closed = TRUE = Secure

- Alarm: Open = FALSE = Door/window open

- Action: Adjust HVAC for infiltration

---

---

✓ **NO vs NC confusion:** Most common wiring error - verify contact type before wiring

✓ **Fail-safe design:** Use NC contacts for critical alarms (wire break = alarm)

✓ **Fire alarm interface:** Always NC contact - must fail to alarm condition

✓ **Controller configuration:** MUST match actual contact type (NO vs NC)

✓ **Contact ratings:** Don't exceed contact amp/voltage rating

✓ **Time delays:** Add 0.5-1 sec delay to prevent contact bounce false alarms

✓ **Wire routing:** Keep binary input wiring away from high-voltage to prevent interference

✓ **Voltage sensing:** Use when no dry contacts available (direct voltage monitoring)

✓ **Status feedback:** Always verify equipment actually operating (BI shows contact state, not mechanical operation)

✓ **Alarm logic:** "Alarm on change" vs "Alarm on state" - choose correct

✓ **Multiple contacts:** Can wire multiple NO contacts in series for "ALL ON" logic

✓ **Multiple contacts:** Can wire multiple NC contacts in parallel for "ANY ALARM" logic

---

**Document ID:** SSO-BINARY-INPUT-001

**Revision:** 1.0

**Next Review:** Dec 2026