**Device Type:** Binary Output - Relay

**Signal:** Binary ON/OFF command from controller

**Power:** 24VAC (coil) / Contacts rated for load voltage

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

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**Common Models:**

- Johnson Controls VMA-1600 series, Honeywell RP/RD series, Functional Devices RIB relays, Siemens S-Series, ICM Controls

**Used For:**

Switching pumps, fans, heat/cool stages, unit heaters, exhaust fans, boilers, chillers, electric heat

- **Coil Voltage:** 24VAC typical (sometimes 120VAC or 24VDC)

* SPST (Single Pole Single Throw) - Common

* SPDT (Single Pole Double Throw) - NO/NC/COM

* DPDT (Double Pole Double Throw) - Two circuits

- **Contact Ratings:**

* Resistive loads: 20-30A typical

* Inductive loads (motors): 1/2 to 2 HP typical

* Pilot duty (FLA): Check amp rating on relay

- **Enclosure:** Panel mount, DIN rail, or NEMA enclosure

- **Wire Type:** 18AWG for coil, 14-12AWG for contacts (load dependent)

**Environment:** 32-140°F, 0-95% RH non-condensing (panel mount)

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- ☑ Safety glasses (ANSI Z87.1)

- ☑ Insulated gloves (if working on powered circuits)

- ☑ Hard hat (mechanical rooms)

- ☑ Voltage-rated tools (if working energized)

- ⚠ **HIGH VOLTAGE** - Contact side may be 120VAC, 208/240VAC, or 277VAC

- ⚠ **ARC FLASH** - Potential when switching high current loads

- ⚠ **ROTATING EQUIPMENT** - Relay may control fans, pumps (LOCKOUT if servicing)

- ⚠ **STORED ENERGY** - Capacitors in some motor circuits

- [ ] **REQUIRED for contact wiring:** Lock out power to load circuit before wiring contacts

- [ ] **NOT required for coil wiring** (if 24V control only)

- [ ] Verify zero voltage with meter before touching contacts

- [ ] For motor loads: Wait for complete stop before approaching

- [ ] Follow NEC Article 430 for motor circuits

- [ ] Overload protection required for motor loads

- [ ] Proper wire gauge for load current

- [ ] Relay must be rated for load voltage and amperage

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- Wire strippers (multi-gauge: 18AWG coil, 14-12AWG contacts)

- Screwdrivers (appropriate sizes)

- Multimeter (DMM) - **REQUIRED**

- Voltage tester (non-contact preferred)

- Wire nuts or terminal blocks

- Label maker

- Torque screwdriver (for high-current terminals)

- Relay (rated for application)

- Wire (appropriate gauge for load)

- Wire nuts or terminal blocks

- DIN rail or mounting hardware

- Enclosure (if not panel mount)

- Fuse or breaker (if required for protection)

- [ ] **CRITICAL:** Verify relay coil voltage matches controller output (24VAC typical)

- [ ] **CRITICAL:** Verify relay contact rating ≥ load current and voltage

- [ ] For motors: Check relay rated for motor HP and voltage

- [ ] Confirm contact configuration (SPST, SPDT, DPDT) matches application

- [ ] Review wiring diagram and load specifications

- [ ] **LOCKOUT power to load circuit**

1. **Mount relay:**

- Panel mount: Secure to DIN rail or mounting holes

- Field mount: Install in appropriate NEMA enclosure

- Verify adequate clearance for wire bending radius

- Leave access for service

2. **Wire relay COIL (Control Side - 24VAC):**

* Wire 1 (hot): Controller binary output terminal (usually labeled C1, C2, etc.)

* Wire 2 (common): Controller 24VAC common

- Tighten coil terminals: 7-9 in-lbs

- Label: "AHU-1-SF" (example: AHU-1 Supply Fan)

3. **Wire relay CONTACTS (Load Side - Line Voltage):**

- **Wire sizing:** Per NEC for load amperage:

* 15A load: 14AWG minimum

* 20A load: 12AWG minimum

* >20A load: Consult NEC Table 310.16

* Line (hot) from breaker → Relay contact (L or line side)

* Load (motor, heater, etc.) → Relay contact (T or load side)

* **Do NOT switch neutral** - code violation for most applications

* COM: Common terminal (line voltage in)

* NO: Normally Open (energized to close)

* NC: Normally Closed (energized to open)

- Tighten contact terminals: 12-15 in-lbs (higher current = tighter)

4. **Install overload protection** (if motor load):

- Separate overload relay or motor starter typically required

- Follow motor manufacturer recommendations

- Size per motor FLA (Full Load Amperage)

5. **Label all wiring:**

- Coil wires: Controller designation

- Contact wires: Load identification

- Include voltage level on contact wiring (e.g., "120VAC - AHU-1-FAN")

6. **Restore power** (after verification)

- [ ] Relay mounted securely

- [ ] Coil wired to controller (24VAC typical)

- [ ] Contacts wired to load (proper gauge wire)

- [ ] All terminals tight (verified with pull-test)

- [ ] Labels applied to all wiring

- [ ] Overload protection installed (motor loads)

- [ ] Power restored

- [ ] Work area cleaned

- [ ] Photos taken

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- **Coil Resistance:** 50-500 ohms typical (24VAC coil)

* NO contacts: Open (infinite resistance)

* NC contacts: Closed (<1 ohm)

* COM to NO: Open

* COM to NC: Closed

- **Coil Voltage:** 24VAC ±10% (21.6-26.4V acceptable)

- **Coil Current:** 50-200mA typical (depends on relay)

- **Audible Click:** Should hear relay "click" when energized

- **Visual Indicator:** Some relays have LED when energized

* NO contacts: Closed (<1 ohm) - **THIS IS WHAT SWITCHES LOAD**

* NC contacts: Open (infinite resistance)

* COM to NO: Closed

* COM to NC: Open

- **Across Load:** Should measure line voltage (120V, 208V, 240V, 277V, etc.)

- **Voltage Drop Across Contacts:** <0.5V typical when closed

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- **Do:** Command relay ON from controller

- **Expect:**

* Hear relay click

* LED illuminates (if equipped)

* Measure 24VAC at coil terminals

- **Pass If:** Relay energizes with audible click

- **Do:** With load power OFF, measure contact continuity

- **Command relay:** OFF → ON → OFF

* OFF: NO contacts open, NC contacts closed

* ON: NO contacts closed, NC contacts open

* Hear click each time

- **Pass If:** Contacts switch properly with each command

- **WARNING:** Load power now ON - high voltage present

- **Do:** Command relay ON from controller

* Relay clicks

* Load energizes (motor runs, heater energizes, etc.)

* Measure voltage across load terminals

- **Pass If:** Load operates when relay commanded ON

- **Do:** Observe motor startup

* Motor starts smoothly (no excessive inrush)

* Motor runs without overheating

* No tripped overload relay

* Normal operating current (measure with clamp meter)

- **Pass If:** Motor operates normally, current within FLA rating

- **Do:** Cycle relay ON/OFF 10 times rapidly

* Relay responds each time

* No sticking or hesitation

* Load starts/stops reliably

- **Pass If:** Reliable operation through multiple cycles

- [ ] Relay appears in controller binary output list

- [ ] Controller can command relay ON/OFF

- [ ] Status feedback correct (if wired)

- [ ] Graphics show relay state

- [ ] Sequence operates correctly (staging, interlocks, etc.)

- [ ] No faults or errors

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1. Measure voltage at controller output: Should be 24VAC when commanded ON

- **If no voltage at controller:** Controller output failed or not programmed

2. Check coil wiring connections tight

3. Test continuity of coil wiring end-to-end: <5 ohms

4. Measure coil resistance: Should be 50-500 ohms

- **If infinity:** Coil burned out - replace relay

5. **If voltage present but no click:** Replace relay (coil failed)

1. **Measure voltage across load terminals:**

- **If no voltage:** Contact wiring problem or power not on

2. **Check contact side power:**

- Measure at breaker/disconnect: Should have line voltage

- **If no voltage:** Breaker tripped or power source issue

3. **Check load wiring:**

- Verify load connected to correct relay terminals

- Check for loose connections

- Test continuity through contacts when energized: <1 ohm

4. **Check overload relay** (motor loads):

- May be tripped - reset and retest

- May need adjustment or replacement

5. **Test load directly** (bypass relay):

- **CAUTION:** Only if qualified for electrical work

- Temporarily wire load directly to power

- **If load works:** Relay contacts bad - replace relay

- **If load doesn't work:** Load failed (motor, heater, etc.)

1. **Command relay OFF** from controller

2. **Measure coil voltage:** Should be 0VAC when OFF

- **If still has voltage:** Controller output stuck ON

3. **Listen for click:** Should click when commanded OFF

- **If no click:** Contacts welded shut - replace relay immediately

4. **Measure across load:** Should be 0V when relay OFF

- **If still has voltage:** Contacts stuck closed - **SAFETY HAZARD**

5. **REPLACE RELAY** if contacts won't open (fire hazard)

1. **Low coil voltage:**

- Measure at relay coil: Should be 24VAC ±10%

- **If <21V:** Voltage drop in wiring or controller issue

- Check wire gauge adequate (18AWG minimum)

2. **Loose coil connections:**

- Check terminals tight

3. **High contact load:**

- Relay undersized for load

- Measure load current with clamp meter

- **If exceeds relay rating:** Replace with higher-rated relay

4. **Defective relay:**

- Replace with known good relay to test

1. **Caused by:** Switching high inrush current (motors, transformers)

2. **Indicators:**

- Black/brown deposits on contacts

- High resistance when closed (>1 ohm)

- Arcing visible when switching

3. **Solutions:**

- Replace relay

- Add inrush current limiting (soft starter for motors)

- Use relay with higher contact rating

- Consider solid-state relay for frequent switching

1. **NOT a relay problem** - motor or overload issue

2. Check motor current with clamp meter:

- Compare to motor nameplate FLA

- **If >FLA:** Motor overloaded, mechanical problem, or failing

3. Check overload relay setting:

- Should be set to motor FLA

- **If too low:** Nuisance tripping - adjust

4. Check for motor problems:

- Bearing failure, seized load, phase loss

5. **If motor current normal:** Overload relay may be defective

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- [ ] Verified coil voltage at relay (24VAC when commanded ON)

- [ ] Verified line voltage at contact terminals (120V, 208V, etc.)

- [ ] Listened for relay click (audible when switching)

- [ ] Measured load current (if motor - compare to FLA)

- [ ] Checked all wiring connections tight

- [ ] Verified relay rated for load (voltage and amperage)

- [ ] Tested load directly if possible (bypass relay)

- [ ] Checked overload relay setting (motor loads)

- [ ] Taken photos of wiring and installation

- **Relay:** [Mfg / Model / Contact Rating / Location]

- **Load:** [Type: Motor/Heater/Fan / HP or Amperage / Voltage]

- **Coil Voltage Measured:** _____ VAC (when commanded ON)

- **Line Voltage Measured:** _____ VAC (at contact terminals)

- **Load Current Measured:** _____ A (with clamp meter)

- **Load Nameplate FLA:** _____ A (for motors)

- **Symptoms:** [No click, clicks but no load, stuck on, chatters, etc.]

- **Relay Clicks:** Yes / No

- **Overload Status:** Set / Tripped / Not applicable

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

- **Field Specialist:** [Phone]

- **Electrician:** [Phone] (if high-voltage issue)

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

- **Dispatch:** [Phone]

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✓ **Relay sizing:** Always size contacts for 125% of load current (safety margin)

✓ **Motor loads:** Relay must be rated for "Pilot Duty" or motor HP

✓ **Inrush current:** Motors draw 5-8× FLA on startup - relay must handle this

✓ **Contact life:** Typical 100,000 operations, less with high current

✓ **Coil voltage:** 24VAC most common, verify matches controller output

✓ **Contact configuration:** SPST most common (single switch), SPDT for changeover

✓ **Overload protection:** Separate overload relay required for motor loads (NEC)

✓ **Wire neutral:** Never switch neutral (code violation) - only switch hot leg

✓ **Stuck contacts:** Fire hazard - replace immediately if contacts won't open

✓ **Contact cleaning:** Don't file contacts - replace relay if pitted/burned

✓ **Solid-state relays:** Consider for high-cycle applications (>10,000 ops/day)

✓ **Status feedback:** Use auxiliary contacts or current sensor for proof of operation

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**Document ID:** SSO-RELAY-001

**Revision:** 1.0

**Next Review:** Dec 2026