Quartz 4

SSO Relay Output

10 min read

Relay Output Module - Quick Reference SSO

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

DEVICE OVERVIEW

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

Specifications:

  • Coil Voltage: 24VAC typical (sometimes 120VAC or 24VDC)
  • Contact Types:
    • 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)

SAFETY - PPE REQUIRED

  • ☑ Safety glasses (ANSI Z87.1)
  • ☑ Insulated gloves (if working on powered circuits)
  • ☑ Hard hat (mechanical rooms)
  • ☑ Voltage-rated tools (if working energized)

HAZARDS

  • ⚠ 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

LOCKOUT/TAGOUT

  • 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

ELECTRICAL CODE COMPLIANCE

  • 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

INSTALLATION CHECKLIST

TOOLS NEEDED

  • 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)

MATERIALS

  • 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)

PRE-INSTALL

  • 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

INSTALL STEPS

  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):

    • FROM CONTROLLER:
      • Wire 1 (hot): Controller binary output terminal (usually labeled C1, C2, etc.)
      • Wire 2 (common): Controller 24VAC common
    • 18AWG wire typical
    • Tighten coil terminals: 7-9 in-lbs
    • Label: “AHU-1-SF” (example: AHU-1 Supply Fan)

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

    • VERIFY POWER OFF with multimeter before touching!
    • Wire sizing: Per NEC for load amperage:
      • 15A load: 14AWG minimum
      • 20A load: 12AWG minimum

      • 20A load: Consult NEC Table 310.16

    • Typical SPST wiring:
      • 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
    • SPDT wiring (if used):
      • 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)
    • Double-check polarity and connections before restoring power

  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)

POST-INSTALL

  • 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

EXPECTED READINGS

PRE-POWER (Power OFF to BOTH Coil and Contacts)

  • Coil Resistance: 50-500 ohms typical (24VAC coil)
  • Contact Continuity (relay de-energized):
    • NO contacts: Open (infinite resistance)
    • NC contacts: Closed (<1 ohm)
    • COM to NO: Open
    • COM to NC: Closed

COIL POWER-UP (24VAC applied to coil)

  • 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

CONTACT VERIFICATION (Relay Energized)

  • Contact Continuity (relay energized):
    • NO contacts: Closed (<1 ohm) - THIS IS WHAT SWITCHES LOAD
    • NC contacts: Open (infinite resistance)
    • COM to NO: Closed
    • COM to NC: Open

LOAD SIDE VOLTAGE (Relay Energized, Power to Contacts ON)

  • Across Load: Should measure line voltage (120V, 208V, 240V, 277V, etc.)
  • Voltage Drop Across Contacts: <0.5V typical when closed

PROOF OUT TESTS

TEST 1: Coil Function Test (Safe - Low Voltage)

  • 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

TEST 2: Contact Switching Test (POWER OFF TO LOAD SIDE)

  • Do: With load power OFF, measure contact continuity
  • Command relay: OFF → ON → OFF
  • Expect:
    • 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

TEST 3: Load Operation Test (FULL SYSTEM TEST)

  • WARNING: Load power now ON - high voltage present
  • Do: Command relay ON from controller
  • Expect:
    • Relay clicks
    • Load energizes (motor runs, heater energizes, etc.)
    • Measure voltage across load terminals
  • Pass If: Load operates when relay commanded ON

TEST 4: Load Verification (Motor Loads)

  • Do: Observe motor startup
  • Expect:
    • 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

TEST 5: Cycling Test

  • Do: Cycle relay ON/OFF 10 times rapidly
  • Expect:
    • Relay responds each time
    • No sticking or hesitation
    • Load starts/stops reliably
  • Pass If: Reliable operation through multiple cycles

TEST 6: Controller Integration

  • 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

TROUBLESHOOTING

RELAY DOESN’T CLICK / NO COIL VOLTAGE

  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)

RELAY CLICKS BUT LOAD DOESN’T RUN

  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.)

RELAY STUCK ON / WON’T TURN OFF

  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)

RELAY CHATTERS / RAPID CLICKING

  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

CONTACTS BURNED / PITTED

  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

OVERLOAD RELAY TRIPPING (Motor Loads)

  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

ESCALATION - COMPLETE BEFORE CALLING

PRE-ESCALATION CHECKLIST

  • 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

PROVIDE THIS INFO

  • 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]

CONTACTS

  • Field Specialist: [Phone]
  • Electrician: [Phone] (if high-voltage issue)
  • Programmer: [Phone] (if sequence/logic issue)
  • Dispatch: [Phone]

COMMON ISSUES & TIPS

✓ 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

Document ID: SSO-RELAY-001
Revision: 1.0
Next Review: Dec 2026

Graph View

Backlinks