Relay Clicking But No Power

Your relay clicks when toggled, but the connected device does not turn on. The relay coil is working, but power is not reaching the load. This guide covers COM/NO/NC wiring errors, high-resistance contacts, load wiring mistakes, and voltage drop issues.

Last updated: April 22, 2026 | 10 min read

Symptoms

• Audible click from relay when toggling ON/OFF
• Relay LED indicator turns ON/OFF normally
• Connected device does not power on
• Multimeter shows 0V on load when relay is ON
• Relay worked before but stopped passing power
• Device powers on intermittently or flickers
• Load works when connected directly to power source

Common Causes

1. Wrong Terminal Wiring Most common mistake. Load connected to NC instead of NO, or COM not connected to power source
2. Burned or High-Resistance Contacts Arcing has damaged relay contacts, creating resistance instead of direct short
3. Insufficient Load Current Some loads draw too little current to create a reliable contact path
4. Loose or Broken Load Wire Poor connection between relay and load device
5. Voltage Drop Across Long Wires Thin or long wires cause voltage drop, especially at high current
6. Faulty Load Device The device itself may be burned out
7. Relay Contact Welded in Open Position Contacts stuck partially open, preventing current flow

Relay Terminal Functions

Most common mistake: Connecting load to NC instead of NO. When relay clicks ON, NC disconnects and NO connects. Load must be on NO.

Correct Wiring Diagrams

AC Power Source 
        
         
        
    
     COM    Relay COM terminal
    
       
        
    
     NO     Relay NO terminal
    
       
       
    
      LOAD     
    
       
       
    AC Neutral 

DC Power Supply (+)
        
        
    
     COM    Relay COM terminal
    
       
        
    
     NO     Relay NO terminal
    
       
       
    
      LOAD     
    
       
       
    DC Power Supply (-) 

Step-by-Step Fixes

1. Verify Terminal Wiring

Use multimeter to check continuity between terminals:

• Set multimeter to continuity mode or resistance ()
• With relay OFF: COM should connect to NC
• With relay OFF: COM should NOT connect to NO
• With relay ON : COM should connect to NO
• With relay ON: COM should NOT connect to NC
• If wiring is correct but no continuity, relay contacts are burned

// Multimeter test procedure:
// 1. Power OFF the relay module and load
// 2. Set multimeter to resistance () or continuity ()
// 3. Test with relay manually activated 
// 
// Correct readings:
// Relay OFF: COM-NC = 0 , COM-NO =  
// Relay ON:  COM-NO = 0 , COM-NC =  
//
// If COM-NO reads high resistance , contacts are burned
// Replace relay module immediately

2. Check Load Connection

Most common wiring mistake load on NC instead of NO:

• Disconnect power completely
• Verify load is connected to NO terminal
• Verify COM terminal is connected to power source
• If load is on NC, it will be ON when relay is OFF, OFF when relay is ON
• Move load wire from NC to NO terminal
• Test again load should now turn ON when relay clicks

3. Test Load Directly

Verify load device itself is working:

• Disconnect load wires from relay
• Connect load directly to power source
• If load works, relay is the problem
• If load doesn't work, device is faulty
• Replace faulty load device

4. Check for High-Resistance Contacts

Burned contacts can pass low current but not high current:

• Measure voltage across load when relay is ON
• Should be near full supply voltage
• If voltage is significantly lower, contacts have high resistance
• Measure voltage across relay contacts when ON
• Should be near 0V; if >1V, contacts are burned
• Replace relay module contacts cannot be repaired

// Voltage drop test:
// Measure voltage across COM and NO terminals with relay ON
// 
// Good contacts: 0.0V - 0.1V 
// Worn contacts: 0.5V - 5V 
// Failed contacts: 10V+ (load won't work at all)
//
// Replace relay if voltage drop exceeds 1V under load

5. Verify Load Current is Sufficient

Some loads draw very low current:

• Relay contacts require minimum current to "wet" and make reliable connection
• Typical minimum: 10-100mA
• Low-power LED bulbs may not draw enough current
• Add a "keep-alive" load in parallel
• Or use a solid-state relay for very low current loads

6. Check for Voltage Drop in Long Wires

Thin or long wires cause voltage drop, especially at high current:

• Measure voltage at load terminals
• If voltage is significantly lower than supply, wires are too thin or long
• For 12V DC systems, use 18 AWG for runs under 5 meters
• For 120V AC, use 14 AWG for runs under 15 meters
• Reduce wire length or increase wire gauge

7. Replace Faulty Relay Module

If contacts are burned or welded:

• Purchase replacement 5V relay module
• Disconnect power and remove old module
• Install new module with same wiring
• Test with simple load first
• For inductive loads , add snubber circuit to prevent future contact damage

Load Type Recommendations

Prevention Tips

• Always connect load to NO terminal for standard ON/OFF control
• Use multimeter to verify continuity before connecting AC power
• Add RC snubber for AC inductive loads
• Add flyback diode for DC inductive loads
• For low-power LED loads, add dummy load in parallel
• Replace relay immediately if contacts show signs of arcing or pitting
• Use solid-state relay for frequent switching or low-current loads

Related Issues

• Relay Not Clicking No sound when toggling
• Relay Stuck OFF Won't turn ON at all
• Relay Stuck ON Won't turn OFF
• Relay Logic Wrong Configuration mismatch

Frequently Asked Questions

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