Start With
Include WithHow To Wire a Relay with Different Pin Diagrams? The Ultimate Guide
Relays are essential components in electrical systems, enabling low-power circuits to control high-power loads. This guide explains how to wire relays with various pin configurations, including step-by-step instructions, diagrams, and practical tips.
1. Relay Basics
A relay consists of:
Coil terminals: Energized by a control signal to activate the relay.
Common (COM) terminal: Central contact that switches between Normally Open (NO) and Normally Closed (NC) contacts.
NO/NC terminals: NO connects to COM when the coil is energized; NC disconnects from COM when energized.
2. Common Relay Types & Pin Diagrams
A. 4-Pin SPDT Relay
Pinout:
Pin 85: Coil (-)
Pin 86: Coil (+)
Pin 30: Common (COM)
Pin 87: Normally Open (NO)
Wiring Steps:
Connect Pin 85 to ground and Pin 86 to a switched +12V source (control circuit).
Link the load (e.g., headlights) between Pin 30 (power input) and Pin 87 (output to load).
Use Case: Automotive lighting control.
B. 5-Pin SPDT Relay
Pinout:
Pin 85: Coil (-)
Pin 86: Coil (+)
Pin 30: COM
Pin 87: NO
Pin 87a: NC
Wiring Steps:
Coil wiring: Pin 85 to ground, Pin 86 to control voltage.
Pin 30 to power supply.
Pin 87 to load (activated when coil is energized).
Pin 87a to secondary load (deactivated when coil is energized).
Use Case: Reversing motor direction or fail-safe circuits.
C. 8-Pin DPDT Relay
Pinout:
Pins 2 & 7: Coil terminals.
Pins 1, 3, 4, 6, 8: COM, NO, and NC for two independent circuits.
Wiring Steps:
Connect coil (Pins 2 & 7) to control voltage.
Wire the first circuit: Pin 1 (COM1) to power, Pin 3 (NO1) and Pin 5 (NC1) to loads.
Repeat for the second circuit: Pin 8 (COM2), Pin 6 (NO2), and Pin 4 (NC2).
Use Case: Industrial control for dual-circuit switching.
3. Wiring Best Practices
Safety First: Disconnect power before wiring. Use insulated tools.
Verify Voltage: Match coil voltage (e.g., 12V DC, 24V AC) to the control signal.
Load Rating: Ensure relay contacts support the load’s current/voltage.
Diode Protection: Add a flyback diode across the coil for DC relays to prevent voltage spikes.
4. Troubleshooting Common Issues
Relay Not Activating:
Check coil connections and voltage.
Test continuity across the coil (typical resistance: 50–200Ω).
Contacts Overheating:
Ensure load does not exceed relay rating.
Clean oxidized contacts with electrical contact cleaner.
5. Applications
Automotive: Fan control, horn activation.
Home Automation: Smart light switching.
Industrial: Motor control, safety interlocks.
By understanding pin configurations and following these guidelines, you can safely wire relays for diverse applications. Always consult the relay’s datasheet for exact pinouts and specifications.
Kevin Chen
Founder / Writer at Rantle East Electronic Trading Co.,Limited
I am Kevin Chen, I graduated from University of Electronic Science and Technology of China in 2000. I am an electrical and electronic engineer with 23 years of experience, in charge of writting content for ICRFQ. I am willing use my experiences to create reliable and necessary electronic information to help our readers. We welcome readers to engage with us on various topics related to electronics such as IC chips, Diode, Transistor, Module, Relay, opticalcoupler, Connectors etc. Please feel free to share your thoughts and questions on these subjects with us. We look forward to hearing from you!
