The standard 24V 8-pin DPDT (Double Pole, Double Throw) relay uses Pins 2 and 7 for the coil, Pins 1 and 8 as the common poles, Pins 3 and 6 for normally closed (NC) contacts, and Pins 4 and 5 for normally open (NO) contacts. This pinout applies to nearly all octal-base 'ICE cube' relays, including industry standards like the Omron MY2 series and Schneider Electric 8501KP models.
The 8-Pin Terminal Map and Schematic Symbols
Before tracing the circuit, you need to map the physical pins to their schematic symbols. The 8-pin relay uses a circular octal base with a plastic keyway (or notch) at the bottom center to prevent backward insertion into the socket. When looking at the bottom of the relay (the pin side) with the keyway at the 6 o'clock position, the pins are numbered 1 through 8 sequentially.
| Pin Number | Function | Schematic Symbol | Physical Location (Keyway at 6 o'clock) |
|---|---|---|---|
| 1 | Common Pole 1 (C1) | Switch pivot point (left side) | Bottom left, closest to keyway |
| 2 | Coil (+ / A1) | Rectangle (often with parallel diode) | Top left |
| 3 | Normally Closed 1 (NC1) | Switch closed on left pivot | Mid-left, above Pin 1 |
| 4 | Normally Open 1 (NO1) | Switch open on left pivot | Top left, above Pin 3 |
| 5 | Normally Open 2 (NO2) | Switch open on right pivot | Top right |
| 6 | Normally Closed 2 (NC2) | Switch closed on right pivot | Mid-right |
| 7 | Coil (- / A2) | Rectangle (shares symbol with Pin 2) | Top right, below Pin 5 |
| 8 | Common Pole 2 (C2) | Switch pivot point (right side) | Bottom right, closest to keyway |
In standard IEC and NEMA schematic diagrams, the coil is drawn as a simple rectangle or a circle with the designation 'K' or 'CR' (Control Relay). The contacts are drawn detached from the coil but share the same alphanumeric tag (e.g., K1-NO, K1-NC). A diagonal line through the rectangle indicates a relay coil, while a parallel diode symbol indicates built-in surge suppression.
Node-by-Node Wiring Trace: Source to Load
A wiring diagram is useless if you cannot trace the physical current path. Below is the exact node-by-node trace for a standard 24V DC control circuit switching a separate load. This assumes you are using a relay socket (like the Omron PYF08A) wired to a terminal block.
- Control Source to Switch: Run a wire from your 24V DC power supply positive terminal to your control device (pushbutton, PLC output, or sensor).
- Switch to Coil (Pin 2): From the control device's output, route the 24V positive to Pin 2 on the relay socket.
Polarity Callout: If your relay has an internal flyback diode (e.g., Omron MY2N-D2), Pin 2 must be positive. Reversing polarity on a diode-equipped relay will forward-bias the diode, shorting the 24V supply and blowing your control fuse.
- Coil Ground Path (Pin 7): Run a wire from Pin 7 directly to the 24V DC negative (0V) ground bus. This completes the coil circuit. When the switch closes, ~30mA to 40mA flows through the coil, generating the magnetic field that pulls the armature.
- Load Power Feed (Pins 1 & 8): Connect your load's main power source (the 'hot' or 'positive' line) to Pin 1 and Pin 8. Because this is a DPDT relay, Pins 1 and 8 are internally isolated from each other until the contacts throw, allowing you to switch two completely different circuits or voltages simultaneously.
- Load Output (Pins 4/5 or 3/6):
- For a circuit that turns ON when the relay energizes, wire your load to Pin 4 (Pole 1) and Pin 5 (Pole 2).
- For a circuit that turns OFF when the relay energizes, wire your load to Pin 3 and Pin 6.
- Load Ground/Return: Connect the other side of your load to the system neutral (for AC loads) or the 0V DC ground bus.
Ground Path Rule: The relay contacts (Pins 1/8 to 4/5) only switch the ungrounded 'hot' or 'positive' leg. Never use a relay to switch the safety ground or equipment grounding conductor (EGC); the ground path must remain continuous and unbroken.
Bench Verification: Testing with a Multimeter
Before applying power to a newly wired panel, verify your connections with a digital multimeter (DMM). Set your meter to the following modes to validate the 24v 8 pin relay wiring diagram physically.
1. Coil Resistance Test (De-energized)
Set the DMM to Ohms (Ω). Place probes on Pin 2 and Pin 7. A healthy 24V DC coil will typically read between 600Ω and 800Ω (based on a 650Ω nominal coil drawing ~37mA). If you read 'OL' (open loop), the internal coil wire is broken. If you read near 0Ω, the coil is shorted.
2. Contact Continuity Test (De-energized)
Set the DMM to Continuity (the beep mode).
* Place one probe on Pin 1 and the other on Pin 3. You should hear a continuous beep (NC path is closed).
* Move the second probe to Pin 4. The meter should read 'OL' (NO path is open).
* Repeat for the second pole: Pin 8 to Pin 6 (beep) and Pin 8 to Pin 5 (OL).
3. Live Voltage Verification (Energized)
With the control switch closed and the relay energized (you should hear/feel the click), set the DMM to DC Volts. Measure from Pin 2 to Pin 7; you must read a stable 24.0V DC (acceptable range 22.8V to 26.4V). If voltage is present but the relay doesn't pull in, check for a voltage drop across the switch wiring indicating undersized control wires.
Frequently Asked Questions
Does a 24v 8 pin relay wiring diagram require a flyback diode?
Yes, if you are switching an inductive load or want to protect your control circuitry from inductive kickback. When the 24V DC coil de-energizes, the collapsing magnetic field generates a high-voltage reverse spike (often exceeding 100V). You can either buy a relay with a built-in diode (look for 'D2' in the part number) or wire an external 1N4007 diode in parallel across Pins 2 and 7. The diode's cathode (stripe) must point toward the positive Pin 2. For 24V AC coils, you would use an RC snubber network or a bidirectional TVS diode instead of a standard flyback diode.
How do I wire a 24v 8 pin relay for a 120V AC load?
The coil circuit (Pins 2 and 7) remains exactly the same, powered by your 24V DC control supply. The change happens entirely on the contact side (Pins 1, 3, 4, 5, 6, 8). You will wire your 120V AC 'Hot' (black wire) to Pin 1 and Pin 8. Your switched AC loads connect to Pin 4 (NO) or Pin 3 (NC). The AC 'Neutral' (white wire) bypasses the relay entirely and wires directly to the loads. Ensure your relay contacts are rated for the AC load; standard octal relays handle 10A at 120VAC, but motors require derating due to high inrush currents. Always consult the manufacturer's contact rating charts for inductive vs. resistive loads.
What happens if I swap the coil pins on a 24V DC 8-pin relay?
If it is a standard relay without internal suppression, swapping Pin 2 and Pin 7 will have no negative effect; the electromagnetic field will still pull the armature in regardless of polarity. However, if the relay has an internal flyback diode, a built-in LED indicator with a reverse-blocking diode, or a polarity-sensitive solid-state front end, reversing the pins will cause the internal diode to conduct immediately. This creates a dead short across your 24V power supply, which will blow the control circuit fuse or trip the power supply's overcurrent protection instantly.
