Latching Relay Wiring Diagram: Step-by-Step Dual-Coil Trace & Pinout

A latching relay maintains its last switched state even after power is removed from the coil, making it the definitive choice for battery-backed systems, energy-efficient control panels, and fail-safe home automation. Unlike standard relays that require continuous holding current (often 30-50mA), a dual-coil latching relay like the Omron MY2K or G6CK series only draws current for the 20-50 milliseconds it takes to physically flip the internal armature.

If you are looking at a latching relay wiring diagram for a dual-coil (Set/Reset) 8-pin device, the direct answer is this: you will wire two separate momentary control circuits to Pins 1, 2, 7, and 8, and route your load through the Common (Pins 3/6) and Normally Open (Pins 4/5) contacts. Below is the exact node-by-node trace, terminal mapping, and meter verification sequence to wire it correctly on the first attempt.

Decoding the Latching Relay Wiring Diagram Symbols

Before touching a wire stripper, you must understand the specific IEC/NEMA schematic symbols used for latching relays, as they differ from standard electromagnetic relays.

• The Coil Rectangles: A standard relay shows one rectangle. A dual-coil latching diagram shows two parallel rectangles, often labeled Set (or S) and Reset (or R).
• The Mechanical Latch Indicator: Look for a diagonal line crossing the coil rectangles, or a small mechanical triangle/latch symbol between them. This indicates the armature physically locks into place.
• Momentary Contacts (NO): The control switches are drawn as standard Normally Open (NO) pushbuttons with a dotted line indicating manual, momentary actuation. They must return to the open state immediately; holding the button down does not damage the relay, but it wastes power and generates heat in the coil.
• SPDT/DPDT Contacts: The load side is drawn as standard switch contacts. However, on an 8-pin dual-coil relay, the Normally Closed (NC) contacts are almost always sacrificed to make room for the second coil.

Terminal and Pin Mapping Table (8-Pin Dual-Coil Octal)

The physical device (such as an 8-pin plug-in relay on a DIN-rail socket) maps its internal coils and contacts to specific base pins. Below is the definitive pinout for a standard 24VDC dual-coil latching relay. Always verify against the specific datasheet (e.g., NEMA ICS 2 standards or manufacturer spec sheets) as 14-pin variants exist.

Node-by-Node Wiring Trace (Source to Load)

This trace assumes a 24VDC control system powering a 24VDC load (e.g., a solenoid valve or a heavy-duty contactor coil). We are tracing the exact path of electrons from the power supply positive terminal, through the control and load circuits, and back to the negative terminal.

1. The Control Circuit (Set Path)

1. Source: Start at the 24VDC Power Supply Positive (+) terminal.
2. Protection: Route a 22 AWG control wire to a 2A fast-acting glass fuse, then to the input terminal of your "SET" momentary pushbutton.
3. Switching: From the output terminal of the SET pushbutton, run a wire to Pin 2 (Set Coil +) on the relay socket.
4. Coil Transit: Current flows through the internal copper winding and exits at Pin 7 (Set Coil -).
5. Flyback Protection: Solder or crimp a 1N4007 flyback diode across Pins 2 and 7. Critical: The diode's cathode (stripe) must point toward Pin 2 (+), and the anode toward Pin 7 (-). This provides a safe path for the inductive voltage spike when the button is released.
6. Ground Return: Route the wire from Pin 7 directly to the 24VDC Power Supply Negative (-) / 0V ground bus.

2. The Control Circuit (Reset Path)

1. Source: Tap the 24VDC Positive (+) bus again, routing through a second 2A fuse to your "RESET" momentary pushbutton.
2. Switching: From the RESET button output, run a wire to Pin 1 (Reset Coil +).
3. Coil Transit & Protection: Current exits at Pin 8 (Reset Coil -). Install a second 1N4007 flyback diode across Pins 1 and 8 (cathode to Pin 1, anode to Pin 8).
4. Ground Return: Route Pin 8 to the 24VDC Negative (-) ground bus.

3. The Load Circuit

1. Load Source: Connect your main load power (e.g., 120VAC or a high-current 24VDC feed) to Pin 3 (COM).
2. Load Output: Connect Pin 4 (NO) to the positive input of your load (e.g., a motor starter coil or lighting bank).
3. Load Ground: Connect the negative/neutral side of your load back to the respective main power ground/neutral.

Verifying Connections with a Multimeter

Before energizing the panel, use a digital multimeter (DMM) to verify your physical wiring against the latching relay wiring diagram. According to best practices outlined by Electronics Tutorials, verifying inductive loads prevents catastrophic PLC and power supply failures.

1. Isolate Power: Ensure the 24VDC PSU is completely off and unplugged. Remove the relay from its socket to test the socket wiring first.
2. Test Coil Continuity (Socket Side): Set your DMM to the 2kΩ resistance range. Place probes on the socket's Pin 2 and Pin 7 slots. You should read the coil resistance (typically 400Ω to 1000Ω depending on voltage rating). Repeat for Pin 1 and Pin 8. If you read 0.0Ω (short) or OL (open), re-check your flyback diode orientation and crimps.
3. Test Flyback Diodes: Switch the DMM to Diode Test mode. Place the red probe on Pin 7 and black on Pin 2. You should read a forward voltage drop of ~0.5V to 0.7V. Reverse the probes; it should read OL. This confirms the diode is blocking DC current but will pass the reverse inductive spike.
4. Test Switch Isolation: Set DMM to Continuity (beep). Place probes across the SET pushbutton terminals. It should only beep when physically pressed. Repeat for the RESET button.
5. Bench Test the Relay: Insert the relay. Apply a temporary 24VDC jumper to Pins 2 (+) and 7 (-). You should hear a distinct mechanical click. Move your DMM (Continuity mode) to Pins 3 and 4. It should beep, confirming the load path is closed. Remove the jumper; the beep should persist (it is latched). Apply 24VDC to Pins 1 (+) and 8 (-). You will hear a second click, and the continuity between 3 and 4 will break.

Latching Relay Wiring Diagram FAQ

Can I use a single-coil latching relay wiring diagram for a dual-coil relay?

No. A single-coil latching relay (like the Finder 20.23) uses polarity reversal to change states. You must send +24V to Pin A and 0V to Pin B to Set it, then reverse the polarity (0V to Pin A, +24V to Pin B) to Reset it. This requires an H-bridge circuit or a specialized DPDT toggle switch. A dual-coil relay has separate, dedicated windings for Set and Reset, meaning you simply pulse positive voltage to the respective coil pin while the other pin remains tied to ground. Mixing up these diagrams will result in a non-functional circuit or a shorted power supply.

Why does my latching relay fail to reset when wired to a PLC transistor output?

PLC transistor outputs (sinking or sourcing) are often limited to 0.5A per channel. While the holding current of a latching relay is zero, the inrush current required to overcome the mechanical latch and permanent magnet can spike to 3 or 4 times the nominal coil current for the first 10 milliseconds. If the PLC transistor cannot supply this peak current, the relay will "buzz" or fail to flip. The fix is to use the PLC output to drive an intermediate standard relay, or use a PLC with relay outputs, or wire a small capacitor (e.g., 470µF) in parallel with the coil to supply the inrush spike.

How do I wire an LED indicator to show the latching relay's state without NC contacts?

Because the dual-coil 8-pin relay sacrifices the Normally Closed (NC) contacts for the reset coil, you cannot use a standard "NC to LED" wiring scheme to show the off-state. Instead, wire a 24VDC LED indicator module (with an internal current-limiting resistor) in parallel with your load on Pins 3 and 4. When the relay is latched ON, the load receives power, and the LED illuminates. If you need an "OFF" indicator, you must purchase a relay with an auxiliary contact block (like the Omron G2A-432N) that provides isolated SPDT contacts specifically for state feedback.