3 Wire Solenoid Valve Wiring Diagram
This is a free printable 3 wire solenoid valve wiring diagram: download the diagram as SVG or open it and print to paper or PDF.
A 3 wire solenoid valve wiring diagram covers valves with a coil, a common return, and a position feedback wire — typically used in industrial and irrigation control systems.
Most people encounter two-wire solenoid valves in irrigation: apply voltage across the two coil terminals and the valve opens or closes. A three-wire solenoid valve adds a third conductor, which serves one of two distinct purposes depending on the application.
In the most common industrial arrangement, the three wires are: (1) coil supply positive (or line), (2) coil supply negative (or neutral/return), and (3) a position feedback signal from an internal limit switch or reed switch. The feedback wire reports whether the valve has physically moved to its commanded position — critical in process control where a valve that receives a signal but fails to open must trigger an alarm rather than be assumed open.
In a second arrangement found in some latching or bistable solenoid valves, the three wires are: (1) common, (2) open coil, (3) close coil. A pulse to the open coil energises the valve open; a pulse to the close coil energises it closed. The valve retains its position without continuous power — significant for battery-powered remote terminal units (RTUs) in water distribution where power consumption is a constraint.
For standard proportional and on/off solenoid valves with feedback, the controller output connects to the coil supply terminals, and the feedback wire returns to a digital input on the PLC or controller. The feedback signal is typically dry contact (potential-free) or a low-voltage signal referenced to the common.
Voltage ratings vary widely: 12 V DC, 24 V DC, 110 V AC, and 230 V AC are all common. Always match the coil voltage to the supply. A 24 V DC coil energised at 230 V AC will burn out instantly. Conversely, a 230 V AC coil energised at 24 V DC will not develop sufficient magnetic flux to open the valve and may overheat due to the DC resistance being lower than AC impedance.
Most industrial solenoid valve coils are DIN 43650 plug-in type (Form A, B, or C connector), making field replacement straightforward without rewiring.
How to wire 3 wire solenoid valve wiring diagram
- Identify the three wires and valve type Obtain the solenoid valve datasheet and confirm whether the third wire is a feedback signal from an internal limit switch or the second coil of a latching valve. Note the coil voltage, current draw, connector type (DIN 43650 Form A/B/C or flying leads), and whether suppression is built in.
- Select the correct supply voltage and protection Match the power supply voltage and type (AC or DC) precisely to the coil rating. For DC coils without built-in suppression, add a flyback diode (e.g. 1N4007 for low-current coils, or a higher-rated fast-recovery diode for large coils) in reverse-parallel across the coil terminals. For AC coils, a metal oxide varistor (MOV) across the coil provides transient suppression.
- Wire the coil supply conductors Connect the positive (or line) supply wire to the coil positive terminal. Connect the return (negative or neutral) wire to the coil return terminal. Use appropriately rated cable for the coil current — typically 0.5–1.5 mm² for 24 V DC coils drawing 0.5–2 A. Route cable away from high-voltage or high-current conductors to minimise interference on the feedback signal.
- Connect the feedback or second coil wire For feedback-type valves: route the third wire back to the digital input terminal on the PLC or controller, with the common wire to input common. For latching valves: connect the open coil wire to the output that will pulse the valve open, and the close coil wire to the output that will pulse it closed. Both outputs share the common terminal.
- Verify polarity and insulation before energising Use a multimeter to measure coil resistance between the two coil terminals (refer to datasheet for expected resistance range). An open circuit indicates a failed coil; a short circuit indicates a winding fault. Check insulation resistance from coil terminals to the valve body (earth) — should be greater than 1 MΩ at 500 V DC for a new coil.
- Energise and confirm operation Apply power and command the valve open. Listen for the click of the plunger seating. Verify flow or pressure change downstream. For feedback-type valves, confirm the PLC digital input changes state within the valve's specified response time (typically 20–500 ms depending on valve size and differential pressure). If the input does not change, the valve may have failed to open mechanically.
Specifications
| Common coil voltages | 12 V DC, 24 V DC, 110 V AC (50/60 Hz), 230 V AC (50 Hz) |
|---|---|
| Typical coil power (small industrial valve) | 3–25 W (DC); 5–30 VA (AC) |
| DIN 43650 connector form | Form A (18 mm), Form B (11 mm), Form C (8 mm) |
| Insulation resistance (new coil) | > 1 MΩ at 500 V DC (coil to body) |
| Response time (on/off valve, typical) | 20–500 ms depending on valve size and pressure |
| Coil temperature class (typical) | Class F (155 °C) or Class H (180 °C) |
| Feedback contact rating (dry contact) | Typically 0.1–1 A at 30 V DC (check datasheet) |
| Applicable standards | IEC 60947-5-1 (low-voltage switchgear), IEC 60068 (environmental testing), ATEX/IECEx (hazardous areas where applicable) |
Safety warnings
- This diagram is for reference and educational purposes only. Electrical and instrumentation work on industrial systems must comply with applicable codes and regulations: NEC / NFPA 70 (USA), BS 7671 (UK), IEC 60364 (international), and any site-specific safety requirements. Work on pressurised systems must also comply with relevant pressure safety regulations.
- Always isolate both the electrical supply and the fluid system before working on a solenoid valve. De-pressurise the line, lock out the electrical supply, and verify dead with a calibrated voltage tester. A valve under pressure can release fluid or gas violently if the body is disturbed.
- Do not exceed the solenoid coil's rated voltage or duty cycle. A coil operated continuously beyond its rated temperature class will overheat, fail, and may cause a fire. Verify that the power supply voltage matches the coil rating exactly — AC and DC ratings are not interchangeable.
- For valves handling flammable, toxic, or high-pressure media, use only valves and coils with the appropriate hazardous area certification (ATEX, IECEx, or equivalent) if the installation is in a potentially explosive atmosphere.
- Ensure the feedback wire and control wiring are separated from high-voltage power conductors to prevent induced interference that can cause false position readings at the PLC input.
Tools needed
- Digital multimeter (voltage, resistance, continuity)
- Insulation resistance tester (500 V DC rated) for pre-commissioning coil check
- Calibrated voltage tester or non-contact voltage tester
- Insulated screwdrivers (VDE rated) for terminal connections
- Wire strippers matched to conductor size
- Crimping tool and insulated ferrules for panel wiring
- Cable labels and marker pen
- Personal protective equipment appropriate to the process media
Common mistakes
- Connecting a DC-rated coil to an AC supply (or vice versa), burning out the coil immediately or preventing it from opening due to incorrect impedance.
- Omitting the flyback diode on a DC circuit, causing repeated PLC output transistor failures from back-EMF spikes when the coil is de-energised.
- Wiring the feedback (third) wire as an additional power wire rather than a signal return, resulting in no feedback function and a potential short circuit.
- Using undersized cable for long valve runs, causing excessive voltage drop across the wiring that reduces coil magnetic force enough to prevent the valve from opening at minimum supply voltage.
- Failing to check whether the coil has a built-in suppression diode before adding an external one — doubling up diodes with mismatched polarities can cause a short circuit.
- Ignoring the valve's minimum operating pressure differential — a solenoid valve designed for 0.5 bar minimum differential will not open reliably on a gravity-fed system with insufficient head pressure.
Troubleshooting
- Valve does not open when energised
- Cause: Supply voltage not reaching the coil, coil burned out, or insufficient pressure differential across the valve Fix: Measure voltage at the coil terminals under energised conditions (voltage drop from no-load to under-load indicates wiring resistance problem). Measure coil resistance and compare to datasheet. Verify the system pressure differential meets the valve's minimum operating specification.
- PLC feedback input does not change state after valve is commanded open
- Cause: Internal limit switch failure, incorrect wiring of the feedback circuit, or valve failed to reach its open position mechanically Fix: Measure continuity of the feedback circuit with the valve physically open (manually override if safe to do so). Check wiring from the third terminal back to the PLC input common. Inspect the valve for mechanical obstruction or contamination preventing full travel.
- Coil becomes excessively hot after a few minutes of operation
- Cause: Coil is rated for intermittent duty but is being held energised continuously, supply voltage is too high, or the coil is a DC type connected to AC supply Fix: Check coil duty cycle rating on the datasheet. If the application requires continuous energisation, use a coil rated for 100% duty cycle. Verify supply voltage. For latching applications, switch to a bistable valve that holds position without continuous coil current.
- Valve chatters or cycles rapidly
- Cause: Supply voltage is at or below the minimum pull-in voltage, causing the plunger to oscillate between open and almost-closed; or AC supply frequency interference with a DC valve Fix: Measure supply voltage at the coil terminals under load. If below the coil's minimum rated voltage, reduce cable length resistance or increase supply voltage. Confirm AC/DC compatibility of the coil.
Frequently asked questions
What is the third wire on a 3 wire solenoid valve used for?
Depending on the valve type, the third wire is either a position feedback signal from an internal limit switch (confirming the valve has actually opened or closed), or a second coil terminal on a latching/bistable valve (one wire opens, one closes, one is common). Always check the valve datasheet to determine which configuration applies.
Can I use a 24 V DC solenoid valve on a 24 V AC supply?
No. A coil rated for DC will have a much lower impedance on AC because the inductive reactance adds to resistance on AC but not DC. On DC, the coil relies solely on its DC resistance; on AC, impedance increases. Using a DC-rated coil on AC may cause it to overheat and burn out due to lower-than-expected impedance limiting current.
Why does my solenoid valve hum or buzz when energised?
Humming on an AC solenoid is normal to a degree — the magnetic flux reverses at line frequency (50 or 60 Hz) causing the plunger to vibrate. Excessive buzzing usually indicates a dirty or worn shading ring on the pole face, low supply voltage, or a contaminated plunger preventing full magnetic closure. DC solenoids should be silent when correctly energised.
How do I wire the feedback wire from a 3 wire solenoid valve to a PLC?
Connect the feedback wire (dry contact return) to a digital input terminal on the PLC. Connect the common wire to the PLC's input common (0 V or COM). When the valve reaches its position, the internal limit switch closes the circuit between the feedback wire and common, pulling the PLC input high or low depending on input type. Verify input voltage and contact rating against PLC specifications.
Do I need a flyback diode when driving a solenoid valve coil from a DC PLC output?
Yes, for DC applications. When a solenoid coil is de-energised, the collapsing magnetic field generates a large voltage spike (back-EMF) that can destroy transistor outputs. A flyback (freewheeling) diode wired in reverse-parallel across the coil terminals clamps this spike. Many modern industrial solenoid valve coils have a built-in suppression diode or varistor — check the datasheet before adding an external diode.
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