Solenoid Valve Wiring: A Technical Guide from Standard Practice to Safety Assurance

In fields such as industrial automation, automotive engineering, and appliance control, the reliable operation of a solenoid valve depends not only on its core working principle but crucially on the quality of the "final step": the wiring. Incorrect wiring can lead to coil burnout, control failure, short circuits, equipment malfunction, and safety hazards.

This guide provides a systematic overview of the correct solenoid valve wiring procedure for technicians, covering the essential preparatory work, the standardized wiring process for different valve types, and post-wiring checks and troubleshooting. We conclude with a recommendation for high-quality products that prioritize wiring reliability.

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I. Pre-Wiring Preparation: Safety and Efficiency First

Before beginning the connection process, three core steps—Tool Preparation, Parameter Verification, and Safety Precautions—must be completed to avoid operational errors caused by inadequate preparation.

1. Essential Tool Checklist

The wiring process requires tools that balance precision and safety:

2. Critical Parameter Verification

The valve's parameters must match the power supply and control system:

Voltage and Frequency: Check the solenoid nameplate for rated voltage (e.g., DC $24\text{V}$, AC $220\text{V}$) and frequency (AC valves only, e.g., $50/60\text{Hz}$). Mismatching the voltage (e.g., connecting a DC $24\text{V}$ valve to an AC $220\text{V}$ source) will instantly burn out the coil.

Coil Resistance: Use a multimeter's Ohm ($\Omega$) setting to measure the coil resistance. Typically, industrial solenoid coils are between a few dozen and a few hundred Ohms. If the resistance is $0$ (short circuit) or infinite (open circuit), the coil is damaged and must be replaced.

Terminal Identification: Familiarize yourself with the terminal markings:

DC Valves: "+" and "-" (distinguish polarity).

AC Valves: "L" and "N" (Live and Neutral).

Feedback Valves: "COM," "NO," "NC" (Common, Normally Open, Normally Closed signal terminals).

3. Safety Precautions

Power Disconnection: Always cut off the power supply before wiring and affix a "Wiring in Progress, Do Not Switch On" tag at the switch.

Environmental Check: If the valve is in a humid or dusty environment (e.g., factory floor, outdoors), check the terminal box seal. Replace with a waterproof terminal box if necessary to prevent short circuits from moisture or dust.

High-Voltage Operation: For high-voltage solenoids (e.g., AC $380\text{V}$), ensure the operator is properly certified for high-voltage work.

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II. Standardized Wiring Procedures for Different Solenoid Valve Types

Wiring varies based on the power type (DC/AC) and functional requirements (standard control/signal feedback).

1. Standard DC Solenoid Valve Wiring (Single Coil, No Feedback)

DC valves require attention to polarity ("+" and "-"):

1. Strip Wire: Use the stripper to remove about $5\sim 8\text{mm}$ of insulation from the power wires. The copper core should be fully inserted into the terminal without excessive exposure.

2. Connect Terminals: Connect the wires to the "+" and "-" terminals. Conventionally, Red is connected to "+" and Black/Blue to "-".

3. Secure Connection: Fully insert the copper core and tighten the terminal screw firmly. Gently tug the wire to confirm it is not loose.

4. Special Terminals: For blade-type terminals (common in automotive solenoids), the wire must be properly crimped onto the corresponding terminal blade before being inserted into the valve connector, ensuring a tight fit.

5. Insulation: If terminals are exposed, use insulating tape to wrap the connection point, ensuring $\ge 3$ layers and overlapping the original insulation by $2\sim 3\text{mm}$.

2. Standard AC Solenoid Valve Wiring (Single Coil, No Feedback)

AC valves do not require polarity distinction but must adhere to Live (L) and Neutral (N) standards:

1. Preparation: Same stripping process as DC valves. Use a multimeter to verify the voltage between "L" and "N" at the power source.

2. Connect Terminals: Connect the Live wire (L) (often Brown/Red) to terminal "L" and the Neutral wire (N) (often Blue/Black) to terminal "N". If the terminals are not marked "L/N," connection can be arbitrary, but standardization (e.g., all AC valves wired "Live on the left, Neutral on the right" within the facility) is recommended for maintenance.

3. Grounding: If the valve has a grounding terminal ("PE," typically Green/Yellow wire), it must be reliably connected with a grounding resistance of $\le 4\Omega$. This prevents the valve casing from becoming energized, which is a major safety hazard.

4. Securing: After connection, insulate any exposed terminals. If the valve is in a high-vibration environment (e.g., production line), use cable ties to secure the wires, preventing terminal loosening over time.

3. Wiring for Solenoid Valves with Signal Feedback (e.g., Position Sensor)

Valves requiring real-time position monitoring have both coil terminals and sensor signal terminals (e.g., "COM," "NO," "NC").

1. Coil Wiring: Complete the power supply connection to the coil terminals first, following the standard DC or AC method.

2. Signal Terminal Wiring: Connect the control system's signal input (e.g., PLC DI module) to the valve's signal terminals:

   • "COM" connects to the signal power negative (or common terminal).

   • "NO" connects to the PLC's Normally Open input (when the spool shifts, NO connects to COM, outputting an "On" signal).

   • "NC" connects to the Normally Closed input (when the spool resets, NC connects to COM, outputting an "Off" signal).

3. Signal Wire: It is highly recommended to use shielded cable (e.g., RVVP 2×0.5mm2) for signal lines to prevent electromagnetic interference (from inverters, motors) from causing false readings. The shield should be grounded at one end (at the control system ground).

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III. Post-Wiring Check and Troubleshooting

After wiring, perform a three-step check (Pre-Power Check, Power-On Test, Troubleshooting) to ensure proper operation.

1. Pre-Power Check

Visual Inspection: Check for damaged wires, exposed copper cores, loose terminal screws, and fully wrapped insulation.

Resistance Re-test: Re-measure the coil resistance to confirm it matches the nameplate. Measure the insulation resistance between the power terminals and the grounding terminal (using a multimeter's Megaohm ($M\Omega$) setting). It should be $\ge 10M\Omega$ to confirm good insulation.

Wiring Sequence Review: Double-check the polarity, Live/Neutral, and signal terminal connections against the wiring diagram.

2. Power-On Test

No-Load Test: For the initial power-on, it is best to disconnect the valve from the fluid lines (no-load state). Power the valve and listen for the characteristic "click" sound (solenoid pull-in), indicating the spool is moving.

Load Test: If the no-load test is normal, connect the fluid lines. Power the valve and observe if the fluid flow turns on and off as expected. If the valve has feedback, use a multimeter to measure the signal output to confirm it is normal (e.g., $24\text{V}$ DC signal between NO and COM when active).

3. Common Wiring Issues and Solutions

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IV. Recommended Solenoid Valves: Airtac for Wiring Reliability

Beyond standard practices, the solenoid valve's wiring design and quality stability directly influence connection efficiency and long-term safety. Airtac (Yadeke), a global pneumatic component brand, offers significant advantages in these areas, making its solenoid valves an excellent choice for industrial applications:

1. Optimized Wiring Design

• Clear Terminal Identification: Airtac terminals use laser-engraved markings (e.g., "+", "-", "L", "N", "PE", "COM," "NO," "NC") that are clear and wear-resistant, preventing connection errors caused by faded labels.

• Diverse Connection Methods: They offer various types to suit different needs: Screw-clamping (for direct wire connection), Blade-type (common in automotive, fast assembly), and Aviation Plug-type (up to IP65 waterproof, ideal for wet/dusty environments, easy maintenance).

• Reverse Polarity Protection: Some Airtac DC valves (like the $5\text{V}$ series with feedback) feature built-in reverse polarity protection. If the DC wires are connected incorrectly, the coil will simply not work instead of burning out, reducing damage from new user errors.

2. Core Component Reliability

• High-Temperature Coils: Coils use enameled wire with a high-temperature rating (155∘C) and a flame-retardant bobbin to prevent aging from continuous power-on. The coil's insulation resistance is typically $\ge 100\text{M}\Omega$ ($500\text{V}$ DC), minimizing short-circuit risks.

• Anti-Loosening Terminals: Terminal screws often feature anti-loosening threads, paired with tin-plated copper terminals (for oxidation resistance). This design ensures connections remain secure even in high-vibration environments, preventing intermittent contact issues.

• Comprehensive Protection: Airtac solenoid enclosures offer protection up to IP67 (for waterproof 4V series), allowing direct use in outdoor or wet conditions without the need for additional protective measures.

In summary, standardized wiring is fundamental to stable solenoid valve operation. Combining standardized procedure with high-quality, user-friendly products like Airtac solenoid valves is the best way to ensure safe, efficient, and long-term stable performance.