FCV18-02 Series

Voltage Control Relay
Over & Under Voltage — Auto Reset

Precision single-phase voltage monitoring relay with independent overvoltage and undervoltage thresholds, adjustable hysteresis, time delay, and automatic reset — perfect for unattended protection of equipment against voltage anomalies.

12–240V AC/DC Supply Over/Under Voltage Protection Auto Reset Adjustable Hysteresis ≤1% / ±1V Accuracy DIN rail mount 18mm slim design 1×SPDT 16A @ 250V AC 0% Setting Deviation IP40 Front
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FCV18-02 Voltage Control Relay with Auto Reset
🔄 Automatic Reset Output automatically re-closes when voltage returns to normal — ideal for unattended or remote installations.
📉 Adjustable Hysteresis Set independent reset thresholds to prevent rapid cycling around the trip point — extends relay and contactor life.
🎯 ≤1% Measurement Accuracy High-precision voltage detection with ≤1% or ±1V accuracy coupled with 0% digital setting deviation.
⏱️ Adjustable Time Delay Configurable delay avoids nuisance tripping during short voltage spikes or dips.
📏 18mm Ultra-Slim Housing Same space-saving design as the FCT18, FCP18 and FCV18 series — fits any crowded control cabinet.
🔧 1×10⁷ Mechanical Life Exceptional durability with 1×10⁷ mechanical operations for long-term reliability.

📋 Models & Ordering

Model Monitoring Voltage Voltage Type Reset Mode Supply Voltage Datasheet
FCV18-02A240 65–260V AC Auto 12–240V AC/DC 📄 Download PDF
FCV18-02A220 165–260V AC Auto 12–240V AC/DC 📄 Download PDF
FCV18-02A48 20–80V AC Auto 12–240V AC/DC 📄 Download PDF
FCV18-02D240 65–260V DC Auto 12–240V AC/DC 📄 Download PDF
FCV18-02D48 20–80V DC Auto 12–240V AC/DC 📄 Download PDF
FCV18-02D12 9–18V DC Auto 12–240V AC/DC 📄 Download PDF

💡 Model selection guide: A prefix = AC monitoring, D prefix = DC monitoring. The number indicates the nominal monitoring voltage range. All models share 12–240V AC/DC supply, auto reset, adjustable hysteresis, and digital push-button configuration.

⚙️ Technical Specifications

🔌 Supply

Supply TerminalsA1 – A2
Supply Voltage12–240V AC/DC
Power ConsumptionAC 3.5VA / DC 2.0W
Voltage Tolerance-15% ~ +10%

🛡️ Monitoring Function

FunctionOver & Under Voltage Protection
Reset ModeAuto Reset
Monitoring TerminalsS1 – S2
Setting Accuracy0% – Digital Setting
Measurement Accuracy≤1% / ±1V
HysteresisAdjustable (1% – 2%)
Time DelayAdjustable via button

🔌 Output

Contact1 × SPDT
Rated Current16A @ 250V AC
Mechanical Life1×10⁷ operations
Electrical Life1×10⁵ operations

📐 Physical & Environmental

Dimensions18 × 90 × 64 mm
MountingDIN rail EN 60715
Protection DegreeIP40 (front) / IP10 (terminals)
Operating Temp.-20°C ~ +55°C
Storage Temp.-30°C ~ +70°C

📜 Standards & Certifications

ComplianceGB/T 14048.5, IEC 60947-5-1, EN 6812-1
Contact ConfigurationSPDT: 11(COM)-12(NC)-14(NO)
Pollution Degree2
Max. Cable SizeAWG 13–20 / 0.4 N·m

💡 Panel LED Indicators

LED Color Status Meaning
Un Green OFF Supply voltage not applied
Un Green ON Supply voltage applied
R Red OFF NC (11-12) contact closed
R Red ON NO (11-14) contact closed

📈 Function Diagram – Overvoltage & Undervoltage Protection (Auto Reset)

FCV18-02 Overvoltage and Undervoltage Protection Function Diagram with Auto Reset

• The relay monitors single-phase voltage via terminals S1–S2.
• When supply voltage A1-A2 is applied and the monitored voltage is within the set thresholds, the output relay R closes (NO contact 11-14 makes).
• If voltage goes above the overvoltage threshold, the output relay R opens after the set time delay. It will re-close when voltage drops below the overvoltage reset value (determined by the set hysteresis percentage).
• If voltage drops below the undervoltage threshold, the output relay R opens after the set time delay. It will re-close when voltage rises above the undervoltage reset value.
• Auto Reset: No manual intervention is required. The relay automatically re-energizes when the monitored voltage returns to within the reset window, making it ideal for unattended equipment protection.

🎬 See it in Action

🔧 Wiring & Terminal Layout

Terminal Identification

A1 — Supply L / + A2 — Supply N / - S1 — Voltage Input (+) S2 — Voltage Input (-) 11 — COM 12 — NC 14 — NO
⚠️ Safety Note: Keep the power supply disconnected during the entire installation process. Carefully check the wiring diagram and follow it correctly. Adhere to the specified voltage and current limits for each connection terminal.

Supply (A1–A2): Connect to 12–240V AC/DC to power the relay.
Monitoring (S1–S2): Connect the circuit whose voltage is to be monitored. For DC models, observe correct polarity.
Output (11-12-14): SPDT contact rated 16A @ 250V AC. Wire in series with the load or alarm circuit.

FCV18-02 Wiring and Terminal Layout Diagram

🛠️ Parameter Setting Guide

  1. Enter Parameter Setting Mode: Press and hold the button until the LED starts flashing. This indicates you have entered the configuration mode.
  2. Set Overvoltage Threshold (U>): Adjust the upper trip voltage. When the monitored voltage exceeds this value, the relay will open after the time delay.
  3. Set Undervoltage Threshold (U<): Adjust the lower trip voltage. When the monitored voltage drops below this value, the relay will open after the time delay.
  4. Set Hysteresis: Choose the hysteresis percentage (typically 1% or 2%). This determines the reset voltage: overvoltage reset = U> × (1 - hysteresis%); undervoltage reset = U< × (1 + hysteresis%). This prevents oscillation around the trip points.
  5. Set Time Delay: Adjust the delay before tripping on voltage faults. This also applies to the initial closing delay upon power-up.
  6. Confirm and Store: After all parameters are adjusted, press and hold the button until the LED stops flashing. The settings are stored and take effect immediately.

🏭 Typical Applications

⚡ Unattended Substations
Automatically protects equipment from voltage swings without operator intervention
🌀 Pump & Fan Motors
Prevents motor burnout from under/over voltage with automatic restart when supply recovers
💡 Lighting Circuits
Safeguards lamps and ballasts from overvoltage while automatically restoring after correction
🔋 Renewable Energy Systems
Monitors battery voltage in solar/wind installations with hysteresis for charge controller staging
🏭 Industrial Automation
Maintains process uptime by allowing automatic recovery from transient voltage events
📡 Telecom Equipment
Protects sensitive communication gear from DC supply anomalies with seamless auto-reset

🔗 Related Products

Explore other voltage monitoring relays in the FCV18 series:

FCV18-01 — Voltage Relay Manual Reset FCV18-02 — Voltage Relay Auto Reset

❓ Frequently Asked Questions

🔹 What does the hysteresis setting do?
Hysteresis defines a dead band between the trip point and the reset point to prevent rapid on-off cycling. For example, with overvoltage set at 140V and hysteresis at 1%, the relay will open at 140V and re-close at 138.6V. This protects contactors and connected equipment from constant switching around the trip threshold.
🔹 How is FCV18-02 different from FCV18-01?
FCV18-01 is a manual reset relay — once tripped, someone must acknowledge the fault to restore output. FCV18-02 is an auto reset relay — it restores output automatically when voltage returns to normal. Additionally, FCV18-02 includes an adjustable hysteresis function that FCV18-01 does not have.
🔹 Can I use FCV18-02 where safety regulations require a manual restart?
No. For applications requiring manual restart after a voltage fault (e.g., for machinery safety), use the FCV18-01 manual reset model. FCV18-02 is designed for applications where automatic recovery is desired and safe.
🔹 How accurate is the voltage measurement?
The FCV18-02 provides ≤1% or ±1V measurement accuracy, combined with 0% digital setting deviation, ensuring highly precise and repeatable voltage monitoring.
🔹 What monitoring voltage ranges are available?
AC models: 65–260V (A240), 165–260V (A220), 20–80V (A48). DC models: 65–260V (D240), 20–80V (D48), 9–18V (D12). Select based on your nominal operating voltage.
🔹 What is the mechanical life of the output contacts?
The relay has an outstanding mechanical life of 1×10⁷ operations. Electrical life is 1×10⁵ operations at rated 16A/250V AC load.

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