FCV18 Voltage Relays for Over & Under Voltage Protection

The FCV18 continuously monitors single-phase AC or DC voltage and trips its output contacts when voltage crosses your preset overvoltage (U>) or undervoltage (U<) thresholds. Unlike a circuit breaker (which trips on short circuits and sustained overloads), the FCV18 protects against gradual voltage abnormalities — sags, surges, and brownouts that can damage sensitive equipment.

Key specifications:

• Monitored voltage: AC 20-80V, 165-260V, 65-270V and DC 9-18V, 20-80V, 65-270V
• Supply voltage: AC 230V, DC 24V, or AC/DC 12-240V (universal)
• Measurement accuracy: ΔV < ±1% / ±1V
• Output: 1×SPDT 16A relay contacts
• Dimensions: 90×18×64mm DIN-rail mount
• Certifications: CE, EAC, RoHS, GB/T 14048.5, IEC60947-5-1

The difference is how the relay restores normal operation after a fault:

• FCV18-01 (Manual Reset): Once voltage crosses the threshold for longer than Tt, the relay trips and stays latched — even after voltage returns to normal. An operator must physically press the reset button on the front panel to restore operation. Use for: critical equipment where unexpected restart could cause damage or injury (compressors, large motors, industrial machinery).
• FCV18-02 (Auto Reset): Once voltage returns to the normal window and stays there, the relay automatically closes its contacts again. No manual intervention needed. Use for: non-critical loads, HVAC systems, general-purpose protection, telecom equipment.

Both models share identical measurement accuracy (±1%), the same 6 voltage monitoring ranges, adjustable trip delay (0.1s–20s), and the same 90×18×64mm DIN-rail form factor.

The FCV18 uses front-face DIP switches and rotary dials for configuration:

Step 1 — Select monitored voltage range (DIP switches 1-2):

• A48 / D48: AC 20-80V or DC 20-80V
• A220 / D220: AC 165-260V (standard 220-240V mains)
• A240 / D240: AC 65-270V or DC 65-270V (wide range)
• D12: DC 9-18V

Step 2 — Set supply voltage (DIP switch 3): A (AC 230V), D (DC 24V), or W (AC/DC 12-240V universal).

Step 3 — Set thresholds with the U> (overvoltage) and U< (undervoltage) dials. The scale runs from 20V to 80V (or 60-270V depending on range). The green LED shows power on; red LED shows relay tripped.

Trip delay (Tt) is the minimum time (0.1s–20s, adjustable) that voltage must stay outside the set window before the relay actually trips. It prevents nuisance tripping from brief transients:

• Motor inrush current causing brief voltage dip during startup
• Lightning strikes causing sub-cycle voltage spikes
• Switching transients from nearby loads

Setting guide: Use a longer Tt (5-20s) for non-critical loads where brief sags are acceptable. Use a shorter Tt (0.1-2s) for sensitive equipment like medical devices or telecom gear where even short voltage excursions are unacceptable.

On FCV18-02 (auto reset), the hysteresis (H) setting (5%–30% adjustable) creates a deadband between trip and release thresholds to prevent rapid chattering when voltage hovers near the setpoint.

Yes. The FCV18 voltage relay is designed for universal use on both 50Hz and 60Hz AC power systems. The relay's internal measurement circuit automatically adapts to the AC frequency it detects — no manual frequency setting is needed.

Three supply voltage options are available:

• A: AC 230V — standard European and Asian mains
• D: DC 24V — low-voltage control circuits
• W: AC/DC 12-240V — universal wide voltage, covers 100-240V globally

Voltage tolerance: -15% to +10% across all supply options. The universal (W) models are recommended for export distributors since one part number covers all global mains voltages.

FCV18 has two terminal groups:

Power supply terminals (A1-A2): Connect to the supply voltage (AC L/N or DC +/-). This powers the relay's internal circuitry.

Monitored voltage terminals (S1-S2): Connect the AC L (or DC+) to S1 and AC N (or DC-) to S2. The relay monitors the voltage between these terminals regardless of whether it shares the power supply circuit.

Output contacts (11-14-12):

• Terminals 11-14: Normally Open (NO) — closes when relay is energized (normal condition)
• Terminals 11-12: Normally Closed (NC) — opens when relay trips (fault condition)

Terminal specs: AWG13-20, stripping length 7mm, torque 0.4N·m. Mounting: DIN rail EN/IEC 60715.

Hysteresis (H) creates a deadband between the trip threshold and the release threshold — it prevents the relay from rapidly cycling on and off when voltage hovers near the setpoint.

For example, with Function A (overvoltage only): If you set U> at 240V with H=20%, the relay trips when voltage reaches 240V. It does NOT release until voltage drops below 240V × (1-20%) = 192V. This 48V window prevents chattering.

Hysteresis is adjustable from 5% to 30% via the front-face dial on FCV18-02. For most industrial applications, 10-20% hysteresis is recommended to balance responsiveness with stability.

Yes. The FCV18's 1×SPDT (Single Pole Double Throw) output relay contacts can interface directly with PLC digital inputs and automation controllers.

Wiring to PLC: connect the PLC digital input between terminals 11 and 14 (NO = Normally Open). When voltage goes out of range, the relay de-energizes, 11-14 opens, and the PLC detects the fault signal. When voltage returns to normal, the relay re-energizes and 11-14 closes.

Output contact rating: 1×16A at 250VAC. For PLC inputs, the actual current through the contact is only a few milliamps, well within the relay's electrical life rating of 1×10⁵ operations.

The FCV18 carries the following certifications for global market access:

• CE — European market compliance
• EAC — Eurasian Economic Union (Russia, Kazakhstan, Belarus)
• RoHS — hazardous substance restrictions for EU and global markets

Manufacturing standards: GB/T 14048.5 and IEC60947-5-1.

Environmental ratings:

• Protection degree: IP20
• Pollution level: 2
• Max installation altitude: ≤2200m
• Operating temperature: -20°C to +60°C
• Storage temperature: -40°C to +85°C
• Temperature coefficient: 0.05%/°C at 20°C

Yes. Fiicco provides comprehensive OEM and ODM services for the FCV18 voltage relay:

• Custom logo and brand labeling on the product housing, packaging, and documentation
• Custom voltage monitoring ranges beyond the standard 6 options
• Custom timing parameters (trip delay, hysteresis range)
• Custom supply voltage options
• Volume pricing for large orders

With our own factory and 10+ years of manufacturing experience since 2013, we support both small custom runs and high-volume production. Contact us at fiicco.com/contact to discuss your requirements.