FCP18-04
Three-Phase Voltage · Adjustable Asymmetry & Phase Loss Protection Relay
Precision Three-Phase Protection with Adjustable Asymmetry Sensitivity
The FCP18-04 is a precision three-phase voltage monitoring relay combining four essential protection functions — over-voltage, under-voltage, adjustable voltage asymmetry (unbalance), and phase sequence/loss detection — in a single ultra-compact 18mm DIN rail module.
Compared with the FCP18-03 (fixed 8% asymmetry), the FCP18-04 offers a 5%~15% adjustable asymmetry threshold, making it ideal for protecting sensitive three-phase equipment that may tolerate slight voltage imbalance but still require protection against severe unbalance. The fixed 5-second time delay prevents nuisance tripping during normal motor startup transients.
Quick Specifications
Why Choose the FCP18-04?
Engineered for industrial reliability with fully adjustable asymmetry sensitivity.
4-in-1 Protection
Over-voltage, under-voltage, adjustable asymmetry, and phase sequence/loss — all monitored by a single relay for complete three-phase protection.
5%~15% Adjustable Asymmetry
Fine-tune the voltage unbalance trip threshold to match the tolerance of your sensitive equipment, from robust motors to precision CNC machines.
16A SPDT Output Relay
High-capacity SPDT output handles direct motor and contactor switching. Mechanical life 10 million cycles, electrical life 100,000 cycles.
Tool-Free Configuration
Four front-panel adjustment button (Un, U>, U<, Asy, Tt) allow fast, screwdriver-free setup. No programming or software tools required.
Fixed 5s Trip Delay
Fixed 5-second time delay prevents nuisance tripping during motor startup current transients, ensuring stable operation in real-world industrial conditions.
Four Protection Functions
Comprehensive monitoring of all critical three-phase fault conditions.
The FCP18-04 monitors all four fault conditions simultaneously. The diagram below illustrates the over-voltage and under-voltage operating regions. The relay trips when the measured voltage exceeds the set threshold (U>) or drops below the set threshold (U<) and holds for the configured time delay (Tt).
The adjustable asymmetry function protects equipment from damaging phase voltage imbalance with a configurable threshold between 5% and 15%. The phase sequence and phase loss function monitors the L1, L2, L3 phase order and immediately detects when any phase is interrupted or reversed.
1. Over-voltage Protection (U>)
When the measured line voltage rises above the adjustable over-voltage threshold (U>) — set between +2% and +20% above the rated voltage (Un) — and remains high for the configured fixed time delay of 5 seconds, the relay trips and opens the output contact. This protects connected equipment from dangerous overvoltage conditions caused by generator overspeed, load rejection, or grid surges.
- Trip threshold: Un + (U> dial % of Un)
- Time delay: Fixed at 5 seconds
- Reset: Automatic reset once voltage returns to normal
2. Under-voltage Protection (U<)
When the measured line voltage falls below the adjustable under-voltage threshold (U<) — set between −2% and −20% below the rated voltage (Un) — and remains low for the fixed 5-second time delay, the relay trips. This prevents motor stalling, overheating, and equipment damage caused by sustained low-voltage conditions from brownouts or overloaded distribution circuits.
- Trip threshold: Un − (|U<| dial % of Un)
- Time delay: Fixed at 5 seconds — prevents nuisance trips from brief motor-start dips
- Application: Essential for motor protection and compressor control systems
3. Voltage Asymmetry / Unbalance Detection (Asy)
Voltage asymmetry (also called voltage unbalance) occurs when the three phase voltages are not equal in magnitude. This is one of the most common causes of three-phase motor overheating and premature failure. The FCP18-04 continuously calculates the unbalance ratio using the formula: Asy = (Umax − Umin) / Uavg × 100%. Unlike the FCP18-03's fixed 8% threshold, the FCP18-04 allows the asymmetry threshold to be adjusted between 5% and 15% via the front-panel Asy dial.
- Trip threshold: 5%~15% adjustable (vs. fixed 8% on FCP18-03)
- Formula: Asy = (Umax − Umin) / Uavg × 100%
- Trip time: After 5-second fixed Tt delay elapses
- Use case: Ideal for sensitive equipment where 8% is too strict or too loose
4. Phase Sequence & Phase Loss Protection
The FCP18-04 continuously monitors the rotational sequence of the three-phase supply (L1 → L2 → L3). If the phase sequence is reversed or any phase is interrupted (open circuit, blown fuse, or cable fault), the relay immediately detects the fault and trips. The red P LED on the front panel provides instant visual status: lit = correct sequence, flashing = fault detected.
- P LED lit (steady): All three phases present and in correct rotation sequence
- P LED flashing: Phase loss (one or more phases missing) or phase sequence reversed
- Trip behavior: Immediate — no additional time delay for phase loss/sequence faults
- Protection scope: Detects single-phase loss, two-phase loss, and reversed phase wiring errors
Technical Specifications
Full electrical and mechanical specifications for the FCP18-04 series.
| Parameter | FCP18-04A / 04C | FCP18-04B / 04D |
|---|---|---|
| System Type | 3-Phase 3-Wire (L1-L2-L3) | 3-Phase 4-Wire (L1-L2-L3-N) |
| Voltage Range (L-L) | 173-275V AC (A) / 310-480V AC (C) | N/A for 4-wire models |
| Voltage Range (L-N) | N/A for 3-wire models | 100-160V AC (B) / 180-278V AC (D) |
| Rated Frequency | 45Hz - 65Hz | 45Hz - 65Hz |
| Voltage Tolerance | −15% to +10% | −15% to +10% |
| Asymmetry Setting | 5%~15% adjustable | 5%~15% adjustable |
| Over/Under Voltage Range | ±(2%~20%) adjustable | ±(2%~20%) adjustable |
| Time Delay (Tt) | 5s fixed | 5s fixed |
| Measurement Accuracy | ΔV less than ±1% | ΔV less than ±1% |
| Temperature Coefficient | 0.05%/°C at 20°C | 0.05%/°C at 20°C |
| Output Contact | 1 × SPDT (NO+NC) | 1 × SPDT (NO+NC) |
| Rated Current | 16A / 250V AC | 16A / 250V AC |
| Mechanical Life | 1 × 107 operations | 1 × 107 operations |
| Electrical Life | 1 × 105 operations | 1 × 105 operations |
| Ambient Temperature | −20°C to +60°C | −20°C to +60°C |
| Mounting | DIN Rail EN/IEC 60715 (35mm) | DIN Rail EN/IEC 60715 (35mm) |
| Dimensions (H × W × D) | 90 × 18 × 64 mm | 90 × 18 × 64 mm |
| Weight | 68g | 68g |
| IP Rating | IP20 | IP20 |
| Standards | GB/T 14048.5, IEC60947-5-1, EN61812-1 | GB/T 14048.5, IEC60947-5-1, EN61812-1 |
Voltage codes: A = 173-275V L-L (3-wire) | B = 100-160V L-N (4-wire) | C = 310-480V L-L (3-wire) | D = 180-278V L-N (4-wire). Other voltages available on request.
Terminal Connections
SPDT relay output with screw-clamp terminals for fast, reliable wiring.
FCP18-04A / 04C — 3-Phase 3-Wire (L1-L2-L3)
FCP18-04B / 04D — 3-Phase 4-Wire (L1-L2-L3-N)
- Always de-energize the panel before wiring
- Verify supply voltage matches the module rating before powering on
- Connect L1, L2, L3 (and N for 4-wire models) to the corresponding system phases
- Terminal 11 = Common, 12 = NC, 14 = NO — wire your load to the appropriate contact
- Use correct wire gauge for 16A load current (min. 1.5mm²)
- Tighten terminal screws to 0.4 N·m torque specification
- Stripping length: 7mm (AWG13-20)
Front Panel & Settings
Configure the FCP18-04 using four adjustment button — no software or programming tools required.
| Parameter | Description | Setting Range |
|---|---|---|
Un |
Rated Input Voltage (system voltage) — the nominal voltage of the three-phase installation | See voltage code table in Models section |
U> |
Over-voltage Trip Threshold — voltage above Un that triggers a trip | +2% to +20% of Un (adjustable) |
U< |
Under-voltage Trip Threshold — voltage below Un that triggers a trip | −2% to −20% of Un (adjustable) |
Asy |
Voltage Asymmetry (unbalance) — dial to set the unbalance trip threshold for your equipment sensitivity | 5% to 15% (adjustable) |
Tt |
Time Delay before trip — the delay period the relay waits before confirming a fault | 5s fixed (no adjustment needed) |
LED Indicator Panel
Un — Green LED
Lit = relay is powered on and monitoring the system
P — Red LED
Lit = correct phase sequence. Flashing = phase reversal. Off = phase loss
R — Red LED
Lit = NO contact (terminals 11-14) is closed, relay is energized
⚙ How to Set Parameters
- Enter setting mode: Press and hold the button until the LED starts flashing.
- Adjust dials: Set
Un,U>,U<,Asy, andTtto your desired values while the LED is flashing. - Confirm: Press and hold the button until the LED stops flashing to save your settings.
Note: When the green LED is on, add 1% to the over/under voltage dial reading to get the actual trip threshold. For example, if the U> dial reads 10% and the green LED is lit, the actual over-voltage trip point = Un + 11%.
Models & Ordering
Choose the voltage configuration that matches your three-phase system.
| Model Code | System Type | Voltage Range (L-L) | Voltage Range (L-N) | Manual |
|---|---|---|---|---|
| FCP18-04A | 3-Phase 3-Wire | 173, 190, 198, 208, 220, 230, 240, 250, 260, 275 V | N/A | PDF ↓ |
| FCP18-04B | 3-Phase 4-Wire | N/A | 100, 110, 115, 120, 127, 133, 139, 145, 151, 160 V | PDF ↓ |
| FCP18-04C | 3-Phase 3-Wire | 310, 328, 345, 365, 380, 400, 415, 440, 460, 480 V | N/A | PDF ↓ |
| FCP18-04D | 3-Phase 4-Wire | N/A | 180, 190, 200, 210, 220, 232, 240, 255, 266, 278 V | PDF ↓ |
FCP18 Family — Model Comparison
Compare all six FCP18 series models to find the right protection configuration for your application.
| Model | Over-voltage | Under-voltage | Asymmetry | Time Delay | Phase Seq. | Phase Loss | Ideal For |
|---|---|---|---|---|---|---|---|
| FCP18-01 | — | — | — | 5s fixed | ✓ | ✓ | Phase sequence/loss only, budget applications |
| FCP18-02 | 2%-20% Adjustable | 2%-20% Adjustable | — | 0.1~30s | ✓ | ✓ | OV/UV + phase protection, no asymmetry needed |
| FCP18-03 | 2%-20% Adjustable | 2%-20% Adjustable | 8% fixed | 0.1~30s | ✓ | ✓ | Full protection incl. fixed asymmetry — general motor & compressor |
| FCP18-04 | 2%-20% Adjustable | 2%-20% Adjustable | 5%~15% adj. | 5s fixed | ✓ | ✓ | Adjustable asymmetry sensitivity — CNC, medical, precision equipment |
| FCP18-05 | — | — | 5%~15% adj. | 0.1~30s | ✓ | ✓ | Asymmetry-only with adjustable sensitivity |
| FCP18-06 | 15% fixed | 15% fixed | 8% fixed | 0.1~30s | ✓ | ✓ | Asymmetry + phase protection, no OV/UV adjustment |
Configuration Examples
Real-world setting examples for common three-phase system voltages.
FCP18-04A — 208V System
| Un (Voltage) | 208V |
| U> (Over) | +10% = 228.8V |
| U< (Under) | −11% = 185.1V |
| Asy (Adj.) | 8% |
| Tt (Delay) | 5s fixed |
FCP18-04C — 400V System
| Un (Voltage) | 400V |
| U> (Over) | +10% = 440V |
| U< (Under) | −10% = 360V |
| Asy (Adj.) | 6% (sensitive CNC) |
| Tt (Delay) | 5s fixed |
FCP18-04B — 120V System
| Un (Voltage) | 120V |
| U> (Over) | +10% = 132V |
| U< (Under) | −11% = 106.8V |
| Asy (Adj.) | 10% |
| Tt (Delay) | 5s fixed |
FCP18-04D — 230V System
| Un (Voltage) | 230V |
| U> (Over) | +15% = 264.5V |
| U< (Under) | −8% = 211.6V |
| Asy (Adj.) | 12% (robust motor) |
| Tt (Delay) | 5s fixed |
See It In Action
Watch the FCP18 series product overview and demonstration.
Typical Applications
The FCP18-04 protects three-phase equipment across a wide range of industrial sectors.
CNC & Machine Tools
Precision protection for CNC machines, VFD-controlled equipment, and automated precision machinery.
HVAC & Compressors
Protect compressors and HVAC equipment with adjustable sensitivity for medical-grade systems.
Power Distribution
Panel-level monitoring in LV/MV switchgear and distribution boards.
Medical Equipment
Protects sensitive medical three-phase equipment requiring precise asymmetry sensitivity.
Industrial Automation
Precision protection for PLC-controlled systems and robotic automation equipment.
Ready to Order or Need More Details?
Download the full technical manual or contact the FIICCO team for pricing, samples, and OEM options.
Frequently Asked Questions
Common questions about the FCP18-04 three-phase protection relay
The key difference is the asymmetry setting: the FCP18-04 has an adjustable asymmetry threshold of 5%~15% (via front-panel Asy dial), while the FCP18-03 has a fixed 8% threshold. The FCP18-04 also has a fixed 5-second time delay, whereas the FCP18-03 offers an adjustable delay of 0.1~30 seconds. The FCP18-04 is better suited for sensitive equipment where fine-tuning of asymmetry sensitivity is required.
Four voltage configurations are available: FCP18-04A (173-275V L-L, 3-wire), FCP18-04B (100-160V L-N, 4-wire), FCP18-04C (310-480V L-L, 3-wire), and FCP18-04D (180-278V L-N, 4-wire). Each model offers 10 preset voltage steps selectable via the Un dial. Other voltages are available on request.
A lower threshold (5-8%) provides stricter protection and is recommended for precision equipment such as CNC machines, medical devices, and variable frequency drives (VFDs) where even slight voltage unbalance can cause overheating or malfunction. A higher threshold (10-15%) is suitable for more robust industrial motors that can tolerate slight imbalance without damage.
No. The FCP18-04 is specifically designed for three-phase systems and requires three-phase input (L1, L2, L3) to operate. For single-phase over/under voltage protection, consider the FCP18-02 series which supports single-phase monitoring.
The fixed 5-second delay is designed to prevent nuisance tripping during the high inrush current period when three-phase motors start. Motor starting currents typically settle within a few seconds; the 5s delay allows normal startup transients to pass without triggering a trip while still providing fast protection against genuine sustained voltage faults.
The FCP18-04 has a single SPDT (single-pole double-throw) relay contact rated 16A/250V AC. Terminal 11 is the common, 12 is normally closed (NC), and 14 is normally open (NO). Wire your load between terminal 11 and terminal 14 for normally open operation — the circuit is energized when the relay trips.
The FCP18-04 is certified to CE, RoHS, and meets the standards of IEC 60947-5-1, GB/T 14048.5, and EN 61812-1. This makes it suitable for industrial automation applications in Europe, Asia, and other global markets.
Yes. FIICCO provides OEM services including custom branding (logo, model number, color), tailored specifications, and custom packaging for orders of 100+ units. Factory-direct pricing ensures competitive costs for OEM customers. Contact us at info@fiicco.com with your requirements and quantity for a tailored quotation.