Quick Answer: Which FCP18 Version Should You Choose?
The VIOX FCP18 is a DIN-rail three-phase voltage monitoring relay used to supervise phase sequence, phase loss, overvoltage, undervoltage, voltage asymmetry, and fault delay depending on the selected function code.
Use this quick table as the first selection filter:
| نیازهای کاربردی | Recommended FCP18 version | چرا |
|---|---|---|
| Simple phase loss and phase sequence protection | FCP18-01 | Basic phase protection with fixed delay |
| General voltage window monitoring | FCP18-02 | Adds adjustable overvoltage and undervoltage limits |
| Motor protection with voltage window, asymmetry, and adjustable delay | FCP18-03 | Broad monitoring with fixed 8% asymmetry and adjustable time delay |
| Motor protection with adjustable asymmetry threshold | FCP18-04 | Adds adjustable 5%-15% asymmetry setting |
| Phase imbalance-focused applications | FCP18-05 | Focuses on phase loss, phase sequence, and adjustable asymmetry |
| OEM panels requiring fixed settings | FCP18-06 | Fixed overvoltage, undervoltage, asymmetry, and delay for simpler commissioning |
The function code is factory-defined. An FCP18-03 cannot be changed into an FCP18-04 by adjusting the front-panel knobs. Select the correct version before ordering.
What Is the VIOX FCP18 Three-Phase Voltage Monitoring Relay?
The FCP18 is a three-phase voltage relay for monitoring power supply conditions in three-phase electrical systems. Depending on the selected version, it can monitor:
- phase sequence;
- phase loss;
- overvoltage;
- undervoltage;
- three-phase voltage asymmetry;
- fault response delay.
The FCP18 normally does لزوماً switch a motor or three-phase load directly. Its output contact is used in a control circuit, typically connected to:
- a contactor coil;
- a programmable logic controller (PLC) input;
- an alarm circuit;
- a control relay;
- a machine interlock circuit.
When the supply condition is acceptable, the output contact allows the control circuit to run. When the relay detects an abnormal voltage condition, the output changes state so the machine can be stopped, blocked from starting, or signaled for inspection.
For a broader explanation of this product category, see VIOX’s guide to رلههای نظارت بر ولتاژ.
Understanding the FCP18 Model Code
A typical model may be written as:
FCP18-03-AThis can be read as:
| Code section | معنی |
|---|---|
| FCP18 | Product series |
| 03 | Function combination |
| الف | Supply voltage and wiring-system version |
The middle function code is the most important selection item. It determines whether the relay includes only phase protection or also includes voltage-window monitoring, asymmetry monitoring, and adjustable delay.
FCP18-01 to FCP18-06 Function Comparison
| Function code | اضافه ولتاژ | افت ولتاژ | Voltage asymmetry | تاخیر زمانی | Phase sequence | Phase loss |
|---|---|---|---|---|---|---|
| FCP18-01 | Not included | Not included | Not included | Fixed 5 s | شامل شده | شامل شده |
| FCP18-02 | 2%-20% adjustable | 2%-20% below nominal, adjustable | Not included | 0.1-30 s adjustable | شامل شده | شامل شده |
| FCP18-03 | 2%-20% adjustable | 2%-20% below nominal, adjustable | Fixed 8% | 0.1-30 s adjustable | شامل شده | شامل شده |
| FCP18-04 | 2%-20% adjustable | 2%-20% below nominal, adjustable | 5%-15% adjustable | Fixed 5 s | شامل شده | شامل شده |
| FCP18-05 | Not included | Not included | 5%-15% adjustable | 0.1-30 s adjustable | شامل شده | شامل شده |
| FCP18-06 | Fixed +15% | Fixed -15% | Fixed 8% | Fixed 5 s | شامل شده | شامل شده |
All six versions include phase-sequence and phase-loss monitoring. The difference is how much voltage-limit, asymmetry, and timing adjustment the application needs.
FCP18 Function Codes Explained
FCP18-01: Basic Phase Protection
The FCP18-01 provides phase sequence protection, phase loss protection, and a fixed 5-second delay. It is the simplest version in the series.
Best suited for:
- simple motor control panels;
- pumps and fans where reverse rotation must be prevented;
- systems where overvoltage and undervoltage are monitored elsewhere;
- applications requiring straightforward phase loss and phase sequence supervision.
Its limitation is clear: if all three phases are present and correctly sequenced, it does not separately evaluate whether the voltage is too high, too low, or unbalanced.
FCP18-02: Adjustable Overvoltage and Undervoltage
The FCP18-02 adds voltage-window monitoring. It is suitable when the main concern is whether the supply voltage stays within acceptable upper and lower limits.
It provides:
- adjustable overvoltage threshold;
- adjustable undervoltage threshold;
- adjustable 0.1-30 s delay;
- phase sequence monitoring;
- phase loss monitoring.
Choose this version for general control cabinets, distribution systems, and industrial machinery where overvoltage and undervoltage are more important than dedicated asymmetry monitoring.
FCP18-03: Comprehensive Protection with Adjustable Delay
The FCP18-03 combines voltage-window protection, fixed 8% asymmetry monitoring, phase sequence, phase loss, and adjustable delay.
Best suited for:
- pumps;
- fans;
- compressors;
- general motor control panels;
- machines that need broad supply monitoring with adjustable response time.
Choose FCP18-03 when the application needs comprehensive protection but the installer needs delay adjustment more than asymmetry adjustment.
FCP18-04: Comprehensive Protection with Adjustable Asymmetry
The FCP18-04 provides adjustable overvoltage, adjustable undervoltage, adjustable 5%-15% asymmetry, phase sequence, phase loss, and a fixed 5-second delay.
Best suited for:
- motor systems with specific imbalance limits;
- sites with known voltage imbalance issues;
- applications where supply balance is more important than timing adjustment;
- standardized panels that can use a fixed delay.
تفاوت اصلی بین FCP18-03 و FCP18-04 is adjustment priority:
| If the application needs… | انتخاب کنید |
|---|---|
| Adjustable time delay | FCP18-03 |
| Adjustable asymmetry threshold | FCP18-04 |
FCP18-05: Asymmetry and Phase Protection
The FCP18-05 focuses on phase loss, phase sequence, adjustable voltage asymmetry, and adjustable time delay. It does not include separate overvoltage or undervoltage thresholds.
Best suited for:
- motors sensitive to phase imbalance;
- systems where voltage level variation is acceptable but imbalance is not;
- installations where another device already handles overvoltage and undervoltage;
- applications requiring adjustable imbalance sensitivity and delay.
FCP18-06: Fixed-Setting Comprehensive Version
The FCP18-06 uses fixed thresholds:
| عملکرد | Fixed setting |
|---|---|
| اضافه ولتاژ | +15% |
| افت ولتاژ | -15% |
| Voltage asymmetry | 8% |
| تاخیر زمانی | 5 s |
This version is useful for OEM panels, high-volume machinery, and installations where field adjustment should be minimized. Its advantage is simpler commissioning. Its limitation is that the thresholds cannot be tuned for different motors, supply conditions, or process requirements.
How Each Protection Function Works
Phase Sequence Protection
A three-phase supply has a defined phase order, commonly described as:
L1 → L2 → L3If two phases are exchanged during installation or maintenance, the phase sequence is reversed. For a three-phase induction motor, reversed phase sequence normally causes reverse rotation.
This can create serious problems in:
- pumps;
- fans and blowers;
- conveyors;
- compressors;
- lifts and hoists;
- machine tools;
- hydraulic power units.
The FCP18 checks the incoming phase order before allowing the controlled equipment to run. If the phase sequence is incorrect, the output contact changes state and can prevent the contactor from energizing.
حفاظت از دست دادن فاز
Phase loss occurs when one of the three supply phases disappears or drops abnormally.
علل شایع عبارتند از:
- blown fuse;
- broken conductor;
- loose terminal;
- damaged cable;
- faulty circuit-breaker pole;
- burned contactor contact;
- upstream supply failure.
A three-phase motor may continue running after losing one phase, especially if it was already rotating. However, the remaining phases can carry higher current, causing rapid overheating and possible winding damage. Phase-loss protection helps stop the machine before the fault becomes a motor failure.
حفاظت در برابر ولتاژ بیش از حد
Overvoltage protection is available in FCP18-02, FCP18-03, FCP18-04، و FCP18-06.
For adjustable versions, the high-voltage threshold can be understood as:
Upper voltage limit: Uhigh = Un × (1 + overvoltage setting)Example for a 400 V system with a 10% overvoltage setting:
Example: Uhigh = 400 V × 1.10 = 440 VIf the monitored voltage remains above the threshold for the applicable delay time, the relay changes its output state.
Sustained overvoltage can stress motor windings, contactor coils, control transformers, power supplies, capacitors, lighting circuits, and electronic controls. This is different from surge protection: the FCP18 monitors power-frequency voltage conditions, not lightning or switching impulse transients.
Undervoltage Protection
Undervoltage protection is available in FCP18-02, FCP18-03, FCP18-04، و FCP18-06.
For adjustable versions, the low-voltage threshold can be understood as:
Lower voltage limit: Ulow = Un × (1 − undervoltage setting)Example for a 400 V system with a 10% undervoltage setting:
Example: Ulow = 400 V × 0.90 = 360 VLow voltage does not only make equipment “weaker.” Depending on the motor and load, it can cause reduced starting torque, longer acceleration time, increased current, overheating, contactor chatter, unstable operation, or unexpected shutdown.
Voltage Asymmetry Protection
Voltage asymmetry, also called voltage imbalance, occurs when the three phase voltages are not equal. The average voltage may look acceptable, but one phase can still be far away from the others.
A simplified asymmetry calculation is:
Voltage asymmetry (%) = (Umax − Umin) ÷ Uavg × 100%
Average voltage: Uavg = (U1 + U2 + U3) ÷ 3مثال:
U1 = 400 V
U2 = 400 V
U3 = 360 V
Uavg = (400 + 400 + 360) ÷ 3 = 386.7 V
Asymmetry = (400 − 360) ÷ 386.7 × 100% = 10.3%A relay with a fixed 8% asymmetry threshold would detect this as abnormal.
Voltage asymmetry can cause unequal phase currents, negative-sequence current in motors, additional heating, torque pulsation, vibration, lower efficiency, and shorter insulation life. Even moderate voltage imbalance can produce a much larger current imbalance in a motor.
Time-Delay Function
Not every voltage disturbance should stop a machine immediately. Short voltage dips can occur during motor starting, transformer energization, generator transfer, large load switching, or utility network disturbances.
The FCP18 delay function helps distinguish short disturbances from sustained faults.
Depending on the version, the delay is:
- fixed at 5 seconds;
- adjustable from 0.1 to 30 seconds.
A shorter delay gives faster protection. A longer delay reduces nuisance trips but allows the equipment to experience the abnormal condition for more time. The delay should be long enough to ignore acceptable transients and short enough to protect the load from sustained supply faults.
Three-Phase Three-Wire and Four-Wire Versions
After selecting the function code, choose the correct wiring-system and voltage version.
The FCP18 is available for:
- three-phase, three-wire systems;
- three-phase, four-wire systems.
در یک three-phase three-wire application, the relay monitors line-to-line voltage across L1, L2, and L3. In a three-phase four-wire application, the relay also connects to neutral and monitors phase-to-neutral voltage.
| Version code | نوع سیستم | Monitoring reference | Catalog nominal voltage options |
|---|---|---|---|
| الف | 3-phase 3-wire | L-L | 173, 190, 198, 208, 220, 230, 240, 250, 260, 275 V |
| ب | 3-phase 4-wire | L-N | 100, 110, 115, 120, 127, 133, 139, 145, 151, 160 V |
| سی | 3-phase 3-wire | L-L | 310, 328, 345, 365, 380, 400, 415, 440, 460, 480 V |
| دی | 3-phase 4-wire | L-N | 180, 190, 200, 210, 220, 232, 240, 255, 266, 277 V |
Always match the relay version to the actual supply system. A 400 V three-phase three-wire system is normally evaluated as line-to-line voltage, while a 230/400 V four-wire system may be monitored through phase-to-neutral voltage depending on the selected version.
Typical FCP18 Control-Circuit Connection
The FCP18 provides one SPDT output contact, commonly identified as:
| ترمینال | معنی |
|---|---|
| 11 | رایج |
| 12 | معمولاً بسته |
| 14 | معمولاً باز است |
A typical control circuit uses the FCP18 output contact in series with a contactor coil or sends the output to a PLC input. When supply conditions are normal, the machine can run. When a voltage fault is detected, the relay changes contact state and the control circuit can drop out the contactor or generate an alarm.
The FCP18 output contact is for control use. It should not be treated as the main switching device for a high-power motor. Use a properly rated contactor, starter, or other switching device to disconnect the load.
Key Catalog Specification Checks
Before final specification, confirm the exact datasheet for the ordered version. The FCP18 catalog data includes the following practical selection points:
| مورد | Catalog direction |
|---|---|
| نصب | DIN rail mounting, EN/IEC 60715 style |
| تماس خروجی | 1 SPDT control contact |
| نشانگر وضعیت | Power and relay status LED indication |
| Supply frequency | 45-60 Hz |
| تنظیم زمان | Fixed or 0.1-30 s depending on function code |
| Enclosure protection direction | IP20 class device for panel installation |
| استفاده معمولی | Control-panel monitoring, not direct motor power switching |
What the FCP18 Does Not Replace
A three-phase voltage relay is one layer of a complete protection system. It does not replace:
| دستگاه | Why it is still needed |
|---|---|
| Circuit breaker or fuse | Short-circuit and overcurrent protection |
| رله اضافه بار حرارتی | Motor overload and heating protection |
| Residual-current device | حفاظت از نشتی زمین |
| Surge protective device | Lightning and switching transient protection |
| Advanced motor protection relay | Current, temperature, stall, jam, or advanced diagnostics |
For motor circuits, the FCP18 should be coordinated with the overcurrent device, contactor, overload relay, and control logic. For the difference between overcurrent protection and voltage supervision, see VIOX’s guide on MCB vs voltage monitoring relay motor protection.
Selection Checklist Before Ordering
Before selecting an FCP18 model, confirm:
| مورد انتخابی | چه چیزی را بررسی کنیم |
|---|---|
| Function code | FCP18-01 to FCP18-06 |
| Wiring system | 3-phase 3-wire or 3-phase 4-wire |
| Nominal voltage | Match L-L or L-N voltage version |
| Required faults | Phase loss, phase sequence, overvoltage, undervoltage, asymmetry |
| Threshold adjustment | Fixed or adjustable settings |
| Delay requirement | Fixed 5 s or adjustable 0.1-30 s |
| Output use | Contactor coil, PLC input, alarm, or interlock |
| Control panel standards | Project-required documentation and approval requirements |
| محیط زیست | DIN rail space, ambient temperature, enclosure protection, wiring size |
The FCP18 catalog references GB/T 14048.5, IEC 60947-5-1, and EN 61812-1. Always verify the latest VIOX datasheet or catalog before final specification, because ratings, voltage codes, and approval documentation can change.
اشتباهات رایج در انتخاب
Mistake 1: Choosing Only by Supply Voltage
Voltage code matters, but it is not enough. Two FCP18 models with the same voltage version can have different protection functions.
Mistake 2: Using FCP18-01 When Voltage Limits Matter
FCP18-01 checks phase loss and phase sequence, but it does not monitor adjustable overvoltage, undervoltage, or asymmetry. If voltage-window monitoring is required, select another function code.
Mistake 3: Confusing Adjustable Delay with Adjustable Asymmetry
FCP18-03 and FCP18-04 are close, but not identical. FCP18-03 gives adjustable delay with fixed asymmetry. FCP18-04 gives adjustable asymmetry with fixed delay.
Mistake 4: Wiring a Three-Wire Version into a Four-Wire Application
Three-wire and four-wire systems are monitored differently. Match the version code to the actual voltage reference used by the panel.
Mistake 5: Treating the Relay Output as a Motor Power Contact
The FCP18 output contact is intended for control circuits. Use it to control a contactor coil, PLC input, or alarm circuit, not to switch a high-power motor directly.
سوالات متداول
What is the main difference between FCP18-03 and FCP18-04?
Both provide overvoltage, undervoltage, phase sequence, phase loss, and asymmetry monitoring. The difference is adjustment priority. FCP18-03 has adjustable delay and fixed 8% asymmetry. FCP18-04 has adjustable 5%-15% asymmetry and fixed 5-second delay.
Which FCP18 version is best for basic phase loss and phase sequence protection?
Use FCP18-01 when phase loss and phase sequence are the only required monitoring functions. It is the simplest version and uses a fixed 5-second delay.
Which FCP18 version should I choose for general motor protection?
For many motor applications, FCP18-03 is a strong starting point because it combines overvoltage, undervoltage, phase sequence, phase loss, fixed asymmetry monitoring, and adjustable delay. If the motor requires a tunable imbalance threshold, consider FCP18-04 instead.
Does the FCP18 replace a thermal overload relay?
No. The FCP18 monitors voltage conditions. A thermal overload relay or motor protection device is still needed for motor overload and heating protection.
Does the FCP18 replace a surge protective device?
No. The FCP18 monitors sustained power-frequency voltage conditions. A surge protective device is used for transient overvoltage caused by lightning or switching events.
Can the FCP18 output contact switch a motor directly?
No. The output contact is intended for control use, such as a contactor coil, PLC input, alarm, or interlock circuit. A properly rated contactor or starter should switch the motor power circuit.
Should I choose a three-wire or four-wire FCP18 version?
Choose the version that matches the actual supply and measurement method. Three-wire versions monitor line-to-line voltage. Four-wire versions use neutral and monitor phase-to-neutral voltage.
نتيجه گيری
The VIOX FCP18 series is not one fixed three-phase voltage relay. It is a function-code family. The correct choice depends on whether the application needs basic phase protection, voltage-window monitoring, asymmetry protection, adjustable delay, adjustable imbalance threshold, or fixed settings for OEM repeatability.
Start with the application requirement, then select the function code, voltage/wiring version, output use, and control-panel coordination. For simple phase protection, use FCP18-01. For voltage-window monitoring, use FCP18-02. For broad motor protection with adjustable delay, use FCP18-03. For adjustable asymmetry, use FCP18-04. For imbalance-focused applications, use FCP18-05. For fixed-setting OEM panels, use FCP18-06.
