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  • New item   -271.89€Two-speed three-phase fan transformer speed controller day/night | TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | SC2A4-25L55
    New item   -271.89€Two-speed three-phase fan transformer speed controller day/night | TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | SC2A4-25L55 1
    New item   -271.89€Two-speed three-phase fan transformer speed controller day/night | TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | SC2A4-25L55 2
    New item   -271.89€Two-speed three-phase fan transformer speed controller day/night | TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | SC2A4-25L55 3
    New item   -271.89€Two-speed three-phase fan transformer speed controller day/night | TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | SC2A4-25L55 4

    Two-speed three-phase fan transformer speed controller day/night | TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | SC2A4-25L55

    Code: SC2A4-25L55
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  • Product description

    Two-speed three-phase fan transformer speed controller day/night | TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | SC2A4-25L55

    SC2A4-25L55 – Sentera Controls two-speed transformer speed controller for three-phase 400 VAC fan motors up to 2.5 A. Two knobs – for high and low speed, switching by an external clock or thermostat (day / night), TK terminals, alarm output.

    Key idea:
    Ventilation that switches to economy mode by itself: high speed during the day, low speed at night or outside working hours. Both speeds are set with knobs, and switching is done by an external clock or thermostat.
    What it is for SC2A4-25L55:
    This model is intended for medium-power fans (up to 2.5 A) – duct fans in offices, classrooms, retail premises or 2–3 smaller fans together.
    Max. motor current
    2.5 A
    Speeds
    2 (high / low), 5 steps each
    Signals
    TK, alarm 230 VAC / 1 A, CC/OC, CL
    Supply / protection
    3×400 VAC + N; IP54

    Operating principle

    The controller is wall-mounted. The 3×400 VAC supply is connected to R, S, T and N, the motor – to U, V, W, the thermal contacts – to TK, a clock or thermostat – to CL, the remote switch-on contacts – to CC (normally closed) or OC (normally open).

    The controller contains two autotransformers. The left knob sets the high speed (speed 1): 0 – 210 – 250 – 290 – 330 – 400 VAC; the right knob – the low speed (speed 2): 0 – 130 – 170 – 210 – 250 – 290 VAC. An external clock switches between these two speeds via the CL terminals.

    The output voltage is SINUSOIDAL – without phase cutting as in electronic controllers. Therefore the motor runs quietly even at low speed, does not heat up due to higher harmonics and does not interfere with other equipment. This is the solution for motors that hum or buzz when controlled by an electronic controller.

    After a power failure the controller restarts automatically. The unregulated 230 VAC / 2 A output (L1) remains on also in standby mode, and a fault is signalled via the 230 VAC / 1 A alarm output. Engineer's note: reducing the voltage of an AC asynchronous motor increases slip, so less energy is saved than with an EC fan or frequency inverter. The strength of a transformer speed controller is reliability, quietness and simplicity, not maximum efficiency.

    Benefits SC2A4-25L55?
    Two-speed day / night mode without separate contactors and without programming – lower costs and noise outside working hours.

    Technical specifications

    Product type Two-speed three-phase fan transformer speed controller
    Manufacturer / code Sentera Controls / SC2A4-25L55
    Series SC2A4 (1.5 / 2.5 / 4 / 6 / 8 / 11 A)
    Supply voltage 3×400 VAC, 50–60 Hz, with neutral (R, S, T, N)
    Max. motor current 2.5 A
    Speed 1 (high), U, V, W 0 – 210 – 250 – 290 – 330 – 400 VAC (left knob)
    Speed 2 (low), U, V, W 0 – 130 – 170 – 210 – 250 – 290 VAC (right knob)
    Speed switching External clock / thermostat via CL terminals
    Unregulated output (L1) 230 VAC, 2 A, 50–60 Hz (on also in standby mode)
    Alarm output (AL, N) 230 VAC, 1 A
    Motor protection TK terminals for motor thermal contacts
    Remote on / off CC (normally closed) and OC (normally open) contacts
    Restart after a power failure Automatic
    Indication Blue LED – device switched on
    Housing Metal, powder-coated RAL 7035
    Protection class IP54 (EN 60529), for indoor use only
    Operating environment -20…+35 °C, 5–95 % rH non-condensing
    Dimensions A 300 / B 325 / C 175 / D 255 / E 255 mm (letter meanings – according to the datasheet drawing)
    Packaging (L × W × H) 340×310×210 mm
    Weight 12.59 kg (net)
    Compliance LVD 2014/35/EU, EMC 2014/30/EU (EN 61326), WEEE 2012/19/EU, RoHS 2011/65/EU

    Manufacturer documentation

    ✔ Recommended by Elektrotechnikos sprendimai

    Original manufacturer documentation – technical data, wiring diagrams and installation instructions.

    Main functions

    • Two speeds with separate knobs – high and low speed are set independently, 5 steps each.
    • Clock input CL – day / night switching by an external clock or thermostat.
    • CC / OC inputs – remote on and off.
    • TK and alarm 230 VAC / 1 A – motor protection and fault signal.
    • Automatic restart – after a power failure the system recovers by itself.
    • Sinusoidal output voltage – quiet motor operation at both speeds.

    Where is it used?

    • Ventilation of offices, retail and public buildings with working / non-working mode
    • Production halls with shift work
    • Warehouses and agricultural buildings
    • Extract systems with a reduced night mode

    On-demand operation

    For the electrician.
    Clock, TK, alarm and remote control are connected directly to the controller terminals.
    For the ventilation installer.
    Both speeds are set on site with knobs, no programming required.
    For the building owner.
    Outside working hours the ventilation automatically runs at low speed – less noise and electricity consumption.

    Application guide: how it is used in practice

    Typical SC2A4-25L55 applications:

    Site What is connected Result Installer's note
    Office, shop Clock relay → CL High speed during working hours, low at night Set both speeds with the knobs according to the air demand
    Production hall Thermostat → CL When the temperature rises it switches to high speed The thermostat contact must be potential-free
    Site with a fire system Fire system contact → CC or OC The fan is switched off by the signal Coordinate the logic with the design
    Control room, BMS AL, N → signal lamp or BMS Motor overheating is signalled immediately Alarm load – up to 1 A
    Fan with damper Damper actuator → L1 The damper is powered continuously, even in standby mode L1 load – up to 2 A

    How to select the controller current

    Rated current of the motor(s) Recommended model
    up to 1.5 A SC2A4-15L55 (1.5 A)
    1.5–2.5 A SC2A4-25L55 (2.5 A) ← this model
    2.5–4 A SC2A4-40L55 (4 A)
    4–6 A SC2A4-60L55 (6 A)
    6–8 A SC2A4-80L55 (8 A)
    8–11 A SC2A4110L55 (11 A)
    Rule: controller max. current ≥ motor rated current (see the motor nameplate). When connecting several fans – motors of the same type – add up their rated currents. Choose a margin if the motor current is close to the model's limit or the fan often runs at the maximum step.
    When to choose another solution: with a built-in programmable timer and LCD – ST2R4; single-speed with NO/NC and alarm – STRA4 or STTA4; for 0-10 VDC control – STVS4; for the simplest control – STR-4.

    Pros

    • Two independently set speeds
    • Switching by an external clock / thermostat
    • TK, alarm, CC / OC inputs
    • Automatic restart after a power failure
    • Sinusoidal output voltage
    • Metal IP54 enclosure

    Cons / limitations

    • No built-in clock – an external clock or thermostat is required (ST2R4 has a built-in one)
    • Step (not stepless) control – the speed is selected from fixed voltages
    • Heavy weight and large dimensions compared with electronic controllers
    • Indoor use only, operating temperature up to +35 °C
    • Not suitable for EC fans and motors controlled by a frequency inverter

    Safety and installation notes

    • Installation and connection must be carried out by a qualified electrician with the power disconnected.
    • Always connect the protective earth (PE).
    • Check that the motor is suitable for voltage control and that its rated current does not exceed 2.5 A.
    • The supply requires a neutral (N).
    • The L1 output is live also in standby mode – take this into account when carrying out work.
    • Connect only dry contacts to the CL, CC, OC inputs.
    • The device is heavy – fix it to a load-bearing wall or structure using suitable fixings.
    • For indoor use only (-20…+35 °C, non-condensing); leave space for cooling.

    Quick selection guide

    2.5 A
    3×400 VAC
    2 speeds
    Day / night
    TK
    IP54
    Suitable when you need:
    • a three-phase fan up to 2.5 A with two speeds controlled by a clock or thermostat;
    • sites with working / non-working hours mode;
    • motors with thermal contacts.
    Check before use:
    • the motor rated current and whether it is voltage-controllable;
    • whether you have an external clock or thermostat for speed switching;
    • the installation location (12.59 kg, up to +35 °C).
    Important reminder: SC2A4-25L55 speeds are switched by an external clock – there is no built-in timer.

    FAQ

    How are the speeds switched?
    With an external clock or thermostat via the CL terminals.
    What voltages can be set?
    High speed: 210 / 250 / 290 / 330 / 400 VAC; low: 130 / 170 / 210 / 250 / 290 VAC.
    Will it restart after a power failure?
    Yes, the datasheet specifies automatic restart.
    How does it differ from ST2R4?
    ST2R4 has a built-in programmable timer, LCD display and USB, while SC2A4 uses an external clock.
    Is there motor protection?
    Yes, TK terminals and a 230 VAC / 1 A alarm output.

    Two-speed three-phase fan transformer speed controller day/night | TK | 2.5A | 400VAC | surface-mounted | IP54 | Sentera Controls | SC2A4-25L55

    Sentera SC2A4-25L55 – two-speed day/night transformer controller for three-phase fans up to 2.5 A, 3×400 VAC, clock input, TK, alarm, CC/OC, sinusoidal voltage, IP54.

    Illustrative image may have been created using AI. The appearance of the product may differ slightly from the image shown. Please refer to the technical specification.

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