SKU A437405-HV Category


Three Phase – Enclosed

£126.00 ex. VAT

Quantity discounts
1-4 5-9 10-19 20+
£126.00 £119.70 £113.72 £108.05


This PR3 range of thyristor stack provides full seamless control of three phase resistive loads, using two thirds control technique.  Signal control is by a dc signal or manual control via a 5kΩ potentiometer. This burst firing control stacks use fast pulse zero volts switching technology, to minimise flicker and eliminate RFI problems, it also incorporates an auto-reset temperature trip, integral semiconductor fuses and heatsink.  This model, which is naturally air cooled and has easy access to signal & power terminals for simple installation.


Suitable for 3-wire, 3-phase floating-star or closed-delta configured resistive loads. This includes the Heating, Ventilating and Air Conditioning (HVAC) market for air curtain applications, but also for furnaces, ovens, dryers and hot plates.


Alarm relay functions (3-way terminal – V/free alarm “NO_NC_C”)

The alarm circuit has voltage free relay contacts and are rated up to 2A @ 125V ac (RMS) load.

The internal supply to the relay is obtained from the transformer via two 20mm 1A fuses.  These are connected to the L1 and L2 phases and therefore the relay and LED can only energise when there is an over-temperature condition, a sensor fault, or a L3 phase loss.

Over temperature protection

When a heatsink temperature of above 90ºC is detected by the sensor, the alarms relay changes state and the LED pulses rapidly.   The power to the load will be disconnected and will not return until the temperature drops to 85ºC.

Temperature sensor loss

LED status changes to ON/OFF (fast pulsing) if the sensor fails

Phase loss with auxiliary supply

When any one of the three phase inputs are missing, the relay changes state and the LED flashes with ON/OFF bursts of 1.5 seconds.  This is only functional with a remote supply

Fault condition

The default setting of DIL switch (SW1) is in the ON position, the alarm relay will be energised under a fault condition.  Changing SW1 to the off position will energise the alarm relay continuously until a fault condition occurs.

Remote supply

The unit will be factory set for an internal supply the switch in the “INT” position.  If there is a requirement for the alarm relay and LED to energise when a phase fault condition occurs, then there is provision for an external 24V ac or dc supply, the switch in the “EXT” position.

Additional information

Download the technical document for this product below.

Download Technical Datasheet
Weight 0.811 kg
Technical Support
customer service United Automation

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