Draw-out circuit breaker with sentinel trip unit 55kA 1250A 3P HW1M312DB

Withdrawable air circuit breaker with Sentinel trip unit – construction and installation

The device is offered in a withdrawable version, allowing safe and quick disconnection of the entire unit from the circuit without the need to dismantle the conductors. The main circuit connections are not fixed – they are joined via a separate housing part, which simplifies replacement or servicing of the device on site. Installation is not performed on a DIN rail, but in a specially designed cabinet or distribution board, ensuring stability and insulation at high currents.

All three poles are protected and configured as 3P3D – meaning each operates independently and is safeguarded against short‑circuit and overload. A high breaking capacity (55 kA at 400 V) ensures the device safely interrupts circuits even under extreme fault conditions typical of large industrial installations or commercial buildings.

Protection and additional functions

The breaker does not include built‑in ground‑fault protection or an over‑voltage trip unit – its operation relies solely on the Sentinel trip unit, which must be installed separately. This provides flexibility: the installer can select the appropriate type of trip unit (thermal, time‑delay, selective) according to the circuit’s characteristics. The unit is supplied without any internal protections – it is a system component that functions only in conjunction with an external module.

It features four auxiliary change‑over contacts – these allow status signalling (on/off), control of external circuits, or integration with SCADA systems. There are no make‑before‑break or normally‑closed auxiliary contacts, so it cannot be used as a “closed‑contact” signalling relay. However, it does have an off‑indicator – a visible external element that clearly shows the device’s state.

Durability and operating conditions

The device is designed for intensive use: it endures 25 000 mechanical cycles and 6 000 electrical cycles – meaning it can be operated frequently manually or by an optional motor drive. Insulation voltage is 1000 V, and impulse withstand voltage is 12 kV, providing safety even during sudden surges.

Closing time is 45 ms – typical for air circuit breakers of this class. Power loss at the rated current (1250 A) is about 187.4 W – a known value controlled by the manufacturer; no additional cooling or special ventilation is required in the cabinet.

IP2X protection indicates only protection against finger contact – the device is neither water‑proof nor dust‑tight. It operates exclusively in dry, closed enclosure type distribution cabinets. Operating voltage: 440 to 690 V AC – ideal for 50 Hz industrial networks in Europe.

All parameters comply with standard PN-EN 60947-2. There is no built‑in motor drive – but one can be added as an option. Mounting on a TH rail or any other DIN rail is not possible.