Overcurrent relay SENTINEL LSI HWW451H

Over‑current and short‑circuit protection with precise control

The SENTINEL LSI (HWW451H) overload trip unit is an electronic protection module that reacts to the difference between the operating current and a safe load level—not only disconnecting the circuit in case of a fault but also providing a pre‑trip warning period. It operates in three zones: long‑term overload, short‑term over‑voltage, and short‑circuit, each of which can be individually adjusted to suit the load characteristics.

Tailored to circuit specifics – no compromises

The long‑term overload trip current is adjustable in the range 0.36 – 1.0 A, allowing precise matching for small installations such as low‑power motors or electronic devices. The overload trip time can be set from 0.5 s up to 25 s, eliminating false trips during brief current spikes—for example, when starting pumps or fans.

For short‑circuit conditions the unit reacts in less than 80 ms, and the trip current can be selected from 9 levels (1× to 10× I_n), enabling reliable operation even with high inrush currents. All settings are independent—there is no locked‑in logic linking the different protections.

Neutral‑line protection and pre‑failure alarm

The module can monitor and limit the neutral‑line current to 50 %, 100 % or 200 % of the rated current; this protection is disableable when not required. Additionally, the unit features a pre‑trip alarm (PTA): when the current reaches 90 % of the set value, the trip unit signals an impending fault. The alarm time is set to 50 % of the configured long‑term overload time, providing crucial early warning for installations where an abrupt cut‑off must be avoided.

Construction and compliance

The device does not provide protection against insulation damage caused by ground‑fault current (GF)—this is not a function of this model. The short‑circuit protection (std) follows the I²t characteristic and can be completely disabled if the circuit does not require it. All parameters are electronically adjustable—no mechanical transformers or batteries are involved.

Note: The maximum trip time for a short‑circuit is 650 ms, and the current‑setting tolerance is ±10 %. This is not a “standard” circuit breaker—it is a tool for installers who need control over every stage of protection.