Phoenix UT 4-HE SI Surge Protection Terminal Block

The Phoenix Contact UT 4-HE SI is a surge protective device integrated into a standard UT 4 terminal block housing. It is designed to protect 24V DC control circuits, sensors, and actuators from damaging overvoltage transients caused by lightning strikes or switching operations. The protection circuit combines a varistor (MOV) and a gas discharge tube (GDT) for common-mode and differential-mode protection, providing a residual voltage of less than 40V at rated surge current.

Protection Technology

The UT 4-HE SI uses a three-stage protection concept: a high-capacity gas discharge tube diverts large surge currents to ground, a series varistor clamps the residual voltage, and a high-speed diode provides final voltage limiting. The module also includes a thermal disconnect device that safely opens the circuit if the varistor degrades beyond specification. The status can be monitored via an optional remote signaling contact (not included). The terminal block is transparent to normal operating voltages up to 30V DC and does not affect signal integrity.

Integration into UT Terminal Strips

The UT 4-HE SI has the same footprint as a standard UT 4 feed-through terminal block, allowing it to be inserted directly into existing terminal strips without requiring additional space. It can be combined with ordinary UT 4 terminal blocks, jumpers, and marking accessories. The top of the housing features a clear "SI" marking and an indicator window that turns from green to red when protection fails (for models with optical indicator).

Application Domains

This surge protection terminal block is essential for control cabinets in exposed locations, such as outdoor installations, industrial plants with long cable runs, or facilities prone to lightning strikes. It protects PLC inputs, relay coils, proximity sensors, and communication lines operating at 24V DC. Typical industries include water/wastewater, wind energy, and manufacturing.