Finder 77.F3.9.024.8671 – 77 Series Modular solid state relays

Why Choose the Finder 77.F3.9.024.8671 Three-Phase Solid State Relay?

The Finder 77.F3.9.024.8671 is a high-current three-phase solid state relay (SSR) designed for reliable, silent and contactless switching of industrial AC electrical loads. Part of the Finder 77 Series, this industrial relay uses semiconductor switching technology instead of mechanical contacts, making it particularly suitable for demanding automation, industrial heating and process control applications.

Featuring an 80 A rated load current, a 24–660 V AC operating load voltage range and a 4–32 V DC control input, the Finder 77.F3.9.024.8671 provides a practical interface between low-voltage electronic control systems and high-power three-phase AC equipment.

The relay incorporates three normally open equivalent semiconductor switching poles and uses random turn-on switching, allowing its outputs to activate without intentionally waiting for the AC supply waveform to cross zero. Its compact industrial housing, contactor-style terminal arrangement and screw connections support integration into machinery and electrical control panels.

Designed for mounting on a suitable metal panel or heatsink, the Finder 77.F3.9.024.8671 is especially well suited to industrial heater control, temperature regulation and other compatible three-phase AC switching applications.

Key Advantages

• Three-phase solid state switching allows control of suitable three-phase AC electrical loads.
• 80 A rated load current supports demanding industrial power switching applications.
• 24–660 V AC operating load voltage range provides flexibility across different industrial AC systems.
• 4–32 V DC control input enables integration with compatible PLCs and electronic controllers.
• Random turn-on switching provides rapid semiconductor activation without waiting for an AC voltage zero crossing.
• Three normally open equivalent outputs provide three-pole AC switching in one device.
• Silent operation eliminates the mechanical clicking associated with conventional electromagnetic contactors.
• Contactless semiconductor switching avoids mechanical contact bounce and contact wear.
• High switching endurance makes the relay suitable for applications requiring frequent operating cycles.
• Low-power DC control allows suitable electronic equipment to control higher-power AC loads.
• Contactor-style terminal arrangement simplifies integration into industrial control panel layouts.
• Panel or heatsink mounting supports effective thermal management.
• Wide operating frequency range supports compatible AC systems operating between 47 Hz and 400 Hz.

Key Features

• Finder 77 Series industrial solid state relay.
• Three-phase AC output switching.
• 3 NO equivalent output configuration (3PST-NO).
• 80 A rated load current.
• 600 V AC rated output voltage.
• 24–660 V AC operating load voltage range.
• 24 V DC nominal control voltage.
• 4–32 V DC control voltage range.
• Random turn-on switching mode.
• 47–400 Hz AC operating frequency range.
• Electronic semiconductor switching without moving output contacts.
• Silent, contact-bounce-free operation.
• Suitable for frequent switching applications.
• Low-power control interface for compatible industrial controllers.
• Three-pole switching arrangement for suitable three-phase circuits.
• Industrial housing with contactor-style terminal layout.
• Screw terminal connections.
• Panel or heatsink mounting.
• −30 to +80 °C ambient operating temperature range, subject to thermal derating.
• Suitable for industrial heater control and compatible process automation equipment.
• RoHS-compliant construction.

High-Current Three-Phase Solid State Switching

The Finder 77.F3.9.024.8671 uses semiconductor devices to switch three AC power circuits without relying on moving mechanical contacts. When the appropriate DC control signal is applied, the relay activates its semiconductor outputs to supply the connected load.

This construction provides several advantages over conventional electromechanical switching devices. Because there are no moving output contacts, the relay operates silently and avoids mechanical contact bounce. It is particularly useful where loads must be switched frequently, such as in automated heating and industrial process equipment.

The three-pole normally open equivalent configuration allows the relay to switch suitable three-phase AC circuits using one compact industrial device. However, unlike mechanical contacts, semiconductor outputs do not provide physical contact separation when switched off.

Its 80 A load rating makes it suitable for higher-current applications, provided that the connected equipment, electrical protection, heatsink and installation conditions meet the manufacturer's specifications.

How Random Turn-On Switching Works

The Finder 77.F3.9.024.8671 uses random turn-on switching, sometimes described as instantaneous switching. When the control input is activated, the semiconductor outputs can begin conducting without deliberately waiting for the AC supply voltage to reach a zero crossing.

This differs from a zero-crossing solid state relay, which delays turn-on until the AC voltage waveform approaches zero. Random turn-on operation is useful in applications where switching behaviour must not be restricted to the next voltage zero crossing.

The appropriate switching method depends on the connected load and the control strategy. For example, zero-crossing switching may be preferable for certain resistive heating applications where minimising electrical interference is the main priority, while random turn-on switching may be required for other control arrangements.

The Finder 77.F3.9.024.8671 is designed for AC output switching. Its DC control input does not make it suitable for switching DC loads.

Thermal Management and Installation Considerations

As with other high-current solid state relays, the Finder 77.F3.9.024.8671 generates heat when its semiconductor outputs conduct current. Correct thermal management is essential for reliable operation and service life.

The relay is intended for mounting on a suitable metal panel or heatsink. The heatsink must be selected with reference to the manufacturer's thermal derating information, the connected load current, ambient temperature and enclosure ventilation.

The 80 A rated current must not be assumed to be available continuously under all installation conditions. The permissible operating current may need to be reduced when the ambient temperature is elevated or the available cooling is insufficient.

Suitable overcurrent protection, wiring, thermal interface materials and electrical isolation arrangements should be included in the system design. Because solid state relays can exhibit off-state leakage current, they must not be used as the sole means of safely isolating electrical equipment.

For motor and inductive load applications, engineers should also check starting current, switching duty and any additional protective components required before selecting the relay.

Typical Applications

• Industrial three-phase electric heater control.
• Process heating and temperature regulation systems.
• Industrial ovens, furnaces and drying equipment.
• Plastic processing and manufacturing machinery.
• Packaging and production equipment.
• Industrial automation requiring high-current AC switching.
• PLC-controlled three-phase electrical loads.
• OEM machinery and electrical control panels.
• Commercial and industrial heating installations.
• Thermal processing and production line equipment.
• Compatible three-phase load control applications.
• Electrical systems requiring silent, contactless switching.