Finder 77.A3.8.230.8671 – 77 Series Modular solid state relays

Why Choose the Finder 77.A3.8.230.8671 Three-Phase Solid State Relay?

The Finder 77.A3.8.230.8671 is a high-performance 25 A three-phase solid state relay (SSR) designed for reliable, silent and contactless switching of industrial AC electrical loads. Part of the Finder Series 77, this industrial switching device combines a 90–280 V AC control input, three normally open equivalent outputs and random turn-on switching in a robust hockey puck-style housing.

Featuring a 25 A rated output current and a 24–660 V AC load voltage range, the Finder 77.A3.8.230.8671 is designed for three-phase heating systems, industrial machinery and appropriately rated motor control applications. Its 3PST-NO equivalent switching configuration enables three AC phases to be controlled simultaneously using a single control signal.

Unlike conventional electromechanical contactors, this solid state relay uses semiconductor switching technology without moving power contacts. This provides silent operation, rapid switching response and freedom from mechanical contact bounce. Its random turn-on characteristic makes it particularly useful in applications where immediate switching response is required, while the contactor-style terminal arrangement simplifies integration into industrial electrical control systems.

Designed for panel or heatsink mounting, the Finder 77.A3.8.230.8671 is suitable for industrial control cabinets, process heating equipment and automated production machinery. Correct heatsink selection and thermal management are essential to achieving the specified output current capability.

Key Advantages

• 25 A three-phase solid state relay for industrial AC load switching.
• Three normally open equivalent outputs allow simultaneous control of three AC phases.
• 90–280 V AC control input for compatible mains-voltage control systems.
• 24–660 V AC output voltage range for a wide variety of three-phase installations.
• Random turn-on switching enables fast activation without waiting for the AC voltage zero crossing.
• Contactless semiconductor switching eliminates mechanical contact wear.
• Silent, spark-free and bounce-free operation during normal switching.
• Contactor-style terminal arrangement with input and output connections on adjacent sides.
• Panel or heatsink mounting supports integration into industrial electrical cabinets.
• Screw terminal connections for straightforward installation.
• 47–400 Hz operating frequency range for suitable AC applications.
• −30 to +80 °C ambient temperature range, subject to load current derating and thermal conditions.
• IP20 protection rating for appropriately protected installations.
• Suitable for industrial heating, machinery, automation and compatible three-phase motor control.

Key Features

• Finder Series 77 industrial solid state relay.
• Three-phase AC switching.
• Output configuration: 3 normally open equivalents (3PST-NO).
• Rated output current: 25 A.
• Output voltage range: 24–660 V AC.
• Nominal control voltage: 230 V AC.
• Control input range: 90–280 V AC.
• Input frequency: 50/60 Hz.
• Switch-on characteristic: Random turn-on.
• Load operating frequency: 47–400 Hz.
• Contactor-style input and output terminal arrangement.
• Hockey puck-style industrial housing.
• Panel or heatsink mounting.
• Screw terminal electrical connections.
• LED indication for control status.
• Operating ambient temperature: −30 to +80 °C.
• Protection rating: IP20.
• Solid state switching without moving contacts.

How Three-Phase Random Turn-On Solid State Switching Works

The Finder 77.A3.8.230.8671 is designed to switch three-phase AC loads electronically using a compatible AC control signal. When the control voltage is applied within its specified 90–280 V AC input range, the relay activates its three semiconductor output channels, allowing power to be supplied to the connected three-phase load.

Its random turn-on switching characteristic means the relay does not deliberately wait for the AC voltage waveform to reach zero before switching on. This provides a rapid response to the control signal and can be advantageous for applications requiring immediate switching or integration with suitable electronic control systems.

Unlike zero-crossing solid state relays, which are commonly selected for particular resistive heating applications, random turn-on relays can be more suitable for certain inductive loads and specialised switching arrangements. However, random turn-on operation may produce greater electrical transients depending on the load and the point of switching. Load characteristics, electromagnetic compatibility and surge protection should therefore be considered during system design.

The three-pole output arrangement allows all three phases of an appropriately rated load to be controlled by one device. This makes the Finder 77.A3.8.230.8671 useful for industrial heating installations, automated manufacturing equipment and selected motor control applications where electronic switching is preferred over a mechanical contactor.

Because the relay operates without moving power contacts, it avoids mechanical contact bounce, audible switching noise and contact erosion associated with conventional electromechanical switching devices. This makes it particularly useful in applications requiring frequent operation, provided that the connected load remains within the relay's electrical and thermal ratings.

Thermal Management and Safe Installation

Solid state relays dissipate heat while conducting current. The 25 A output rating of the Finder 77.A3.8.230.8671 must therefore be considered together with the selected heatsink, ambient temperature, installation orientation and enclosure ventilation.

The relay is designed for direct panel mounting or mounting onto a suitable heatsink. Where necessary, an appropriately rated heatsink and suitable thermal interface material should be used to maintain the semiconductor operating temperature within the manufacturer's limits. The maximum permissible continuous load current may be lower than 25 A under unfavourable thermal conditions.

Appropriate upstream short-circuit protection must also be provided. Semiconductor relays can be sensitive to fault currents, and the selection of protective devices should follow the manufacturer's recommendations for the intended load and electrical installation.

As with other solid state relays, the Finder 77.A3.8.230.8671 can allow leakage current when the output is switched off. It does not provide the physical contact separation of a mechanical isolator and must not be used as the sole means of safety isolation. A suitable disconnecting device should be provided for maintenance and electrical safety.

Typical Applications

• Three-phase industrial heating element control.
• Industrial ovens and process heating equipment.
• Temperature-controlled manufacturing systems.
• Industrial machinery and automated production lines.
• Three-phase resistive load switching.
• Compatible three-phase motor control applications.
• Packaging and processing machinery.
• Industrial process control systems.
• Automated electrical load switching.
• Factory control panels and industrial electrical cabinets.
• PLC-controlled switching through a suitable AC control interface.
• OEM equipment requiring silent three-phase switching.
• High-frequency switching applications within the relay's specified limits.