Finder 77.21.8.230.8250 – 77 Series Modular solid state relays

Why Choose the Finder 77.21.8.230.8250 Solid State Relay?

The Finder 77.21.8.230.8250 is a high-performance 25 A AC-output solid state relay (SSR) designed for reliable, silent and contactless switching in industrial automation, heating control, lighting systems and electrical control panels. Part of the Finder Series 77 modular solid state relay range, this device combines TRIAC semiconductor switching technology with zero-crossing operation and an integrated heat sink.

Featuring a 230 V AC nominal output voltage and a 19–305 V AC switching range, the Finder 77.21.8.230.8250 provides a rated load current of 25 A under specified operating conditions. Its 230 V AC nominal control input, with a control voltage operating range of 40–305 V AC, makes it suitable for integration into compatible mains-voltage control circuits.

The relay incorporates one normally open solid state output (1 NO / SPST-NO) and uses zero-crossing switching to activate the connected load near the AC voltage zero crossing. Its compact 22.5 mm housing, integrated heat sink, screw-type box-clamp terminals and 35 mm DIN rail mounting make it a practical choice for professional industrial electrical installations.

Key Advantages

• 25 A rated AC load current for appropriately rated industrial switching applications.
• 19–305 V AC switching range for compatible single-phase AC loads.
• 40–305 V AC control input range for flexible mains-voltage control.
• Zero-crossing switching to reduce switching transients in suitable AC applications.
• TRIAC semiconductor output eliminates mechanical switching contacts.
• Silent operation without mechanical relay clicking.
• Spark-free and contact bounce-free switching for dependable electronic operation.
• Integrated heat sink for thermal management.
• 6 kV impulse insulation between input and output circuits.
• 22.5 mm modular housing for efficient control panel installation.
• 35 mm DIN rail mounting for straightforward assembly.
• IP20 protection rating for use inside suitable electrical enclosures.

Key Features

• Finder Series 77 modular solid state relay.
• Type 77.21 single-channel AC-output configuration.
• TRIAC semiconductor switching technology.
• Zero-crossing turn-on characteristic.
• One normally open solid state output (SPST-NO).
• 25 A rated output current at 40 °C.
• 230 V AC nominal output voltage.
• 19–305 V AC output switching range.
• 230 V AC nominal control voltage.
• 40–305 V AC control voltage operating range.
• 50/60 Hz AC operation.
• Integrated heat sink and protective housing.
• 6 kV input-to-output impulse insulation.
• High-speed electronic switching.
• High electrical endurance without mechanical contact wear.
• Low control circuit power consumption.
• Box-clamp electrical terminals.
• Relay-style terminal arrangement with input and output terminals on opposite sides.
• 35 mm DIN rail mounting.
• IP20 degree of protection.

Reliable Zero-Crossing AC Switching for Industrial Loads

The Finder 77.21.8.230.8250 uses TRIAC semiconductor technology to control AC electrical loads without the mechanical contacts found in conventional electromechanical relays. When a suitable AC control voltage is applied to the input, the electronic output switches on and supplies the connected load.

Its zero-crossing switching characteristic enables the relay to begin conduction close to the point where the AC waveform crosses zero voltage. This can reduce electrical interference and switching stress in compatible resistive and lighting applications.

Because the relay contains no moving switching contacts, it operates silently and without mechanical contact bounce. These characteristics are particularly useful in systems requiring frequent switching, such as electric heating control, lighting automation and industrial process equipment.

The 25 A output rating provides capacity for a range of industrial loads, subject to the applicable utilisation category, ambient temperature and thermal conditions. The relay's integrated heat sink helps dissipate semiconductor losses during operation. Appropriate load derating must be applied where necessary.

The relay also supports specified lighting loads, including incandescent, halogen, fluorescent and LED lighting systems. Actual load selection must account for starting current, driver characteristics, switching frequency and the manufacturer's applicable load ratings.

With 6 kV input-to-output impulse insulation, the relay provides electrical separation between its control and load circuits. Its relay-style terminal arrangement places the control and output connections on opposite sides of the housing, supporting organised panel wiring.

Important: Solid state relays can pass a small leakage current when switched off and do not provide the same physical contact separation as mechanical isolators. Appropriate circuit protection and a separate means of electrical isolation must be provided where required.

Typical Applications

• Industrial electric heating control.
• Resistive heater and heating element switching.
• Commercial and industrial lighting control.
• LED lighting and lighting driver switching.
• Fluorescent and energy-saving lamp control.
• Industrial machinery and manufacturing equipment.
• Solenoid and contactor control circuits.
• Industrial process automation.
• Building automation and electrical control systems.
• Electrical distribution and control panels.
• PLC-controlled AC load switching.
• Applications requiring silent and frequent switching.
• OEM machinery and electrical control cabinet construction.