Why Choose the Finder 77.21.9.024.8251 Solid State Relay?
The Finder 77.21.9.024.8251 is a 25 A modular solid state relay (SSR) designed for reliable, contactless switching in industrial automation, electrical control panels and machinery applications. Part of the Finder 77 Series, this relay combines semiconductor switching technology with an integrated heat sink and compact DIN-rail mounting construction.
Featuring a 4–32 V DC control input and a 19–305 V AC switching range, the Finder 77.21.9.024.8251 provides an effective interface between low-voltage electronic control systems and AC electrical loads. Its single normally open (SPST-NO) output is rated at 25 A under specified operating conditions, making it suitable for appropriately rated heating, motor control and industrial switching applications.
The random turn-on switching function allows the relay to respond to an applied control signal without waiting for the next AC voltage zero crossing. Combined with silent operation, high switching speed, 6 kV input-to-output insulation and a slim 22.5 mm housing, this model offers a practical solution for industrial installations requiring frequent and dependable electronic switching.
Key Advantages
- 25 A rated load current for suitable industrial AC switching applications.
- 4–32 V DC control input for integration with compatible electronic control systems.
- 19–305 V AC switching range for a broad selection of AC loads.
- Random turn-on operation for applications requiring rapid switching response.
- Contactless semiconductor switching eliminates mechanical contact bounce and arcing.
- Silent operation compared with conventional electromechanical relays.
- Integrated heat sink supports thermal management during operation.
- 6 kV input-to-output insulation under specified impulse test conditions.
- 22.5 mm modular housing for space-efficient control-panel installation.
- 35 mm DIN-rail mounting for straightforward installation.
- Box-clamp screw terminals for secure electrical connections.
- IP20 protection rating for installation within suitable electrical enclosures.
Key Features
- Finder 77 Series modular solid state relay.
- Model: 77.21.9.024.8251.
- Switching technology: TRIAC semiconductor output.
- Output configuration: 1 normally open (SPST-NO).
- Rated output current: 25 A at 40 °C.
- Rated output voltage: 230 V AC.
- Output switching voltage range: 19–305 V AC.
- Control voltage range: 4–32 V DC.
- Switching mode: Random turn-on.
- Maximum peak current: 400 A for 10 ms under specified conditions.
- Repetitive peak off-state voltage: 800 V.
- Input-to-output impulse insulation: 6 kV (1.2/50 µs).
- Integrated heat sink and protective housing.
- Silent, spark-free and bounce-free switching.
- Control and load terminals positioned on opposite sides.
- Housing width: 22.5 mm.
- Mounting: 35 mm DIN rail.
- Terminal arrangement: Box-clamp screw terminals.
- Protection classification: IP20.
Technical Specifications
- Manufacturer: Finder
- Series: 77 Series
- Model: 77.21.9.024.8251
- Product type: Modular solid state relay
- Output technology: TRIAC
- Output contact equivalent: 1 NO / SPST-NO
- Rated output current: 25 A at 40 °C
- Rated output voltage: 230 V AC, 50/60 Hz
- Output switching voltage range: 19–305 V AC, 50/60 Hz
- Control input voltage: 4–32 V DC
- Switching characteristic: Random turn-on
- Maximum peak current: 400 A for 10 ms
- Repetitive peak off-state voltage: 800 V
- Input-to-output insulation: 6 kV (1.2/50 µs)
- Off-state leakage current: 1 mA
- Ambient operating temperature: −20 to +80 °C
- Enclosure width: 22.5 mm
- Enclosure dimensions (H × W × D): 83.3 × 22.5 × 120.3 mm
- Mounting: 35 mm DIN rail (EN 60715)
- Terminal type: Box-clamp screw terminals
- Thermal management: Integrated heat sink
- Protection rating: IP20
- Compliance: CE, UKCA and RoHS
- Product category: Solid State Relays
High-Speed Random Turn-On Switching for Industrial Automation
The Finder 77.21.9.024.8251 uses a semiconductor switching element rather than mechanical contacts to control an AC load. When a suitable 4–32 V DC control signal is applied, the relay activates its TRIAC output, allowing current to flow through the connected load. Because the device uses random turn-on switching, it does not deliberately wait for the AC voltage to cross zero before initiating conduction.
This operating principle makes the relay useful for applications where a short switching response is desirable, including certain motor control and industrial automation circuits. Its integrated heat sink assists with thermal management, while its contactless construction supports frequent switching without mechanical contact wear. The relay must be correctly rated for the load, operating temperature, heat dissipation and required protective devices. As a TRIAC-based SSR, it is intended for AC load switching and is not a substitute for an isolating switch.
Typical Applications
- Industrial automation and electronic load switching.
- PLC-controlled AC loads using compatible DC control outputs.
- Industrial motor control applications requiring random turn-on switching.
- Electrical heating equipment and temperature control systems.
- Industrial machinery and automated production equipment.
- Contactors and solenoid control circuits.
- Conveyor and material handling control systems.
- OEM machinery requiring silent semiconductor switching.
- Industrial electrical control panels and DIN-rail assemblies.
- Applications requiring frequent, bounce-free AC switching.
