Schneider SSD1A320BDC1 Solid State Relay

The Schneider SSD1A320BDC1 is a panel-mount solid state relay (SSR) designed for switching AC loads up to 20 A at 600 V AC. It features a DC input control voltage range of 4-32 V DC, making it compatible with PLC outputs, microcontrollers, and other low-voltage control signals. The relay uses zero-crossing switching technology, which turns on only when the AC sine wave crosses zero volts, minimizing electrical noise and inrush current. This SSR is ideal for resistive loads such as heaters and lamps, as well as for light inductive loads. The SSD1A320BDC1 includes an internal snubber circuit to protect against voltage spikes, and it is housed in a UL-recognized plastic case suitable for DIN rail or panel mounting.

Technical Specifications

Load voltage range: 48-600 V AC (50/60 Hz). Load current: 20 A continuous (resistive), 10 A for inductive loads. Surge current: 250 A for one cycle. Input control voltage: 4-32 V DC. Input current: 5-15 mA. Switching type: zero-crossing turn-on, random turn-off. Off-state leakage current: < 1 mA. On-state voltage drop: < 1.5 V at 20 A. Isolation voltage: 4000 V AC (input to output). Response time: < 0.5 µs for turn-off, < 0.5 ms for turn-on (zero-crossing delay). Operating temperature: -30°C to +80°C. Dimensions: 58 mm × 45 mm × 27 mm. Weight: 100 g. Mounting: panel or heat sink (required). Protection: integrated varistor (MOV) for overvoltage suppression.

Key Features

• 20 A load current at 600 V AC, zero-crossing switching

• Wide input range: 4-32 V DC (compatible with 5V, 12V, 24V logic)

• High isolation: 4000 V AC between input and output

• Built-in snubber (MOV) for inductive load protection

• LED indicator for input status

• Panel mount with optional heat sink (sold separately)

• UL, CE, RoHS compliant

Operation and Applications

The SSR is used to control AC loads where frequent switching is required or where mechanical relay contacts would wear out. Typical applications include temperature control of industrial ovens and furnaces (PID cycling), lamp dimming (phase control not available with zero-crossing; for resistive heaters only), switching of solenoids and small contactors, and replacement of electromechanical relays in high-cycle applications. The zero-crossing feature reduces electromagnetic interference (EMI) and extends load life. For inductive loads (motors, transformers), derating is required; consult the derating curve in the datasheet.

Installation and Heat Management

Mount the relay on a suitable heat sink to dissipate heat (the relay alone does not dissipate enough). For 20 A continuous, a heat sink with thermal resistance ≤ 1.5°C/W is recommended. Apply thermal grease between the relay base and heat sink. Connect the AC load to terminals (1) and (2) (no polarity). Connect the DC control voltage to terminals (3) and (4): positive to terminal 3, negative to terminal 4. The input LED will illuminate when voltage is applied. Use wire size 14 AWG for load terminals. Ensure clearance from other components. The relay is not internally fused; provide external fuse protection (e.g., 25A fast-blow).

Maintenance and Safety

Solid state relays have no moving parts and require no maintenance. However, heat sink surfaces should be kept clean. Check torque on terminals annually. The relay may fail shorted; in such case, the load will remain on continuously. For critical applications, use a backup mechanical contactor. Do not exceed the rated current or voltage. The relay is not suitable for DC loads (see datasheet for DC version).

Environmental and Compliance

The SSD1A320BDC1 is UL 508 listed, CSA certified, and CE marked. It meets RoHS. Operating temperature: -30°C to +80°C. Storage: -40°C to +125°C. Humidity: 5-95% non-condensing.

Conclusion

The Schneider SSD1A320BDC1 solid state relay offers reliable, noiseless switching of AC loads up to 20 A. Its zero-crossing feature, wide input range, and built-in protection make it a suitable choice for industrial heating, lighting, and motor control applications where high cycle rates are required.