Watlow CLS208 24–280 VAC Input/Output SSR with LED Status Indicator Product Introduction

The Watlow CLS208 is a compact,high-reliability solid-state relay(SSR)designed for switching AC loads up to 8 amps at voltages from 24 VAC to 280 VAC.Housed in a standard 17.5 mm wide DIN-rail mountable package,it is engineered for demanding industrial heating applications where long life,silent operation,and high switching cycle endurance are critical—such as plastic molding,semiconductor processing,food packaging,and laboratory ovens.

Unlike electromechanical relays,the CLS208 uses zero-cross switching technology,which turns the load on only when the AC sine wave crosses zero volts.This minimizes electrical noise(EMI),reduces inrush current stress,and eliminates contact arcing,significantly extending both the relay’s life and the lifespan of connected heating elements.

The module features an integrated LED status indicator(illuminates when input signal is active),built-in overvoltage protection,and high dielectric isolation between control and load circuits.It is fully compatible with Watlow temperature controllers(e.g.,F4T,ELD,PM Plus)and commonly used in Watlow EZ-Zone®RM power distribution panels.

Application Scenario

At a medical device manufacturer producing IV bag sterilizers,frequent failures of electromechanical relays caused unplanned downtime during validation runs.Each failure required chamber cooldown and recalibration—costing~$12,000 per incident.The team replaced all 8 A heater relays with Watlow CLS208 SSRs.The zero-cross switching eliminated voltage spikes that previously degraded cartridge heaters,while the silent,spark-free operation met cleanroom EMI requirements.Over 18 months,zero SSR failures were recorded across 42 sterilization units.Maintenance staff reported that the bright red LED made troubleshooting heater activation issues“instant”—reducing mean-time-to-diagnose by 90%.The upgrade paid for itself in under 6 months through avoided downtime and extended heater life.

Technical Parameters

Parameter Value/Description

Model CLS208

Manufacturer Watlow Electric Manufacturing Co.

Type Single-pole,single-throw(SPST)AC Solid-State Relay

Load Voltage Range 24 to 280 VAC(50/60 Hz)

Maximum Load Current 8 A continuous(resistive load,e.g.,heating elements)

Control(Input)Voltage 3 to 32 VDC(wide-range logic-compatible input)

Switching Method Zero-cross turn-on(minimizes EMI and inrush)

Mounting DIN rail(35 mm,EN 60715 compliant)

Width 17.5 mm(1-module DIN size)

LED Indicator Red LED—ON when input signal is active

Isolation Voltage≥4,000 VAC(input to output)

Operating Temperature-30°C to+80°C(derating above 50°C may apply)

Cooling Natural convection(no fan required at≤8 A)

Certifications UL,cUL,CE,RoHS,TÜV(pending exact batch)

Life Expectancy>100 million operations(vs.~100k for mechanical relays)

Terminals Screw-clamp terminals,accepts 14–22 AWG wire

Key Advantages&Innovation Highlights

Zero Maintenance:No moving parts=no contact wear,bouncing,or replacement schedules.

EMI Suppression:Zero-cross firing prevents radio-frequency interference—critical in labs and electronics manufacturing.

High-Speed Compatibility:Works seamlessly with PWM or time-proportional outputs from modern PID controllers.

Space Efficient:Narrow 17.5 mm profile allows high-density mounting in compact panels.

Drop-In Upgrade:Direct replacement for many legacy electromechanical relays or competing SSRs(e.g.,Crydom CX240D8).

Typical Wiring

Input(+):Connect to controller’s DC output(e.g.,24 VDC from F4T alarm relay)

Input(–):Connect to common/ground

Output(L1):Line(hot)from AC power source

Output(T1):To one terminal of heating element

Heater Other Terminal:Connected to neutral/return

Note:Always fuse the AC load circuit per NEC/IEC standards.Use heat sinks or derate if ambient>60°C or current>6 A continuous.

Compatible/Alternative Products

Crydom CX240D8–Functionally equivalent SSR

Carlo Gavazzi RA280D08–Similar DIN-rail AC SSR

Omron G3NA-208B–Popular alternative with same ratings

Watlow CLS216–16 A version for higher-power heaters

Watlow EZ-Zone RM Panels–Pre-engineered power distribution systems using CLS series SSRs

Installation&Best Practices

Mount vertically on standard 35 mm DIN rail.

Torque terminals to 0.5–0.6 N·m to prevent overheating.

Keep SSR away from high-heat sources(e.g.,transformers).

For currents>6 A,ensure adequate ventilation or use adjacent empty slots for cooling.

Always use an external overcurrent protection device(fuse or breaker).

Conclusion

The Watlow CLS208 embodies the shift from mechanical to solid-state switching in thermal process control.By delivering silent,reliable,and maintenance-free actuation of heating loads,it enhances system uptime,improves process consistency,and reduces total cost of ownership—especially in high-cycle or precision applications.

Whether you’re building a new oven,retrofitting a legacy extruder,or sustaining a pharmaceutical lyophilizer,the CLS208 is a proven,compact solution trusted across global industries.