SST-2 Freeze Protection Thermostat

The C-UL-US listed SST–2 Freeze Protection Thermostats replace electromechanical thermostats in cost-sensitive applications requiring ground fault equipment protection (GFEP). The SST–2 is listed by Underwriters Laboratories to Standard UL 873 for Temperature- Indicating and -Regulating Equipment.

The SST–2 operates heaters at temperatures below 40°F (4.4°C) and turns them off above 42°F (5.5°C). The external temperature sensor (supplied) is a NEC Class 2 device rated for wet locations.

The SST–2 features a built-in 30 mA GFEP that is digitally filtered to minimize false tripping. A ground fault must be manually reset with the TEST/RESET switch before heater operation can be resumed. The GFEP function is automatically tested along with the heaters whenever power is applied and once every 24 hours thereafter for additional safety.

The SST–2 includes an alarm relay with an isolated SPDT 1 AMP contact. The alarm relay is reverse acting and is normally closed unless there is a ground fault condition, GFEP circuitry fails a test, or when there is a bad temperature sensor.

The SST–2 Freeze Protection Thermostats operate from automatically selected operating voltages of 120, 208, 240 or 277 volts, single-phase. They control heater loads of up to 30 amps while consuming less than 2 watts when idling. The temperature sensor is an NEC Class 2 device that can be located up to 2,000′ (610 m) away from the SST. They operate in non-hazardous environments in a temperature range extending from −40° to 131°F (−40° to 55°C). The rugged non-metallic enclosure is appropriate for installation in indoor or outdoor locations suitable for NEMA 4x applications.


Area of use Nonhazardous locations
Approvals C-UL-US Listed Type 873 Temperature Regulating Equipment
Protection NEMA 4X
Cover attachment Polycarbonate cover, machine screws
Entries 1 × 3/4″ entry (bottom right) for NEC Class 2 connections 
3 × 1-1/16″ entries (bottom left and left) for supply and load power
Material Polycarbonate
Mounting Wall mounted
Front Panel Interface
Status indicator SUPPLY (green) power applied 
SUPPLY (green, flashing) bad thermistor 
HEAT (yellow) call for heat 
GFEP (red) ground fault condition 
GFEP (red, flashing) failed 
GFEP (red, flashing, rapid) GFEP test in progress
Remote Interface (SST–2 only)
Alarm relay Isolated SPDT 1 AMP Class 2 contact
Summary alarms No Power 
Ground Fault Condition
GFEP function test failure 
Bad or missing Thermistor
Supply voltage 120, 208, 240 or 277 volts, single phase (automatically selected)
Contact type Two Form A DPST
Maximum ratings Voltage: 277 VAC 
Current: 30 amps
High Limit Thermostat
Set point 40°F (4.4°C)
Dead band 2°F (1°C)
Sensor type Thermistor network
Circuit type NEC Class 2
Lead length Up to 2,000′ (610m) using 12 AWG 2-wire jacketed cable Up to 500′ (152m) using 18 AWG 2-wire jacketed cable
Ground Fault Equipment Protection (GFEP)
Set point 30 mA
Automatic self-test Mode A: Verifies GFEP function before contactors operate
Mode B: Verifies GFEP and heaters every 24 hours
Manual test/reset TEST/RESET switch of front panel
Operating temperature −40°F to 130°F (−40°C to 55 °C)
Storage temperature −67°F to 167 °F (−55°C to 75 °C)