Trafag EXAS 409/419 Ex Indu Ambistat Room Thermostat

Explosion-protected room thermostat for pump houses, stores and enclosures

The Trafag EXAS 409/419 Indu Ambistat is an explosion-protected thermostat for sensing room or ambient air temperature in hazardous areas. It is marked II 2 G/D with Ex db eb IIC T6 Gb for gas and Ex tb IIIC T80 °C Db for dust, and is certified to IECEx, ATEX and UKEX.

Unlike the EXS thermostats, which use a remote capillary bulb, the Ambistat has an open copper sensor coil mounted on the housing so it responds to the air around it. A liquid-filled sensor operates the microswitch directly, so the thermostat needs no auxiliary power. Typical uses are frost protection and overheating alarms in pump houses, analyser shelters, battery rooms and heated cabinets.

Technical specifications of the EXAS 409/419

Switch rating and standard products

The standard Ex microswitch is rated 250 VAC at 5 A resistive (5 A inductive) and 125 VAC at 5 A. On DC the rating is 0.25 A at 250 V, 0.5 A at 125 V, 1 A at 50 V and 5 A at 30 V resistive. Mechanical life is one million cycles.

Trafag lists two standard types with short lead time. The EXAS33 is a type 419 for minus 30 to plus 30 degrees C and the EXAS60 is a type 419 for 0 to plus 60 degrees C, both with a fixed 2.5 degree differential and a nickel-plated copper sensor.

Setting the switch point and installing

Type 409 is adjusted from outside with a knob and scale. Type 419 is adjusted inside the housing, which allows the optional switch point locking, a factory-fixed and sealed set point, or a customer-specified preset. Trafag notes that a preset is made without a guarantee on switching accuracy, so verify the switching temperature in the plant before relying on it for protection duty.

Mount the thermostat in any position away from direct heat sources, and not directly in the airflow of a heater, so that it reads a true reading of the air temperature. Terminate with screw terminals for 1 to 2.5 square millimetres and keep the certified gland and sealing arrangement that the Ex certificate requires.

How the Trafag EXAS 409/419 works

The Ambistat is a thermostat with a liquid-filled sensor. When the air temperature changes, the liquid expands or contracts and moves a diaphragm that operates the microswitch directly, so the unit needs no auxiliary power. The sensor is an open copper coil on the housing, so it senses the air in the room and not a pipe or a tank. The switch is a floating change-over contact, and the thermostat has an explosion-protected housing marked II 2 G/D with Ex db eb IIC T6 Gb and Ex tb IIIC T80 degrees C Db.

Where the EXAS 409/419 is used

• Pump houses.
• Analyser shelters.
• Battery rooms.
• Heated cabinets and stores.
• Frost protection and overheating alarms in hazardous areas.

Selection checklist for the EXAS 409/419

• Type 409 with external adjustment or 419 with internal adjustment.
• Range of -30 to +30 degrees C, or 0 to +60 degrees C.
• Switching differential of 2.5 degrees C, not adjustable.
• Floating change-over contact.
• Switch rating of 250 VAC at 5 A resistive.
• Ex protection type, with IECEx, ATEX and UKEX certificates.
• Ambient range of -30 to +60 degrees C.
• IP65 and humidity up to 95 percent.
• Cable entry M20 x 1.5, cable 4 to 13 mm.
• Weight of about 950 g.

Installation, commissioning and maintenance notes

Mount the thermostat where it senses representative air, away from heaters, doors and direct draughts. Make the cable connection through a gland that is suitable for the explosion protection type, and close the housing as the instructions say. The type 419 is set inside the housing, so set the switch point before closing it. Check the switch point with a reference thermometer, and record the setting and the date.

Requesting a quotation for the Trafag EXAS 409/419

Send the type, the temperature range and the number of units. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

Standard types

Two standard types are listed: the EXAS33 for -30 to +30 degrees C and the EXAS60 for 0 to +60 degrees C, both type 419.

Switch life

The mechanical life of the standard Ex microswitch is one million cycles.

Housing and sensor

The housing is coated AlSi9Cu3, and the sensor is copper or nickel-plated copper.

Thermostat records

Record the type, the setting and the room of each thermostat.

Choosing the right type and range

Use the 0 to +60 degrees C range for overheating alarms in warm rooms, and the -30 to +30 degrees C range for frost protection. Choose type 409 when the setting must be changed from outside, and type 419 when the setting should be protected inside the closed housing. Check that the zone, gas group and temperature class of the area match the marking.

Accuracy

The repeatability is 0.5 percent of full scale and the scale accuracy is 2 percent of full scale.

Documents and quotation

The attached document is the Trafag EXAS 409/419 Ex Indu Ambistat datasheet (H72128v, 12/2025). The instructions (H73172) and certificates are published separately by Trafag.

For a quotation, send the type (409 or 419), temperature range, sensor material and any locking option. See Temperature Instrumentation for related instruments.