How to select and test thermostats for cooling or heating applications

Thermostats are a necessary tool for managing the temperature inside electrical enclosures. Electrical components generate heat during operation, and in the event of overheating can cause damage to the components or even lead to a fire

Fandis thermostats effectively control the internal temperature of the enclosure ensuring the optimal operating temperature for the components inside. Thermostats are usually combined with devices such as a fan or heater.

How to choose the correct thermostat for your application?

The TRT series single thermostats in the Fandis Orangis range are divided into two types:

• Single normally open (NO) contacts, which connect the circuit when the relay is activated.
•  Single normally closed (NC) contacts, which disconnect the circuit when the relay is inactive.

Thermostats with single normally open contacts (NO)

Fandis’ normally open single contact thermostats have the function of managing ventilation and cooling systems. They are easily distinguished by the blue-coloured knob.

The definition of a normally open contact (also abbreviated as NO) could lead to some confusion regarding its application. The contact is defined as “normally open” when the ambient temperature is lower than the set temperature, and therefore, the connected cooling unit (such as a fan) remains switched off. Let’s assume the room temperature rises and exceeds the value set on the thermostat; the contact closes (close on rise), turning on the fan.

Thermostats with single normally closed contacts (NC)

The second type of Fandis thermostat is a normally closed single contact. It is used to switch and control heating systems, such as anti-condensation heaters and is distinguished by its red-coloured knob.

In these thermostats, the contact is “normally closed” (also abbreviated as NC). When the ambient temperature is lower than the set temperature causing the connected heating device to turn on.

As the room temperature increases and when it reaches and exceeds the set temperature value, the contact opens (open on rise), turning off the heating device.

To summarise – the Fandis range consists of the following:

• TRT-10A230V-NO: Thermostat with blue knob with normally open (NO) contact, close on rise (the contact closes as the temperature increases);
• TRT-10A230V-NC: Thermostat with red knob with normally closed contact (NC), open on rise (the contact opens as the temperature increases).

Both models are available with temperature settings in both °C and °F.

Quality control

All Fandis thermostats are tested individually before leaving the production line, therefore ensuring its functionality, reliability and accuracy out in the field.

How to test a thermostat

For correct operation, the variable value is not the temperature indicated on the temperature set knob, but rather, the ambient temperature.

To test a NO thermostat (blue knob), the best method is to set a temperature value on the thermostat that is higher than the ambient temperature. At this point, the connected fan is off. Using any source of heat, such as a hair dryer, heat the air surrounding the thermostat. When the ambient temperature exceeds the set temperature, the fan should turn on.