Tamper-proof (Pre-set) Thermostat NT 39-F: Contact breaker/NC (red casing) for regulating heaters or for switching signal devices when temperature has fallen below the minimum value. The contact opens when temperature is rising.
Tamper-proof (Pre-set) Thermostat NT 40-F: Contact maker/NO (blue casing) for regulating filter fans, heat exchangers, cooling devices or for switching signal devices when temperature limit has been exceeded. The contact closes when temperaure is rising.