An ESTI cartridge inserted in the recess of the base plate holds the switch in the 'on' position. The aluminium base plate of the switch being in close contact with the apparatus to be protected attains the temperature of the latter. With the temperature exceeding the limit set by the ESTI cartridge the latter bursts, releasing the switch, wh ich then breaks the circuit of the current. After a new ESTI cartridge has been inserted, the switch is operational at once.

For the purpose of controlling the interior of appliances, apparatus etc. or of being as near as possible to the heat source the safety switch is equipped with a probe. The ESTI cartridge is inserted into the bottom part of the probe and holds the switch through a spring-loaded locking-pin. When the cartridge comes into action the locking-pin releases the switch, thus producing the desired reaction. The EST 15/1 is supplied with a 1/2" cap nut with a gas pipe thread to permit installing the cartridge in a protection tube.

Application: oil cooled transformers, air heaters, drying ovens, hardening furnaces, distilling apparatus etc.