Why does not thermal switch action when temperature reaches the rated value?

In my 15 years experience of serving the bimetal thermal switch customers, this question was asked too many times. Different applications or operating engineers would have different situations. But most of  possible reasons which might cause the thermal switch not action properly are as follows:

1. The temperature rise speed is too fast. For example, the temperature rises to the prescribed value in very short time. Then, the bimetal inside of thermal switch has no enough time to reaction. The temperature of bimetal is still much lower than the rated value or outside temperature. So, the thermal switch would not action. The first trip off temperature would much higher than the rated value. It is so called overshot. This problem can be solved by controlling the temperature rising speed, or making thermostat action 3 cycles. Then, the thermal switch would action properly.
2.  There might be misunderstanding for rated temperature. It means a tolerance range,  normally 10℃, instead of the specific value. For example: a thermostat is rated at 100℃, the common action temperature range is 95~105℃. It is not just 100℃ only. So,  the action temperature for some units can be 104 or 105℃. These units are qualified products.
3.  The thermal switch is malfunctioned. The temperature might be out of tolerance, or the two contacts of thermal switch were burned and connected together forever. It would be a serious defection and might cause fire or other safety problems.
4. Other uncertain reasons also are possible, like incorrect mounting method, improper temperature setting, damage during shipping etc. To solve these problems, we need to analyze the samples together with the applied product. Some mock-up tests are necessary.

 

Most of thermal switches provided by Yangzhou Wuyue Electric Co., Ltd have both UL and VDE approval. All products are 100% tested before releasing to our noble customers according to ISO9001 and TS16949 quality system. The defective rate we promise to our customer is 100 ppm.

 

Low temperature thermal switch 17AME-H