I know that most safety standards require the equipment to remain safe under single fault conditions. In this case the single fault I would consider would be that of failure of the thermostat (i.e short circuited)
The first thing to consider would be, can the failure of this device allow the temperature to reach a hazardous level taking into account, touch temperatures, thermal limits on other components in the vicinity (electrical and mechanical) and possibility of ignition. If the answer is yes then this component is safety critical as its failure can lead to an unsafe condition. If this is so then a protection measure would have to be taken to ensure that the equipment remained 'safe' under single fault conditions. Now you have one component for control and one component for protection, the protective device only operating when the equipment is out of control. In a previous job I had to run a test on some equipment that included a heating element. as a result of fault testing the control circuit the element became so hot its metal fins melted and dripped into the bottom of the enclosure! The problem was resolved with a series thermal cutout mounted on the element body. Hope this is helpful... Regards. ____________________Reply Separator____________________ Subject: Re:Protection or Control? Author: [email protected] List-Post: [email protected] Date: 21/09/00 15:46 forwarding for [email protected] ____________________Reply Separator____________________ Subject: Protection or Control? Author: "Luiz Claudio" <[email protected]> List-Post: [email protected] Date: 9/20/00 9:59 PM I have a question to those who are familiar with the safety requirements established electrical appliance standards. A bimetal thermostat is usuallly used to control the temperature of a certain ambient within certain limits. Can it also be considered as a protection device? I'm not going to give my oppinion to avoid any possibility of biased answers. But, please, give your oppinion. If you have a reference publication which I could use as a reference for a work to be presented, please include it in your answer. If not, no problem. Just give your oppinion. Please answer this message to my personal email address: [email protected] Thanks a lot, Luiz ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
