In a project, we are to place several components inside of an enclosure. Some of these components are to be considered safety critical, and their specified operating conditions must not be exceeded. The problem is that most manufacturers specify the maximum ambient temperature for their product, but since it will be placed inside of an enclosure it is not trivial to me where to measure that ambient temperature.

One of the components used is a contactor, Omron J7KN-22D-4, with a datasheet available at: https://assets.omron.eu/downloads/datasheet/en/v3/j06e_j7kn_motor_contactor_datasheet_en.pdf

It specifies two different operating ambient temperatures:

Maximum ambient temperature, open: -40°C to +60°C Maximum ambient temperature, enclosed: -40°C to +40°C

My interpretation of this is that the specified temperature is the air temperature outside of the enclosure, and that they assume the air temperature inside of that enclosure will rise by 20°C.

The product we are designing will eventually be sent to a test lab, such as Intertek, that will have the last saying in this. But it would be great if we could design according to the correct constraints.

Does anyone has an idea of where to measure, and what temperature that is the limit in this case?


I talked to the compliance manager at the clients company, and he tells me that he doesn't know either. He told me to document how I measure and make the decisions.

For now I think I will try to measure the worst case air temperature in the top of the enclosure and declare that to be my ambient temperature.


As pointed out, the datasheet says that the data is according to IEC 60947-4-1, EN 60947-4-1 and VDE 0660. I don't have access to any of these standards currently.

I do have access to SS-EN 60947-1, that includes IEC 60947-1:2007, which states the following:

Ambient air temperature is that existing in the vicinity of the equipment if supplied without enclosure, or in the vicinity of the enclosure if supplied with an enclosure.

Further down it says that for certain types of equipment this is stated in their relevant product standard. Which might be the case for my contactor. So the real answer is probably written in IEC 60947-4-1.

  • 1
    \$\begingroup\$ The datasheet you linked to says "Data according to IEC 60947-4-1, EN 60947-4-1, VDE 0660" - do any of those standards give the measurement specifications? \$\endgroup\$ Nov 19, 2019 at 20:54
  • \$\begingroup\$ I don't know, since we don't have that standard in our library. I am afraid that the answer might be there. We do have the first part, IEC 60947-1, which actually states regarding "Ambient air temperature" that it is the air temperature that is existing in the vicinity of the equipment, or in the vicinity of the enclosure if supplied with and enclosure. Further it says that some equipment, e.g. circuit-breakers and overload relays, is defined in their relevant product standards. Thanks for the comment, it made me look in the (probably) right places! \$\endgroup\$
    – Jonatan G
    Nov 20, 2019 at 12:23

1 Answer 1


Just thinking out loud without expert knowledge --

I guess this depends on the distribution of heat generation in the enclosure. If a single component generates much heat, you will have large heat gradients and the geometry of the device and thermal conductivity of the parts should be considered. If there instead are many small heat sources, I expect small temperature differences within the box making the measurement location largely irrelevant. A thermal camera or power consumption analysis should answer this quickly.

Secondly; I doubt the temperature rating of the contactor is that precise. Just the rough difference between +40 C and +60 C specification depending on enclosure hints that the manufacturer could have maybe a +- 10 C number in mind. If so, the exact location of measurement is also less important.

Finally, you have the interesting problem of deciding what to do if the temperature exceeds specification. If the measurement is just to test your general solution, just measure everywhere on your evaluation devices. If final usage is outdoors I suppose you do need a overheating warning and shutdown mechanism.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.