I have had a number of equipment installers contact me this summer and express concerns about the temperature of the outdoor electronics that they are handling. In some cases, the electronics is too hot to hold. In every case, the temperatures of the products has been within specifications. I tell installers that a circuit card can be as hot as 95 °C and the components on it can be even hotter. Figure 1 illustrates the conditions that we design for. Note that the telecommunications industry often designs to Telcordia specifications, which are the basis of the temperature numbers that we use.
Figure 1 also mentions a commonly used junction temperature objective, which I discuss more here.
Figure 2 shows how hot something like this feels on human skin by showing burn time versus temperature (Source: "The Burn Wound", Chapter 1, Barret and Dziewulski).
So touching something that is at a temperature of 95 °C will cause a burn very quickly – it is just 5 °C less than the temperature of boiling water.
Personally, I always wear gloves.
I have an objective of limiting the junction temperatures of parts in my designs to no more than 110 °C. I cannot always meet that objective. The US Navy set that junction temperature as an objective years ago in its reliability guidelines and is commonly used to this day in the design of electronic gear rated for outdoor use. Here is an example from the datasheet of the Cree SMD LED, which uses 110 °C as its maximum junction temperature.
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