This question started as a design specific question but is (now) more of a general question going forward onto other PCB product designs...
For now, I am designing an I/O PCB and want to mix supply voltage (+24V) and signal I/O onto one Molex (36-pin) type header. I plan to use 12 pins (non-adjacent) for +24V/0V, these will power (2-3mA/device) 12ea prox-type (PNP) sensors. The lion's share of the load will be 6 pins (adjacent) for +24V/0V that will power 3 external 2A contactors; duty-cycle TBD.
The datasheet does not offer any current/thermal/loaded-pins graphs but the general current rating (per pin) is 3A. My research is telling me that rating connectors for current/thermal is very subjective in terms of the datasheet's current rating per pin. Current density, plating, exposure to open-air, PCB/plug conductor size, ambient air temp and the list goes on; all play into the over-all power/thermal rating of any connector.
That said, no one-size-fits-all and to provide all of the details and worst-case scenarios could be exhaustive and perhaps this type of question is too general for ESE. I spent a reasonable amount of time looking for some technical guide-lines for rating connectors but have yet to find a one-stop-shop in an effort to demonstrate and design in due-diligence.
Finally, here is my question. How do I rate/de-rate connectors for ampacity?