Derate connector voltage to 25% of rated operating voltage
.... Operating voltage = Connector rating / 0.25
Derate connector operational temperature by 50oC
.... Connector rating = operating temperature + 50oC
Current is normally specified as some number of pins carrying some specific amount of current, at some defined temperature. Normally the maximum current per pin ,or number of pins, is provided at ambient temperature. Increase the current carried over any particular pin and the number of pins carrying current must decrease. Decreasing the amount of current over the defined pins may allow more pins to carry current.
2mm Hard Metric Connector
The graph above shows the derating curves for a 2mm Hard Metric connector used in cPCI and other applications. In this case the graph provides three curves;
Red Curve allowing all pins to carry current [the lowest amount of current]
Blue Curve allowing every other pin to carry current.
Black Curve with only alternate pins on alternate rows carrying current.
So in this case every pin on the connector can carry current [Red], but each pin is limited to 1.6 amps, or about 1.4 amps at ambient temperature. However the black curve would normally be more realistic with only a quarter of the pins carrying current. Note that all three curves fall off at the same rate and end at a maximum temperature of 125C. However each curve starts with a different amount of maximum current at 0C based on the number of pins carrying current.
The maximum current is determined by the connector, the contacts and the size of wires attached to it. The maximum voltage of a connector depends on the spacing between contacts and insulating material used to secure the contacts in place. As in any system the maximum possible voltage decreases with increasing altitude, because arcing occurs over shorter gaps.
Refer to this page for a manufacturers listing for Connectors
Derating guidelines for other devices; Guideline for Derating Electronic Components
These are general engineering guidelines for connector derating. Of course connectors are produced in many different shapes and styles. Connectors that are produced for backplane standards have their maximum current rating defined within the interface standard, along with the associated pins that are defined to carry current, or power.
Connectors that are used in general applications, not controlled by a specification, have their maximum current defined by some number of pins. The difference being a design that does not use an interface standard may end up with more pins carrying current and exceeding the maximum rating of the connector. In addition, the connector may end up with all the pins carry power residing right next to each other. This causes the connector to have a hot spot which may exceed the temperature of the thermal plastic insulator holding the pins together.