Page 27 - ConnectorSupplier.com 2019 Mil/Aero eBook

Derating allows for test and specimen variations and is further required because the current-carrying capacity may be further limited by external factors, such as the size of the wire and the unequal distribution of loaded circuits. A derating curve is obtained by reducing the current values of the basic current-carrying curve by a factor of 0.8.
A derating curve derived from a basic current-carrying curve. The shaded area shows the allowable operating range.
However, the headline performance of a connector pin may not reveal the whole story. Take, for example, the CMM Micro connector range, which is designed to meet or exceed the electrical and mechanical performance requirements of IEC 60512-5-2 Test 5b, as well as older MIL-DTL-55302F and BS-9525-F0033 standards. CMM connector signal pins are nominally rated at 3A, while power pins are rated for up to 20A. However, their current- carrying capacity, which defines the maximum current that can pass through the pins without causing temperature elevation greater than 30°C for low-frequency (LF) signal contacts and 40°C for high-power (HP) contacts, depends on the number of contacts within any specific connector configuration.
Nicomatic’s modular CMM Micro connectors meet or exceed the electrical and mechanical performance requirements of IEC 60512-5-2 Test 5b, MIL-DTL-55302F, and BS-9525-F0033 standards and offer more than 20 million arrangements.
CMM testing performed in accordance with IEC 60512-5-2 Test 5b shows that the current-carrying curve flattens out at 3A for around 50 contacts, which is why 3A is quoted as the current limit for each signal pin even though, in truth, it’s more of a worst-case limitation. If a CMM connector configuration had fewer than 50 signal pins, then the current-carrying capability of each pin increased without exceeding the same 30°C temperature elevation. For
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