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adequate special guidelines for medical devices.
All values given here are valid for mated connectors, provided that they were terminated with adequate cable using correct procedures. Other standards recommend a calculation using the test voltage as a basis with the application of a safety factor. For example, the BS 9520 specification recommends setting the operating voltage at Test Voltage ÷ a Safety Factor of 3 for test voltages between 500V and 3kV and Test Voltage ÷ a Safety Factor of 1.5 for test voltages greater than or equal to 3kV, and similar recommendations are provided in the EIA-364-20 and former MIL-STD-1344 Method 3001 standards.
 A comparison of IEC 60664 and BS 9520/EIA-364-20 operating voltage methodologies.
This method takes the measured test voltage of the connector into account but does not consider the long- term environmental effects or the specific behavior of different insulator materials. As such, this methodology is generally recommended for connectors with low duty cycles (or “on-time”) and little exposure to environmental factors, like scientific instruments and some laboratory equipment.
There is no precise rule for selecting the best method for determining operating voltage. So, design engineers should carefully evaluate the application at hand, consider its operating conditions, and refer to any relevant safety standards.
4. Frequency Effects
Both operating voltage methods described above are valid for conventional DC or low-frequency AC conditions but, at higher frequencies, the physical characteristics of the insulating material can significantly affect connector performance. Additionally, since connectors aren’t isolated elements, it’s important for designers to evaluate the response of the entire system, including cables and other devices, in such critical situations.
At low frequencies, electrical charges on the surface of the insulator move according to their relative freedom of movement, so the duration of a cycle is sufficient enough to relax the local accumulated charges. At high frequencies (typically above the kilohertz range), the simultaneous displacement of these charges leads to the well-known corona effect or partial discharge, which accelerates breakdown.
High-frequency pulsed signals are particularly critical because they exhibit very high ∂u/∂t values. As such, no specific guidelines can be given to adapt operating voltage to these conditions. In all instances, they require individual testing. However, as a rule of thumb based on IEC 60664 data, one can safely estimate that derating down to 50% may be needed in critical kHz frequencies.

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