Clearance concerns dielectric breakdown through air and is strongly influenced by peak voltage and transient (impulse) conditions. A 500 V pulse is still a 500 V peak stress. IEC 60664 specifically distinguishes working voltage, recurring peak voltage, and short-duration transient overvoltage, and clearances can be dimensioned against peak or withstand voltage.
Creepage means tracking along an insulating surface is affected by the duration of voltage stress, contamination, moisture, material CTI and material group. IEC 60664 explicitly lists time under voltage stress as one of the factors affecting creepage, and its conventional creepage tables are based on long-term RMS voltage stress. Between two inaccessible internal conductors, the pin-to-pin insulation may instead be functional insulation—provided that failure of that insulation does not create another hazard. That's the key issue. I suggest you employ a regulatory consultant or engage services of an NRTL to assess. Ralph From: Richard Nute <[email protected]> Sent: September 28, 2026 1:19 PM To: [email protected] Subject: Re: [PSES] Spacings Hi Steve: The connector should have electrical ratings, both voltage and current per pin. One question I have is the heating effect of running the same (rated) current per pin throughout the connector. – whether this construction is included in the ratings. Since the voltage (and current) are “secondary” circuits, transient voltages should be minimum or none. Therefore, spacings (both C&C) need only be for rated voltage, not for transient voltages. Hi-pot test is rated voltage plus some margin. (Maybe raise the hi-pot test voltage to breakdown to determine the margin.) Best regards, Rich Note: The IEEE is doing away with my [email protected] <mailto:[email protected]> e-mail forwarding address. My fall-back e-mail address is [email protected] <mailto:[email protected]> . From: Steve Brody <[email protected] <mailto:[email protected]> > Sent: Sunday, September 27, 2026 7:13 PM To: [email protected] <mailto:[email protected]> Subject: [PSES] Spacings Hi experts, I have a client who is using a cable with a 50 pin connector carrying 500VDC at 1 ms bursts to one pin at a time. 25 of the pins are ground, and the other 25 are used for the DC voltage. The odd number pins are used for the ground nd the even numbered pins are dc. There is another cable configured in the same manner, but this one has 300VDMS and ground. The AC is also for a short bursts of time but I don't know the timing. Does the fact that the voltages are not continuous reduce the C&C? Can a hypot test be used to confirm that there is not a problem even if the C&C are less than Appendix K? Both the AC and DC are derived from several circuits, but they come from an approved AC SMPS that will fold back should there be a short and then recover. None of the voltages are accessible. Thanks, Steve Brody [email protected] <mailto:[email protected]> C - 603 617 9116 _____ This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to [email protected] <mailto:[email protected]> All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/[email protected]/ <https://www.mail-archive.com/[email protected]/%20> Website: https://ewh.ieee.org/soc/pses/ <https://ewh.ieee.org/soc/pses/> Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) <https://ewh.ieee.org/soc/pses/list.html> List rules: https://pses.ieee.org/wp-content/uploads/2024/12/EM-PSTC-List-Rules.pdf For help, send mail to the list administrators: Mike Sherman at: [email protected] <mailto:[email protected]> Rick Linford at: [email protected] <mailto:[email protected]> For policy questions, send mail to: Jim Bacher at: [email protected] <mailto:[email protected]> _____ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC <https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1> &A=1 - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to [email protected] All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://pses.ieee.org/wp-content/uploads/2024/12/EM-PSTC-List-Rules.pdf For help, send mail to the list administrators: Mike Sherman at: [email protected] Rick Linford at: [email protected] For policy questions, send mail to: Jim Bacher: <[email protected]> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
