Hi Brian:
This does not answer your questions, but MAY give you an analysis tool:
CLEARANCE is standards name for AIR INSULATION.
CREEPAGE DISTANCE is standards name for DISTANCE ACROSS THE SURFACE OF SOLID
INSULATION.
Hope to meet you at the Symposium!
Best regards,
Rich
From: Brian Gregory [mailto:brian_greg...@netzero.net]
Sent: Friday, April 26, 2024 4:12 PM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: [PSES] Couple of loosely related safety questions
1. Clearances for US Safety:
I'd cite the relevant standards, but they are so alike (identical Clearance
tables), and so alike to UL 508, I'll defer. Here's the question:
When citing clearance spacing from "uninsulated live components" does one
measure from the edge of a PCB to the enclosure well, or only from the live
components, like a pad, or the bottom pin of a thru-hole cap?
1a. what sort of passivation or RTV could make those live components not
"uninsulated"?
2. Slots to increase creepage for high-voltage components
A FET that's rated for say 600V does not have to follow PCB-creepage rules
for 600V, is clearly stated places like UL 1741, ยง26.1.1 exception #8. For
other components, like say 1000V caps in 0805 packages or FET driver chips
the requirements aren't as clear. Is a slot needed to maintain creepage or
not if the component is properly rated? It does appear from a TI support
page for dual-bridge converters, that slots are recommended in order to
prevent contamination that may compromise the components isolation
performance.
My gut says: no, slots are not needed between component terminals on a PCB,
but could be recommended for sensitive parts, like FET drivers.
Thoughts?
Colorado Brian
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