Re: [PSES] IEC 62368-1: clearance and creepage

2024-04-27 Thread Boštjan Glavič 
Hi John

After resistor you might have ES1 circuit and safety distances do not apply. 
However resistor need to comply with special requirements of Annex G.

See table 4 for ES1 limit for DC current. I think it is 2mA. You have to 
simulate short accross resistor unles resistor comply with searate requirements


Similar as limited current circuit in 60950-1.


I hope this helps.

Best regards
Bostjan Glavic
SIQ Ljubljana


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Od: John Woodgate 
Poslano: sobota, april 27, 2024 4:18:41 PM
Za: EMC-PSTC@LISTSERV.IEEE.ORG 
Zadeva: [PSES] IEC 62368-1: clearance and creepage

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It isn't clear to me whether the requirements of 5.4.2 and 5.4.3 (Edition 4) 
apply if the product remains safe with relevant clearances and creepages 
short-circuited (one at a time). The specific case is at a point fed by a 1 kV 
DC source behind two 4.7 megohm resistors in series. Please advise.


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Re: [PSES] Couple of loosely related safety questions

2024-04-27 Thread Ralph McDiarmid 
Brian, for a rigorous determination of creepage and of clearance you need to
also determine and assign:

 

1.  Over-voltage Category ( affects Clearance )
2.  Pollution Degree  ( micro-environment affecting Creepage )
3.  Basic (simple separation) or Reinforced (protective separation)
boundaries (if the end-product standard distinguishes)

 

If you can determine that slots are needed to increase a creepage path
because of physical constraints, then the minimum allowable width of that
slot needs to be determined.  

 

The application of std UL840 is permitted as an alternative for the
determination of spacings, with some strings attached to the end-product
standard ( e.g. UL1741 referencing UL840)

 

It’s a long and winding, foggy road to follow when determining minimum
spacings for an electronic assembly.  Isolation planning, assignment of
working voltages (RMS and peak) across isolation boundaries is usually a
good first step.  

 

Your MOSFET lead spacing doesn’t need to follow PCB rules, but the PCB does.
You may need to measure distance between PCB pads for the device and if then
decide if those pads might need slots between them.

 

Ralph

 

From: Brian Gregory  
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, §26.1.1 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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[PSES] IEC 62368-1: clearance and creepage

2024-04-27 Thread John Woodgate 
It isn't clear to me whether the requirements of 5.4.2 and 5.4.3 
(Edition 4) apply if the product remains safe with relevant clearances 
and creepages short-circuited (one at a time). The specific case is at a 
point fed by a 1 kV DC source behind two 4.7 megohm resistors in series. 
Please advise.



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John Woodgate, Rayleigh, Essex UK
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