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Clearance for PCB copper with >100V difference between them?

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treez

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Hi
The 6 PTH’s shown are for the secondary pins of a offline 180-265VAC flyback with NP/NS = 4:1. (Vout = 24V)
The 3 RHS holes are the secondary side switching node.

At 265VAC, these holes go 93V below secondary ground. The red copper pour surrounding the holes is top copper pour of the secondary +24V rail. In other words, there is a voltage of 117V peak between these PTH’s and the surrounding copper pour. The copper pour is only 0.3mm clear of the holes.

Do you agree that this is a violation of EN62368?
According to the following document, the clearance should be at least 0.6mm

https://www.alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf

What are your thoughts? Are there any “get out clause’s” here?
 

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G'day treez,

You really need to read, then re-read and read the standard again... The devil is in the detail. I've worked with 60950 which I'll hazard a guess 62368 likely incoporates.. You can't just refer to that document you suggest.. To conform to the relevant parts of 62368 you will need to verify your design against it. It will list the min creepage and clearances based on factors such as being a primary or secondary circuit, RMS vs peak voltages, over-voltages, altitude, the pollution level (sealed enclosure, vented, dust, humidity etc), and the insulation. I suggest you study the creepage and clearance distances within the spec. If it were a secondary circuit, you have a sufficiently low pollution degree and conformal coating with sufficient breakdown there may be a conformance path. However, you will need to determine this based on the use cases. I haven't got 62368 yet, but, 60950 has Annex G - Alternative Method for Determining Minimum Clearances which would be a good read by the sounds of things.

EDIT - Just found this:

EN62368-1 3rdedition will contain a refinement of the requirements for creepage and clearance including a new prescriptive option (Annex X which will be based on EN60950 tables). This is due to be published in Q3/4 2018

source: https://www.cieonline.co.uk/en62368-1-what-engineers-need-to-know/
 
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