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Components in parallel to creepage\clearance
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Components in parallel to creepage\clearance
Components in parallel to creepage\clearance
Components in parallel to creepage\clearance
Components in parallel to creepage\clearance
Components in parallel to creepage\clearance
Components in parallel to creepage\clearance
Components in parallel to creepage\clearance
Components in parallel to creepage\clearance
Components in parallel to creepage\clearance
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creepage distance, iec 60601 - medical electrical equipment, medical device electronics and electrical equipment, mop (means of protection)
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  Post Number #9  
Old 13th February 2018, 09:22 PM
rothlis

 
 
Total Posts: 29
Re: Components in parallel to creepage\clearance

Quote:
theoretically, you can't use 4.5 because it uses the requirement in the standard as a point of reference (the alternate solution has to be "comparable"), so if the requirement is illogical, you are back to square one.
As I read it, clause 4.5 says only that the residual risk needs to be comparable. That seems easily achievable in this case since a design which strictly complies with the standard and one which simply uses the component as intended are going to have effectively identical risk profiles.

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  Post Number #10  
Old 13th February 2018, 10:00 PM
Peter Selvey

 
 
Total Posts: 894
Re: Components in parallel to creepage\clearance

Of course it's up to the individual engineer how you want to write it up.

My worry would be that a reviewer would see it this way:

- standard says 500Vdc dielectric is needed for every part (1 MOP)
- manufacturer claims a 25V transistor rating is equivalent (1 MOP)

Clearly, the probability of failure is vastly different between these two solutions, perhaps the 25V rating is 1000 times more likely to fail than a part that can handle 500V. They are not comparable.

So why is 25V rating acceptable? The answer comes from considering the overall probability and severity of harm. In that view, both solutions result in negligible risk. The 500V option is a orders of magnitude better, but both solutions have tiny risk that we can call it negligible, and hence comparable.

But it seem unfair to force manufacturers to do this kind of analysis every time there is an obvious mistake in the standard. Keep in mind 4.5 says "scientific data" and "comparative studies". It's not walk in the park. And there is a risk that upstream reviewers might not understand the negligible concept or the rationale why the standard is wrong.
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