> From: Peter
> Sent: Wednesday, December 21, 2005 3:12 AM
>
> > You seem to put a lot of standard related issues here
> > for PCB design. I think it is nice to know this
> > kind of things in general for PCB design and for
> > electronics design in general.
> 
> Yes but I am trying to make up my mind on essential things like board 
> size and configuration (which cannot be changed later - as opposed to 
> the layout, which can). I.e. I want covering figures for 
> clearances and  so on so I can move things later if needed.
> 

I see and I think you are doing the right thing. Maybe to
get hold of some standards will help even though they
might not be cheap. I also guess that you might be in
the industrial automation field which needs to take
care of many standards.

If board space is not an issue then of course it 
is good to cover all the possible applicable standards. 
This may not be the case though. Even for the basics like
creepage distance and clearance, there are so many different 
standards. Typically my design follows EN50178/EN50020/UL508/UL840 
depending on the application and I think there are many more 
standards out there. There are also different interpretations
from the standard experts and the certification body 
(very similar: the lawyers and the judges might have different 
interpretations of the law) and it is sometimes quite
difficult to decide the correct things to do. ;-(

This is quite like EMC requirement. Different product
need to fulfill different standards. For us we need to
consider EN60947-5-2/EN61326/EN50295/EN61000-6-2/NAMUR NE21
depending on the product. It makes no sense to fulfill
NE21 (which is quite tough) if not necessary.

Regards,
Xiaofan
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