Hello Rich,

To my opinion ferrite powder cores must be treated as a non-conductor, not as 
an isolator. As creepage distances exist to prevent conducting and tracking by 
pollution between live parts and accessible conductors, I consider this is 
acceptable.
If some isolation function existed for the ferrite, or it would reduce a 
clearance, it would be not acceptable.

Make sure however that the ferrite is not replaced by an powder iron core, 
which is much more like a conductor. 

Gert Gremmen

CE-test, qualified testing, 
Consultant partner of Dutch PTT in analog PSTN  equipment.

Consultancy, Compliance tests for EMC and Electrical Safety
15 Great EMC-design tips available !
Visit our site  :  http://www.cetest.nl 



-----Oorspronkelijk bericht-----
Van:    [email protected] [SMTP:[email protected]]
Verzonden:      woensdag 25 februari 1998 23:48
Aan:    [email protected]
Onderwerp:      TNV Transformer Spacings

Hello All,

I received some transformer samples for a modem front end circuit that
are supposed to have been designed to UL1950 and IEC950 creepage
dimensions.  It appears that the spacings would be correct if the core
material was not considered. I believe this to be an oversight made by
the transformer designer.  

Is the ferrite core considered a conductive material? If so, do the
primary-secondary distances apply to each winding and the core material?

Thanks in advance, 

Rich Kalian
Aware, Inc. 
[email protected]


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