From: Bernie McEwen-LBM022 <[email protected]> Subject: RE: TNV Transformer Spacings
Gert and Rich, Ferrite a non-conductor? - at about 50kR across a cube, ferrite is hardly a non-conductor. For creepage distance, the surface of ferrite must be treated as a conductor. In order for a barrier to be maintained across a transformer, the ferrite core must be designated to be on one side of the barrier; creepage distance and clearance must be maintained between the core and the windings on the other side. Rich is correct: if the ferrite core intrudes to reduce the air gap, or creepage distance to less than those specified in ...950, then the transformers aren't compliant. Send them back. Changing to a powder iron core will not worsen the situation. Ferrite is powdered iron loaded ceramic: FERR-ite Regards, Bernie McEwen > ---------- > From: [email protected][SMTP:[email protected]] on behalf of > [email protected]%INTERNET[SMTP:cetest#064#cetest.nl%[email protected] > .com] > Reply To: [email protected]%INTERNET > Sent: 26 February 1998 08:09 > To: '[email protected]' > Subject: RE: TNV Transformer Spacings > > 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] > >
