Michael,
A large percentage of the PCBs I design operate with high voltages somewhere
on them.
I design meet to UL standards for 1000Vdc and have no trouble with the
spacings involved with using FR-4 material.
I have seen FR-4 specified as having CTI values of 175 and up. I specify
that for our boards the material must have a CTI of > 200 and have not had a
problem.
Note however that as far as UL are concerned the clearance and creepage
required on your PCB will depend on its final use. You may need to track
down the UL standard appropriate to the equipment you are designing. As an
example, the PCBs I design are covered by UL508C (Power Conversion
Equipment) under which I need 5mm creepage at 1000Vdc in a Pollution Degree
2 environment. This can be figure can be reduced by the application of a
conformal coating if required. If I were designing PCBs for television sets
I would need to work to a different UL standard which would call for a
different set of spacings. Conforming to UL standards can be a nightmare
sometimes!
Good Luck
LINDEN DOYLE
Product Development Engineer
Zener Electric Pty Ltd
[EMAIL PROTECTED]
Ph: +61 2 9795 3600
Fax: +61 2 9795 3611
-----Original Message-----
From: Michael Biggs <[EMAIL PROTECTED]>
To: 'Protel EDA Forum' <[EMAIL PROTECTED]>
Date: Thursday, 16 May 2002 06:31
Subject: [PEDA] Materials Group from UL 840
>I have this question for anyone Please,
>I am referring from a UL standard chart for materials group tables related
>to the CTI performance level category values of insulation materials that
>are specified in the Standard for Polymetric Materials - Short Term
Property
>Evaluations, Ul 746A, to be included in the groups with a range of CTI
>values (eg. CTI >= 600 {PLC=0}, - 400< CTI < 600 {PLC =1 }, 175 <= CTI <
400
>{PLC = 2 or 3}, 100 <= CTI < 175 {PLC =4}).
>Note: PLC stands for Performance Level Category, and CTI stands for
>Comparative Tracking Index.
>
>Does anyone use this or require certain board material with CTI rating in
>order to achieve certain accepatble creepage distances especially when
using
>higher voltages?
>
>
>
>
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