[log in to unmask] wrote:

> can you please tell me how to figure the minimum allowable air gap on
> a PCB
> for any given voltage?
>
> thanks
>
> Howard Kaminsky
>
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   Depends on the product and what certification it needs but UL uses
the spacing recommended in IPC D 275, which for 110 VAC differences in
voltage is 62.5 mils minimum for conductors that are covered with
soldermask.  If you are switching a 110 volt hot line through a relay
there is no spacing limitation except what you are comfortable with, but
the hot to neutral and neutral to ground minimums is 62.5 mils for those
traces covered with solder mask.

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