John-
The only difference between BASIC and SUPPLEMENTARY insulation is a
thickness ("through-insulation") requirement. SUPPLEMENTARY insulation
must have a minimum through-insulation distance of 0.4mm. BASIC
insulation has no requirement for distance through insulation. (See
sub-clause 2.9.4.1 of UL1950.)
Dwight
--
DWIGHT HUNNICUTT
Sr. Compliance Engineer
****************************
* <[email protected]> *
* VINA Technologies,Inc. *
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John Honeycutt wrote:
>
> Joe,
> Thanks for your very understandable explanation.
> I have read the sections you described in UL1950_3, however I still don't
> have a clear understanding of the difference between "basic" and
> "supplementary" insulation.
> John
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of [email protected]
> Sent: Wednesday, October 14, 1998 10:06 AM
> To: [email protected]
> Subject: Re: Ground on Tip & Ring
>
> In a message dated 98-10-13, John Honeycutt writes:
>
> << It is unclear to me if connecting the midpoint of the series connected
> capacitors to the ground etch which connects to the PCB mounting bracket,
> which ultimately is attached to the computer chassis, violates safety in
> certain countries, i.e. Norway. >>
>
> John:
>
> If you connect the midpoint to chassis ground, your capacitors will bridge
> the
> safety isolation barrier. For equipment that is not permanently grounded
> (i.e., a typical PC), most countries require "basic" insulation per clause
> 6.2.1.2 of IEC 950. You can meet this requirement with a 1000 volt rms
> rated
> cap whose leads meet the creepage and clearance requirements.
>
> Norway and Sweden both require "supplementary" insulation, which imposes
> more
> stringent requirements. A conservative choice here would be to use a
> safety-
> rated Y1 cap, which IEC 950 specifically allows in clause 2.2.8.1 for
> bridging
> "reinforced" insulation. This would be overkill, but it would get the job
> done. Alternatively, I believe you could use a Y2 cap, which IEC 384-14
> defines as suitable for bridging supplementary insulation.
>
> Y1 and Y2 caps are readily available in through-hole, ceramic disk form with
> radial leads. They are used in almost all switching power supplies that
> connect to the AC power mains, to reduce emissions. The only vendor I know
> that makes a surface mount Y1 cap is Murata Erie.
>
> Joe Randolph
> Telecom Design Consultant
> Randolph Telecom, Inc.
> 781-721-2848
