[SI-LIST] Re: 48V power distribution
- From: steve weir <weirsp@xxxxxxxxxx>
- To: Murphy Jack-MGI2488 <jackmurphy@xxxxxxxxxxxx>, tcuratolo@xxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Tue, 19 Oct 2004 10:59:12 -0700
Jack, thanks. I will have to go back and look, but in the old days of 1950
we got a pass on the telecom equipment for SELV, and then with 1950A, my
understanding has been that the pass was revoked. I have carried that
impression around for the decade or so since 1950A came and went over a
decade ago. Now I will have to see if I have been laboring under a
misconception for a decade.
Regards,
Steve.
At 01:30 PM 10/19/2004 -0400, Murphy Jack-MGI2488 wrote:
>Steve,
>
>The low voltage safety limit is actually >60Vdc or >42.4Vpeak. Under
>those limits the circuit is considered SELV and spacings do not
>apply. For centralized DC power inputs, UL requires a 500Vac (707Vdc)
>hipot test between 48Vdc/RET and chassis to verify isolation. We make
>CO-type equipment powered via a -48Vdc centralized DC power source and we
>use UL60950-1 for Product Safety.
>
>A 48Vdc battery power system has a float up to 60Vdc which is still under
>the SELV limit.
>
>The National Electric Code has DC power source limitations (voltage vs
>current) that they classify Class 2 or 3. I'll admit that I'm not very
>familiar with the NEC.
>
>Jack Murphy
>SR Compliance Engineer
>Motorola BCS
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>On Behalf Of steve weir
>Sent: Tuesday, October 19, 2004 1:06 PM
>To: tcuratolo@xxxxxxxx; si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: 48V power distribution
>
>
>Tom, the biggest issue is that 48V exceeds the 42V low-voltage safety limit
>and so requires substantially greater clearances. A 24V system is under
>that limit and does not face the same problem. 48V also changes the
>dynamics of available semiconductors. 12V systems and to a certain extent,
>24V systems can leverage the super low on resistance and low capacitance
>FETs and diodes. The last issue is one of magnetics and practical
>form-factors. Given you work for Vicor, you should be pretty familiar with
>those and how taller primary to output ratios aggravate same.
>
>Regards,
>
>
>Steve
>At 02:04 PM 10/19/2004 +0000, tompegbel wrote:
>
> >Is there a good resource/document for addressing the concerns in
> >bussing 48V power in a multilayer board? The recently popular 12V or
> >lower intermediate bus approach has limitations as voltages get lower
> >and current gets higher. There appears to be new approaches of using a
> >higher bus voltage (24V or 48V) for distribution since this was
> >explored in the 80's with the advent of distributed power and now more
> >recently with VoIP type designs. Any assistance appreciated
> >
> >
> >
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