[SI-LIST] Re: HIGH DC Current on GND Plane

Yes, Telcordia's GR-63 Zone 4 is the most severe earthquake test.
That the rack failed is of no surprise: some test labs will re-use racks
(they are costly) and the normal failure mode is near the weld at the
bottom (the stress is quiet large).
The obvious solution is to use a Zone 4 rack (was your rated to Zone
4?).

As you said, I've been through some of these tests over the last 15
years: the configuration has to be typical, power/signal cables
included. I never witnessed a traffic hick-up (due to motion) unless
there was a major failure (keep in mind that it is an objective to be
functional during the test, a requirement to be functional before/after
the test).

P.S. Our box is rated @ 4 kW (120 A max).

Regards,=20
Naftali

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Bill Owsley
Sent: June 19, 2007 1:51 PM
To: kgrhoads@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: HIGH DC Current on GND Plane

This should be fun...
  I've got this piece of telecom gear with a 48VDC supply at about 130
amps that has to pass the most severe earthquake test, zone 4? (memory
skip there) and it's all cabled up to each of blades and out of test
area (nevermind why, customer wants it, I think for the video) and it
all has to function through the test.  The telecom passed, the rack
failed, for those that wonder.  So for those of us standing on a stable
reference plane - earth, the test bed endured some significant motional
effects.  Someone could contribute the max G's and displacements if they
like.
  There were no recorded errors from the electronics. =20
  But next time I'm going to hook up a couple more sensors to look for
this effect.
 =20
"Kevin G. Rhoads" <kgrhoads@xxxxxxxxxxxx> wrote:
 =20
>I have a midplane carrying 60Amps of current
> ...
>Is there anything else that can go wrong due to this DC , AC current=20
>mixing in planes ??

Most of the issues have already been addressed. However, there is one
case which can crop up here that has not been raised, so I will comment
on that.

1) V =3D d/dt(LI) normally L is constant, so only dI/dt is considered.
But with 60 amps you have a lot of I and large H,B fields can result.

2) at this point MOTIONAL effects are no longer trivially ignorable
as negligible. THey may not matter, but you can't dismiss them out
of hand. That is because motion can change the effective L (or M for
mutual inductance) and with large I small dL/dt can still give large
voltages. V=3D d(LI)/dt =3D L dI/dt + I dL/dt You need to get a
handle on dL/dt, which leads to:

3) what size is the board? Will it experience vibration? Any moving
parts nearby? If yes to vibration or motion -- how near? how fast?
Are the things moving conductors? (like cable bundles flapping in
the breeze or vibrating or flex couplings or ...)

HTH
Kevin
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