RE: Static Discharge
Lary,
Thanks for the information. Using the clamp device is what I have meant in
the 2nd option, and using bleeding resistor is good only for on-going
charges accumulation.
You are right that the case of applying already charged cable with high
voltage across it is much sever and potentialy
distructive case if not handled correctly.
Yair.
> -----Original Message-----
> From: Larry Miller [SMTP:ldmiller@xxxxxxxxxxxxxxxxxx]
> Sent: &bet; &samekh;&pe;&tet;&mem;&bet;&resh; 18 2000 16:02
> To: Yair Darshan; 'Dieter Knollman'; stds-802-3-pwrviamdi@xxxxxxxx
> Subject: RE: Static Discharge
>
> Unfortunately, that does not work.
>
> The problem is not that of a connected cable charging up, but that of
> having a pre-charged cable (with no built-in resistors) suddenly being
> plugged into the RJ-45 connector.
>
> What you get is a sub-nanosecond rise time pulse with several hundred
> millijoules of stored energy. This pulse is coming from a resonant cable
> so what you see is an exponentially decaying damped oscillatory discharge.
> 5 kV on a 25-foot cable, 700 to 900 V on a 100-m cable.
>
> If you are lucky, both connector pins mate at the same time and you get
> the common-mode rejection of the magnetics helping you by not passing some
> of this through to the PHYs. A worse case is if only one pin of a pair
> mates, and you get differential transfer through the magnetics.
>
> We (and PHY vendors here) have seen as much as 60 volts appear on the PHY
> pins.
>
> In any case a bleeder resistor that would absorb this would have to be
> such a low value that it would interfere with normal signals. We have had
> good luck with diode clamping networks that have a dynamic (clamping)
> impedance on the order of 1 ohm.
>
> This is, fortunately, a comparatively rare phenomenon that usually only
> occurs when a cable is being plugged in in a new installation. Careful
> network installers would make sure that they discharged all cables BEFORE
> plugging them in, dont'cha fellas?
>
> We have had a few Environments from Hell where a dry climate, combined
> with moving belts on assembly lines (opportunistic Van der Graaf
> generators!), have caused constant, repetitive failures. You know who you
> are out there....(grin)
>
> Larry
>
> -----Original Message-----
> From: Yair Darshan [SMTP:YairD@xxxxxxxxxxxxxx]
> Sent: Saturday, September 16, 2000 2:41 PM
> To: 'Dieter Knollman'; stds-802-3-pwrviamdi@xxxxxxxx
> Subject: RE: Static Discharge
>
>
> The 2kv cap is not suppose to leak.
>
> Assuming that the energy level develops on low capacitance value
> (few
> nano-farads), than a "bleed" resistor located between the positive and the
>
> negative feeding lines of 10 to 100K can discharge it (lower value -
> better
> results).
>
> Better way is to clamp the voltage developed from excessive charges
> by using
> low impedance path that activated at a certain voltage that fits
> the system requirements at normal working conditions.
>
> Yair.
>
>
>
> Darshan Yair
> Chief R&D Engineer
> > PowerDsine Ltd. - Powering Converged Networks
> > 1 Hanagar St., P.O. Box 7220
> > Neve Ne'eman Industrial Zone
> > Hod Hasharon 45421, Israel
> Tel: +972-9-775-5100, Cell: +972-54-893019
> Fax: +972-9-775-5111
> > E-mail: < <mailto:yaird@xxxxxxxxxxxxxx>>.
> > <http://www.powerdsine.com>
> >
>
>
>
>
> > -----Original Message-----
> > From: Dieter Knollman [SMTP:djhk@xxxxxxxxxx]
> > Sent: a, noeiao 15, 2000 6:53 PM
> > To: stds-802-3-pwrviamdi@xxxxxxxx
> > Subject: Static Discharge
> >
> >
> > Hi,
> >
> > My background is telephony. I'm totally new to 802.3, so please excuse
> > my ignorance.
> > One thing that appears strange is the lack of an intentional discharge
> > path for the potential on the cable.
> > The only means that I have found is breakdown of the common mode
> > termination capacitors.
> > Are these caps with 2 kV rating intended to be leaky?
> >
> > On POTS line interfaces the Tip lead is typically biased around ground
> > and serves as a discharge path to earth ground for Analog Sets. Do the
> > IP Phones require a discharge path via the LAN?
> >
> > Dieter Knollman
> > DMTS
> > Lucent
> > djhk@xxxxxxxxxx
> >
>