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Dear team
Section 33.4.1 (Isolation) refers to "frame ground"
and section 33.4.1.1.2 refers to "protective ground". Are these intended to be
the same thing? If so would it be best to use a single term? (I hope this
isn't opening a can of worms - the existing IEEE802.3 also uses both
terms...).
In 33.4.2 (Fault Tolerance), figure 33-14 includes
a node marked "PG" - presumably "protective ground". Is it appropriate to
define PG within Clause 33, or to refer to it? I see that it is defined
within Clause 14.3, but not apparently elsewhere within
IEEE802.3. Where PG is used in the existing clause 14.3 it is first
referred to in the text: "the ground for all common mode tests is circuit PG,
the Protective Ground for the AUI".
Figures 33-15, 33-16, 33-17 and 33-18 show a ground
or chassis symbol, but without the "PG" text, unlike Figure 33-14. Should the
text "PG" be added? "PG" seems to be present in corresponding Clause 14
figures.
Figure 33-17 uses a different symbol for the ground
or chassis node. Should this be the same symbol as for the other figures?
There are two instances of the ground symbols in
both figures 33-17 and 33-18 - should any inference be taken about whether
they are in fact connected together?
That's it - sorry to be a pedantic pain
again.
Actually, the reason I've been looking at this is
I'm trying to work out how to interconnect the RJ45 chassis ground,
the "ground" on the primary side of the PD PSU and the ground on the secondary
side of the PD PSU. It seems common practise to connect a high voltage cap from
the transformer CT to the RJ45 chassis ground, but what happens when the PD is
an a plastic box? Should the chassis ground connect by another capacitor
to the secondary side GND, as I see in some PHY reference designs?
Or by a low-resistance link? Or both? If anyone who understands
this can point me in the right direction I'd appreciate it (but not if you think
I'm just looking for free consultancy!!! Actually, I'm happy to pay a bit
to get this sorted...)
Regards -
Charles Palmer Technical Director, DSP Design Ltd
email: charles@xxxxxxxxxxxxx 7 Tapton Park Innovation Centre, Brimington Rd, Chesterfield S41 0TZ, UK ph: +44 (0) 1246 545 918 |