[SI-LIST] Re: gigabit ethernet trace length

This is technically correct but not practically correct. Safety
approvals have two parts -- one where you take a device, drawings, and
component specifications in to get an approval. The second is follow-up
services where the listing body representative visits the factory to
confirm that each instance of that design has the same characteristics
as the one which was tested in their labs. Since a PCB is not a listed
component there needs to be another way to prove isolation is sufficient
for that instance. This can be done in the factory with a high-pot test
for each PCB, but most manufacturers are not keen on this time and
expense.

The net result is that it is far easier to use the creepage and
clearance specifications for your class of device, separating SELV
circuits and planes from hazardous voltages.

BTW, Ethernet is considered hazardous since its wiring can go through
the same areas as AC, and a single fault could energize the line.

                                        Curt

Curt McNamara. P.E.=20
Senior Electrical Engineer=20
Logic Product Development=20
411 Washington Ave. N Suite 101=20
Minneapolis, MN 55401=20
Tel 612-436-5178=20
Fax 612-672-0443=20
curtm@xxxxxxxxxxx=20
www.logicpd.com=20
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Lee Ritchey
Sent: Tuesday, May 30, 2006 7:01 PM
To: Thompson, Gary D (Gary); Peterson, James F (FL51);
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: gigabit ethernet trace length


The 2KV isolation goal is easy to meet.  Just route the signals on layer
2 or below and you have it.  All common dielectrics used in PCBs have a
voltage rating of at least 1KV per mil of thickness.  Rarely is a
laminate layer between signal and plane less than 4 mils.  You can even
meet this goal on the surface by making sure that neighboring circuits
on the outer layers are at least 2 mm away.


> [Original Message]
> From: Thompson, Gary D \(Gary\) <Gary@xxxxxxxxx>
> To: Peterson, James F \(FL51\) <james.f.peterson@xxxxxxxxxxxxx>;
<si-list@xxxxxxxxxxxxx>
> Date: 5/30/2006 3:38:47 PM
> Subject: [SI-LIST] Re: gigabit ethernet trace length
>
> Just keep in mind that part of the Ethernet spec includes 2KV=20
> isolation (one of the reasons for the transformer, after all). If you=20
> can keep the isolation region in tact for 6-8", there's no reason it=20
> won't work.
>
>
>
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
=3D3D=3D
>
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
=3D3D=3D
> =3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
> Gary Thompson                        Phone: (512) 821-6521
> Systems/Applications Engineering       FAX: (512) 821-6810
> Agere Systems                       Mobile: (512) 751-8115
> Multi-Service Networking Division    Email: gary@xxxxxxxxx
>
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
=3D3D=3D
>
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
=3D3D=3D
> =3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx=20
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Lee Ritchey
> Sent: Tuesday, May 30, 2006 2:49 PM
> To: Peterson, James F (FL51); si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: gigabit ethernet trace length
>
>
> Not a problem, works just fine.  Don't know what might be behind the=20
> restriction someone put on you.
>
>
> > [Original Message]
> > From: Peterson, James F \(FL51\) <james.f.peterson@xxxxxxxxxxxxx>
> > To: <si-list@xxxxxxxxxxxxx>
> > Date: 5/30/2006 11:59:01 AM
> > Subject: [SI-LIST] gigabit ethernet trace length
> >
> > greetings,
> >
> > In a 1000BaseT Ethernet circuit, I would like to extend the=20
> > distance=3D20 between the magnetics and the RJ-45 connector to about =
6

> > to 8 inches=3D20 (including good SI practice : ref planes, =
controlled=20
> > Z, matched=3D20 lengths, etc.). Everything I read says that you =
can't=20
> > do that, that it
>
> > must be less than an inch, but I don't understand why. Can=20
> > someone=3D20 explain?
> >
> > thanks -
> > Jim Peterson
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