EMI & Cat5

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anybody have any experience with cat6 and 440 volt power lines.  we've run
parallel to them for a while and everything works perfectly.  i thought you
werent supposed to do this?

smowk


Re: EMI & Cat5


Smowk wrote:

> anybody have any experience with cat6 and 440 volt power lines.  we've run
> parallel to them for a while and everything works perfectly.  i thought
> you werent supposed to do this?
>

It's a bad idea, because you can induce enough voltage in the wires, to
cause a hazard.  It generally won't bother the NICs though, as the
frequencies used to carry the data are well above those used for power and
they're also supposed to be able to withstand several hundred volts,
without creating a safety hazard.  Now if you were to touch the cat6
conductors, while also touching some grounded metal, you might see why
you're not supposed to do that.



Re: EMI & Cat5


>Smowk wrote:
>
>> anybody have any experience with cat6 and 440 volt power lines.  we've run
>> parallel to them for a while and everything works perfectly.  i thought
>> you werent supposed to do this?
>>
>
>It's a bad idea, because you can induce enough voltage in the wires, to
>cause a hazard.  It generally won't bother the NICs though, as the
>frequencies used to carry the data are well above those used for power and
>they're also supposed to be able to withstand several hundred volts,
>without creating a safety hazard.  Now if you were to touch the cat6
>conductors, while also touching some grounded metal, you might see why
>you're not supposed to do that.
>


How does anything get induced into the CAT5/5e/6 wire? The pairs are
twisted and carefully balanced to meet CATx specs and certification.
When CAT3 was new there was lots of discussion about EMI and if any
was found it was only in the most extreme situations. One way CAT5e
wire differs from CAT3 is carefull symetric twists, which cancel out
induced currents from external magnetic fields.

For that matter, for the OP, 440 volts is a "don't care" or even a
plus since it halves the amperage and it's amps, not volts that create
a magnetic field.  

IMO Follow construction codes and be happy.  

--

a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.


Re: EMI & Cat5


Al Dykes wrote:

> How does anything get induced into the CAT5/5e/6 wire? The pairs are
> twisted and carefully balanced to meet CATx specs and certification.
> When CAT3 was new there was lots of discussion about EMI and if any
> was found it was only in the most extreme situations. One way CAT5e
> wire differs from CAT3 is carefull symetric twists, which cancel out
> induced currents from external magnetic fields.
>
> For that matter, for the OP, 440 volts is a "don't care" or even a
> plus since it halves the amperage and it's amps, not volts that create
> a magnetic field.

There's both common mode and differential mode coupling.  Twisted pairs
reduce only the differntial mode coupling.  As for coupling, there's both
inductive and capacitive coupling between the power and lan cables.  There
will be some of both.



Re: EMI & Cat5


>Al Dykes wrote:
>
>> How does anything get induced into the CAT5/5e/6 wire? The pairs are
>> twisted and carefully balanced to meet CATx specs and certification.
>> When CAT3 was new there was lots of discussion about EMI and if any
>> was found it was only in the most extreme situations. One way CAT5e
>> wire differs from CAT3 is carefull symetric twists, which cancel out
>> induced currents from external magnetic fields.
>>
>> For that matter, for the OP, 440 volts is a "don't care" or even a
>> plus since it halves the amperage and it's amps, not volts that create
>> a magnetic field.
>
>There's both common mode and differential mode coupling.  Twisted pairs
>reduce only the differntial mode coupling.  As for coupling, there's both
>inductive and capacitive coupling between the power and lan cables.  There
>will be some of both.
>


Small amounts of common mode currents/volatges are blocked by the
transformers used to couple the cable to the circuity.

This document is interesting. (The text I've quoted is about 3/4 down)

My reading of the document says that in the normal home/office/light
manufacturing environment EMI is a non-issue with an ethernet plant
built to proper CAT5/5e spec and proper grounding of the hubs,
switches and computers.  The Allen-Bradley paper also addresses heavy
industry applications where I imagine the ground currents could make
common mode issues interesting.  

Shielded cable comes off worse than UTP.  

     http://www.ab.com/networks/enetpaper.html

     "Testing was performed on a system where the communications
     conductors (four-pair Ethernet cables) were placed in wire
     ladder-ways. These cables were placed along side conductors
     carrying 480 V drive-control voltages connecting the controller
     and a high-horsepower motor. The differential voltage coupled
     into the Ethernet cables varied, depending on the type of cable
     tested.

     The picture in Figure 12 shows the cable routing with respect to
     the drive conductors. Table 3 shows the differential voltages
     measured on the communications cables. The additional CMRR is
     referenced to the shielded cable. The shielded cable is used as a
     reference because this cable provides adequate performance in
     environmental testing for Ethernet modules.

     It is worth noting that there were no physical layer
     communications errors during this sequence of testing"
     [....]
     "The four-pair Ethernet cables were tightly strapped to the
     high-current secondary of the welding conductors and routed in
     close proximity to the weld tip. This setup provided both
     magnetic and radiated noises during the welding event. Figure 13
     shows the routing of the cables on the robot arm. A
     telecommunications analyzer was used to generate 100Mbit NRZ data
     that was sent to a pair of Fast Ethernet transceivers for
     encoding and decoding into MLT3 type data. The telecommunications
     analyzer provided bit-level error detection. The performance
     statistics were recorded for each of the five cables
     tested. Surprisingly, zero data errors were recorded for each of
     the five cables tested during the welding events."

--

a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.


Re: EMI & Cat5


Al Dykes wrote:

>>There's both common mode and differential mode coupling.  Twisted pairs
>>reduce only the differntial mode coupling.  As for coupling, there's both
>>inductive and capacitive coupling between the power and lan cables.  There
>>will be some of both.
>>
>
>
> Small amounts of common mode currents/volatges are blocked by the
> transformers used to couple the cable to the circuity.

I was thinking more of a safety hazard.  As I mentioned earlier,
interference to data is likely not an issue.  Still, it's a good idea to
maintain separation.



Re: EMI & Cat5


>Al Dykes wrote:
>
>>>There's both common mode and differential mode coupling.  Twisted pairs
>>>reduce only the differntial mode coupling.  As for coupling, there's both
>>>inductive and capacitive coupling between the power and lan cables.  There
>>>will be some of both.
>>>
>>
>>
>> Small amounts of common mode currents/volatges are blocked by the
>> transformers used to couple the cable to the circuity.
>
>I was thinking more of a safety hazard.  As I mentioned earlier,
>interference to data is likely not an issue.  Still, it's a good idea to
>maintain separation.
>


From a safety standpoint CAT5 is the same as any low voltage wiring
and if you install to local codes you'll be safe.  
--

a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.


Re: EMI & Cat5


> There's both common mode and differential mode coupling.
> Twisted pairs reduce only the differntial mode coupling.  As for
> coupling, there's both inductive and capacitive coupling between
> the power and lan cables.  There will be some of both.

Yes, but _some_ isn't necessarily significant or even noticable.

Voltage will drive capacitive coupling.  There are fractional
picofarads per meter in a twisted pair.  A foreign conductor
(inside another sheath) will haveseveral orders of magnitude less
capacative copling.  The twisting will make that coupling roughly
identical to each leg of the pair.  I wouldn't worry about less
than kV levels, and then first for safety.  I wouldn't be surprised
to hear of ethernet running fine parallel to clean 15 kV.

Current produces magnetic fields.  Voltage doesn't matter.  Changes
in magnetic fields induce current.  That makes transformers work
and AC preferred for power distribution.  But 60 Hz is way below
the sampling/detection frequency for ethernet so won't interfere
with anything.  On top of that, the twisting evens out induction.

-- Robert





Re: EMI & Cat5


Robert Redelmeier wrote:

> Current produces magnetic fields.  Voltage doesn't matter.  Changes
> in magnetic fields induce current.  That makes transformers work
> and AC preferred for power distribution.  But 60 Hz is way below
> the sampling/detection frequency for ethernet so won't interfere
> with anything.  On top of that, the twisting evens out induction.
>

If you go back, you'll find I mentioned that interference is not likely.  A
more real concern, is safety.  You cannot guarantee that insulation will
not fail.  You cannot guarantee that the power wiring is up to code with no
failures.  Therefore, the best policy is separation of data cables, from AC
power.  99 times out of a hundred, there'll likely be no problems, but
there's always that one time.




Re: EMI & Cat5



> Robert Redelmeier wrote:
>
> > Current produces magnetic fields. Voltage doesn't matter. Changes
> > in magnetic fields induce current. That makes transformers work
> > and AC preferred for power distribution. But 60 Hz is way below
> > the sampling/detection frequency for ethernet so won't interfere
> > with anything. On top of that, the twisting evens out induction.
> >
>
> If you go back, you'll find I mentioned that interference is not
likely.  A
> more real concern, is safety.  You cannot guarantee that insulation
will
> not fail.

Well, generally speaking that's why the power cables are often in EMT
metallic tubing or flex, which is grounded so that an insulation failure
won't cause shock hazard or fire.

> You cannot guarantee that the power wiring is up to code with no
> failures.  Therefore, the best policy is separation of data cables,
from AC
> power.  99 times out of a hundred, there'll likely be no problems, but
> there's always that one time.

Murphy's  Law.




Re: EMI & Cat5



> > Robert Redelmeier wrote:
> >
> > > Current produces magnetic fields. Voltage doesn't matter. Changes
> > > in magnetic fields induce current. That makes transformers work
> > > and AC preferred for power distribution. But 60 Hz is way below
> > > the sampling/detection frequency for ethernet so won't interfere
> > > with anything. On top of that, the twisting evens out induction.
> > >
> >
> > If you go back, you'll find I mentioned that interference is not
> likely.  A
> > more real concern, is safety.  You cannot guarantee that insulation
> will
> > not fail.
>
> Well, generally speaking that's why the power cables are often in EMT
> metallic tubing or flex, which is grounded so that an insulation failure
> won't cause shock hazard or fire.

Another way to take into account the concern that the wire insualtion
can fail it to use insulating conduit. For example in Finland many
builings you can find electrical tubing made of plastic material
and wires in them. I wire insulation fails, the tube still works
as insulation, so no fire or shock.


--
Tomi Engdahl (http://www.iki.fi/then /)
Take a look at my electronics web links and documents at
http://www.epanorama.net /


Re: EMI & Cat5



> Al Dykes wrote:
>
> > How does anything get induced into the CAT5/5e/6 wire? The pairs are
> > twisted and carefully balanced to meet CATx specs and certification.
> > When CAT3 was new there was lots of discussion about EMI and if any
> > was found it was only in the most extreme situations. One way CAT5e
> > wire differs from CAT3 is carefull symetric twists, which cancel out
> > induced currents from external magnetic fields.
> >
> > For that matter, for the OP, 440 volts is a "don't care" or even a
> > plus since it halves the amperage and it's amps, not volts that
create
> > a magnetic field.
>
> There's both common mode and differential mode coupling.  Twisted
pairs
> reduce only the differntial mode coupling.  As for coupling, there's
both
> inductive and capacitive coupling between the power and lan cables.
There
> will be some of both.

It's mostly inductive, because the signal cable isn't running in the
same conduit, but adjacent to the power lines, which in most cases are
shielded from the signal cable with a metal conduit.  If the conduit is
metallic, then there's no capacitive coupling, because the metallic
conduit is grounded.




Re: EMI & Cat5


>
>> Al Dykes wrote:
>>
>> > How does anything get induced into the CAT5/5e/6 wire? The pairs are
>> > twisted and carefully balanced to meet CATx specs and certification.
>> > When CAT3 was new there was lots of discussion about EMI and if any
>> > was found it was only in the most extreme situations. One way CAT5e
>> > wire differs from CAT3 is carefull symetric twists, which cancel out
>> > induced currents from external magnetic fields.
>> >
>> > For that matter, for the OP, 440 volts is a "don't care" or even a
>> > plus since it halves the amperage and it's amps, not volts that
>create
>> > a magnetic field.
>>
>> There's both common mode and differential mode coupling.  Twisted
>pairs
>> reduce only the differntial mode coupling.  As for coupling, there's
>both
>> inductive and capacitive coupling between the power and lan cables.
>There
>> will be some of both.
>
>It's mostly inductive, because the signal cable isn't running in the
>same conduit, but adjacent to the power lines, which in most cases are
>shielded from the signal cable with a metal conduit.  If the conduit is
>metallic, then there's no capacitive coupling, because the metallic
>conduit is grounded.
>
>


any won't _any_ metalic conduit attenuate an AC magnetic field by
induction and resistive loss?  I have no feel for what magnitude the
effect is.

--

a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.


Re: EMI & Cat5



> anybody have any experience with cat6 and 440 volt power lines.  we've
run
> parallel to them for a while and everything works perfectly.  i
thought you
> werent supposed to do this?

The reality is that some places limit you to running the
datacomm/telecomm cabling in the same raceway adjacent to high current
cables.  I should stress that the voltage is not as important as the
current because the coupling is mostly by electromagnetic induction, not
by electrostatic induction.

My main concern about running them side by side is not day-to-day
interference, but when high fault currents go thru the power cabling,
usually from lightning, possibly causing the induction of high currents
into the datacomm cabling, and possibly damaging the equipment at the
ends.

> smowk




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