Cat5 and Power Cable

Cat5 and Power Cable

Post by Bob Sim » Sat, 14 Jun 2003 23:06:50



I want to run Cat5 for Ethernet near and parallel to power cable.  The
power cable is 277V 20A 60Hz for fluorescent lighting with "clean"
electronic ballasts.  The power cable is inside 1" metal conduit.  I
do not plan the put the Cat5 in conduit.

1) Will 100Mb Ethernet be impared by induced interference from the
power cable?
2) What about interference to gigabit Ethernet?
3) Is it important to tie down the Cat5 to make sure it does not touch
the conduit carrying power?

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Cat5 and Power Cable

Post by Glen Herrmannsfeld » Sun, 15 Jun 2003 03:26:24



Quote:> I want to run Cat5 for Ethernet near and parallel to power cable.  The
> power cable is 277V 20A 60Hz for fluorescent lighting with "clean"
> electronic ballasts.  The power cable is inside 1" metal conduit.  I
> do not plan the put the Cat5 in conduit.

> 1) Will 100Mb Ethernet be impared by induced interference from the
> power cable?
> 2) What about interference to gigabit Ethernet?
> 3) Is it important to tie down the Cat5 to make sure it does not touch
> the conduit carrying power?

UTP ethernet is fairly insensitive to such signals.  The ability to keep a
100MHz signal inside a twisted pair also keeps other differential mode
signals out.  Transformer coupling keeps common mode signals from bothering
the signal.   Gigabit may be a little more sensitive, but you shouldn't
notice that.

Metal conduit is very good at keeping signals apart.  Definitely don't run
cat5 inside the same conduit.  Though I would be surprised if it caused
problems, it is definitely against the electrical code in the US, and
probably other places.

There was a discussion once about putting a common mode 120V AC signal on a
UTP cable and testing its ability to run ethernet.  I never tried it,
though.  The transformers are supposed to be good to 500V or 1000V, so it
would probably work.

If you run an a factory full of arc welders (it was asked here before) you
might worry about this, otherwise you most likely don't need to.   I believe
tying to metal conduit is fine, unless that is against the electrical codes.
I know they make  raceway divided into two paritions, one for AC power
wiring, the other for network wiring.

-- glen

 
 
 

Cat5 and Power Cable

Post by Gary Breuckma » Tue, 17 Jun 2003 12:26:05




> I want to run Cat5 for Ethernet near and parallel to power cable.  The
> power cable is 277V 20A 60Hz for fluorescent lighting with "clean"
> electronic ballasts.  The power cable is inside 1" metal conduit.  I do
> not plan the put the Cat5 in conduit.

> 1) Will 100Mb Ethernet be impared by induced interference from the power
> cable?
> 2) What about interference to gigabit Ethernet? 3) Is it important to
> tie down the Cat5 to make sure it does not touch the conduit carrying
> power?

I do not think powerline noise will be a problem, however, when you
say "tie down" be sure not to ty-wrap the cable to anything tightly -
if you distort the cable (ie., flatten it, no longer round) you will
disrupt the characteristics of the cable.   The cable should be strung
through rings or other supports, or loose ty-wrap circles, not pulled
tight!

-- Gary Breuckman

 
 
 

Cat5 and Power Cable

Post by Bob Sim » Wed, 18 Jun 2003 00:30:01





<snip>
> > Is it important to tie down the Cat5 to make sure it does not touch the
> > conduit carrying power?

> I do not think powerline noise will be a problem, however, when you
> say "tie down" be sure not to ty-wrap the cable to anything tightly -
> if you distort the cable (ie., flatten it, no longer round) you will
> disrupt the characteristics of the cable.   The cable should be strung
> through rings or other supports, or loose ty-wrap circles, not pulled
> tight!

> -- Gary Breuckman

Gary (and Glen),
Thanks for the advice on Cat5 immunity from induced noise and also the
information about flattening it with tight ties.  While I had
envisioned simply laying my Cat5 cable on the support structure that
holds the conduit (unless I had to keep it away from the conduit), I
was not previously aware that overzealous tightening was deleterious.
Thanks again for the tip.
Bob Simon
 
 
 

Cat5 and Power Cable

Post by Glen Herrmannsfeld » Wed, 18 Jun 2003 03:22:13



(snip including suggestions about wire tie tightness)

Quote:> Thanks for the advice on Cat5 immunity from induced noise and also the
> information about flattening it with tight ties.  While I had
> envisioned simply laying my Cat5 cable on the support structure that
> holds the conduit (unless I had to keep it away from the conduit), I
> was not previously aware that overzealous tightening was deleterious.
> Thanks again for the tip.

Probably hand tightening is fine.  There is a tool that will make it really
tight and automatically cut off the excess.  They can get really tight.  The
cable impedance depends on the wire spacing in the pair.  Most cables just
have two wires twisted together.  There are some that have them actually
bonded together, sort of like a miniature zipcord (like household lamp
cord).  I think it takes a special tool to separate them to put the
connectors on, though.

-- glen

 
 
 

Cat5 and Power Cable

Post by Gary Breuckma » Mon, 30 Jun 2003 13:41:45


Quote:> Probably hand tightening is fine.  There is a tool that will make it
> really tight and automatically cut off the excess.  They can get really
> tight.  The cable impedance depends on the wire spacing in the pair.
> Most cables just have two wires twisted together.  There are some that
> have them actually bonded together, sort of like a miniature zipcord
> (like household lamp cord).  I think it takes a special tool to separate
> them to put the connectors on, though.

The CAT-5 ethernet cable is 4 twisted pairs, with two pairs really being
used here, one pair for transmit and one for receive.

If you ty-wrap the cables too tightly, you change the relative spacing
between the pairs, and can increase the cross-talk between them
as well as other characteristics.   It's especially important at the two
ends, where the transmit levels are highest and the receive levels the
lowest, and that's unfortunately where they tend to get ty-wrapped
the most   :(

-- Gary Breuckman

 
 
 

1. Cat5 and Power Cable

I want to run Cat5 for Ethernet near and parallel to power cable.  The
power cable is 277V 20A 60Hz for fluorescent lighting with "clean"
electronic ballasts.  The power cable is inside 1" metal conduit.  I
do not plan the put the Cat5 in conduit.

1) Will 100Mb Ethernet be impared by induced interference from the
power cable?
2) What about interference to gigabit Ethernet?
3) Is it important to tie down the Cat5 to make sure it does not touch
the conduit carrying power?

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