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Default NEC question: low-voltage wiring crossing 120v wiring.

I am running network cables -- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.

Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?

Perce
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Thu, 29 Sep 2011 15:19:42 -0400, "Percival P. Cassidy"
wrote:

I am running network cables -- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.

Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?

Perce

no issue even with cat5 or cat5e non sheilded - as long as your space
above the ceiling is not an air plenum - and then you just need plenum
rated cat5
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sep 29, 5:30*pm, wrote:
On Thu, 29 Sep 2011 15:19:42 -0400, "Percival P. Cassidy"

wrote:
I am running network cables *-- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.


Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?



*no issue even with cat5 or cat5e non sheilded - as long as your space
above the ceiling is not an air plenum - and then you just need plenum
rated cat5


What's the reasoning behind plenum rating a computer cable? Is there
some fire-reasoning behind it or what? What's the difference between
rated and non-rated cable?

R
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Thu, 29 Sep 2011 17:07:32 -0700 (PDT), RicodJour
wrote:

On Sep 29, 5:30Â*pm, wrote:
On Thu, 29 Sep 2011 15:19:42 -0400, "Percival P. Cassidy"

wrote:
I am running network cables Â*-- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.


Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?



Â*no issue even with cat5 or cat5e non sheilded - as long as your space
above the ceiling is not an air plenum - and then you just need plenum
rated cat5


What's the reasoning behind plenum rating a computer cable? Is there
some fire-reasoning behind it or what? What's the difference between
rated and non-rated cable?

R

Fire rating. Plenum cable will not support combustion when flame is
removed - will not flame on it's own - and different smoke. Non-plenum
rated is not allowed in an air return.
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Default NEC question: low-voltage wiring crossing 120v wiring.

On 9/29/2011 2:19 PM, Percival P. Cassidy wrote:
I am running network cables -- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.

Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?

Perce


the only thing they taught us to avoid is running parallel to high
current cables. But if you're using shielded cable, even that shouldn't
matter. And i don't imagine any cable in a house to be high current
except the range line and the line to the a/c unit. Lay away!

--
Steve Barker
remove the "not" from my address to email


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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sep 29, 8:07*pm, RicodJour wrote:
On Sep 29, 5:30*pm, wrote:





On Thu, 29 Sep 2011 15:19:42 -0400, "Percival P. Cassidy"


wrote:
I am running network cables *-- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.


Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?


*no issue even with cat5 or cat5e non sheilded - as long as your space
above the ceiling is not an air plenum - and then you just need plenum
rated cat5


What's the reasoning behind plenum rating a computer cable? *Is there
some fire-reasoning behind it or what? *What's the difference between
rated and non-rated cable?

R- Hide quoted text -

- Show quoted text -


If it's a plenum that means something is pumping air through it to the
rest of the building. Can you think of a better way to speed
combustion and spread smoke he asked rhetorically?
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Default NEC question: low-voltage wiring crossing 120v wiring.


"RicodJour" wrote in message
...
On Sep 29, 5:30 pm, wrote:
On Thu, 29 Sep 2011 15:19:42 -0400, "Percival P. Cassidy"

wrote:
I am running network cables -- shielded, if that makes a
difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.


Is it OK for the network cables to lie on the ceiling support
members,
and thus beneath the Romex? Or should the network cables be above
the
Romex? Or should one or both be in conduit? -- more precisely,
should
what is now Romex be redone with individual conductors in conduit?



no issue even with cat5 or cat5e non sheilded - as long as your
space
above the ceiling is not an air plenum - and then you just need
plenum
rated cat5


[What's the reasoning behind plenum rating a computer cable? Is there
some fire-reasoning behind it or what? What's the difference between
rated and non-rated cable?]

Some wire (non plenum rated), when it burns in a fire, will put off
toxic smoke. You wouldn't want toxic smoke to be sent through all the
air ducts!

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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sep 29, 5:30*pm, wrote:
On Thu, 29 Sep 2011 15:19:42 -0400, "Percival P. Cassidy"

wrote:
I am running network cables *-- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.


Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?


Perce


*no issue even with cat5 or cat5e non sheilded - as long as your space
above the ceiling is not an air plenum - and then you just need plenum
rated cat5


If there is romex there already, then let's hope it isn't plenum
space.

Only in commercial buildings would I expect space above suspended
ceilings to be used as air plenum (return air is drawn through it on
its way back to the hvac system), and commercial building code
anywhere in N.America requires power conductors to be in conduit or
armored cable, and data cabling to be in either conduit (in which
case, it might not need to be plenum rated) or a cable tray, the
better to prevent it from collapsing into the space during a fire,
blocking egress and creating a hazard for firefighters. At least
that's how it was explained to me.

Single-family residential code doesn't say anything about low-voltage
cabling except that you can't put it in the same boxes as 120V.

Having said that, I think laying it onto the suspended ceiling, as I
understand the OP is proposing, is going to be a pain whenever someone
wants to lift a panel. I'd find some clips to tack it to the joists.

I wouldn't expect simple romex runs to be an interference problem for
data communications. Fluorescent ballasts, light dimmers, fan speed
controls and any kind of motor or switching power supply, maybe.

Chip C
Toronto
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sep 29, 10:43*pm, wrote:
On Thu, 29 Sep 2011 17:07:32 -0700 (PDT), RicodJour









wrote:
On Sep 29, 5:30*pm, wrote:
On Thu, 29 Sep 2011 15:19:42 -0400, "Percival P. Cassidy"


wrote:
I am running network cables *-- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.


Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?


*no issue even with cat5 or cat5e non sheilded - as long as your space
above the ceiling is not an air plenum - and then you just need plenum
rated cat5


What's the reasoning behind plenum rating a computer cable? *Is there
some fire-reasoning behind it or what? *What's the difference between
rated and non-rated cable?


R


Fire rating. Plenum cable will not support combustion when flame is
removed - will not flame on it's own - and different smoke. Non-plenum
rated is not allowed in an air return.


Yes, but my question was whether the OP's above-ceiling space is
actually a plenum. I had assumed the question was residential, a
basement and the space was not used for airflow. Granted, that's
reading a lot into it, but perhaps they were bad assumptions.

Here are some interesting (but boring!) videos of the different cable
ratings burning.
http://www.l-com.com/multimedia/vide....aspx?ID=13100
Quite a difference between plain vanilla PVC and rated cable.

R
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Default NEC question: low-voltage wiring crossing 120v wiring.

On 09/30/11 11:23 am, RicodJour wrote:

I am running network cables -- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.


Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?


no issue even with cat5 or cat5e non sheilded - as long as your space
above the ceiling is not an air plenum - and then you just need plenum
rated cat5


What's the reasoning behind plenum rating a computer cable? Is there
some fire-reasoning behind it or what? What's the difference between
rated and non-rated cable?


Fire rating. Plenum cable will not support combustion when flame is
removed - will not flame on it's own - and different smoke. Non-plenum
rated is not allowed in an air return.


Yes, but my question was whether the OP's above-ceiling space is
actually a plenum. I had assumed the question was residential, a
basement and the space was not used for airflow. Granted, that's
reading a lot into it, but perhaps they were bad assumptions.

Here are some interesting (but boring!) videos of the different cable
ratings burning.
http://www.l-com.com/multimedia/vide....aspx?ID=13100
Quite a difference between plain vanilla PVC and rated cable.


You are correct: this is a residential setting, with a suspended ceiling
installed in the basement.

Perce



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Default NEC question: low-voltage wiring crossing 120v wiring.

responding to
http://www.homeownershub.com/mainten...ng-664640-.htm
DA wrote:
Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit?


Are you concerned with EMI (electromagnetic interference) or fire safety?

For fire safety NEC wants you to stay 6+ inches away from the power cables
and that should also be far enough for EMI to be negligible. That shield
on the network cables is absolutely unnecessary in a residential home, but
since you already go it, do not ground it on either end. I presume you
won't be able to ground it correctly at the outlet end anyhow, so just let
it float. It'll be useless as an EMI shield (which you don't need anyway)
but might prevent some kinking and cinching.

However, if you can return the cable, I would strongly advise to do so and
get a smaller diameter UTP - you'll be able to pull more cables through
the same size hole and that will come handy during the install. In a home
made of essentially wooden sticks (often times "engineered wooden sticks")
you don't want to make holes bigger than absolutely necessary.

It may be a moot point in a wooden home, but I would always locate low
voltage cables below high voltage power. If cables are the cause of the
fire, it would always be the power ones, not low-voltage, and the fire
would want to go up. The less burning material above it the better. But
again, would probably make little difference if everything around is wood.

Good luck!

-------------------------------------
/\_/\
((@v@)) NIGHT
()::) OWL
VV-VV



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Default NEC question: low-voltage wiring crossing 120v wiring.

On 09/30/11 12:58 pm, DA wrote:

Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit?


Are you concerned with EMI (electromagnetic interference) or fire safety?


My question was about the NEC, which is concerned with fire safety.

For fire safety NEC wants you to stay 6+ inches away from the power cables
and that should also be far enough for EMI to be negligible. That shield
on the network cables is absolutely unnecessary in a residential home, but
since you already go it, do not ground it on either end. I presume you
won't be able to ground it correctly at the outlet end anyhow, so just let
it float. It'll be useless as an EMI shield (which you don't need anyway)
but might prevent some kinking and cinching.


The shield is to eliminate interference to my amateur radio station.
This was a problem with unshielded cables.

However, if you can return the cable, I would strongly advise to do so and
get a smaller diameter UTP - you'll be able to pull more cables through
the same size hole and that will come handy during the install. In a home
made of essentially wooden sticks (often times "engineered wooden sticks")
you don't want to make holes bigger than absolutely necessary.


No holes have to be drilled: the network cables pass over the tops of
the partition walls.

Perce
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Fri, 30 Sep 2011 11:36:06 -0400, "Percival P. Cassidy"
wrote:

On 09/30/11 11:23 am, RicodJour wrote:

I am running network cables -- shielded, if that makes a difference --
above suspended ceiling where there is already 120V Romex wiring in
places. This 120V wiring is stapled to the joists at intervals.

Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit? -- more precisely, should
what is now Romex be redone with individual conductors in conduit?

no issue even with cat5 or cat5e non sheilded - as long as your space
above the ceiling is not an air plenum - and then you just need plenum
rated cat5

What's the reasoning behind plenum rating a computer cable? Is there
some fire-reasoning behind it or what? What's the difference between
rated and non-rated cable?


Fire rating. Plenum cable will not support combustion when flame is
removed - will not flame on it's own - and different smoke. Non-plenum
rated is not allowed in an air return.


Yes, but my question was whether the OP's above-ceiling space is
actually a plenum. I had assumed the question was residential, a
basement and the space was not used for airflow. Granted, that's
reading a lot into it, but perhaps they were bad assumptions.

Here are some interesting (but boring!) videos of the different cable
ratings burning.
http://www.l-com.com/multimedia/vide....aspx?ID=13100
Quite a difference between plain vanilla PVC and rated cable.


You are correct: this is a residential setting, with a suspended ceiling
installed in the basement.

Perce

But we still don't know how the cold air returns work. If the cold air
return just dumps into the ceiling, and the ceiling is open to the
furnace room - and the furnace drawr return air from the furnace room
- it's a plenum. Ditto if the cold air return had an opening into the
basement, which is now semi-blocked by the dropped ceiling, so it is
drawing return air from above the ceiling. Neither is a proper approch
- but I've seen stranger!!!
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sep 30, 12:58*pm, DA wrote:
responding tohttp://www.homeownershub.com/maintenance/NEC-question-low-voltage-wir...

DA wrote:
Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit?


Are you concerned with EMI (electromagnetic interference) or fire safety?

For fire safety NEC wants you to stay 6+ inches away from the power cables


You have a cite for that? In addition to not believing it, it's hard
to see what difference 6 inches is going to make. I
regularly see low voltage cables of all kinds stapled near
Romex.





and that should also be far enough for EMI to be negligible. That shield
on the network cables is absolutely unnecessary in a residential home,


but
since you already go it, do not ground it on either end. I presume you
won't be able to ground it correctly at the outlet end anyhow, so just let
it float. It'll be useless as an EMI shield (which you don't need anyway)


Says who? A Farraday cage is a Farraday cage
whether it's grounded or not.



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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sat, 1 Oct 2011 07:42:27 -0700 (PDT), "
wrote:

On Sep 30, 12:58Â*pm, DA wrote:
responding tohttp://www.homeownershub.com/maintenance/NEC-question-low-voltage-wir...

DA wrote:
Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit?


Are you concerned with EMI (electromagnetic interference) or fire safety?

For fire safety NEC wants you to stay 6+ inches away from the power cables


You have a cite for that? In addition to not believing it, it's hard
to see what difference 6 inches is going to make. I
regularly see low voltage cables of all kinds stapled near
Romex.





and that should also be far enough for EMI to be negligible. That shield
on the network cables is absolutely unnecessary in a residential home,


but
since you already go it, do not ground it on either end. I presume you
won't be able to ground it correctly at the outlet end anyhow, so just let
it float. It'll be useless as an EMI shield (which you don't need anyway)


Says who? A Farraday cage is a Farraday cage
whether it's grounded or not.

My experience has been an ungrounded sheild just becomes an antennaa




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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sat, 01 Oct 2011 11:56:49 -0400, wrote:

On Sat, 1 Oct 2011 07:42:27 -0700 (PDT), "
wrote:

On Sep 30, 12:58*pm, DA wrote:
responding tohttp://www.homeownershub.com/maintenance/NEC-question-low-voltage-wir...

DA wrote:
Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit?

Are you concerned with EMI (electromagnetic interference) or fire safety?

For fire safety NEC wants you to stay 6+ inches away from the power cables


You have a cite for that? In addition to not believing it, it's hard
to see what difference 6 inches is going to make. I
regularly see low voltage cables of all kinds stapled near
Romex.





and that should also be far enough for EMI to be negligible. That shield
on the network cables is absolutely unnecessary in a residential home,


but
since you already go it, do not ground it on either end. I presume you
won't be able to ground it correctly at the outlet end anyhow, so just let
it float. It'll be useless as an EMI shield (which you don't need anyway)


Says who? A Farraday cage is a Farraday cage
whether it's grounded or not.

My experience has been an ungrounded sheild just becomes an antennaa


It can, if the equipment is junk. It can also be a rather nasty current path
if the "local grounds" aren't.
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sat, 01 Oct 2011 15:54:57 -0400, wrote:

On Sat, 01 Oct 2011 12:00:27 -0500, "
wrote:

Says who? A Farraday cage is a Farraday cage
whether it's grounded or not.

My experience has been an ungrounded sheild just becomes an antennaa


It can, if the equipment is junk. It can also be a rather nasty current path
if the "local grounds" aren't.


That is why you only ground one end. You are not providing a current
path, just a drain for whatever transients the shield would catch.


Prezactly.

In the case of data cabling, STP is really pretty rare and they do
very well running gigabit ethernet over UTP. Most of it is just that
they are a lot better at noise rejection in the adapter itself. The
idea that anything generated in a 20a Romex running next to a CAT-5 is
going to spike an ethernet adapter is ludicrous.


STP is used if the hardware is dirty. Over the last few decades, LAN hardware
has been cleaned up to where it's not needed. STP helps the "antenna
problem", above, but it shouldn't be needed anywhere.

When I was in the cabling biz at IBM I set un an experiment with CAT-3
trying to break an Ethermet or a Token Ring LAN doing every urban
legend bad thing anyone could think of (loops of cable over
fluorescent ballasts, running next to 480v 1600a feeders, taped to the
raceway, telephone in the same cable, exceeding the 300' rule, etc)
Basically I couldn't break it.


10-baseT, 4/16MB T/R only?

What did have an effect, kinks in the cable, sloppy terminations and
driving a staple through the cable. Those were handy for the second
phase of the experiment, finding bugs doing TDR with a scope.


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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sat, 01 Oct 2011 19:59:33 -0400, wrote:

On Sat, 01 Oct 2011 17:21:18 -0500, "
wrote:

When I was in the cabling biz at IBM I set un an experiment with CAT-3
trying to break an Ethermet or a Token Ring LAN doing every urban
legend bad thing anyone could think of (loops of cable over
fluorescent ballasts, running next to 480v 1600a feeders, taped to the
raceway, telephone in the same cable, exceeding the 300' rule, etc)
Basically I couldn't break it.


10-baseT, 4/16MB T/R only?


The original installation was 16mb TR but we also tried 10/100
Ethernet and it ran clean at 100 mb doing big file transfers and
looking at the logs. For the "over length" test I hooked the kludge we
had up to a new 300' spool so we had that plus the other hundred foot
baseband cable we were playing with and whatever was in the rack,
cables etc.


I'm somewhat surprised 100BaseT worked over CAT-3.

The whole thing got started when someone said we were having problems
because the router (in a rack) was backed up to the equipment room
wall where they had that 1600a service.

The router was bad.


Hate it when that happens.

I hooked up the spool, just for playing with TDR to get a little more
time down the wire but I had to try it. ;-)


TDRs are great tools. Too bad they're so rare (I suppose the people who know
how to use one are even more rare).
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sat, 01 Oct 2011 19:59:33 -0400, wrote:

On Sat, 01 Oct 2011 17:21:18 -0500, "
wrote:

When I was in the cabling biz at IBM I set un an experiment with CAT-3
trying to break an Ethermet or a Token Ring LAN doing every urban
legend bad thing anyone could think of (loops of cable over
fluorescent ballasts, running next to 480v 1600a feeders, taped to the
raceway, telephone in the same cable, exceeding the 300' rule, etc)
Basically I couldn't break it.


10-baseT, 4/16MB T/R only?


The original installation was 16mb TR but we also tried 10/100
Ethernet and it ran clean at 100 mb doing big file transfers and
looking at the logs. For the "over length" test I hooked the kludge we
had up to a new 300' spool so we had that plus the other hundred foot
baseband cable we were playing with and whatever was in the rack,
cables etc.

The whole thing got started when someone said we were having problems
because the router (in a rack) was backed up to the equipment room
wall where they had that 1600a service.

The router was bad.

I hooked up the spool, just for playing with TDR to get a little more
time down the wire but I had to try it. ;-)

twisted pair is MUCH more forgiving than co-ax. Had a network set up
with co-ax and the system was SLOW and unreliable. Found all sorts of
25-50 foot cables coiled up under desks where 5-10 feet would have
been more than adequate. When I talked the customer into using
"appropriate" lengths, the system came to life.
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sat, 01 Oct 2011 21:14:12 -0400, wrote:

On Sat, 01 Oct 2011 19:26:46 -0500, "
wrote:

On Sat, 01 Oct 2011 19:59:33 -0400,
wrote:

On Sat, 01 Oct 2011 17:21:18 -0500, "
wrote:

When I was in the cabling biz at IBM I set un an experiment with CAT-3
trying to break an Ethermet or a Token Ring LAN doing every urban
legend bad thing anyone could think of (loops of cable over
fluorescent ballasts, running next to 480v 1600a feeders, taped to the
raceway, telephone in the same cable, exceeding the 300' rule, etc)
Basically I couldn't break it.

10-baseT, 4/16MB T/R only?

The original installation was 16mb TR but we also tried 10/100
Ethernet and it ran clean at 100 mb doing big file transfers and
looking at the logs. For the "over length" test I hooked the kludge we
had up to a new 300' spool so we had that plus the other hundred foot
baseband cable we were playing with and whatever was in the rack,
cables etc.


I'm somewhat surprised 100BaseT worked over CAT-3.


So was everyone but then there were a lot of people who said you would
never see copper running at a gigabyte. Now it is old technology.

bit?

That's sorta cheating, though. It's no one wire/pair.

The whole thing got started when someone said we were having problems
because the router (in a rack) was backed up to the equipment room
wall where they had that 1600a service.

The router was bad.


Hate it when that happens.

I hooked up the spool, just for playing with TDR to get a little more
time down the wire but I had to try it. ;-)


TDRs are great tools. Too bad they're so rare (I suppose the people who know
how to use one are even more rare).


We were doing TDR on a Tektronics 485.


What were you using as the pulse generator? I used HP 140s (w/TDR plugins) in
college and 7904s (7S10/7S11s) in IBM. There have been many times I wished I
had one around.


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Default NEC question: low-voltage wiring crossing 120v wiring.

On Sat, 01 Oct 2011 22:05:39 -0400, wrote:

On Sat, 01 Oct 2011 20:32:11 -0500, "
wrote:

On Sat, 01 Oct 2011 21:14:12 -0400,
wrote:

On Sat, 01 Oct 2011 19:26:46 -0500, "
wrote:

On Sat, 01 Oct 2011 19:59:33 -0400,
wrote:

On Sat, 01 Oct 2011 17:21:18 -0500, "
wrote:

When I was in the cabling biz at IBM I set un an experiment with CAT-3
trying to break an Ethermet or a Token Ring LAN doing every urban
legend bad thing anyone could think of (loops of cable over
fluorescent ballasts, running next to 480v 1600a feeders, taped to the
raceway, telephone in the same cable, exceeding the 300' rule, etc)
Basically I couldn't break it.

10-baseT, 4/16MB T/R only?

The original installation was 16mb TR but we also tried 10/100
Ethernet and it ran clean at 100 mb doing big file transfers and
looking at the logs. For the "over length" test I hooked the kludge we
had up to a new 300' spool so we had that plus the other hundred foot
baseband cable we were playing with and whatever was in the rack,
cables etc.

I'm somewhat surprised 100BaseT worked over CAT-3.

So was everyone but then there were a lot of people who said you would
never see copper running at a gigabyte. Now it is old technology.

bit?


yes sorry

That's sorta cheating, though. It's no one wire/pair.


it is still 500 a pair.


1000BaseT uses four pairs, so it's 250Mb per. Three bits are encoded per
pair, per symbol, so the symbol rate is 62.5MHz (MBaud).

The whole thing got started when someone said we were having problems
because the router (in a rack) was backed up to the equipment room
wall where they had that 1600a service.

The router was bad.

Hate it when that happens.

I hooked up the spool, just for playing with TDR to get a little more
time down the wire but I had to try it. ;-)

TDRs are great tools. Too bad they're so rare (I suppose the people who know
how to use one are even more rare).

We were doing TDR on a Tektronics 485.


What were you using as the pulse generator? I used HP 140s (w/TDR plugins) in
college and 7904s (7S10/7S11s) in IBM. There have been many times I wished I
had one around.


You just use that 18" cable nobody seems to know why the have and
couple the trigger out on the side to the" in" with a BNC "T" and
bounce that signal down the line. You sync on the fall of the trigger
pulse and look for the echo. It really works pretty well but you need
a fast scope since you are looking at nanoseconds. You ain't doing it
with a 453 unless you have some real long wire.


Ah, it seems they're using the trigger out as the pulse generator. Neat, but
I'm surprised it's fast enough. That rise time is critical. Even the antique
HP TDR pulsers were something like 25pS.

I think a guy in Raleigh figured that out. It was part of the 7800
remote support training.
I really only did it once to fix something but I did find the
offending drywall screw in a coax on a 100' run in 3 tries.
(found the screw heads that were close with a magnet and backed them
out with a screwdriver)
Third one was the charm. Once I took the screw out it worked so well
they left the coax in the wall.


Slick. ;-)
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Default NEC question: low-voltage wiring crossing 120v wiring.

On Oct 1, 11:56*am, wrote:
On Sat, 1 Oct 2011 07:42:27 -0700 (PDT), "





wrote:
On Sep 30, 12:58*pm, DA wrote:
responding tohttp://www.homeownershub.com/maintenance/NEC-question-low-voltage-wir...


DA wrote:
Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit?


Are you concerned with EMI (electromagnetic interference) or fire safety?


For fire safety NEC wants you to stay 6+ inches away from the power cables


You have a cite for that? *In addition to not believing it, it's hard
to see what difference 6 inches is going to make. I
regularly see low voltage cables of all kinds stapled near
Romex.


and that should also be far enough for EMI to be negligible. That shield
on the network cables is absolutely unnecessary in a residential home,


but
since you already go it, do not ground it on either end. I presume you
won't be able to ground it correctly at the outlet end anyhow, so just let
it float. It'll be useless as an EMI shield (which you don't need anyway)


Says who? *A Farraday cage is a Farraday cage
whether it's grounded or not.


*My experience has been an ungrounded sheild just becomes an antennaa



- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -


A metal shield is just that. It shields whatever is inside
it from an electric or varying magnetic fields outside it.
That is basic physics and requires no ground. So, the
shield itself could be an antenna, but the conductor
within is shielded.
  #23   Report Post  
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Posts: 8,589
Default NEC question: low-voltage wiring crossing 120v wiring.

On Sun, 2 Oct 2011 05:47:01 -0700 (PDT), "
wrote:

On Oct 1, 11:56*am, wrote:
On Sat, 1 Oct 2011 07:42:27 -0700 (PDT), "





wrote:
On Sep 30, 12:58*pm, DA wrote:
responding tohttp://www.homeownershub.com/maintenance/NEC-question-low-voltage-wir...


DA wrote:
Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit?


Are you concerned with EMI (electromagnetic interference) or fire safety?


For fire safety NEC wants you to stay 6+ inches away from the power cables


You have a cite for that? *In addition to not believing it, it's hard
to see what difference 6 inches is going to make. I
regularly see low voltage cables of all kinds stapled near
Romex.


and that should also be far enough for EMI to be negligible. That shield
on the network cables is absolutely unnecessary in a residential home,


but
since you already go it, do not ground it on either end. I presume you
won't be able to ground it correctly at the outlet end anyhow, so just let
it float. It'll be useless as an EMI shield (which you don't need anyway)


Says who? *A Farraday cage is a Farraday cage
whether it's grounded or not.


*My experience has been an ungrounded sheild just becomes an antennaa



- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -


A metal shield is just that. It shields whatever is inside
it from an electric or varying magnetic fields outside it.
That is basic physics and requires no ground. So, the
shield itself could be an antenna, but the conductor
within is shielded.


Not really true. Whatever (common mode) is inside can couple to the shield,
making it the antenna. This stuff is symmetrical, so the same happens
outside-in. The key is that the twists make the common mode cancel on the
differential signal, within limits. The shield keeps in any common-mode
radiation but it must be grounded to do so.

The shield does *nothing* to magnetic fields.
  #24   Report Post  
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Posts: 18,538
Default NEC question: low-voltage wiring crossing 120v wiring.

On Sun, 2 Oct 2011 05:47:01 -0700 (PDT), "
wrote:

On Oct 1, 11:56Â*am, wrote:
On Sat, 1 Oct 2011 07:42:27 -0700 (PDT), "





wrote:
On Sep 30, 12:58Â*pm, DA wrote:
responding tohttp://www.homeownershub.com/maintenance/NEC-question-low-voltage-wir...


DA wrote:
Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit?


Are you concerned with EMI (electromagnetic interference) or fire safety?


For fire safety NEC wants you to stay 6+ inches away from the power cables


You have a cite for that? Â*In addition to not believing it, it's hard
to see what difference 6 inches is going to make. I
regularly see low voltage cables of all kinds stapled near
Romex.


and that should also be far enough for EMI to be negligible. That shield
on the network cables is absolutely unnecessary in a residential home,


but
since you already go it, do not ground it on either end. I presume you
won't be able to ground it correctly at the outlet end anyhow, so just let
it float. It'll be useless as an EMI shield (which you don't need anyway)


Says who? Â*A Farraday cage is a Farraday cage
whether it's grounded or not.


Â*My experience has been an ungrounded sheild just becomes an antennaa



- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -


A metal shield is just that. It shields whatever is inside
it from an electric or varying magnetic fields outside it.
That is basic physics and requires no ground. So, the
shield itself could be an antenna, but the conductor
within is shielded.

In the case where the digital data in the cable is interfering with
Amature Radio signals, all an ungrounded sheild will do is collect and
radiate that signal - in otherwords it will be a capacitively coupled
(or possibly even inductively coupled) radiator. With one end
grounded, it effectivel traps and stops the signal - keeping it from
interfering with the radio.
Grounding both ends can cause all kinds of other problems - but
apparently there ARE situations where double-end grounding can be
called for
  #25   Report Post  
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Posts: 430
Default NEC question: low-voltage wiring crossing 120v wiring.

" wrote:

I'm somewhat surprised 100BaseT worked over CAT-3.


When we moved into this house in 1996, I pulled CAT-3 through it, thinking 10mb
is plenty. I am now running gigabit over it just fine. The longest run is
maybe 25 feet, so that is a help. But it works. -- Doug


  #26   Report Post  
Posted to alt.home.repair
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Posts: 6,399
Default NEC question: low-voltage wiring crossing 120v wiring.

On Oct 2, 12:14*pm, "
wrote:
On Sun, 2 Oct 2011 05:47:01 -0700 (PDT), "





wrote:
On Oct 1, 11:56*am, wrote:
On Sat, 1 Oct 2011 07:42:27 -0700 (PDT), "


wrote:
On Sep 30, 12:58*pm, DA wrote:
responding tohttp://www.homeownershub.com/maintenance/NEC-question-low-voltage-wir...


DA wrote:
Is it OK for the network cables to lie on the ceiling support members,
and thus beneath the Romex? Or should the network cables be above the
Romex? Or should one or both be in conduit?


Are you concerned with EMI (electromagnetic interference) or fire safety?


For fire safety NEC wants you to stay 6+ inches away from the power cables


You have a cite for that? *In addition to not believing it, it's hard
to see what difference 6 inches is going to make. I
regularly see low voltage cables of all kinds stapled near
Romex.


and that should also be far enough for EMI to be negligible. That shield
on the network cables is absolutely unnecessary in a residential home,


but
since you already go it, do not ground it on either end. I presume you
won't be able to ground it correctly at the outlet end anyhow, so just let
it float. It'll be useless as an EMI shield (which you don't need anyway)


Says who? *A Farraday cage is a Farraday cage
whether it's grounded or not.


*My experience has been an ungrounded sheild just becomes an antennaa


- Hide quoted text -


- Show quoted text -- Hide quoted text -


- Show quoted text -


A metal shield is just that. *It shields whatever is inside
it from an electric or varying magnetic fields outside it.
That is basic physics and requires no ground. *So, the
shield itself could be an antenna, but the conductor
within is shielded.


Not really true. *Whatever (common mode) is inside can couple to the shield,
making it the antenna. *


It most certainly is true. Go Google "Faraday Cage"
or look up Maxwell's Equations.




This stuff is symmetrical, so the same happens
outside-in. *


Yes, it's symmetrical, which is why surrounding an
antenna with a Faraday cage would render it ineffective.

The key is that the twists make the common mode cancel on the
differential signal, within limits. *


That's true but unrelated to shielding.


The shield keeps in any common-mode
radiation but it must be grounded to do so.


Following that logic, if run a microwave oven on
an extension cord without a ground wire, it will
spew microwaves all over the kitchen. Of course
it doesn't, because it's a Faraday cage, which
requires no ground.



The shield does *nothing* to magnetic fields.- Hide quoted text -


That is correct with regard to STATIC magnetic fields.
It most certainly does shield varying magnetic fields.
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