Multipurpose cable, was Re: Input Please!!
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On 5/27/00 at 2:07 AM, Kevin <kevco@g...> wrote:
> Any Suggestions or Problems
Yep. Don't.
When the phone rings it puts about 90VAC common mode across tip and ring.
Sometimes this voltage can run as high as 130V, but it's usually lower. Think
about what will happen to the lines that are right next to it. Twisted pair only
protects against so much. There's a reason that competent installers NEVER run
phone and data on the same cable. They always get seperate runs.
Otherwise....POOF. At the very least your RS485 network will go haywire when the
phone rings.
Also, there will be a significant limit to what kind of current you'll be able
to deliver to your loads. The 24ish guage wire found in cat5 cable is only good
for an amp or so, tops, and the series resistance of all that wire....ugh,
especially when it comes to you ground (ground loops).
If you want to do something like that, there are numerous prebonded multipurpose
cables that are available. They usually consist of run of coax or two (video),
cat5 (data), a few sets of shielded twisted pairs (line level audio), and a few
largish speaker type cables for good measure. They're not cheap, but they're one
of the few ways to do it right.
-dave
Discretion is the better part of valor
dave paton http://homepage.mac.com/dpaton dave at ieee dot org
> Any Suggestions or Problems
Yep. Don't.
When the phone rings it puts about 90VAC common mode across tip and ring.
Sometimes this voltage can run as high as 130V, but it's usually lower. Think
about what will happen to the lines that are right next to it. Twisted pair only
protects against so much. There's a reason that competent installers NEVER run
phone and data on the same cable. They always get seperate runs.
Otherwise....POOF. At the very least your RS485 network will go haywire when the
phone rings.
Also, there will be a significant limit to what kind of current you'll be able
to deliver to your loads. The 24ish guage wire found in cat5 cable is only good
for an amp or so, tops, and the series resistance of all that wire....ugh,
especially when it comes to you ground (ground loops).
If you want to do something like that, there are numerous prebonded multipurpose
cables that are available. They usually consist of run of coax or two (video),
cat5 (data), a few sets of shielded twisted pairs (line level audio), and a few
largish speaker type cables for good measure. They're not cheap, but they're one
of the few ways to do it right.
-dave
Discretion is the better part of valor
dave paton http://homepage.mac.com/dpaton dave at ieee dot org
Comments
> > Any Suggestions or Problems
>
> Yep. Don't.
>
I agree. CAT5 cable is called UTP cable which is unsheilded twisted pair.
This mean that the cable is totally unsheilded this is because it is
made to carry signals that are balanced, and any interference will appear
on both signals and will be cancelled out by the device.
If you want to try anyway just roll out about a 100' of cable and do
some tests.
Bean, thitt@i...
>
>Yep. Don't.
In addition to cross-pair coupling of the A/C and the amperage limitation,
consider:
Problem 1. how will you protect against un-intentional mis-connections.
Telephone RJ-11 jack will fit into a data RJ-45 socket. Someone may plug
the data cable from their network card into the RJ-45 socket.
Solution: At least use color coded jacks, better, terminate in a non RJ-45
connector. If you use RJ-45, make sure that the telco signal pair ends up
on the center two pins--a feeble attempt to make sure that you will not
inadvertently connect the telco A/C into the D/C signals (and puts it in the
right place for the RJ-11 connector pins).
Problem 2. there are never enough signal paths after a wire pull,
especially a couple of months later after the mess is all cleaned up.
Solution: Pull at least two cables. Then you can dedicate one cable to
higher voltage, A/C, telco signals. The data in another cable, and the D/C
power in perhaps a third. Then you can use a larger size D/C conductor,
sized for the anticipated amperage draw. Guiding principles are:
a) minimum 20% spare everything;
b) wire is cheap/labor is not; and
c) follow good wire routing practices--separation of A/C and D/C wire
trunks, have D/C and data wires cross A/C wires at right angles, and do not
route near florescent or other inductive devices.
Problem 3: one ground conductor for three D/C power supply wires means that
the ground conductor should be rated for the sum of the amperage draws of
the positive supply lines. Also mentioned was ground loop problems.
Solution: run a pair of wires for each D/C power circuit. Or at least make
sure that each conductor is sized for the load it will _potentially_ carry.
Carefully consider the ramifications of ground loop potential differences.
In summary: be cautious, and test thoroughly.
Regards,
Daniel