Telco-style push down blocks and stranded cable
Roy Smith
Having finally gotten fed up with the spaghetti in our machine
room, I've decided to redo all the terminal wiring using telco-style
pushdown blocks. For historical reasons, we've got about 100 lines coming
into the machine room for 40 ports -- some are lines run to offices in
anticipation of future needs, some are lines no longer in use but which
might be needed again some day.
What I want to do is set up a panel with a termination for each
port on one side and a termination for each external line on the other and
patch between them as necessary. Since patching won't be frequent, I don't
need anything as fancy as plug-in patch panels; re-doing a punchdown jumper
will be easy enough. The problem is that we've got miles of Belden 8723
(stranded shielded twisted pair) all through the building and I understand
that punchdown blocks are made to only work with solid wire. Has anybody
tried using stranded wire in punch-down blocks? Will it work? The last
thing I want is to have hundreds of connections start to work themselves
loose in a year or two.
We wire our runs like this:
1 ----------------------------------- N/C
Computer 2 ----------------------------------- 3 Terminal
End 3 ----------------------------------- 2 End
7 =================================== 7
The frame ground is connected to the shield only at the computer
end and xmit and rcv are each twisted with a signal ground (we run 9600
over 250+ feet, and one 19.2k line over about 100 feet with no problems, so
I must be doing something right). If the 20-30 feet between the patch
panel and the computer is 8723, as is the external line, will I loose much
if I make the patch between them plain unshielded solid phone wire? Do
impedance mismatches make any difference at these rates, or should I just
be worried about how many feet of wire are exposed to EMI, or are the noise
margins good enough that I shouldn't even worry about that? I suppose it's
obvious, but I guess I should mention that we're talking RS-232.
--
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016
"you can't spell deoxyribonucleic without unix!"
Henry N. Holtzman
Let me repeat, do not use standard punch down blocks and stranded wire.
Even if you get a good connection, you will probably sever all but one
or two strands of the wire. Next time you work on the block you may
pull on the cable and break the remaining strands.
In fact, you should not use standard punch down blocks with anything
but wire which is meant to go in them. If you use the wrong gauge or
the wrong softness wire then you can either ruin the block, or get a
bad (immediately, or time decaying) connection.
Now for the brighter side:
There are companies that make stranded wire punch down blocks.
One of them is Gentner, another is ADC. Contact a broadcast audio
supply store for more specific information. Call the business number
of one of your local radio stations and ask for the Chief Engineer if
you can't find anybody in the yellow pages. S/he will undoubtably
have a made purchases somewhere.
-Henry
Disclaimer: I don't make or sell punch down blocks; I just use 'em.
Jeffrey Silber
We use Belden stranded cable (8243? I am at home, so I am not sure), but it is
22 ga stranded. We punch those down all of the time. By the way, if you are
buying a punch down tool GET A GOOD ONE! We bought a cheap one from Black Box
(where we buy our blocks) and it really was unpleasant. I finally coughed up
the $80 or so to buy the spring loaded version from Jensen Tools and my tech
will now speak to me again!
--
A million here, a million there ... they all add up.
********************************************************************************
Jeffrey A. Silber/sil...@tcgould.tn.cornell.edu
Business Manager/Cornell Center for Theory & Simulation in Science & Engineering
George Robbins
>
> Having finally gotten fed up with the spaghetti in our machine
>room, I've decided to redo all the terminal wiring using telco-style
>pushdown blocks. For historical reasons, we've got about 100 lines coming
>into the machine room for 40 ports -- some are lines run to offices in
>anticipation of future needs, some are lines no longer in use but which
>might be needed again some day.
>
The idea is if you stuff wire with insulation into a limited gap, the
insulation will be displaced and the wire will make a good connection.
If the wire is to wrong size, or compressible, or the insulation
doesn't behave properly, you'll have nothing but problems in the
long run...
--
George Robbins - now working for, uucp: {ihnp4|seismo|rutgers}!cbmvax!grr
but no way officially representing arpa: cbmvax!g...@seismo.css.GOV
Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
Bob Bickford
>
> What I want to do is set up a panel with a termination for each
> port on one side and a termination for each external line on the other and
> patch between them as necessary. Since patching won't be frequent, I don't
> need anything as fancy as plug-in patch panels; re-doing a punchdown jumper
> will be easy enough. The problem is that we've got miles of Belden 8723
> (stranded shielded twisted pair) all through the building and I understand
> that punchdown blocks are made to only work with solid wire. Has anybody
> tried using stranded wire in punch-down blocks? Will it work? The last
> thing I want is to have hundreds of connections start to work themselves
> loose in a year or two.
>
(or your successor <grin>) if you try it. The whole mechanical design
of the silly things (telco punch-down blocks) is centered around a
single solid strand of the right size. If you stick to that, they're
wonderful, though.
On your wiring, the way you've set that up should give you wonderful
performance. I was running between two and three hundred feet at 9600
baud on just plain old telco wire (doubled the signal ground) and it
worked fine.... In fact, I believe the entire building was wired that
way.
Using the shield is both good and bad..... good if you have or
suspect EMI problems, bad on long runs because of the extra
capacitance. Don't have my Belden catalog handy, but I seem to
recall that the stuff you mention is low-cap, so you should be ok.
--
Robert Bickford {hplabs, ucbvax, lll-lcc, ptsfa, msudoc}!well!rab
terrorist cryptography DES drugs cipher secret decode NSA CIA NRO IRS
coke crack pot LSD russian missile atom nuclear assassinate libyan RSA
The above is food for the NSA line eater. Add it to your .signature and
you too can help overflow the NSA's ability to scan all traffic going in or
out of the USA looking for "significant" words. (This is not a joke, sadly.)
pa...@osu-eddie.uucp
At Ohio State, we have been using punchdown blocks for quite a while. They
seem to work just fine, but we use only single conductor (3 conductor
telephone wire) to wire and cross connect. You might try striping about
1/4 inch and tinning it, then punching in the tinned part. (or, how to make
stranded into single conductor wire).
-- Paul Placeway
Ohio State CIS dept.
pa...@ohio-state.ARPA
cbosgd!osu-eddie!paul
Art Zemon
I have a couple of hundred terminal wires running through
telephone punch down blocks and am very happy with the
arrangement. The stranded wire works fine and the punch
down block cuts the insulation of the thicker wire just
fine.
You can also buy blocks with a 50 pin connector prewired on
them. Then you buy cables which split from a 50 pin
connector into six DB25 connectors. Add an extension cord
of the right length and you don't have to do any
complicated wiring between the computer and the punch down
blocks.
I've gotten my stuff from LANplex and am extemely happy
with both the products and the services. They have some
offices on the East coast. The number of the local office
is (714)680-8686. They should be able to get you in touch
with someone closer to you.
Good luck,
--
-- Art Zemon
FileNet Corporation
Costa Mesa, California
...! {decvax, ihnp4, ucbvax} !trwrb!felix!zemon
Art Zemon
>Do not use standard punch down blocks and stranded wire.
>
>Let me repeat, do not use standard punch down blocks and stranded wire.
>
>Even if you get a good connection, you will probably sever all but one
>or two strands of the wire. Next time you work on the block you may
>pull on the cable and break the remaining strands.
>
>In fact, you should not use standard punch down blocks with anything
>but wire which is meant to go in them. If you use the wrong gauge or
>the wrong softness wire then you can either ruin the block, or get a
>bad (immediately, or time decaying) connection.
I disagree with all of that. I'm using standard telco
style punch down blocks and have had nothing but good
experiences. The blocks show no appreciable signs of wear
(and even if they do die early, they only cost about $13).
I have used a number of different brands of standed cable,
all about 22 or 24 gauge. Removing the cables is tough;
the blocks hold on very tight and the cables are not broken
by the "teeth." I have examined a number of cables after
removal and the strands are not broken.
Feel free to write or call if you have more questions. My
phone number is (714)966-2344.
Tim Pozar
>
>At Ohio State, we have been using punchdown blocks for quite a while. They
>seem to work just fine, but we use only single conductor (3 conductor
>telephone wire) to wire and cross connect. You might try striping about
>1/4 inch and tinning it, then punching in the tinned part. (or, how to make
>stranded into single conductor wire).
>
I missed the previous postings. I assume your discussing the merits
of punch/crunch/66 blocks. We're using the blocks for high density, quick
changing connections for audio at our station. I'm using Belden 8451 wire
with the blocks. 8451 is a 22ga., foil shield with drain wire, single
pair, stranded cable. We punch it down with the insulation intact with a
standard punch tool. Stripping the wire first, because of the density of
the connections, is not a good idea. The exposed wire is too vunerable to
shorts with frayed wires and the wire laying across other connections.
Before we decided to use stranded wire we tested punch connections with
8451, 8450 (solid), and several other brands of simular wire, one being
Naglix. I also have been using 8451 with these blocks for the past 6
years. During this years I haven't had one connection that I have had to
repunch due to oxidation or bad punches.
. Before we punch down the connections, we paint the blocks with a
non-oxidizer from Caig Labritories. Just for my peace of mine...
I would like to add that we also research differant type of
connection blocks. We also have results originated by the military
comparing different type of connections vs. life expectancy. If anyone is
interested in this data, you can send me mail and we can make arrangements
for sending it to you.
Tim Pozar
Brian Kantor
The system we devised for using them is that each computer port is
connected to modular plugs (we use the ones from MOD-TAP), and a
"hydra" which takes the individual modular plugs and brings them to
telco-style 50-pin plug inside the computer system (Unibus cabinet,
etc). A 25-pair cable with appropriate connectors takes this to a
dual-connectorized 66 block on the wall. For ports which connect to
our LAN or which run to rooms with clusters of terminals, a similar
cable leaves the other half of the 66-block and runs either to a hydra
and modular plugs into the LAN box, or to another punchblock (single
connectorized is ok here) and punched-down inside wire to terminals, or
to a "harmonica" (the other sex of a hydra: modular jacks on a 50-pin
connector). This way my cross-connect wiring for the majority of our
connections (in the computer room, at least) consists of bridging clips
and is very fast to connect.
Essentially, all RS-232 connections entering the computer room
terminate on a punchblock. In laboratories and terminal rooms where
I'm likely to have a cluster of connections (i.e., more than 2), I
place a 66-block with 50-pin connector and run a 25-pair cable with
connectors back to the computer room, where it terminates in another
66-block. Cross-connect is done by bridging clips or 3-pair inside
wire. For less-dense terminals, either a punchblock is nearby serving
several rooms, or I string longer runs of 3-pair. I've got 200 and
300 foot runs running at 19,200 and 9600 bps with no problems.
I've also bought a couple of items for troubleshooting - I have a nifty
little connector that you can slip onto the punchblock terminals and
plug a modular connector into - that connects to a breakout box or
datacomm analyzer and you can tap into any line in or out of the
computer without unplugging anything. If you need to isolate a
connection, you can pop the bridging clips, or simply unplug the
modular plug at the terminal or computer. Fast fast FAST to
troubleshoot!
Standardization: We chose a 6-conductor scheme (which gives 8 ports
on a punchblock, cable, hydra, or harmonica) so that we could wire
modems, printers, and terminals the same way. (Our LAN boxes look like
modems and need DTR and CD in addition to the normal TD, RD, and SG, so
we have one spare wire left over. On modems, that spare wire is RI.)
We use only two kinds of connectors (called a 260 and a 523 by Mod-Tap)
and stock them in both sexes. A cable with a 260 connector on both
ends is a straight-through cable suitable for connecting to a modem or
LAN box on one end, and a computer or terminal on the other (assuming
the computer is DTE, which most are these days). A directly-wired
terminal (or other DTE device, such as a printer) will still have a 260
connector on it, but the port on the computer will have a 523 connector
for that line, which gives a null modem to connect the DTE to the
computer DTE port.
Our modem telephone lines are wired similarly, but we use 4-conductor
cable there to match the 2-pair inside wiring that the phone company
uses. (By the way, ThePhoneCo is happy to terminate incoming lines on
one of our connectorized 66 blocks. We just tell them to "terminate on
customer-provided RJ21X" and they do it just right.) With 4-conductor
modular stuff, you get 12 per cable/block/hydra/harmonica.
All this stuff is available from MOD-TAP. We buy a lot of it from
other people too. What with the installation of our LAN and rewiring
most of the campus, we've probably installed more than 2000 RS-232
connections using variations of this system, and found it to work quite
well.
DEC and others have similar systems with slightly different standards.
Brian Kantor UCSD Office of Academic Computing
Academic Network Operations Group
UCSD B-028, La Jolla, CA 92093 USA
Disclaimer: just because I said it doesn't mean its right. Think for
yourself.
r...@phri.uucp
A while ago (in article <25...@phri.UUCP>), I asked for advice on
re-doing the terminal wiring in my machine room. The basic situation is
that we've invested a lot of time and money in stranded wire. I want to
get rid of the rats-nest wiring and find punchdown blocks a very attractive
way to go, but I've heard that you can't put stranded wire in them.
True to Usenet form, if you ask a simple question, you get at least
six different, mutually exclusive, answers. I havn't done a careful count,
but it looks like we're about evenly split between "sure, go ahead and do
it; it works fine, I've wired up half of Texas like that." and "anybody who
tells you it's OK to put stranded wire in punchdown blocks deserves to be
shot!". Oh well. I tend to believe the latter, partly because that seems
to be the word from people that I have reason to trust. But then again,
suposedly reputable people have told me just the opposite. Draw your own
conclusions. For what it's worth, the folks at Glasgal Communications also
don't like putting stranded wire in punchdown blocks.
There were a smattering of replies posted to the net over the past
couple of weeks; they are not included in the summary. Thanks to everyone
who responded; my apologies if I missed anyone. Comments [in brackets with
my initials, like this -- RHS] are my additions. Elipsis [...] indicate
sections I've cut out to save space. And, no, I havn't yet figured out how
I'm going to solve this mess. Next building I wire up, I'm going to use
solid wire, but it's too late now.
/roy
----------------
From: Bob Paver <cmcl2!ames!im4u!milano!paver>
Organization: MCC, Austin, Texas
Having just finished cabling a 200,000 square foot building with lots of
twisted pair, I'll offer my "professional" opinion.
Telephone punch blocks WILL cut the stranded wire. The edges of the
"clip" that holds the wire are sharp (enough to cut the insulation on
the wire). We used punch blocks (mfg. by Ortronics; bought from Anixter
I believe) that are designed (supposedly) for stranded wire. The "clips"
have rounded edges. So far so good. What we found, however is that
the punch blocks are constructed such that one has to punch both wires
into the same clip. This often results in a loose connection. If we had
to do it again, we'd use something else.
The most recent catalog from Black Box shows circuit boards with modular
(RJ-11) jacks that appear to be suitable for stranded wire. I've never
seen one so am not sure
----------------
From: David G. Cantor <hplabs!d...@CS.UCLA.EDU>
We (UCLA Mathematics Department) have been using punch blocks and such
for several years. We have runs of over 500 feet at 9600 baud using
standard Telco twisted pair (NOT SHIELDED) and have very few problems.
The reason is, of course, that the power wiring in commercial buildings
is all in steel conduit and so is shielded from our wiring. We use
slightly different wiring from you with 5 wires (in effect, DTR in both
directions) and use patch panels using 6 pin modular jacks. We have
punch blocks in many locations.
Impedance mismatches are not a problem.
I wouldn't want to connect stranded wire to a punch block. Punch blocks
are designed to make a good connection by spring pressure against solid
wire. And the probability of a short (from a mislaid strand) is quite
high.
Let me make a simple-minded suggestion. Buy some 1/8 inch thick by 3
inch wide plastic strips, 2 1/2 feet long. and mount machine screws on
them, from the back, using one 1 inch 6-32 screw and one nut. Then
mount the strips to a wall. Wires can then be fastened to these screws
using two washers and one more nut. The screws can be mounted in groups
of three, horizontally, say every inch. Thus five strips would take
all of your cables with some to spare and two strips would take all of
your ports with plenty to spare. Then, after all terminals and ports
are connected, you can mount the jumpers on top using a nut and two more
washers (alternatively you can connect the jumpers between the same nuts
as the other wires).
The telcos used terminal strips like this until about 15 or 20 years ago.
----------------
From: sun!amdcad.AMD.COM!phil (Phil Ngai)
Organization: Advanced Micro Devices, Sunnyvale, California
> What I want to do is set up a panel with a termination for each
>port on one side and a termination for each external line on the other and
>patch between them as necessary.
Good plan. That is what we do. Works great. Cheap, too. For us,
quality and reliability is most important but when you can have a low
price too, it's wonderful. We have tried RJ-11 patch panels and had
some problems. Not a lot, but we have none with the punch down
blocks. Wire is something that The Phone Company really knew how to
handle.
> I understand that punchdown blocks are made to only work with solid wire.
> [...] The last thing I want is to have hundreds of connections start to
> work themselves loose in a year or two.
You are correct to be concerned. One of our buildings in Texas was
wired for voice with stranded by mistake (not by our group) and they
have intermittent problems. The problem is that the clip which pierces
the insulation and contacts the wire doesn't have enough spring action
to follow the compression of the stranded wire. Solid wire, as you can
imagine, resists compression much better and provides a much more
reliable connection. This is for the 66 block.
There are blocks designed to work with both solid and stranded. Have
you talked to your local telco supply house? Here in California we
like Anixter Brothers. [I havn't yet called them, but they are on my
list -- RHS] They are a national company, I think. Also there is
Graybar. If you get really stuck, maybe ATT can help.
> The frame ground is connected to the shield only at the computer
> end and xmit and rcv are each twisted with a signal ground
This also sounds like a good technique.
> If the 20-30 feet between the patch
> panel and the computer is 8723, as is the external line, will I loose much
> if I make the patch between them plain unshielded solid phone wire?
No problem. Your cross connect (the telephone term) won't be more than
five or six feet, right? [right -- RHS]
> Do impedance mismatches make any difference at these rates?
At these data rates, absolutely not. Impedance mismatches are
important when the period of a bit is comparable to the time it takes
a signal to propogate down the cable. If the reflection settling time
is a small fraction of the bit period, it will never be seen.
> should I just be worried about how many feet of wire are exposed to EMI?
I wouldn't even worry about that in an office environment, except for
florescent lamp ballasts and they can usually be handled by rerouting
the cable.
----------------
From: cmcl2!seismo!rochester!kodak!ornitz (barry ornitz)
Organization: Eastman Kodak Co, Rochester, NY
I do not believe that the stranded wire will work well in your application.
A simple approach might be to use punch blocks with paralleled connections:
solder the stranded wire to one terminal and use solid wire from a paralleled
terminal to patch elsewhere. If you do not have blocks with paralleled
terminals, use short wire lengths of solid wire to jumper to an adjacent
terminal pin. Only the terminal pins with stranded wire will be soldered so
the "bite" of the punched-in connections will not be degraded.
As a rule of thumb, line length must usually be over one twentieth of a
wavelength before impedance mismatch creates any problems. This works out
to about 2500 feet for 19.2 KB so I am sure this will cause no problems with
differing types of wire you are considering.
One way to handle the shielding is to use a zipper shielding braid over the
entire bundle of wires. Alternately you could run shielded wires in and out
of a metal box with the punch blocks located inside. Ground the box and
connect the cable shields to the box. If you are not concerned about looks,
aluminum foil can be used to shield the bundle. A spiral wrap ground wire
over the foil is a good way to make connections.
----------------
From: cmcl2!j...@mtune.ATT.COM
Organization: AT&T ISL Middletown NJ USA
At risk of pushing my own company's products, we have a whole building in
Middletown NJ wired up with 110 hardware, not the 66E blocks to which I
think you are referring. The 110 hardware is the building block of AT&T's
Premises Distribution System. It does work with stranded wire, it is easy
to make patches, you can do pretty much anything you want with it. There
are enough different configurations that a lot of things are possible -
factory-or-field terminated, 3/4/5 pair blocks, logical closet layout, and
so forth. The down side is that it costs a lot (I think - I never bought
any 66E blocks! Any patch cables other than 3-pair cost an arm and a leg
though).
----------------
From: cmcl2!harvard!axiom!lpi!jdc
Organization: Language Processors Inc., Waltham MA
Roy: I have done what you are want to do and punching stranded wire into
telco blocks works just fine even though it is more difficult to handle
than solid copper wire. Here are a few suggestions:
1) Invest in a good impacting termination tool. In case you don't know
what I mean it is a tool wherein the blade is spring loaded so that
at the last moment it "snaps" forward cutting off the excess wire
cleanly without effort. It works beautifully on 24 ga. solid copper
wire but may take a couple "snaps" to cut off the stranded wire.
2) Buy a spare blade at the same time you get the tool. If you nick the
blade you can forget about terminating stranded wires.
3) Use 2-pair, 24 ga. solid, unjacketed wire for your patches. It comes on
1000 ft. spools.
4) Lay out your patch panel so there is room for wire guides and then use
them. I saw a settup where a guy tried to do all the connections
point-to-point and it was a disaster!
5) If you have any thought of ever installing a MICOM port-selector (which
is very easy if you install your patch panel correctly) you might
consider punching your terminal lines in the following order,
3 - Received Data
7 - Ground (or DSR, on a micom it can be either)
2 - Transmitted Data
20- DTR
Your should also do you computer lines the same way. This way your NULL
cross-over is made via your patching wires.
This is the order that MICOM uses for its interface so if you used telco
blocks that have been prewired with group terminators you could just
plug the MICOM between the two sides of you patch panel, strip out the
patching wires and have yourself a network.
I've rewired two different companies using telcos and for RS232 I wouldn't
have it any other way. I even have some custom parts that I order that
give me extra flexibility on the patch panel and remote connections.
----------------
From: David Marston <cmcl2!harvard!dartvax!marston>
I have punched stranded wire onto Telco-type punchblocks; it works but it
isn't ideal. It seems to help if you give the termination an extra squeeze
with pliers after punching. The (chemical) type of insulation may have an
effect on the results, also--ours are PVC.
----------------
From: sun!hplabs!rutgers!ems!barker
Organization: EMS/McGraw-Hill, Eden Pairie, MN
I would recommend against using stranded wire in telco punch
blocks. As you said, they are intended for solid wire. I'm not sure what
to reommend that you use for stranded wire.
As far as shielding and EMI go... I would advise you to use
shielded wire where ever possible and to ground it at no less than 1 end,
preferably both. [I was under the impression that grounding both ends
doesn't give any better shielding, and in fact is bad because it causes
ground loops; can anybody comment on this? --RHS] Two things govern a
cables suseptability (sp?) to EMI, shielding and proximity to EMI sources.
EMI sources are not only computers, but power supplies, florescent lights
and also other cables. I've heard of people running 2 long unshielded runs
of RS-232 cable right next to each other (ie. 1 for a remote terminal and
one for a remote printer) only to find that when one of the devices is on
and idle, it picks up the data intended for the other. This is due to the
fields generated in one of the cables being induced into the other.
----------------
From: sun!hplabs!rutgers!meccts!mecc!sewilco
Organization: Minn Ed Comp Corp, St. Paul
Find a nearby cabling company and ask them what they've got for stranded
cable. Dave Olson at Computer Systems Products, here in Minneapolis, says
that insulation-displacement connectors (ie, punchdown blocks) don't work
well with stranded cable. The wires deform as the insulation is deformed,
and the contact points slice strands and otherwise make for loose
connections.
For a year I've been using a cabling system based on RJ-45 connectors. These
are the 8-wire version of the RJ-11 telephone modular connectors. RJ-11
cabling systems are available, and with their four wires should work well.
Components for these are available from CSP, Black Box, and many other
sources.
If your existing 100 wires are mostly separate cables and you can't justify
a patch panel, maybe you can just get a dozen RJ-11 wall plates or surface-
mount jacks (3" square boxes). When you need to change an old cable,
connect it to a jack. You'll eventually end up with all the jacks neatly
mounted on a plywood panel.
If some of the 100 wires are in telephone-style 25-pair cables you can
terminate it with what is called an "Amphenol" connector (you've seen
them on multiline phones). It might be best to have a cabler do this.
These can be connected to converters to RJ-11.
On the terminal and/or computer you'll need a data jack, which converts
from RJ-11 to DB25 (and a cheap cable from the data jack to the "patch
panel"). Black Box is expensive; CSP list is $6.95.
With a little study, I found I could easily cost-justify this cabling
system. If changing one cable uses $8 of your time, these cables pay for
themselves after two or three cable changes. If putting in new cables,
the 25-pair cables are cheaper than single cables over a distance of
less than four feet (yes, 4 feet!) if more than a few terminals are grouped
together.
----------------
From: Jim Wright <allegra!ulysses!ecsvax!jcw>
We do it a lot. We use Belden 8457 (12-cond) and 8444 (4-cond) to run to
offices, and we use 8444 to patch between blocks. We have run up to 1000
feet (rs232) at 9600 bps. We don't connect anything to pin 1... we use 2,
3, 7, and 20, because DTR from the terminal is used to wake up our Develcon
Dataswitch (we also have terminals wired similarly connected to Timeplex
switching muxes and DEC terminal servers). In six years of doing this in a
large network with at least 300 terminals, I don't think there have been
more than a half-dozen times when we had a bad connection where the
insulation wasn't sufficiently pierced by the connector on the block. As
for impedance... remember, this is all unbalanced, so you could just as
well use barbed wire. [I don't understand this comment. Why does a
balanced line have to be impedence matched, but not an unbalanced line?
I'm used to thinking of balanced meaning like TV twinlead, and unbalanced
meaning like coax -- RHS] We patch with 8444 so that it is easier to follow
which wires go where in this maze of spaghetti. But using solid wire
without an external sheath (a la Telco) means that a given bundle of
conductors will have less cross-sectional area... this can become important
with a LOT of patching.
----------------
From: allegra!@EDDIE.MIT.EDU:ph...@hermes.ai.mit.edu (Paul Rubin)
[Note: this gets my award for "unparsable return address of the month" -- RHS]
1. I expect stranded wire will lose pretty bad with punchdown blocks,
because of the way the punchdown tool works.
2. Punchdown is a gigantic pain in the neck; why don't you use
modular telephone-style cables (available in 4, 6, or 8 conductor)?
I don't expect it would be much more expensive than punchdown.
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From: hplabs!hpscda!hpscdw!garyg
Stranded wire seems to work OK if your wire size is 1-2 gauges larger than
the smallest rated for the punchblock. It just needs to be big that the
strands don't get pushed aside while the insulation is being displaced.
We have runs of over 400' running in 25 pair phone cables in an R&D lab,
totally unshielded, 8 circuits per 25 pair, without any crosstalk or noise
problems. Your mileage may vary. If anything, the shielded cable with it's
higher capacitance may cause problems. Good luck!
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From: sun!cognito!randolph (Randolph Fritz)
Organization: Sun Microsystems, Mountain View
> Has anybody tried using stranded wire in punch-down blocks? Will it work?
It won't -- sorry. Try screw-terminal barrier strips instead. You could
bring your existing "cable plant" -- your terminal cables -- to barrier
strips and re-wire your computer room with solid wire.
> If the 20-30 feet between the patch panel and the computer is 8723,
> as is the external line, will I loose much if I make the patch
> between them plain unshielded solid phone wire?
Generally, you should see no problems as long as you do not leave
unterminated quads running into your computers -- capacitive coupling
between send and receive lines produces an on-again off-again loopback. A
more serious problem with RS-232 is ground shifts and ground loops. If the
money is available, I would strongly recommend the use of line-powered
line-drivers. These things prevent vast amounts of grief, but were costly
last time I looked (but look again -- that was almost a year ago).
Two further suggestions:
Glasgal Communications (Northvale, NJ) offers a very good line of
cable management products. If you have a need for serious telco-
style equipment, connection frames and so forth, try Greybar Electric.
Nevada-Western (San Jose, CA?) makes a very useful line of
connectors and patch panels.
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From: cmcl2!ihnp4!ihdev!dlr
Organization: AT&T Bell Laboratories
Having just gone through something like you describe at a field test site,
I would suggest that you go ahead and try the setup you describe, but with
a couple of minor changes.
1. When you terminate the stranded wire in the pushdown block, solder the
incoming side to the pushdown block for stability. This will prevent
unraveling of the strands. Only do this if there are only minor changes
over time. Unsoldering the blocks gets messy and tedious.
2. On the cables running from the termination blocks to the computer, I
suggest some sort of shielding, even if it is only taking the wires and
twisting them into cables (labeling the pairs, of course) and then wrapping
them with lead or copper foil (if available) or getting shielded 25-pair
cables from your local wiring source (should be some of that type of wire
around for the old 6-button key system phones).
----------------
From: cmcl2!ihnp4!ihlpf!spear
You might try the little spring loaded clips that you can buy at radio
shack - these work well for twisted wire and are fairly cheap. I am
talking about the ones with a button and a hole beneath it which closes on
the wire when the button is not depressed.