roy@phri.UUCP (01/28/87)
A while ago (in article <2551@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!dgc@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!jhc@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:phr@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. ---------------- 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! ---------------- 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. ---------------- 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. -- 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!"