wdw@aucs.UUCP (02/09/87)
Most of the terminals on our campus are presently connected to the wall
with four-prong plugs. We are considering wiring new terminals with
either four-wire or six-wire modular jacks. If anyone has had bad
experiences with these connectors I'd appreciate hearing your warnings.
In particular are these connectors any more sensitive to noise than
what we have been using.
Many thanks.
--
UUCP: {seismo|watmath|utai|garfield}!dalcs!aucs!wdw
BITNET: {wdwvax|wdw}@Acadia
Internet: {wdwvax|wdw}%Acadia.BITNET@WISCVM.WISC.EDUed@mtxinu.UUCP (02/10/87)
>Most of the terminals on our campus are presently connected to the wall >with four-prong plugs. We are considering wiring new terminals with >either four-wire or six-wire modular jacks. If anyone has had bad >experiences with these connectors I'd appreciate hearing your warnings. >In particular are these connectors any more sensitive to noise than >what we have been using. We've been using modular hardware for terminals for a few years, with no ill effects. The modular gear shouldn't be any more noise-prone than other connectors. I offer two cautions, however. First, modular connectors are not very robust mechanically - they don't stand up well to repeated insertion/removal cycles. Second, there is no standard way in which they're wired, so care in desigining the system is needed. In particular, be careful of polarity reversals: standard modular-to-modular cables put a half twist in each pair. Also, the connections are paired from the middle out, so that 4- and 6-wire systems can be made compatible: ----- 6wire ----- -- 4wire -- C1 B1 A1 A2 B2 C2 I recommend using a standard cabling model, and building the connectors at the modular-to-DB25 end in two or three different ways to make the connections work the way you want. -- Ed Gould mt Xinu, 2560 Ninth St., Berkeley, CA 94710 USA {ucbvax,decvax}!mtxinu!ed +1 415 644 0146 "A man of quality is not threatened by a woman of equality."
wayne@fmsrl7.UUCP (02/11/87)
In article <299@mtxinu.UUCP> ed@mtxinu.UUCP (Ed Gould) writes: >>Most of the terminals on our campus are presently connected to the wall >>with four-prong plugs. We are considering wiring new terminals with >>either four-wire or six-wire modular jacks. If anyone has had bad >>experiences with these connectors I'd appreciate hearing your warnings. > >I offer two cautions, however. First, modular connectors are not very >robust mechanically - they don't stand up well to repeated >insertion/removal cycles. Second, there is no standard way in which >they're wired, so care in desigining the system is needed. In the department I do work for here at Ford, we are using RJ-45 connectors (8 line modular) for our serial communications. Here is the wiring layout: Revised RJ45 standard (Version 1R5 09/24/86) Black RJ45 DB Gray RJ45 RJ 11 RJ 12 RJ 45 DTE DCE 25 DCE DTE I/O Name ----- ----- ----- ------ ------ -- ------ ------ --- ----------------- 1 Blue Gray 5 Blue Orange IN - Remote receive OK 1 2 Orange Brown 8 Brown Gray IN - Remote device up 1 2 3 Black Yellow 3 Green Red IN - Data in 2 3 4 Red Green 7 Yellow Black - Ground 3 4 5 Green Red 7 Black Yellow - Ground 4 5 6 Yellow Black 2 Red Green OUT - Data out 6 7 Brown Orange 20 Gray Brown OUT - Local device up 8 Gray Blue 4 Orange Blue OUT - Local recieve OK You may ignore the color codes, these are for RJ-45/RS232 connectors purchased from Black Box (412) 746-5530 $9.95@. Reasoning behind this layout: 1) Using crossed wiring, ANY two devices may be connected. Snap a cable between 2 terminals and they talk, no need to locate a null modem cable. Note that we do not use "straight through" cables (what most people recommend for computers). If you have spent as many hours fighting RS232 "standard connections" as I have, you will appreciate the joy inherent in this. 2) If all you need is TD, RD and ground, all you need is 4 line cable (RJ-11). Cheap, cheap :-) 3) If you need only TD, RD and devices available, you can use 6 line cable (RJ-12). Inexpensive. 4) If you need hardware handshaking, 8 line cable (RJ-45) will do it all. 5) The DB25 connections above are advisory, not absolute. The connector is responsible for having the appropriate signals on the correct RJ lines. Bolt the things on so they become part of the device. 6) Black Box also sells DB-9/BJ45 connectors so we can make PCs conform as well. The time savings in using this system is enormous. The only waste is the 2 ground lines in the center. We have been using this for some time with no problems (the latest revision was for color codes, Black Box changed the order of the colors). If you have any questions, feel free to mail or call me. For all the people who worry about ignorant people coming around and connecting our data lines to the phone company: - We generally keep everything plugged in so there are no open lines or ports to use. - With the number of cables we have, even the telephone repair men are intimidated. - We try to restrict access to authorized people. - If you are going to use wall jacks, I suggest that you label them so that people know better than to plug their phone in. -- ===== Your life is your own fault! ============== Rebel or be oppressed! ===== Michael R. Wayne (313) 322-3986 UUCP: {epsilon|ihnp4}!mb2c!fmsrl7!wayne Working at (but not employed by) Ford Motor Company ** This space for rent ** Since I am an independent consultant, the above opinions ARE my employers. ===== Are your moral/ethical/religious/political beliefs really rational? ====
rhorn@infinet.UUCP (02/17/87)
The growing popularity of using the RJ series connectors (aka
`telephone modular jacks') for terminal cabling is exposing a lot of
people to a major risk. These jacks are directly interchangable with
normal telephone jacks, and you can be sure that people will make
mistakes and plug terminals into telephone equipment. This can do
tremendous damage, and may even pose a health risk.
When a telephone rings, the ring signals are a pulsed DC that can
reach as high as 150 volts! In terms of vaporized semi-conductors,
this is just as destructive as plugging your connector into an electric
outlet. The frequency, voltage, and power don't quite match standard
electric power but they are more than enough to totally destroy any
unprotected electronics.
The health risk arises from the potentially poor grounding of the
digital electronics. These circuits are not normally designed to be
safe with 150 volts on them. This risk may be shortlived since the
digital circuit will quickly self destruct. Telephone extension
cables with RJ connectors pose a greater hazard. When the phone rings
there is high voltage on that connector. If a child is chewing on it
when the phone rings there is a real risk of death from electrocution.
(The hazard to adults is lower since they don't normally chew on
cables, and the power levels are low enough that the odds are in favor
of a nasty jolt instead of fatal one.)
Beware of using these connectors in inappropriate circumstances. (I
was warned quite thoroughly by our Mechanical Design people when I
suggested it. I learned then for the first time that telephones are
not UL approved, nor will they ever be, because of this 150 volt
risk.)
--
Rob Horn
UUCP: ...{decvax, seismo!harvard}!wanginst!infinet!rhorn
Snail: Infinet, 40 High St., North Andover, MAberger@clio.UUCP (02/20/87)
Normal ringing voltage is usually in the 90 - 100 volt range, but the warning is good notwithstanding. It's usually a 20 Hz. alter- nating current. Also keep in mind that phone lines have 45 volts across them, and that the polarity changes when the phone is off hook. That's quite enough to damage most semiconductor equipment improperly plugged into the phone line.
zemon@felix.UUCP (02/21/87)
In article <625@infinet.UUCP> rhorn@infinet.UUCP (Rob Horn) writes: >The growing popularity of using the RJ series connectors (aka >`telephone modular jacks') for terminal cabling is exposing a lot of >people to a major risk. These jacks are directly interchangable with >normal telephone jacks, and you can be sure that people will make >mistakes and plug terminals into telephone equipment. This can do >tremendous damage, and may even pose a health risk. You're absolutely right. I solved this by using RJ-45 sockets/plugs for my terminal equipment. The RJ-45 is 8 pins wide instead of the 4 on the RJ-11. This allows a *really* dumb user to plug his telephone handset in the computer wiring but the terminal plug is physically too large to be inserted into the telephone wiring socket. I like this wiring solution. I kept all the advantages of the modular phone wiring and avoided the electrical hazards. The only disadvantage I have heard of is that the RJ-45/RJ-11 plugs don't have much of a duty cycle life. But I don't really care. They hardly ever get unplugged and if one ever breaks, a new plug costs me about $.25 and takes about one minute to crimp on. -- -- Art Zemon FileNet Corporation Costa Mesa, California ...!hplabs!felix!zemon
rjn@hpfcmp.UUCP (02/22/87)
re: Use of RJ-series modular plugs/jacks in computer applications I strongly discourage the use of RJ connectors for anything other than telco applications, due to the damage potential of telco ring voltage. An alternative is the AMP SDL (Shielded Data Link) family of connectors. These are based on the same wiping-wire design as the RJ, but: * Are mechanically incompatible with RJ. You can't insert an RJ into an SDL socket, and vice versa. The SDLs are thinner from top to bottom and are wider due to having the latches (2) on the sides. * The SDLs are shielded, which reduces EMI emissions and reduces EMI and static discharge susceptibility. If you are building a product for sale, you are extremely unlikely to pass FCC Class A / VDE A (much less B) if you send data any faster than audio frequencies thru unshielded RJ cable. * The housing of the SDL is metal, and is longer than RJ, providing better strain relief. * SDLs are available with mechanical keying, in case your cabling is not symetrical, or in case your devices (like ours) have an "upstream" and "downstream" socket. Be aware, tho, that it is possible to force a miss-keyed SDL plug. HP uses SDLs for our HP-HIL (Human Interface Link) daisy-chain interface to keyboards, mice, tablets, knobs, barcode readers, touchscreens and other desktop critters. We're reasonably happy with SDL. Early HP150 PCs and our current Series 300 4-port MUX are RJ-equiped, and I have heard stories of folks blowing them up by plugging them into phone lines. This can't happen (and hasn't) with SDL. Regards, Hewlett-Packard Bob Niland 3404 East Harmony Road [ihnp4|hplabs]!hpfcla!rjn Fort Collins CO 80525
straka@ihlpf.UUCP (02/24/87)
I was under the impression that most (some, I KNOW) phone switches make checks of the line for impedance, voltage, etc. BEFORE they ring the line to ensure that neither party can hurt each other (within some limits). If some offending condition exists, the connection is not made, and the originator sent to reorder, or something. Maybe there is somebody out there who can shed some more light on the subject. -- Rich Straka ihnp4!ihlpf!straka
wdw@aucs.UUCP (02/24/87)
At the request of our engineer I posted the original query about the advisability of Modular jacks for terminal connections. Several replies mentioned the possible electrical hazard (to people or machines) if the wrong device is connected to the wrong jack. I enclose the following findings from our engineer. |I have made some measurements this morning and found the following: | |These are not theoretical values, but actual measurements. | | - Normal idle state of the phone line: 50V DC - If I put my fingers | across the line, I am not able to feel the voltage. | | - Ringing voltage is 82V RMS which is 100V Peak to Peak AC. If I put | my fingers on the line while it is ringing, I am able to feel a |tingling feeling. | | - The frequency of the ring is 33 Hz. It is a clean looking Sine | wave. | | - One side of the line is tied to ground. Therefore measurements from |one side of the line to ground are the same as measuring across the |line. The other side to ground always measures near zero volts. We have decided to use six-wire modular jacks (two jacks per faceplate) with both jacks wired in parallel. We'll use the inner pair for the phone connection and the outer two pair for the terminal connection. This should allow either device to be plugged into either jack with no harm to either. -- UUCP: {seismo|watmath|utai|garfield}!dalcs!aucs!wdw BITNET: {wdwvax|wdw}@Acadia Internet: {wdwvax|wdw}%Acadia.BITNET@WISCVM.WISC.EDU
DEFRANCO@RADC-TOPS20.ARPA.UUCP (02/26/87)
Concerning the discussion of modular jacks and related electrical data:
1. Most telephone switches operate at -48VDC nominal, actually closer to
-52V with battery systems. This provides operating power for your telephone.
Any voltage drop is due to line losses.
2. Ringing systems vary from switch to switch. Old standards used 105VAC
20 Hz nominal ringing placed across the line. Frequencies used can range
from 16 2/3 to 33 Hz, most often on party lines. Other schemes include
divided ringing, i.e. ring signal is placed only on one of the two wires
leading to the phone superimposed on the DC power supply, with steering
diodes used in detector circuits. In most cases, private line telephones
use line-to-line or "bridged" ringing, which most modems are designed to
recognize.
3. The DC polarity of your telephone line does not change when you answer
a call. Older electromechanical switching systems used the "reverse
battery" technique within the switchtrain to recognize answer. There should
not be any effect on a modem even with these systems.
4. Newer electronic switching systems usually do a "foreign battery" and
"AC" test before a connection is made, but only to protect the switching
equipment. The phone company really doesn't care about your equipment
except be sure it doesn't hurt theirs.
5. Modular jacks are designed to withstand all the normal electrical
stresses imposed by regular telehpone systems, including the AC ringing
voltages, and are specified to some extent within the FCC Regulations
governing interconnect between private and common carrier systems. While
the mechanical capabilities depend upon the manufacturer's materials
and quality control, variations are expected to be minor.
6. If you wish to positively avoid misconnecting computer equipment with
telephone lines, do as suggested - use radically different types of
connectors. Otherwise, simply insure that the equipment can withstand the
maximum electrical stress presented by the telephone system.
Remember that modems built for telephone connections are designed to
handle telephone line stresses - or should be.
Most building communications distribution systems I have had a
hand in designing use common access boxes for both voice and data
connections, using either dual 4 pin modular jacks or single 8 pin
ones. Obviously, some attention must be paid to the jacks when a
line is connected, but decent labelling and minimal user instructions
are all that are normally required to avoid problems.
Hope this helps someone.
Carl DeFranco "Calendars help you keep
DeFranco@radc-tops20.arpa track of appointments
you missed."
Disclaimer: "My boss doesn't even know I'm writing this, let
alone agree with it."
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