bob@alsys1.aecom.yu.edu (Bob Lummis) (11/29/90)
Does anyone have a recommendation for lightning protection on 10Base-T links that go through a direct-buried cable between two buildings? The buried portion of the cable is about 300 feet long. I plan to put 10Base-T transceivers at each end immediately at the building entrance points, then run the AUI cables upstairs to equipment locations. Is there some kind of thingee that I can connect between the twisted pairs and ground at each end of the cable that will short lightning-caused current surges to ground but that will not disturb 10Base-T signals? Preferably the thingees would act non-destructively (i.e. not just melt or vaporize). I think the cable TV industry uses some kind of diode-like device that does this while not interfering with TV signals. But I don't know what it is. -- Bob Lummis, Director, Research Information Technology (bob@aecom.yu.edu) Albert Einstein College of Medicine, Bronx, NY 212-430-4211 FAX:212-430-2488
kwe@buit13.bu.edu (Kent England) (11/29/90)
In article <398@alsys1.aecom.yu.edu> bob@alsys1.aecom.yu.edu (Bob Lummis) writes: >Does anyone have a recommendation for lightning protection on 10Base-T >links that go through a direct-buried cable between two buildings? The >buried portion of the cable is about 300 feet long. I plan to put 10Base-T >transceivers at each end immediately at the building entrance points, then >run the AUI cables upstairs to equipment locations. > This is really a very bad idea. It is not worth the apparent savings. If you must use twisted pair between buildings (such as for phones) I would recommend you follow telco practice and use fuse blocks and bus bars to ground the twisted pair cable sheath. But 10BaseT is different from tip and ring. If you want to use 10BaseT, it would really be much better to use a pair of fibers and a pair of fiber optic transceivers between a couple of 10BaseT concentrators, one in each building. The fiber provides excellent ground isolation between buildings, which is the problem you are really addressing. Fiber also is not susceptible to lightning strike induced potentials. If you insist on twisted pair, you will end up with problems due to ground potential differences and the way that Ethernet interface manufacturers and PC makers ground their equipment. In any case, it is best not to rely on the end node to deal with potentially large ground potential differences, particularly those induced by lightning strikes. It is very expensive to replace lots of PC components after every summer thunderstorm. Perhaps some of the many many people I have talked to over the years about these sorts of problems will speak up and confirm my position. Don't make the same mistake. 10BaseT is a *local* medium. --Kent
haas%basset.utah.edu@cs.utah.edu (Walt Haas) (11/30/90)
In article <69636@bu.edu.bu.edu> kwe@buit13.bu.edu (Kent England) writes: >In article <398@alsys1.aecom.yu.edu> > bob@alsys1.aecom.yu.edu (Bob Lummis) writes: >>Does anyone have a recommendation for lightning protection on 10Base-T >>links that go through a direct-buried cable between two buildings?... > This is really a very bad idea... > If you want to use 10BaseT, it would really be much better to >use a pair of fibers and a pair of fiber optic transceivers between a >couple of 10BaseT concentrators, one in each building. The fiber >provides excellent ground isolation between buildings, which is the >problem you are really addressing. Fiber also is not susceptible to >lightning strike induced potentials... > Perhaps some of the many many people I have talked to over the >years about these sorts of problems will speak up and confirm my >position. Don't make the same mistake. 10BaseT is a *local* medium. OK, sure. We have a conduit between two buildings maybe a hundred feet apart. Computer in one building, terminals in the other. Somebody (not me) pulled copper wire for RS232 connection. Next electrical storm hit the hill near the buildings, produced a big enough ground potential difference to fry all the transistors in the RS232 interfaces. They asked me what to do. I said put in a fiber link with RS232 converters at each end. They did. End of problem. -- Walt Haas haas@ski.utah.edu
cmilono@netcom.UUCP (Carlo Milono) (11/30/90)
At 300 feet, you are *really* pushing the limits of 10BASET; in addition,
do you honestly want to run AUI cable for the riser?! I concur with the
other posters:
1) Lightning strikes is a problem
2) Ground Potential (ground ain't ground...it's relative)
3) Fiber is good for you (ask any mother or doctor)..it will
be a framework for FDDI in the future as well. Go FOIRL.
4) Put MPR's at each end with some FOIRL-to-10BASET adapter or
run multiple strands between buildings and continue the fiber
as the vertical/riser...THEN go TP. The cost of fiber is in
the labor, not the material...besides the costs have been dropping.
I know of customers who have used the above mentioned products from AT&T
and were (and are) very pleased with the results and price/performance...
they even have FDDI products now.
--
+--------------------------------------------------------------------------+
| Carlo Milono: netcom!cmilono@apple.com or apple!netcom!cmilono |
|"When a true genius appears in the world, you may know him by this sign, |
|that the dunces are all in confederacy against him." - Jonathan Swift |
+--------------------------------------------------------------------------+bob@alsys1.aecom.yu.edu (Bob Lummis) (12/01/90)
In a previous posting I asked for information on how to protect direct- buried copper cable from lightning and still be able to use it for 10base-T. Judging from the many responses, I must not have made clear that I am not *choosing* to use buried copper for 10base-T. Virtually every response explained to me that fiber will be much better. I have no choice in the matter. I know the advantages of fiber and in fact am using it between all other campus buildings. However, for this particular run, for political/money reasons, it is mandatory to use pre-existing directly-buried copper telephone pairs for ethernet. I have no choice in the matter except not to network that building. Hence the question: how best to protect that type of link from lightning? -- Bob Lummis, Director, Research Information Technology (bob@aecom.yu.edu) Albert Einstein College of Medicine, Bronx, NY 212-430-4211 FAX:212-430-2488
bruce@ccavax.camb.com (Barton F. Bruce) (12/04/90)
In article <403@alsys1.aecom.yu.edu>, bob@alsys1.aecom.yu.edu (Bob Lummis) writes: > In a previous posting I asked for information on how to protect direct- > buried copper cable from lightning and still be able to use it for 10base-T. As long as you simply want an answer to your question... This is NOT a recommendation. AS others have pointed out, you are doing a 'NO-NO'. Old carbon gap type arrestors are generally being replaced by gas tube devices that don't develop carbon dust noise as the the years go by. Even better, the 3 electrode gas tubes clamp both sides of the line and ground together simultaneously if any 2 of the electrodes arc. Gas tubes can absorb a lot of energy, but are not as fast as some weaker diodes. The diodes alone would get smoked pretty quickly. Used together, you get the best of both. Another type of protection often included in CO or building entrance protectors is called a 'heat-coil'. This is a relatively slow acting mechanism to protect from fires caused by high current low voltage problems such as power line crosses to 110v which is to low to fire normal protectors (which have to pass ringing superimposed on 48vdc). Such a power line cross must be cleared before the cooking relatively small guage wire becomes a fire hazzard. The protectors at the subscriber end of the wire are more to protect people, and may well let equipment get zapped. Some of the newer 3 electrode gas tube subscriber arrestors might be what you want, but the CO grade plug in modules are best. You should have this class protection on ALL pairs entering each building, not just for this application. The blocks that take these plug in arrestors come in 100 pair, 25 pair, 10, and even 6 pair configurations. Some have long stub cables to splice into larger cables at the entrance of each CO. The other side of that type of block might well be wire wrap tails. In the smaller sizes, they may look like '66' punch blocks and have various combinations of punch, tail, and RJ21x (25 pair amphenol 'telco' connector) in and/or out. The CO grade arrestor world is split in two. Reliable, NTI, ATT, Cook (well they are NTI, now), and Porta Systems all make interchangable modules with gold MALE pins protruding from each plug in module. They all fit each other's blocks. Porta Systems also has their own desing that is a tad cheaper. It has tin plated round FEMALE holes that plug onto square MALE protruding pins in the base block. I only go into this detail because I LIKE Porta SysteM's premium module (the Delta series). It is available to fit the 'other' style blocks, but if you order their blocks, you will have to use their modules (no big deal, as long as you order the right pieces). The Delta modules have 3 electrode gas tubes, diodes, and heat coils, and backup air gaps all in one package. I think the heat coils are used by folks using T1 (1.544 mhz) and probably T2 (~2 x T1), but I wonder if the heat coil has any signifucant impedence at enet speed. Ask. There is more than one type of heat coil available in the modules, and, though the normal nominal voltage of 230 is what you will get by default (to not fire with ringing + 48vdc) and is #95BCDXN-230, there are several LOWER or even HIGHER standard voltages available. You probably want the LOWEST they offer. If you are ysing the same cable for other services, try to get some of the optional colors for different voltages. Often RED modules are the normal voltage, but are reserved for 'special' ckts. The plug in modules are also available in carbon block, and 2 electrode styles as well as only heat coil, or only sneak current fuse, as well as straight through specials for high voltage testing. You can terminate different pairs as you please. The carbon modules are well under $2, the Delta(tm) modules are up near $9 each. There are many possibilities in between. If you have 10s of thousands of these in each of hundreds of COs, you worry about what you specify. With your project, I would go for the 'good' stuff. An empty 10 pair block that is 66 type punch in and out probably costs $25. If you are getting literature from Porta Systems, ask for their stuff that describes deploying heat-coil and sneak-current fuses at appropriate ends of inside plant, as well as whatever they have on lightning protection. Porta Systems in in Soyosett (sp?) NY. If you just want home entrance grade one or few pair blocks, try TII Industries in Farmingdale (also NY), but this is hardly the same class stuff. BTW the ground on the block needs to get to a good quality ground as close by as possible. There are pages that can be written about that connection, but I am going to stop here.
kla@kampi.hut.fi (Kimmo Laaksonen) (12/11/90)
This may be the thingee you're looking for: We have an extensive terminal network at the campus based on RS422 balanced lines (2 pairs/terminal). Because RS422 is balanced the signals are all "floating" with respect to ground. To protect against static discharges etc. all long runs of cable (cables between buildings) are protected with Motorola Mozorb devices (sorry, don't remember the part number). This is a very fast semiconductor surge protection device. It's the only one I know that works against spikes fast enough. Gas discharge devices utilized by phone companies et al. aren't just that fast. The Mozorbs are bipolar, so they protect against positive & negative spikes. We connect one to each line of the pairs (that's 4/line at both ends), and ground them well. Mozorbs come in various power ratings: 600 W, 1.5 kW, and so on. I think we use the 1.5 kW variety (quite small package). Mozorbs are set to open like zeners at various voltages. I think ours are at 6.3 V, which seemed like enough. RS422 is nominally 5 V, and most receiver ICs are rated max. input voltage at c. 6 V, so we figured that'll give us enough protection. And so it seems: buildings where RS422 receivers blew during lightning storms, have caused not much trouble after Mozorbs were installed. For 10Base-T I don't know the voltages used, but they must be stated in the standard. If you think Mozorbs sound what you need, contact your local Motorola dealer for data sheets, and look up a voltage close to what the standard says (not too close, you wouldn't want the device to open in normal situations; on the other hand not too far, because then the receivers will blow before the Mozorb opens). ------------------------------------------------------------------------ Kimmo Laaksonen Internet: kla@hut.fi Helsinki University of Technology uucp: ..!mcvax!tut!santra!kla Computing Centre BITNET: KLA@FINGATE Otakaari 1, SF-02150 Espoo, Finland phone: int'l 358 0 451 4308
pat@hprnd.rose.hp.com (Pat Thaler) (12/14/90)
First a disclaimer: My field of expertise is LANs, particularly IEEE 802.3
and 10BASE-T, not safety. You should consult a safety engineer about
what is required in the way of surge suppression and fusible links in
your situation. Also, my opinions are my own and not necessarily
those of IEEE 802.3.
In comp.dcom.lans, kwe@buit13.bu.edu (Kent England) writes:
(After recommending using fiber instead.)
If you insist on twisted pair, you will end up with problems
due to ground potential differences and the way that Ethernet
interface manufacturers and PC makers ground their equipment. In any
case, it is best not to rely on the end node to deal with potentially
large ground potential differences, particularly those induced by
lightning strikes. It is very expensive to replace lots of PC
components after every summer thunderstorm.
Walt Haas relates an experience with an RS-232 link which someone
ran between buildings.
I agree with Kent and Walt that it would be best to use fiber optics
between buildings, but the statements about grounding do not apply
to 10BASE-T. (The question of finding adequate surge suppressors
and the limited distance do apply.)
There is a fundamental difference between 10BASE-T and RS-232. RS-232
sends single ended signals and a ground between the DTEs at each end.
Differences in ground potentials at the two ends of the link can cause
the link to fail to function. Larger differences in ground potenetials
can damage equipement or even cause safety hazards.
10BASE-T sends differential signals with no ground path between the
equipment. It does not depend on connected equipment being at a uniform
ground potential. Single-ended signalling would be unlikely to be reliable
over twisted pair at this data rate and distance. The 10BASE-T standard
requires isolation between the twisted pairs and the equipment which will
withstand one of the following electric strength tests:
1500 Vrms at 50 to 60 Hz for one minute (see IEC 435, 5.3.3) or,
2250 Vdc for 1 minute (see IEC 435, 5.3.3) or,
2400 V impulse test (10 impulses with peak voltage of 2400 V, 1.2 us
rise time, 50 us fall time, rep rate of not less than 1 sec;
see IEC Publication 60).
These values of isolation are the same as those in ECMA-97 Local Area
Networks Safety Requirements. (You may want to get a copy of this as
it discusses safety and interbuilding cables. ECMA is the European
Computer Manufacturers Association.) This isolation is also on a par
with isolation values generally used in telephone equipement.
Why such high values of isolation?:
Service between buildings was not an objective of 10BASE-T and the distance
of 100 m is short for a between building application. However, it is
likely for 10BASE-T connections to share patch panels and wire bundles
with phone service. This implies a possibility of misconnection of
10BASE-T equipment to wires going outside the building. Therefore, it
is prudent to require the same kind of isolation necessary for saftey
in case of such a misconnection.
The isolation listed is not enough by itself to provide safety in case
of direct lightning strikes. It is my understanding that cables coming
into the building should be protected with surge suppression devices
which limit the voltage to 1500 V peak or less and with fusible links
which protect the surge suppression devices from a high power fault
such as a mains fault. These then limit transient voltages inside
the building to the point where the isolation protects the user and
(probably) the equipment. (I say probably because a very fast rise
time transient might produce enough differential signal to damage the
receiver.)
At least some surge suppressors have a lot of capacitance. Connecting
them may cause unacceptable degredation of the signal. I don't know
if devices are available which will provide the protection needed without
degrading the signal. This is particularly true when the link is near
maximum length because you can't tolerate much degredation. If there
are devices which work, I would like to hear about them.
Pat Thalercmilono@netcom.UUCP (Carlo Milono) (12/18/90)
Having worked in C.O.'s and outside plant in my telephone past, I know of
the importance of practicing 'safe wiring'. I am now in the computer biz
and also had the same questions about protection.
I ran across an advertisement in Data Communications (December '90), which
pitches LAN Data Line Surge Protectors.
[ Disclaimer - I haven't tried them, I don't own stock, and am not employed
by them. ]
The company is Patton Electronics Co.
(301) 975-1000
The products pictured show *only* coaxial adapters, each with a hefty braided
ground strap to shunt the transient voltage to chassis ground. The literature
says that the protectors use 'sophisticated multi-stage hybrid circuits that
include Silicon Avalanche Diodes (SAD's) for quick response and superior
protection against trnasients. Patton's SAD's have a typical response time
of less than 5ns and can handle repeated surges of 1.5 KiloWatts per wire.
Unlike MOV's, Patton's SAD's won't deteriorate in performance as they are
subjected to repeated surges."
BTW, they are also available for Arcnet LAN equipment. The ad references
IEEE std. 802.3 "Network Safety Requirements" 8.7.2 ...........
--
+--------------------------------------------------------------------------+
| Carlo Milono: netcom!cmilono@apple.com or apple!netcom!cmilono |
|"When a true genius appears in the world, you may know him by this sign, |
|that the dunces are all in confederacy against him." - Jonathan Swift |
+--------------------------------------------------------------------------+