Index Home About Blog
Subject: Cable Repair,  Splicers and a Cable "Environmental Problem"
Date: 15 Oct 89 13:04:57 EDT (Sun)
From: Larry Lippman <kitty!larry@uunet.uu.net>

In article <telecom-v09i0445m05@vector.dallas.tx.us> gentry@kcdev.uucp (Art 
Gentry) writes:

> > 2. When one of those lines is damaged out in the middle of nowhere,
> > and the damage is _inside_ the cable, how do they locate it?
> > Moreover, how do they splice in a new piece of cable?  In other
> > words, how do they connect up those hundreds of individual lines?
> > It would be like trying to rewire a spinal cord.
 
> Ahhhh, back in the good-ol-days....:-} All the wires within a cable
> are color coded, in pairs.  In larger cables, pairs were grouped into
> bunches, which in turn, were color coded themselves.  So while tedious,
> it was not overly difficult to match pairs in a splice.

	Many Telecom readers are, to some extent, familiar with the
color code used on polyethylene insulated cables (PIC) in which each
pair is individually color-coded and arranged in groups of 25-pairs,
with these groups in turn being identified with colored binder
strings.  The above color code uses ten colors, and begins with
white/blue for pair 1, white/orange for pair 2, white/green for pair
3, etc., ending with violet/slate for pair 25; binder group
identification is made with colored tape or string using the above ten
colors.  The complete color code has already been posted by others to
Telecom, and it is not my intent to repeat it here.

	The above color code with individual pair identification is
used on both inside station wiring and outside PIC distribution cable.
However, pulp-insulated cable does NOT have identification of
individual pairs.  There is still a significant amount of
pulp-insulated cable in service, especially with high pair counts of
1,500 to 2,700 pairs.

	Pulp-insulated cable uses only three pair colors: white/green,
white/red and white/blue.  Binder groups within the cable come in
sizes of 25, 26, 50, 51, 100 and 101 pairs, depending upon the wire
gauge, pair count and style of the pulp-insulated cable.  For cables
with 400 or more pairs, the binder group size is generally 100 or 101
pairs.

	Each of the pairs in such a binder group has the SAME color
code!  As an example, a 404-pair pulp-insulated cable will typically
have four binder groups: (1) 100 pairs of white/green plus a red/blue
tracer pair; (2) 100 pairs of white/red plus a red/blue tracer pair;
(3) 100 pairs of white/blue with a red/blue tracer pair; and (4) 100
pairs of white red with a red/blue tracer pair.  The total pair count
in this example is 404 pairs, and note that there are 200 pairs which
have a white/red color code.  The tracer pairs are generally reserved
as spare or maintenance pairs.

	To make matters even more confusing, many pulp-insulated
cables have no binder strings or tape!  The binder groups have a twist
which allows their identification as a unit, and the relative position
of the binder groups when the cable is viewed in cross-section allows
the identification of the particular binder group.  Such binder groups
are therefore arranged in concentric layers, with each layer being
divided into binder segments.  There are also umpteen different binder
coding schemes used for pulp-insulated cable.  For the sake of
simplicity, while I am using the term "binder group" in this article,
in reality I am referring to a cable "unit", which may in fact not
have any binding strings or tape.

	As a result of the above, believe me, a damaged pulp-insulated
cable is a real mess!  Also, bear in mind that PIC cable did not come
into general use until the 1950's, so prior to that time
pulp-insulated cable was the ONLY type of outside plant cable.

	Restoration of a damaged pulp-insulated cable is performed by
tone tracing or other electronic identification means on EACH AND
EVERY pair.  Restoration starts by picking a red/blue tracer pair as a
means of establishing telephone communication between the cable
splicer and the central office.  At least there aren't that many
tracer pairs to choose from. :-)

	The cable splicer cuts back the cable and attempts to identify
the binder groups, starting with the CO-side FIRST.  Picking one
binder group at a time, a craftsperson in the CO sends tracing tone on
the first pair in a binder group.  A test probe with a sensitive
amplifier is used at the cable site to detect this test tone and
therefore identify the pair.  Such a tone tracing arrangement works by
capacitive coupling between the test probe and the cable pairs, so a
cable splicer can rapidly scan for tone by merely brushing the test
probe against fanned-out cable pairs.

	As soon as the CO-side of a pair is identified, the pair is
placed in a numbered slot on a "restoral board", and a connection is
made to the pair using insulation-piercing clips.  A restoral board
consists of two boards (a CO-side and a subscriber-side) with 100
pairs of insulation-piercing connections on each board, with several
feet of cable between the two boards.  The restoral board has two
functions: (1) to temporarily tag the identified conductors of a
binder group; and (2) to provide a temporary electrical connection
prior to splicing of the CO and subscriber sides of the severed cable.
More than one set of restoral boards may be used in a cable break, but
it does get crowded around the splice area pretty fast!

	Identifying the CO side of the severed cable is the EASY part,
made even easier with the use of a "front tap shoe" which connects to
a protector block in the CO.  A front tap shoe may make contact with
as many as 100 pairs at a time, and using a test cable will
conveniently terminate the pairs on a test panel used to apply tracing
tone.  There are also semi-automatic cable identification devices,
like those made by Automation Products, which send a coded signal on
each of 100 pairs, so that no craftsperson is necessary in the CO
other than to change the front tap shoe to another 100 pairs.  A cable
splicer uses a field identifier unit with a digital readout to
identify the pair number on a given pair in the binder group under
test.

	After the CO side of the binder group has been identified
using the above method, next comes the NOT SO EASY part.  A second
cable splicer then heads for the closest cross-connection box on the
subscriber side of the severed cable.  The first task is to establish
a talk pair to the cable splicer at the break.  Local battery for
talking is provided by a cable-splicer's test set, traditionally the
WECO 76C, although newer devices are now available.

	The second cable splicer then successively sends tracing tone
across each pair at the cross-connection box, which the first cable
splicer identifies at the site of the cable break.  The identified
pairs are then placed on the subscriber-side of the restoral board,
which not only tags their identity, but makes a temporary electrical
connection.

	What makes identification of the pairs on the subscriber-side
of the cable break difficult is that it is unlikely that the full pair
count of the cable will terminate at just one cross-connect location.
A high pair-count cable may in fact have its pairs terminated at a
dozen or more different cross-connection points, EACH of which will
have to be visited in order to send tracing tone to the cable break
site and identify the full pair count.  Sometimes pairs never even
terminate at a cross-connect location, but instead terminate directly
at a large customer location - which is yet another place that may
have to be visited.

	In most instances, none of the above tracing effort is
necessary in the case of a PIC cable break, since each pair in PIC
cable is by its very nature self-identifying through its own color and
that of its binder group color.  One does not truly appreciate this
"feature" of PIC cable until one experiences the effort necessary to
repair a pulp-insulated cable.

	Installing new pulp-insulated cable was not so difficult since
at intermediate splices pairs in a binder group were merely joined at
random.  Identification was only necessary at termination points.

	An additional problem is that in most cases it is not possible
to pull enough slack in a damaged cable to reconnect the severed
pairs.  A length of jumper pair wire is therefore placed in the
splice, and now one has TWO splices for every pair: one for each side
of the jumper.

	Yet another problem is that the sheath must be cut back at
least a foot in each direction of the cable break in order to
"visualize" and therefore identify the binder group placement.  For a
badly mangled cable it may be necessary to splice a complete length of
cable between the severed ends since 2-feet is about the limit to the
length of any one splice case.

	And to make matters even worse, how would you like to be a
cable splicer doing this work 15 feet above the ground working in a
small tent in sub-zero weather?  A motor vehicle accident that knocks
down a utility pole will create this exact situation!

	While a cable splicer's job has little glamor, it does have
some excitement and some hazards, and it is just as essential as that
of a switchman in the CO.  One of the most common hazards in working
with aerial cable today is electric shock from streetlight fixtures
with a broken ground that are attached to a utility pole.  In large
cities with extensive underground distribution, telephone cables may
often share manholes with high-voltage electric power distribution
cables.  The ultimate nightmare of a cable splicer is to accidentally
cut into a power cable instead of a telephone cable; a lead-sheathed
power cable is indistinguishable from a lead-sheathed telephone cable.
Such an accident has in fact happened on more than one occasion over
the years.

	In previous years the job of a cable splicer was more artisan
in nature, especially involving the working of lead used to join the
lead sheaths of cables and make splice cases.  The ultimate display of
"lead craftsmanship" was in the "wiping of a joint" which formed the
rounded end of a splice case where the cable entered the larger
diameter splice.  While many lead-sheathed cables still exist, today
there is very little hot lead work; lead cables are usually fitted
into conventional two-part separable splice cases using sealing tape
and a compression-type closure.  In previous years, many a cable
splicer has been burned from spilled molten lead or spilled hot
paraffin (used to "boil out" moisture from damaged pulp-insulated
cable).

	I'll close this article with an interesting bit of "cable
trivia".  First, some background.

	Many CO buildings still in use in large cities were
constructed between 1915 and 1930.  Such buildings have seen many
generations of telephone apparatus and have been "modernized" on a
number of occasions.  New apparatus is always installed and wired
before old apparatus is removed.  Telephone cable in CO buildings is
supported on "cable rack", which may be as wide as 24 inches.  Cable
is built up in layers, with the oldest cable being at the bottom of
the cable rack; the bottom layer is laced to the cable rack with waxed
twine ("12 cord", for the benefit of any WECO people reading this who
have "paid their dues" :-) ).  Each successive layer of cable is laced
to the previous layer.  It is not unusual in a large CO to have a
SOLID mass of cable 2 feet wide by 2 feet high on a single cable rack.

	In the above situation, much of the lower "layers" of cable in
a cable rack will be non-working cable which connected apparatus that
was removed years ago.  The labor necessary to remove such old cable
is significant, so usual practice is to just leave the lower layers in
place.  As a shortage of wiring space develops, an operation referred
to as "cable mining" is performed to remove the bottom layers of cable
and re-stitch the upper, working layers back to the cable rack,
thereby freeing up space for new cable layers.

	Cable mining is only done when absolutely necessary, so if
space is still available it is not unusual for a cable rack to have
bottom layers of cable that are 60 or more years old.  Such a
situation still exists today in many older metropolitan CO buildings.

	An interesting "environmental" problem has been "discovered"
in the past 10 to 15 years which now dictates that cable mining be
conducted with the utmost care.  There are actually two problems:

1.	Plastic sheaths for central office power and signal cable did
	not come into general use until the 1950's.  Prior to this time
	cable sheaths were made from cotton or silk.  In the case of
	power cable, some styles of cable were covered with an asbestos
	sheath to prevent accidental fires.  While asbestos-sheathed
	power cable has not been used since the 1950's, much of this
	cable still remains on cable racks. 

2.	While it may be hard to imagine today, large CO's were periodically
	plagued with mice during the 1920's and 1930's.  These mice would
	chew on cable, thereby causing faults.  Mice particularly loved
	the area around cord positions at DSA and toll operator facilities;
	the mice like to run on the inside multiples of such cord boards.
	Crumbs of food brought in by operators would attract such mice.

	In an effort to control this mice problem, some brilliant WECO
	engineer (who in all fairness did not know any better) during the
	1920's came up with the clever idea of impregnating the cloth
	sheath of central office and switchboard cables with ARSENIC in
	order to deter the mice from chewing the cables.  As a result,
	some CO cable installed during the 1920's and 1930's contains
	arsenic.

	So, today, some cable mining must be carried out with the
utmost caution in order to avoid the hazards of asbestos and arsenic!

<> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
<> UUCP  {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry
<> TEL 716/688-1231 | 716/773-1700  {hplabs|utzoo|uunet}!/      \uniquex!larry
<> FAX 716/741-9635 | 716/773-2488      "Have you hugged your cat today?" 

Subject: Some Realities About Repair of Damaged Aerial Telephone Cables
Date: 17 Mar 91 23:40:50 EST (Sun)
From: Larry Lippman <kitty!larry@uunet.uu.net>

In article <telecom11.210.4@eecs.nwu.edu> john@zygot.ati.com (John
Higdon) writes:

> This talk about the problems in Rochester reminds me of a telling
> situation that happened right here in my neighborhood a couple of
> years ago.

> Almost simultaneously the cable, ALL of my phone lines, and the
> electricity went dead. A short time later, fire engines were screaming
> down the street. It seems that some trees had caught fire in the next
> block and had taken out all the services on the poles nearby.
> [details deleted]

> What is interesting is the order in which the services were restored.

	I don't see anything surprising here, as I will point out in
detail.

> Within a very short time after the fire was extinguished the cable was
> restored. I have some battery operated TVs and was able to observe
> this for myself.

	There are one, or perhaps two aluminum-sheathed coaxial cables
involved.  The necessary splices for two coaxial cables can be made in
less than ten minutes, with the greatest amount of time being that
required to get the ladder in position.  Lashing say, twenty feet of
new of coaxial cable would probably not require more than half an
hour.

> An hour or so after that, the electricity came back on.

	No big deal, either.  My guess is twenty minutes per
individual primary or secondary conductor per pole span, and/or sixty
minutes per pole span for new triplex with one or two service drops.

> As it turned out, telephone service was restored by late afternoon,
> about twenty-four hours after the outage began. Not very impressive.

	I suspect you may be rather harsh on the local telephone
company.  Since you have not described the type of cable or estimated
a pair count (which I suspect you probably could do), I can't give a
really specific response.  However, I'll address a few general issues.

	First, in the case of damage to a telephone cable, it is
necessary to cut out an entire defective section, and replace it with
a new section of cable which must be spliced at *both* ends.  If you
had a 100 pair cable, one would have to splice 100 pairs at one end of
the section, and 100 pairs at the other, for a total of 200 pairs or
400 individual wire connections.

	If it were a major feeder cable, the pair count could be 200,
400, 600 or more pairs - multipled by two for the number of splices.

	While much cable splicing is performed using multiple splices
that splice 25 pairs at one time (like 3M MS2, WECo 710, etc.),
instead of the traditional one-wire B-connector or 3M UG connector,
such splicing still takes time.  The last thing that any cable splicer
wants is to go back and open up a splice because of a split or
transposed pair.

	The worse possible scenario is that the damaged cable was
lead-covered pulp insulation.  Ever see the color coding on a 101 pair
pulp cable?  You have fifty pairs of white/green, fifty pairs of
white/red plus a red/blue tracer pair.  Repair of such a cable
requires identification of EACH pair from BOTH the CO end and the
subscriber end.  Consider how much labor is required if say, you had a
404-pair or higher pair-count pulp cable.

	The cable in question may well be pressurized; it certainly
will be if it is a pulp cable.  Repair of damaged pressurized cable
usually involves building a "pressure" dam at each end using epoxy
cement, along with creating a pneumatic connection to temporarily
purge the cable with dry nitrogen.  Pneumatic continuity is later
restored when the splices are complete.

	Sheath preparation of aerial cable requires care in order to
maintain a low-impedance grounding path, in addition to any sealing
requirements if the cable is pressurized.

	Following a cable break, the first thing that a telephone
company will usually do is check their outside plant records to see of
any emergency services or special service lines are affected.  If
*justified*, "restoral boards" may be set up at both ends of the
damaged cable section to effect temporary continuity for critical
pairs.  Using a restoral board approach, critical pairs could be
temporarily restored in a few hours; the longest delay is searching
plant records and getting pair identification data to the field.
Placing restoral boards crowds the damage site and significantly
prolongs the repair and splicing process.  Ain't no way that restoral
boards will be used for POTS pairs.

	If many pairs are affected, a craftsperson in the CO may pull
the protectors to open the circuits and clear any potential permanent
signal alarms.  Following the cable repair, the protectors are then
replaced to restore service.

	All of the above takes *time*.  My guess is that a two-person
crew can replace a 100 pair cable section in about six hours if the
cable is PIC and unpressurized.  A four-person crew can reduce that
time by about one third.  A longer time is required if more than 100
pairs are involved, but it is not a linear relationship since certain
common work must be performed regardless of the number of pairs (i.e.,
a 200-pair cable may require only 20% more time than a 100-pair).  If
the cable is pulp, all bets are off.  A well-utilized 101 pair pulp
cable may well require fifty or more labor-hours to repair due to all
of the necessary identification procedures.

> The cable company had its act together. Its service restoral (while
> hardly essential) was first rate.

	Give me a break.  Their repair effort was absolutely trivial
by any reasonable comparison!

> PG&E took three hours to restore service. PG&E is probably the worst
> electric utility on the planet so for them it was probably miraculous.

	Sounds about right for one pole span.  No big deal here; one
visually matches a few wires.  Not even any color codes to match. :-)
No checking of plant records is even required (except to identify any
life-support locations).

> But wiping up the rear was Pac*Bell, who was too wimpy to even
> begin work on its cable until the next day.

	First of all, unless there is some dire crisis (sorry, but
POTS service does not qualify), a telephone company will generally not
work on aerial cables while the electric power utility is still
working on the same poles.  This is just standard safety practice in
the telephone industry; I'm sorry if you think it's "wimpy".  The fact
that the CATV company completed their repair before the electric power
utility does surprise me, however.

	Replacing aerial cable during nighttime hours (which I assume
we have here) is a very undesirable situation due to the difficulty in
obtaining good site illumination.  Yes, I know there are such things
as flood lights, but the attention to detail necessary for telephone
cable repair work is orders of magnitude greater than for electric
power lines.  If solely POTS subscribers were affected, and if the
damage occurred at night, in my opinion a reasonable "value judgment"
on the part of telephone company outside plant supervision would be to
wait until morning.

	So, let's say damage occurred at 7:00 PM, the electric utility
completed its work by 10:00 PM, the telephone company elected to
repair on the day shift, and one shift was required to effect repairs,
the overall time to restore service may well be 24 hours.  While you
may not be very happy about the situation, this is just a fact of
life.


Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231       {boulder, rutgers, watmath}!ub!kitty!larry
FAX:   716/741-9635   [note: ub=acsu.buffalo.edu] uunet!/      \aerion!larry

Date: Sun, 17 Mar 91 23:01 PST
From: John Higdon <john@zygot.ati.com>
Reply-To: John Higdon <john@zygot.ati.com>
Organization: Green Hills and Cows
Subject: Re: The Order of Repair

"Marc T. Kaufman" <kaufman@neon.stanford.edu> writes:

> Let's see ... the cable company had one "pair" to restore, and was
> probably lowest on the pole, having been established last.

It is a dual cable system. Have you ever worked with the type of coax
that is used in cable systems? It is semi-rigid and a bear to
manipulate. Also, it is installed ABOVE the telco cable (as are most
that I have seen around the country). So the cable people had to work
around the damaged telco cable to fix the TV feed. The fact that PG&E
was working on the 12KV lines did not seem to bother them much.

> PG&E also had one pair to restore, well maybe four if the pole had
> the maximum number of house drops.

PG&E had house drops, three 12KV primary wires and a transformer to
replace. Maybe since it was that company's negligence which caused the
fire a decision was made to hustle it.

> I don't blame the phone company for not wanting to work while PG&E is
> on the pole stringing 12KV wires.  And how easy is it to put up a new
> splice box (or two) in the rain with only the truck's spotlight for
> illumination?

That is a good excuse for after the sun went down (at 9PM), but what
were they doing for the previous seven hours? When electricity came
back, there were still three or four hours of daylight left. Actually,
this is a common story with Pac*Bell. When the trouble people come out
and determine that the job will require cable splicers, then you can
be assured that it will be a "next day" job. Besides, what would one
need a phone for anyway? To report a fire? :-)


        John Higdon         |   P. O. Box 7648   |   +1 408 723 1395
    john@zygot.ati.com      | San Jose, CA 95150 |       M o o !

 






































































































































































































Index Home About Blog