atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring Curious about lead/pulp cables

Recently, I was working in the basement of one of the older buildings in town. I discovered the old main feeder cable for the building and followed it through several perfectly wiped splices, each providing a drop to a terminal block, which then broke out with bridal wire (I think its called) to each of the units in the building. I was fascinated to find the installation virtually untouched since it was installed. None of it was still in service, a newer 100 pair drop was installed some 20 years ago and the buttset confirmed this. The main question I have is how did the installer/splicer make heads or tails of this stuff. One of the drops was cut, so I didn't feel bad cutting off about an 8 inch piece to display with my collection. I stripped back a couple inches and I know that's not enough to see any pair twists, but there was some color coding. There are reddish wires, white ones and white with a black stripe. The particular piece I grabbed appears to be 16 pair. Does that sound right? I'm really curious about this stuff now that I've actually seen it in the flesh. At first I wanted to take a big chunk out to keep, but then I thought about how neat it was to find it so pristine that I left it alone for someone else to find. I hope it's left alone.

I could be wrong but I think the white with black stripe pair was for the splicer to use to talk from manhole to manhole.

Pulp cable always included at least one spare pair. While it was often used as a talk pair as mentioned, it could also be used to replace a failed pair. 25, 50 and 100 pair cables were 26, 51 or 101. Above that, it became 202, 303, 404, etc.

The pairs were all one color per binder, however different binders were different colors, white/green, then white/red, and so on.

The core of the cable was waxed so that all of the pairs stayed in exactly the same position in the binder. Looking at the cut end of the binder, the pairs could be peeled away in clockwise or counter-clockwise order and with practice, they could be kept in the correct order. Over time, it was determined that since any pair could be any color, the general manner in which splicing was accomplished was to tone each pair while splicers talked to each other over the spare pair. That way, they didn't have to be so careful in holding the core intact. This also helped in instances where they might we working on an existing splice.

Although pulp/paper insulated pair cable was originally designed because suitable plastic compounds had not yet been invented, it continued to be manufactured well into the 1980s with an overall polyethylene outer jacket. This was because paper insulation took up considerably less space than plastic, hence smaller cable diameters which worked well in congested ducts, vaults and manholes.

The problem with these cables is that they must be pressurized in order to block water penetration. If water got into a splice, the paper would swell and the cable would be ruined. Maintaining this pressurization required sensors (transducers) to be attached to splices that would send an alarm to the central office via a dedicated pair to alert maintenance staff of a pressure leak. Since each transducer was on an independent circuit, they could pinpoint the location of the leak and fix it quickly.

Paper-insulated cable was invented before colored plastic material was perfected for wire insulation. The lower count cables (6 pairs through 51 pairs) pretty much follow the same rules that apply to the larger subscriber cables, that range from 51 to 3,000 pairs. The difference is just in the number of pairs, so I will explain the bigger ones and you can get an idea of what's going on.

The pairs are arranged in groups of 50 pairs. All the pairs in a group are color coded the same. The Tip sides are always white (actually a bit off-white) and the Ring sides have a solid color. These colors are red, blue, orange and green. Looking at the end of a cut cable, you can see the groups arranged in concentric layers. There will be groups of red, blue and orange, seemingly random in their placement. There will be only one group in each layer that is colored green/white. That is the starting point for counting the groups.

Looking towards the field (called the "block" as in city block) one counts the groups clockwise starting with the green/white group. The mnemonic is "clock to the block." Looking back towards the CO, the groups are counted counterclockwise. "CO to COunter."

The splicer, after having prepared the splice (a whole lesson in itself) will connect all the pairs of the most central green/white group, randomly. The he will continue to select the next group, using the clock-wise/counter-clockwise method of counting the groups. Again, the 50 pairs are spliced randomly.

Once there is continuity from the field all the way back to the CO through all the intermediate splices, the next operation requires two splicers. They establish a talk wire, using a test set that sends tone and also can be used to provide talk battery. For simplicity, they pre-arrange which group to use for the talk wire. The guy in the CO sends tone on the first random pair in the green group. He waits for the field splicer to find the pair with his probe, and when he does, he tells the CO guy that he has identified it. Both splicers than take the loose end of the pair and push it through a slip of paper that has 50 holes punched in it, with the holes numbered from 1 through 50. This paper is called a "splicing board" and the process is called "boarding the pairs."

Finally, before the cable splices are wiped and pressure-tested, any defects are corrected at intermediate splices. the first piece of cable in the CO is then assigned to terminals on the MDF and the last piece of cable in the field is assigned to a terminal either on a pole, on the ground, or in a building.

Because lead/paper cable cannot easily be opened and closed in the field (generally because it has been placed in ducts in the ground, the manufacturer includes so-called "interstitial pairs."

(Continued) These pairs are colored with weird color combinations, such as red/black, yellow/blue, etc. They were placed in the "interstices" of the cable. That's a medical term that generally refers to the nerves that occupy the nooks and crannies of the brain. These are used to compensate for defective pairs that were identified during the manufacturing process. At each splice, the splicer finds those pairs and makes them continuous all the way along the run. Later, they can be used to by-pass defects. The number of interstitial pairs usually is one pair per 100 to 150 normal pairs. They can be quickly identified, and therefore they are often used for establishing a talk wire.

So, Ed and I each read your message from yesterday, each went about our business for a day, and each sat down at our respective computers to answer your inquiry about paper cable using almost the same words, AT THE EXACT SAME TIME. Where's Rod Serling when you need him???

What Arthur calls a "splicing board" we called a tag board and the direction of count away from the CO we referred it to the customer is always right. Different terms in different parts of the country.

Perhaps, Arthur, but you gave a much more detailed explanation than I did.

Great explanations, both of you guys.

I'm glad the OP appreciated what he saw. That kind of work was as much an art as anything.

Jim

No kidding, Jim. They made lead-sheathed cable look like artwork that rivals the nicest plumbing installations. Those days are gone for sure.