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heard. It all depends on what the tel co wants the loop to be used for. If a loop has gotten to be very popular with the local population or used
frequently for conferences, etc. the tel co may filter the loop to stop the unwanted "traffic". Usually, the filter will be removed after a few
months, though.
94. How Ma Bell Works by The Jolly Roger
In this article, I will first describe the termination, wiring, and terminal hardware most commonly used in the Bell system, and I will include
section on methods of using them.
LOCAL NETWORK
The local telephone network between the central office/exchange and the telephone subscribers can be briefly described as follows:
From the central office (or local exchange) of a certain prefix(es), underground area trunks go to each area that has that prefix (Usually more
than one prefix per area.) At every few streets or tract areas, the underground cables surface. They then go to the telephone pole (or back
underground, depending on the area) and then to the subscribers house (or in the case of an apartment building or mutli-line business, to a
splitter or distribution box/panel). Now that we have the basics, I'll try and go in-depth on the subject.
UNDERGROUND CABLES
These are sometimes inter-office trunks, but usually in a residential area they are trunk lines that go to bridging heads or distribution cases. The
cables are about 2-3 inches thick (varies), and are either in a metal or pvc-type pipe (or
similar). Rarely (maybe not in some remote rural areas) are the cables just 'alone' in the ground. Instead they are usually in an underground
cement tunnel (resembles a small sewer or storm drain.) The manholes are heavy and will say 'Bell system' on them. They can be opened with
«
a inch wide crowbar (Hookside) inserted in the top rectangular hole. There are ladder rungs to help you climb down. You will see the cable
pipes on the wall, with the blue and white striped one being the inter-office trunk (at least in my area). The others are local lines, and are
usually marked or color coded. There is almost always a posted color code chart on the wall, not to mention Telco manuals describing the
cables and terminals, so I need not get into detail. Also, there is usually some kind of test equipment, and often Bell test sets are left in there.
BRIDGING HEADS
The innocent-looking grayish-green boxes. These can be either trunk bridges or bridging for residences. The major trunk bridging heads are
usually larger, and they have the 'Western Electric' logo at the bottom, whereas the normal bridging heads (which may be different in some
areas -depending on the company you are served by. GTE B.H.'s look slightly different. Also, do not be fooled by sprinkler boxes!) They can be
found in just about every city. To open a bridging head: if it is locked (and you're feeling destructive), put a hammer or crowbar (the same one
you used on the manhole) in the slot above the top hinge of the right door. Pull hard, and the door will rip off. Very effective! If it isn't locked (as
usual), take a 7/8 inch hex socket and with it, turn the bolt about 1/8 of a turn to the right (you should hear a spring release inside). Holding the
bolt, turn the handle all the way to the left and pull out. To Check for a test-set (which are often left by Bell employees), go inside - First check
for a test-set (which are often left by Bell employees). There should be a panel of terminals and wires. Push the panel back about an inch or
so, and rotate the top latch (round with a flat section) downward. Release the panel and it will fall all the way forward. There is usually a
large amount of wire and extra terminals. The test-sets are often hidden here, so don't overlook it (Manuals, as well, are sometimes placed in
the head). On the right door is a metal box of alligator clips. Take a few (Compliments of Bell.). On each door is a useful little round metal
device. (Says 'insert gently' or 'clamp gently - do not overtighten' etc..) On the front of the disc, you should find two terminals. These are for
your test set. (If you don't have one, dont despair - I'll show you ways to make basic test sets later in this article). Hook the ring (-) wire to the
'r' terminal; and the tip (+) wire to the other. (By the way, an easy way to determine the correct polarity is with a 1«v LED. Tap it to the term.
pair, if it doesn't light, switch the poles until it does. When it lights, find the longer of the two LED poles: This one will be on the tip wire (+).
Behind the disc is a coiled up cord. This should have two alligator clips on it.. Its very useful, because you don't have to keep connecting and
disconnecting the fone (test set) itself, and the clips work nicely. On the terminal board, there should be about 10 screw terminals per side.
Follow the wires, and you can see which cable pairs are active. Hook the clips to the terminal pair, and you're set! Dial out if you want, or just
listen (If someone's on the line). Later, I'll show you a way to set up a true 'tap' that will let the person dial out on his line and receive calls as
normal, and you can listen in the whole time. More about this later... On major prefix-area bridging heads, you can see 'local loops', which are
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