jdearin@pacsbb.bpa.bell-atl.com (John Dearing) (08/04/89)
[Moderator's Note: I am sorry to advise that the original subject title
and header info was lost in transit between chinet and here. I reconstructed
the header, however the body of his letter made it here intact, and follows
below. PT]
Patrick,
I hope that this reply gets thru to you (email is sometimes flaky). In a
recent Telecom Digest article you asked what the color code was for
telephone wiring. As a Services Technician with over 14 years of service
with Bell of Pennsylvania, I thought I'd reply. The system employed
throughout the (used-to-be) Bell System was actually very simple. There wer
five colors assigned to "tip" and five colors assigned to "ring". This
gives a total combination of twenty-five pairs (very convenient!).
The colors assigned to the "tip" are;
white wt
red rd
black bk
yellow yl
violet vi
The colors assigned to the "ring" are;
blue bl
orange or
green gr
brown br
slate sl (sometimes mistakenly called gray)
Standard phone convention is to identify the "tip" first and then the
"ring" when referring to a pair. Thus, the first five pairs of a telephone
cable are the "white" pairs;
white/blue wt/bl
white/orange wt/or
white/green wt/gr
white/brown wt/bn
white/slate wt/sl
The next five are the "red" pairs:
red/blue rd/bl
red/orange rd/or
red/green rd/gr
red/brown rd/bn
red/slate rd/sl
And so on, until all twenty five pairs are identified. What happens
when there are more than twenty-five pairs in a cable? Simple, enclose each
twenty-five pair group in a color coded binder. And guess what the color
coding is for the binder. Yep, the same as the wires in the binder. The
first binder group is the "white/blue" binder the second is the
"white/orange" binder, and so on. If it is necessary to refer to the
twenty-sixth pair of a fifty pair cable it is referred to as "two
white/blue" or 2-wt/bl. The seventy-ninth pair in a one-hundred pair cable
is called "four white/brown" or 4-wt/bn. This all holds true for the first
twenty-four binders in a cable. The twenty-fifth binder is a little
different, and my recollection is a little hazy but I believe the binder
colors are white-white-blue. Yes that's two whites and a blue. It might be
two blues and a white. It's been a long time since I was in a cable over
six hundred pairs. One thing I know for sure is that they double up on one
of the binder colors after the twenty-fourth binder group.
There is also a convention for the positioning the pairs on connecting
blocks. The Ring is usually on the Right and the Tip is usually on the Top.
As you can see there is a pattern here, Ring-Red-Right and Tip-Top. I guess
this was done to make it easier for us dumb installers to remember! |-)
The only difference in the color coding between telephone cable (the
stuff used outside and strung along poles or underground in conduit) and
telephone inside wiring (the gray colored stuff in the walls and up in the
ceiling) is that the inside wire has each pair traced with the color of its
mate. That is, the first pair is a white wire with a blue tracer and its
mate is blue with a white tracer. This is done to avoid "splitting" a pair.
Splitting is getting the ring of one pair and the tip of another. In
outside phone cable each pair is twisted with its mate and the chances of
splitting a pair are not as great (although it's been known to happen ;-)).
With wiring done inside a house, a little history is in order. Back when
we had party-lines,(I know, we still do, but very few still in service and
none available for new service) three wires were necessary because a ground
was required to make the bell ring. So, the original phone wiring had three
conductors, red, green and yellow. Red and green were ring and tip
respectively and yellow was the ground. Then people started getting away
from party lines and into princess and trimline phones with lights in the
dial. The yellow was no longer the ground and a black wire was added and
the yellow and black were used to supply power for the lamps from a small
transformer. Time marches on, and now people are getting second lines
installed in their homes. Since the new phones get the power for their
lamps from the phone line directly, the yellow and black are now "spare".
The yellow is usually the ring and black is the tip. Of course, houses that
have been pre-wired with six-pair inside wire would normally have line 1 on
the white/blue pair and line 2 on the white/orange pair. In many pre-wire
installations I have found that the sixth pair (red/blue) was used for
transformer power, although I don't believe that was ever an official
practice.
I hope that this info is of some help. Feel free to put this into the
Digest, if you want.
John Dearing (jdearin @ pacsbb)