Submission for mod.telecom
la...@kitty.uucp.uucp
> red and green connected to two posts and that the wire going to the phone had
> the green connected to the red and the red connected to the green. Does this
> matter? (ie is the line polarized or does it just act like two wires with
> A/C electricity. Thanks in advance
A telephone line has polarity, since direct current is used to
excite the telephone instrument. Such excitation not only powers the
telephone transmitter (i.e., microphone), but operates any DTMF (i.e.,
Touch-tone) dial circuit, dial pulsing circuit (in newer solid-state
telephones), electronic tone ringer, solid-state network in newer telephones,
etc. In addition, DC current flow through the telephone loop indicates to
the central office apparatus that the telephone requests service and is in use
(called loop signaling).
While the telephone ringing signal sent from the central office
is 20 Hz AC, the AC is superimposed upon a DC signal, so there is still
always a DC potential present. The purpose of such superimposition is to
assure immediate and reliable detection of called party answer ("ring trip").
The nominal on-hook (i.e., telephone is idle) DC voltage across
a conventional telephone loop is -48 volts. Notice that I use the word
"conventional", since a small but nevertheless significant percentage of
telephone lines run through subscriber line concentrators or loop extenders;
under these circumstances, the on-hook voltage can be as little as -6 volts
DC or as high as -96 volts DC, depending upon the type of concentrator or
loop extender apparatus.
The vernacular used to describe telephone line polarity are the
terms "tip" and "ring". The tip side of the line is in effect positive
ground, and the ring side of the line is in effect a negative battery
voltage (i.e., - 48 volts DC). While I have called the tip side of the
line a "positive ground", it is not a true ground since the actual ground
connection occurs in the central office apparatus through the DC resistance
(typically 200 ohms) of an inductor or transformer winding. As a result,
the on-hook measurement of the tip side of the line to an earth ground
(i.e., water pipe) at the subscriber location will show a small voltage
differential. On-hook measurement of the ring side of the line to earth
ground at the subscriber location will show the nominal -48 volts.
The following are some common equivalent designations for the tip
and ring polarity of a telephone subscriber line:
DESIGNATION TIP RING NOTES
green wire of green/red pair X
red wire of green/red pair X
black wire of black/yellow pair X #1
yellow wire of black/yellow pair X #1
white wire of white/blue pair X #2
blue wire of white/blue pair X #2
white wire of white/orange pair X #3
orange wire of white/orange pair X #3
L1 terminal in telephone set X
L2 terminal in telephone set X
+T terminal in telephone set X #4
-T terminal in telephone set X #4
NOTE 1: When used as pair for second telephone line in 4-wire cable
NOTE 2: White is equivalent to white wire with blue stripes, and
blue is equivalent to blue wire with white stripes when striped
cable is used.
NOTE 3: White is equivalent to white wire with orange stripes, and
orange is equivalent to orange wire with white stripes when striped
cable is used; typically used for second telephone line in a
multi-pair cable.
NOTE 4: Common designation for GTE/Automatic Electric telephones
Most telephones manufactured today are polarity independent; i.e.,
the telephone will work even if tip and ring are reversed. However, not
all telephones are polarity independent; two notable exceptions are:
telephones used for multi-party lines (which are fortunately disappearing!);
and older Touch-tone telephones (whose dial won't work if tip and ring are
reversed.
Even though most telephones are polarity-independent, it is still
a good idea to maintain correct color/terminal polarity in any telephone
wiring. Why? Because it will simplify troubleshooting. As an example,
say you experience a loud hum on your telephone line; a typical cause is
either tip or ring accidentally shorted to earth ground. If you remove your
telephone instruments from their jacks, and isolate the inside wiring from
the outside line, using an ohmmeter you can determine which wire is shorted
to ground. If you detect ground leakage on say, the tip side of the line,
you will know exactly which color of wire and which terminal is to be suspect
throughout the entirety of your inside wiring.
Maintaining proper tip/ring polarity on all outside cables is very
important to the telephone company, since various kinds of test equipment
and procedures used from the central office can pinpoint the precise location
of a cable fault; an important assumption for many of these fault-locating
procedures is that the outside cables always have tip/ring correspondence.
<> Larry Lippman @ Recognition Research Corp., Clarence, New York
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Michael Natkin
In article <870313041...@seismo.CSS.GOV> la...@kitty.UUCP writes:
> Maintaining proper tip/ring polarity on all outside cables is very
>important to the telephone company, since various kinds of test equipment
>and procedures used from the central office can pinpoint the precise location
>of a cable fault; an important assumption for many of these fault-locating
>procedures is that the outside cables always have tip/ring correspondence.
>
><> Larry Lippman @ Recognition Research Corp., Clarence, New York
I've always wanted to know how the locating of cable faults works -
i have some hypotheses, but maybe you would care to edify myself and
other readers on this subject?
michael natkin
nat...@degas.berkeley.edu
Jon Solomon
and they found it by using a buzzer on the line which they tested for using
a probe connected to their butt-in set. It was fun to watch.
--jsol
-------
gary%perc...@tektronix.tek.com.uucp
There are several methods used by the telco's for line testing. The simplest
is that all cables have a known (very precisely) resistance and capacitance per
foot. If a short is applied at the end of a cable (or a known resistance, etc),
then a calibrated ohmmeter can tell you how far away the short is. If you are
looking at a clean open, you can apply the same principle with a capacitance
meter (though, in practice, it is not as accurate). By knowing WHAT is hanging on the end of your cable, you can quickly tell the status of the pair AND the
station. This is why the telco's fought so hard about registration. They
really didn't care about the equipment, they just need to know what it "looks"
like, for trouble isolation purposes.
la...@kitty.uucp.uucp
In a recent reply to my original article, rdsnyder@MIT-CCC writes:
> > DESIGNATION TIP RING NOTES
> > green wire of green/red pair X
> > red wire of green/red pair X
> > black wire of black/yellow pair X #1
> > yellow wire of black/yellow pair X #1
> >
> > NOTE 1: When used as pair for second telephone line in 4-wire cable
>
> The yellow/black pair above is reversed.
> Yellow is TIP of the second pair in quad (4 cond. Gr/Rd/Yl/Bk cable) and
> black is RING of the second pair.
Sorry, but you are incorrect. Black is always TIP and yellow is
always RING. This true not only for inside station wiring, but for outside
direct burial two-pair "B" Service Wire. I refer to AT&T System Practices
Sections 461-610-100 and 460-300-143 as examples in case anyone doubts
my statement.
You may be confused by looking at the end of a modular plug and
thinking that TIP is one side of center, and RING is the other; the pin
locations on modular connectors are transposed every other pair (up to
the full 4-pairs for an RJ-45).
> The yellow/black pair is also used in key systems as the A/A1 pair. The
> station equipment shorts A & A1 together while off-hook.
In this application, the A-lead is the actual control line, and
the A1-lead is ground. The A-lead is always the "tip" conductor and the
A1-lead is always the "ring" conductor, when the two are in the same pair.
> White, red, black, yellow and violet are tip, and blue, orange, green,
> brown, and slate are ring.
Except, of course, when white/red, white/black, and yellow/red
is used for distributing frame jumper pairs... :-)
<> Larry Lippman @ Recognition Research Corp., Clarence, New York