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> I noticed that coming into our home that the plate with outside wires had
> 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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