Never
begin installation of telephone wiring devices on a roughed-in job until
the rough-in wiring has been tested for shorts, grounds, and opens.
When
starting with a verified rough-in telephone wiring system, it is possible
with proper methods to detect an error in device wiring at the time the
error is made. This way, if device installation is completed and a problem
shows up, it is likely that the fault lies in the device termination rather
than with the building wiring.
Failure
to install proper wiring and devices before occupancy can also cause serious
disagreements and builder or homeowner dissatisfaction. These problems often
arise when the occupant requests additional lines from the exchange carrier,
only to be told the wiring is inadequate or "defective." Avoid
these disputes by using proper materials and methods in the first place.
Some
sophistication is required when troubleshooting telephone wiring systems
because there are many ways problems can be created if the multi-color coded
conductors are not properly matched, and devices not correctly wired. Polarity
must always be observed, especially when making the transition from one
color code to another. Most electrical house wiring problems show up immediately
with a blown fuse or activated circuit breaker-but many telephone wiring
system problems do not show up immediately, and often seem to get more complicated
if repairs are attempted by untrained persons.
Always
use proper materials to prevent trouble. The best wire choice is UL
listed, NEC Article 800 compliant, four twisted-pair jacketed inside wire.
Quad wire (pairs not individually twisted) is generally not suitable because
it is only designed to carry one analog voice circuit (the other wires are
for ground and accessory functions). Thus Quad wire should not be used with
multiple lines, key systems, PBX systems, digital phone sets, or data applications.
Perform
the following tests for each pair, after having made sure that the system
is not connected to the network ("pull the plug" at the demarcation
point first) or, more accurately, do not connect to the network prior to
completely installing and testing all components.
In
commercial applications, test horizontal runs prior to cross-connecting
at the telecommunications closet, if one is present.
2T.2.1. BASIC TESTING BEFORE TRIM-OUT
1)
Do a visual inspection of wire color matching to assure that the right access
line is assigned to the right set of pairs, and that Tip (+) and Ring (-)
are assigned to the proper pins.
2)
Next, test each pair for a) continuity, b) shorts to ground, c) shorts to
other pairs ("crosses") d) reversed polarity ("roll").
Diagram: Common Wiring Faults
2T.2.2. USING A BATTERY AND VOLT-OHM METER (RESIDENTIAL)
- 1) Find a reliable ground connection, and check each lead at each outlet
for a short(s) to ground. There should be no continuity between any of
the leads and earth ground.
- 2) Assure that the network is disconnected. Then connect the battery
across the Tip and Ring leads of each pair at the closest point available
to the demarcation point, but not on the network side. Connect the positive
side to Tip and the Negative side to Ring.
- 3) Go to each outlet and perform the following tests with the volt-ohm
meter for each pair:
- 3a) Verify that the polarity of each pair is correct with Tip at
positive voltage and Ring at negative.
- 3b) Verify that there is no continuity with any other pair at the
outlet by checking the Tip lead against all other leads, and then
the Ring lead against all other leads.
2T.2.3. USING A SPECIALIZED CONTINUITY TESTER
Most
continuity testers provide one or more LEDs to indicate shorts, opens, and
polarity. The tester provides battery voltage and if a short exists, the
appropriate LED will light.
- 1 ) With the leads unterminated at either end, connect the continuity
tester across the leads of each pair in succession. Test also at the outlet
for continuity between the Tip lead of each pair with all other leads,
and then the Ring lead with all other leads, to assure that there are
no shorts to them.
- 2) Then short the far end by metallic means. The tester will light the
appropriate LEDs to indicate proper polarity. (A toner and probe can be
used to identify the proper cable, if necessary.)
Note:
This part of the test is usually not performed in high-volume commercial
installations.
2T.2.4. USING A TONE GENERATOR AND INDUCTIVE PROBE
These
tools are used together in identifying one specific pair from others. The
tone generator (toner) is attached to one end of a vacant pair which must
be traced to find the location of a fault, or identified so it can be spliced
for a new circuit. Then the probe is used to "pick up" the tone,
tracing the tone signal either along the wire or at the other end. For this
test it is assumed that a continuity tester has already been used to verify
continuity, polarity, and lack of shorts, yet a fault still exists.
- 1) Connect the toner to the leads at the outlet.
- 2) Take the probe to the distribution device or telecommunications closet.
When the probe is held near the pair carrying tone, the tone will be quite
strong. (Some lesser volume may be picked up on adjacent leads or pairs,
but this is normal.) The pair carrying tone can be verified
by touching the tip of the probe across the leads. The tones will cease
if that pair is the one carrying the tone. At this point, assuming the
continuity tests showed no faults, the leads are normally "punched
down" in commercial applications. In residential applications they
may already have been terminated at the distribution device.
- 3) With the toner still on at the outlet, a buttset can be connected
across the pair. The impedance of the buttset provides additional information.
It should pick up the tone, which should be relatively loud. If the tone
is faint, an open (break) in the circuit is likely. If the tone is not
heard at all with the buttset, the likely fault is a short.
- 4) In Commercial applications, an earth ground point is available in
the telecommunications closet. Test for shorts to ground by attaching
one lead of a continuity tester to that ground and running the other lead
down the clips of the punchdown block (assuming the clips are accessible).
In this manner the test for shorts to ground can be made after the leads
are terminated.
2T.2.5. TESTING FOR SHORTS AND OPENS
(CONTINUITY)
The
continuity setting of the Tone Test Set is used to locate shorts and verify
continuity (no opens). A full short is indicated with a continuously lit
green LED. A resistive or dirty open condition is indicated by a dim or
blinking LED.
- 1) Locate and identify each pair on both the outgoing and incoming roughed-in
wiring.
- 2) Test the tester (to verify it is operational) by touching the leads
together and looking at the LED for indication of a full short (steady
LED). Connect the test set leads to the outgoing pair (polarity does not
matter here) and set the test set switch to CONT. There should be no indication
of continuity until the same pair on the incoming (return feed) is shorted.
Any continuity indication before shorting the return feed pair means there
is a fault within the pair (or multiple grounds). Only when the return
feed is shorted should there be a solid short indicated by a continuous
unchanging LED like you see when shorting the leads of the tone test set.
If the LED is dim or blinking, there is a resistance or intermittent fault
in the pair. Poor splicing or corroded splices will result in a high-resistance
loop. The resistive connection or splice must be located with the probe,
and corrected using a splicing tool, before connecting the circuit. Dial
tone connections to a resistive loop will result in static noise, poor
dialing and ringer operation, and low loop current.
2T.2.6. TESTING FOR CROSSES
A
cross is a common fault caused by sloppy device wiring which allows a short
to develop between two terminals. Usually this occurs because too much bare
copper conductor is stripped and then the tail is not trimmed after connection.
Testing
for crosses involves using the continuity mode of the toner to locate any
electrical path from either conductor of one pair to either side of another
pair. This is done as follows:
- 1) Attach one test set clip to the tip side of a pair (this is your
fixed lead). Using the other lead, check for continuity to both sides
of every other pair.
- 2) Next, change the fixed lead to the ring side of the same pair and
repeat Step 1.
- 3) Repeat this sequence for each pair. If there is any continuity indication,
a cross is present in the wiring.
If
a cross is located before any devices are installed, it is likely that a
nail or other fastener has been driven into the roughed-in wiring. Before
the wiring can be completed, a cross must be located and repaired, or isolated
out of the system.
2T.2.7. TESTING FOR SPLITS
A
split occurs when two wires of a pair are split (separated) and improperly
matched with wires from another pair (for example, tip lead of pair #1 matedwith
ring lead of tip #2). A split will normally be located during the tests
for opens and continuity previously described. Splits most often occur during
splicing operations in low light, or when the splicer is tired or distracted.
- 1) Connect the tone test set in the TONE mode to the two wires in one
pair at the end of the cable.
- 2) Using the speaker probe, trace the tone along the cable pairs to
the splice location. Once there, identify the wires you believe are the
pair of interest, and use the probe tip to short these two wires.
If
the pair is split, the tone will remain strong when the wires are shorted.
If
the pair is straight (not split), the tone will disappear when the wires
are shorted.
Splits
can also be isolated using a lineman's test set with the Tone Test Set.
Refer to your lineman's test set instructions for details.
2T.2.8. TESTING FOR REVERSED POLARITY
(ROLLS)
A
rolled pair results when the tip and ring leads are reversed in connecting
to the network. This may be done while splicing or installing a device.
Proper polarity is essential for proper operation of some tone dials. A
roll will not affect rotary dialing.
If
a true tone telephone set does not produce tone beeps when the keypad is
pushed, polarity may be reversed. If changing the polarity causes the set
to beep as the keys are pushed, but numbers are not dialed (i.e., dial tone
stays on), then the central office is not equipped to provide touch dialing
on that particular line. Some telcos charge a monthly fee to provide touch
dialing capability on a line; if the fee is not paid, they may inhibit tone
dialing electronically.
If
a push button set produces dial pulses when the keypad is operated, the
set is not really a tone set. It may be called a "universal dialing
set" but it does not signal to the central office with tones. When
the keypad is operated, numbers are pulsed out just like a standard rotary
dial. This type of set is easily identified by the letters "TE-19"
(Terminal Equipment-Rotary) as the last three items in the FCC registration
number printed on a label attached to the telephone. If the last three letters
are "TE-T" (Terminal Equipment-Tone), then the set is a "true
tone set" that signals the central office with tones instead of rotary
dial pulses.
The
Leviton Tone Test Set is equipped for polarity testing with a visual indicator.
If dial tone is connected to the pair under test, the presence of a roll
can be detected as follows:
- 1) With the test set in the OFF position, plug in the tone test set
with the modular connector.
- 2) Observe the LED. A green LED indicates correct polarity; red means
reversed polarity (a 'roll').
If
this polarity test is performed with the toner connected to a pair using
the test clips instead of the modular plug, you must be certain you are
connecting the leads to the proper conductor. Tip is normally positive (connect
the black lead) while ring is normally negative (connect the red lead).
If
using central office battery (dial tone) for this test, you must be sure
to check polarity during the dialtone BEFORE a number is dialed. Polarity
will sometimes be reversed by the central office during completion of a
call.
Some
people prefer to test polarity with a buttset and tone test set, without
dial tone connected. There are several methods that will work. The first
method uses the two test devices together:
- 1 ) Switch the Leviton tone test set to the CONT position. In this setting,
the battery inside the unit is connected to the test leads. Connect the
red test lead to ring, and the black lead to tip of the pair under test.
- 2) Clip on the buttset with the switch in the monitor position. Be sure
to observe polarity when connecting the buttset (red lead to ring, black
to tip). Indicators on the buttset will show voltage is present and there
is proper polarity (refer to your buttset instructions for details).
- 3) Using a modular breakout adapter, you can plug directly into each
device and connect the buttset leads to the adapter.
Some
installers prefer to use a 12-volt lantern battery as the source:
- 1) Simply plug the tone test set directly into each modular jack, instead
of using a modular adapter and the buttset clip leads.
- 2) If polarity appears reversed at ALL devices, first check the network
polarity at the demarc jack. Then check at the common connecting point
to see if the roll is there, affecting all devices. If the roll appears
on ALL devices beyond a certain point, check the continuing connections
at the device just before that point. If only one device shows a roll,
the problem is probably in the connection of that single jack.
If
you discover the pair rolled on the network side, report the problem to
the utility. Do not reverse the inside wiring system to accommodate a network
reversal -- the network error may be detected at any time and "made
normal." This would reverse your connection again, resulting in a callback.
