[Code of Federal Regulations]
[Title 7, Volume 11]
[Revised as of January 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 7CFR1755.403]
[Page 486-513]
TITLE 7--AGRICULTURE
CHAPTER XVII--RURAL UTILITIES SERVICE, DEPARTMENT OF AGRICULTURE
PART 1755--TELECOMMUNICATIONS STANDARDS AND SPECIFICATIONS FOR MATERIALS, EQUIPMENT AND CONSTRUCTION--Table of Contents
Sec. 1755.403 Copper cable telecommunications plant measurements.
(a) Shield or shield/armor continuity. (1) Tests and measurements
shall be made to ensure that cable shields or shield/armors are
electrically continuous. There are two areas of concern. The first is
shield or shield/armor bonding within a pedestal or splice and the
second is shield or shield/armor continuity between pedestals or
splices.
(2) Measurement techniques outlined here for verification of shield
or shield/armor continuity are applicable to buried cable plant.
Measurements of shield continuity between splices in aerial cable plant
should be made prior to completion of splicing. Conclusive results
cannot be obtained on aerial plant after all bonds have been completed
to the supporting strand, multigrounded neutral, etc.
(3) Method of measurement. (i) The shield or shield/armor resistance
measurements shall be made between pedestals or splices using either a
Wheatstone bridge or a volt-ohm meter. For loaded plant, measurements
shall be made on cable lengths that do not exceed one load section. For
nonloaded plant, measurements shall be made on cable lengths that do not
exceed 5,000 feet (ft) (1,524 meters (m)). All bonding wires shall be
removed from the bonding lugs at the far end of the cable section to be
measured. The step-by-step measurement procedure shall be as shown in
Figure 2.
(ii) Cable shield or shield/armor continuity within pedestals or
splices shall be measured with a cable shield splice continuity test
set. The step-by-step measurement procedure outlined in the
manufacturer's operating instructions for the specific test equipment
being used shall be followed.
(4) Test equipment. (i) The test equipment for measuring cable
shield or shield/armor resistance between pedestals or splices is shown
in Figure 2 as follows:
[[Page 487]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.024
(ii) A cable shield splice continuity tester shall be used to
measure shield or shield/armor continuity within pedestals or splices.
(5) Applicable results. (i) The shield or shield/armor resistance
per 1000 ft and per kilometer (km) for cable diameters and types of
shielding materials are given in Table 1 (English Units) and Table 2
(Metric Units), respectively as follows:
Table 1--Shield Resistance @ 68 deg.F (20 deg.C) Cable Diameters Versus Shield Types
[English Units]
----------------------------------------------------------------------------------------------------------------
Nominal resistance ohm/1000 ft.
Outside diameter inches (in.) -----------------------------------------------------------------------------
A B C D E F
----------------------------------------------------------------------------------------------------------------
0.40-0.49......................... 0.77 1.54 1.65 1.96 2.30 5.51
0.50-0.59......................... 0.64 1.28 1.37 1.63 1.91 4.58
0.60-0.69......................... 0.51 1.03 1.10 1.31 1.53 3.67
0.70-0.79......................... 0.44 0.88 0.94 ........... 1.31 3.14
[[Page 488]]
0.80-0.89......................... 0.38 0.77 0.82 ........... 1.14 2.74
0.90-0.99......................... 0.35 0.69 0.74 ........... 1.03 2.47
1.00-1.09......................... 0.31 0.62 0.66 ........... 0.92 2.20
1.10-1.19......................... 0.28 0.56 0.60 ........... 0.84 2.00
1.20-1.29......................... 0.26 0.51 0.55 ........... 0.77 1.84
1.30-1.39......................... 0.24 0.48 0.51 ........... 0.71 1.70
1.40-1.49......................... 0.22 0.44 0.47 ........... 0.65 1.57
1.50-1.59......................... 0.21 0.41 0.44 ........... 0.61 1.47
1.60-1.69......................... 0.19 0.38 0.41 ........... 0.57 1.37
1.70-1.79......................... 0.18 0.37 0.39 ........... 0.54 1.30
1.80-1.89......................... 0.17 0.35 0.37 ........... 0.51 1.24
1.90-1.99......................... 0.16 0.33 0.35 ........... 0.49 1.17
2.00-2.09......................... 0.15 0.31 0.33 ........... 0.46 1.10
2.10-2.19......................... 0.15 0.29 0.31 ........... 0.43 1.03
2.20-2.29......................... 0.14 0.28 0.30 ........... 0.42 1.00
2.30-2.39......................... 0.14 0.27 0.29 ........... 0.40 0.97
2.40-2.49......................... 0.13 0.25 0.27 ........... 0.38 0.90
2.50-2.59......................... 0.12 0.24 0.26 ........... 0.36 0.87
2.60-2.69......................... 0.12 0.23 0.25 ........... 0.35 0.83
2.70-2.79......................... 0.11 0.22 0.24 ........... 0.33 0.80
2.80-2.89......................... 0.11 0.22 0.24 ........... 0.33 0.80
2.90-2.99......................... 0.11 0.22 0.23 ........... 0.32 0.77
3.00-3.09......................... 0.10 0.21 0.22 ........... 0.31 0.73
3.10-3.19......................... 0.10 0.20 0.21 ........... 0.29 0.70
3.20-3.29......................... 0.10 0.20 0.21 ........... 0.29 0.70
3.30-3.39......................... 0.09 0.19 0.20 ........... 0.28 0.67
3.40-3.49......................... 0.09 0.18 0.19 ........... 0.26 0.63
3.50-3.59......................... 0.09 0.18 0.19 ........... 0.26 0.63
3.60-3.69......................... 0.08 0.17 0.18 ........... 0.25 0.60
3.70-3.79......................... 0.08 0.17 0.18 ........... 0.25 0.60
3.80-3.89......................... 0.08 0.16 0.17 ........... 0.24 0.57
3.90-3.99......................... 0.08 0.16 0.17 ........... 0.24 0.57
4.00-4.99......................... 0.07 0.15 0.16 ........... 0.22 0.53
----------------------------------------------------------------------------------------------------------------
Where: Column A-10 mil Copper shield.
Column B--5 mil Copper shield.
Column C--8 mil Coated Aluminum and 8 mil Coated Aluminum/6 mil Coated Steel shields.
Column D--7 mil Alloy 194 shield.
Column E--6 mil Alloy 194 and 6 mil Copper Clad Stainless Steel shields.
Column F--5 mil Copper Clad Stainless Steel and 5 mil Copper Clad Alloy Steel shields.
Table 2.--Shield Resistance @ 68 deg.F (20 deg.C) Cable Diameters Versus Shield Types
[Metric Units]
----------------------------------------------------------------------------------------------------------------
Nominal Resistance ohm/km
Outside diameter millimeters (mm) -----------------------------------------------------------------------------
A B C D E F
----------------------------------------------------------------------------------------------------------------
10.2--12.5........................ 2.53 5.05 5.41 6.43 7.55 18.08
12.7--15.0........................ 2.10 4.20 4.49 5.35 6.27 15.03
15.2--17.5........................ 1.67 3.38 3.61 4.30 5.02 12.04
17.8--20.1........................ 1.44 2.89 3.08 ........... 4.30 10.30
20.3--22.6........................ 1.25 2.53 2.69 ........... 3.74 8.99
22.9--25.1........................ 1.15 2.26 2.43 ........... 3.38 8.10
25.4--27.7........................ 1.02 2.03 2.16 ........... 3.02 7.22
27.9--30.2........................ 0.92 1.84 1.97 ........... 2.76 6.56
30.5--32.8........................ 0.85 1.67 1.80 ........... 2.53 6.04
33.0--35.3........................ 0.79 1.57 1.67 ........... 2.33 5.58
35.6--37.8........................ 0.72 1.44 1.54 ........... 2.13 5.15
38.1--40.4........................ 0.69 1.34 1.44 ........... 2.00 4.82
40.6--42.9........................ 0.62 1.25 1.34 ........... 1.87 4.49
43.2--45.5........................ 0.59 1.21 1.28 ........... 1.77 4.26
45.7--48.0........................ 0.56 1.15 1.21 ........... 1.67 4.07
48.3--50.5........................ 0.52 1.08 1.15 ........... 1.61 3.84
50.8--53.1........................ 0.49 1.02 1.08 ........... 1.51 3.61
53.3--55.6........................ 0.49 0.95 1.02 ........... 1.41 3.38
55.9--58.2........................ 0.46 0.92 0.98 ........... 1.38 3.28
58.4--60.7........................ 0.46 0.89 0.95 ........... 1.31 3.18
61.0--63.2........................ 0.43 0.82 0.89 ........... 1.25 2.95
[[Page 489]]
63.5--65.8........................ 0.39 0.79 0.85 ........... 1.18 2.85
66.0--68.3........................ 0.39 0.75 0.82 ........... 1.15 2.72
68.6--70.9........................ 0.36 0.72 0.79 ........... 1.08 2.62
71.1--73.4........................ 0.36 0.72 0.79 ........... 1.08 2.62
73.7--75.9........................ 0.36 0.72 0.75 ........... 1.05 2.53
76.2--78.5........................ 0.33 0.69 0.72 ........... 1.02 2.39
78.7--81.0........................ 0.33 0.66 0.69 ........... 0.95 2.30
81.3--83.6........................ 0.33 0.66 0.69 ........... 0.95 2.30
83.6--86.1........................ 0.29 0.62 0.66 ........... 0.92 2.20
86.4--88.6........................ 0.29 0.59 0.62 ........... 0.85 2.07
88.9--91.2........................ 0.29 0.59 0.62 ........... 0.85 2.07
91.4--93.7........................ 0.26 0.56 0.59 ........... 0.82 1.97
94.0--96.3........................ 0.26 0.56 0.59 ........... 0.82 1.97
96.5--98.8........................ 0.26 0.52 0.56 ........... 0.79 1.87
99.1--101.3....................... 0.26 0.52 0.56 ........... 0.79 1.87
101.6--103.9...................... 0.23 0.49 0.52 ........... 0.72 1.74
----------------------------------------------------------------------------------------------------------------
Where: Column A--10 mil Copper shield.
Column B--5 mil Copper shield.
Column C--8 mil Coated Aluminum and 8 mil Coated Aluminum/6 mil Coated Steel shields.
Column D--7 mil Alloy 194 shield.
Column E--6 mil Alloy 194 and 6 mil Copper Clad Stainless Steel shields.
Column F--5 mil Copper Clad Stainless Steel and 5 mil Copper Clad Alloy Steel shields.
(ii) All values of shield and shield/armor resistance provided in
Tables 1 and 2 in (a)(5)(i) of this section are considered
approximations. If the measured value corrected to 68 deg.F (20 deg.C)
is within 30 percent (%) of the value shown in Table 1 or 2,
the shield and shield/armor shall be assumed to be continuous.
(iii) To correct the measured shield resistance to the reference
temperature of 68 deg.F (20 deg.C) use the following formulae:
R68=Rt/[1+A(t-68)] for English Units
R20=Rt/[1+A(t-20)] for Metric Units
Where:
R68=Shield resistance corrected to 68 deg.F in ohms.
R20=Shield resistance corrected to 20 deg.C in ohms.
Rt=Shield resistance at measurement temperature in ohms.
A=Temperature coefficient of the shield tape.
t=Measurement temperature in deg.F or ( deg.C).
(iv) The temperature coefficients (A) for the shield tapes to be
used in the formulae referenced in paragraph (a)(5)(iii) of this section
are as follows:
(A) 5 and 10 mil copper = 0.0021 for English units and 0.0039 for
Metric units;
(B) 8 mil coated aluminum and 8 mil coated aluminum/6 mil coated
steel = 0.0022 for English units and 0.0040 for Metric units;
(C) 5 mil copper clad stainless steel and 5 mil copper clad alloy
steel = 0.0024 for English units and 0.0044 for Metric units;
(D) 6 mil copper clad stainless steel = 0.0019 for English units and
0.0035 for Metric units; and
(E) 6 and 7 mil alloy 194 = 0.0013 for English units and 0.0024 for
Metric units.
(v) When utilizing shield continuity testers to measure shield and
shield/armor continuity within pedestals or splices, refer to the
manufacturer's published information covering the specific test
equipment to be used and for anticipated results.
(6) Data record.Measurement data from shield continuity tests shall
be recorded together with anticipated Table 1 or 2 values (see paragraph
(a)(5)(i) of this section) in an appropriate format to permit
comparison. The recorded data shall include specific location, cable
size, cable type, type of shield or shield/armor, if known, etc.
(7) Probable causes for nonconformance.Among probable causes for
nonconformance are broken or damaged
[[Page 490]]
shields or shield/armors, bad bonding harnesses, poorly connected
bonding clamps, loose bonding lugs, etc.
(b) Conductor continuity.After placement of all cable and wire plant
has been completed and joined together in continuous lengths, tests
shall be made to ascertain that all pairs are free from grounds, shorts,
crosses, and opens, except for those pairs indicated as being defective
by the cable manufacturer. The tests for grounds, shorts, crosses, and
opens are not separate tests, but are inherent in other acceptance tests
discussed in this section. The test for grounds, shorts, and crosses is
inherent when conductor insulation resistance measurements are conducted
per paragraph (c) of this section, while tests for opens are inherent
when tests are conducted for loop resistance, insertion loss, noise, or
return loss measurements, per paragraphs (d), (e), or (f) of this
section. The borrower shall make certain that all defective pairs are
corrected, except those noted as defective by the cable manufacturer in
accordance with the marking provisions of the applicable cable and wire
specifications. All defective pairs that are not corrected shall be
reported in writing with details of the corrective measures attempted.
(c) Dc insulation resistance (IR) measurement. (1) IR measurements
shall be made on completed lengths of insulated cable and wire plant.
(2) Method of measurement. (i) The IR measurement shall be made
between each conductor and all other conductors, sheath, shield and/or
shield/armor, and/or support wire electrically connected together and to
the main distributing frame (MDF) ground. The measurement shall be made
from the central office with the entire length of the cable under test
and, where used with all protectors and load coils connected. For COs
containing solid state arresters, the solid state arresters shall be
removed before making the IR measurements. Field mounted voice frequency
repeaters, where used, may be left connected for the IR test but all
carrier frequency equipment, including carrier repeaters and terminals,
shall be disconnected. Pairs used to feed power remote from the CO shall
have the power disconnected and the tip and ring conductors shall be
opened before making IR tests. All conductors shall be opened at the far
end of the cable being measured.
(ii) IR tests are normally made from the MDF with all CO equipment
disconnected at the MDF, but this test may be made on new cables at
field locations before they are spliced to existing cables. The method
of measurement shall be as shown in Figure 3 as follows:
[[Page 491]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.025
(iii) If the IR of the conductor cannot be measured because of
breakdown of lightning arresters by the test voltage, the arrester units
shall be removed and the conductor IR retested. If the IR then meets the
minimum requirements, the conductor will be considered satisfactory.
Immediately following the IR tests, all arrester units which have been
removed shall be reinstalled.
(3) Test equipment. (i) IR measurements shall be made with either an
insulation resistance test set or a direct current (dc) bridge type
megohmmeter.
[[Page 492]]
(ii) The IR test set shall have an output voltage not to exceed 500
volts dc and shall be of the hand cranked or battery operated type.
(iii) The dc bridge type megohmmeter, which may be alternating
current (ac) powered, shall have scales and multiplier which make it
possible to accurately read IR from 1 megohm to 1 gigohm. The voltage
applied to the conductors under test shall not exceed ``250 volts dc''
when using an instrument having adjustable test voltage levels. This
will help to prevent breakdown of lightning arresters.
(4) Applicable results. (i) For all new insulated cable or wire
facilities, the expected IR levels are normally greater than 1,000 to
2,000 megohm-mile (1,609 to 3,218 megohm-km). A value of 500 megohm-mile
(805 megohm-km) at 68 deg.F (20 deg.C) shall be the minimum acceptable
value of IR. IR varies inversely with the length and the temperature.
(ii) The megohm-mile (megohm-km) value for a conductor may be
computed by multiplying the actual scale reading in megohms on the test
set by the length in miles (km) of the conductor under test.
(iii) The objective insulation resistance may be determined by
dividing 500 by the length in miles (805 by the length in km) of the
cable or wire conductor being tested. The resulting value shall be the
minimum acceptable meter scale reading in megohms.
(iv) Due to the differences between various insulating materials and
filling compounds used in manufacturing cable or wire, it is impractical
to provide simple factors to predict the magnitude of variation in
insulation resistance due to temperature. The variation can, however, be
substantial for wide excursions in temperature from the ambient
temperature of 68 deg.F (20 deg.C).
(v) Borrowers should be certain that tip and ring IR measurements of
each pair are approximately the same. Borrowers should also be certain
that IR measurements are similar for cable or wire sections of similar
length and cable or wire type. If some pairs measure significantly
lower, borrowers should attempt to improve these pairs in accordance
with cable manufacturer's recommendations.
Note: Only the megohm-mile (megohm-km) requirement shall be cause
for rejection, not individual measurement differences.
(5) Data record.The measurement data shall be recorded. Suggested
formats similar to Format I, Outside Plant Acceptance Tests--Subscriber
Loops, or Format II, Outside Plant Acceptance Tests--Trunk Circuits, in
Sec. 1755.407 or formats specified in the applicable construction
contract may be used.
(6) Probable causes for nonconformance.(i) When an IR measurement is
below 500 megohm-mile (805 megohm-km), the cable or wire temperature at
the time of testing must then be taken into consideration. If this
temperature is well above 68 deg.F (20 deg.C), the measurement shall
be disregarded and the cable or wire shall be remeasured at a time when
the temperature is approximately 68 deg.F (20 deg.C). If the result is
then 500 megohm-mile (805 megohm-km) or greater, the cable or wire shall
be considered satisfactory.
(ii) Should the cable or wire fail to meet the 500 megohm-mile (805
megohm-km) requirement when the temperature is known to be approximately
68 deg.F (20 deg.C) there is not yet justification for rejection of
the cable or wire. Protectors, lightning arresters, etc., may be a
source of low insulation resistance. These devices shall be removed from
the cable or wire and the cable or wire IR measurement shall be
repeated. If the result is acceptable, the cable or wire shall be
considered acceptable. The removed devices which caused the low
insulation resistance value shall be identified and replaced, if found
defective.
(iii) When the cable or wire alone is still found to be below the
500 megohm-mile (805 megohm-km) requirement after completing the steps
in paragraph (c)(6)(i) and/or paragraph (c)(6)(ii) of this section, the
test shall be repeated to measure the cable or wire in sections to
isolate the piece(s) of cable or wire responsible. The cable or wire
section(s) that is found to be below the 500 megohm-mile (805 megohm-km)
requirement shall be either repaired in accordance with the cable or
wire manufacturer's recommended procedure or shall be replaced as
directed by the borrower.
[[Page 493]]
(d) Dc loop resistance and dc resistance unbalance measurement.(1)
When specified by the borrower, dc loop resistance and dc resistance
unbalance measurements shall be made on all cable pairs used as trunk
circuits. The dc loop resistance and dc resistance unbalance
measurements shall be made between CO locations. Measurements shall
include all components of the cable path.
(2) Dc loop resistance and dc resistance unbalance measurements
shall be made on all cable pairs used as subscriber loop circuits when:
(i) Specified by the borrower;
(ii) A large number of long loops terminate at one location (similar
to trunk circuits); or
(iii) Circuit balance is less than 60 dB when computed from noise
measurements as described in paragraph (e) of this section.
(3) Dc resistance unbalance is controlled to the maximum possible
degree by the cable specification. Allowable random unbalance is
specified between tip and ring conductors within each reel. Further
random patterns should occur when the cable conductor size changes.
Cable meeting the unbalance requirements of the cable specification may
under some conditions result in unacceptable noise levels as discussed
in paragraph (d)(6)(iii) of this section.
(4) Method of measurement. The method of measurement shall be as
detailed in Figures 4 and 5.
(5) Test equipment. The test equipment is shown in Figures 4 and 5
as follows:
[[Page 494]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.026
[[Page 495]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.027
(6) Applicable results. (i) The measured dc loop resistance shall be
within 5% of the calculated dc loop resistance when
corrected for temperature.
(ii) The calculated dc loop resistance is computed as follows:
(A) Multiply the length of each different gauge by the applicable
resistance per unit length as shown in Table 3 as follows:
[[Page 496]]
Table 3.--DC Loop Resistance @ 68 deg.F (20 deg.C)
------------------------------------------------------------------------
Loop resistance
American wire gauge (AWG) -------------------------------
ohms/1000 ft ohms/km
------------------------------------------------------------------------
19...................................... 16.1 52.8
22...................................... 32.4 106.3
24...................................... 51.9 170.3
26...................................... 83.3 273.3
------------------------------------------------------------------------
(B) Add the individual resistances for each gauge to give the total
calculated dc loop resistance at a temperature of 68 deg.F (20 deg.C).
(C) Correct the total calculated dc loop resistance at the
temperature of 68 deg.F (20 deg.C) to the measurement temperature by
the following formulae:
Rt=R68x[1+0.0022xt--68)] for English Units
Rt=R20x[1+0.0040x(t--20)] for Metric Units
Where:
Rt = Loop resistance at the measurement temperature in ohms.
R68 = Loop resistance at a temperature of 68 deg.F in ohms.
R20 = Loop resistance at a temperature of 20 deg.C in ohms.
t = Measurement temperature in deg.F or ( deg.C).
(D) Compare the calculated dc loop resistance at the measurement
temperature to the measured dc loop resistance to determine compliance
with the requirement specified in paragraph (d)(6)(i) of this section.
(iii) Resistance varies directly with temperature change. For copper
conductor cables, the dc resistance changes by 1% for every
5 deg.F (2.8 deg.C) change in temperature from 68 deg.F
(20 deg.C).
(iv) The dc resistance unbalance between the individual conductors
of a pair shall not exceed that value which will result in a circuit
balance of less than 60 dB when computed from noise measurements as
described in paragraph (e) of this section. It is impractical to
establish a precise limit for overall circuit dc resistance unbalance
due to the factors controlling its contribution to circuit noise. These
factors include location of the resistance unbalance in relation to a
low impedance path to ground (close to the central office) and the
magnitude of unbalance in short lengths of cable making up the total
circuit length. The objective is to obtain the minimum unbalance
throughout the entire circuit when it is ascertained through noise
measurements that dc resistance unbalance may be contributing to poor
cable balance.
(v) Pairs with poor noise balance may be improved by reversing tip
and ring conductors of pairs at cable splices. Where dc resistance
unbalances are systematic over the total trunk circuit or loop circuit
length, tip and ring reversals may be made at frequent intervals. Where
the unbalances are concentrated in a shorter section of cable, only one
tip and ring reversal should be required. Concentrated dc resistance
unbalance produces maximum circuit noise when located adjacent to the
central office. Concentrated dc resistance unbalance will contribute to
overall circuit noise at a point approximately two-thirds (\2/3\) of the
distance to the subscriber. All deliberate tip and ring reversals shall
be tagged and identified to prevent plant personnel from removing the
reversals when resplicing these connections in the future. The number of
tip and ring reversals shall be held to a minimum.
(vi) A systematic dc resistance unbalance can sometimes be
accompanied by other cable parameters that are marginal. Among these are
pair-to-pair capacitance unbalance, capacitance unbalance-to-ground, and
150 kilohertz (kHz) crosstalk loss. Engineering judgment has to be
applied in each case. Rejection of cable for excessive dc resistance
unbalance shall only apply to a single reel length, or shorter.
(7) Data record.The measurement data for dc loop resistance and dc
resistance unbalance shall be recorded. Suggested formats similar to
Format I for subscriber loops and Format II for trunk
[[Page 497]]
circuits in Sec. 1755.407 or formats specified in the applicable
construction contract may be used.
(8) Probable causes for nonconformance. Dc loop resistance and dc
resistance unbalance are usually the result of the resistance of
individual conductors used in the manufacture of the cable. Resistance
unbalance can be worsened by defective splicing of the conductors
(splicing connectors, improper crimping tool, etc.).
(e) Subscriber loop measurement (loop checking). (1) When specified
by the borrower, insertion loss and noise measurements shall be
performed on subscriber loops after connection of a line circuit to the
loop by the one person method using loop checking equipment from the
customer access location. For this method, the central office should be
equipped with a 900 ohm plus two microfarad quiet termination and a
milliwatt generator having the required test frequencies; or a portable
milliwatt generator having the desired frequencies may be used,
especially, where several small offices are involved.
(2) At a minimum, insertion loss and frequency response of
subscriber loop plant shall be measured at 1,000, 1,700, 2,300, and
2,800 Hertz (Hz). When additional testing frequencies are desired, the
additional frequencies shall be specified in the applicable construction
contract.
(3) Measurements of insertion loss and noise shall be made on five
percent or more of the pairs. A minimum of five pairs shall be tested on
each route. Pairs shall be selected on a random basis with greater
consideration in the selection given to the longer loops. Consideration
shall be given to measuring a large percentage, up to 100 percent, of
all loops.
(4) Method of measurement--(i) Insertion loss. The step-by-step
measurement procedure shall be as shown in Figure 6. The output level of
the milliwatt generator tones shall be determined prior to leaving the
CO. This shall be accomplished by dialing the milliwatt generator number
from a spare line at the MDF and measuring with the same equipment to be
used in the tests at customer access locations. The output levels shall
be recorded for reference later. Insertion loss measurements shall be
made across the tip and ring terminals of the pair under test. Figure 6
is as follows:
[[Page 498]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.028
(ii) Noise. The step-by-step measurement procedure shall be as shown
in Figure 7. Prior to leaving the CO for testing, dial the 900 ohm plus
two microfarad quiet termination from a spare pair and measure the
termination to determine that it actually is quiet. Circuit noise
(noise-metallic) shall be measured at the customer access location
across the tip and ring terminals of the pair under test. Power
influence (direct reading with loop checking equipment) shall be
measured at the customer access location from tip and ring conductors-
to-ground (this connection is completed via the test
[[Page 499]]
unit). The power influence measurement includes the entire talking
connection from the quiet termination to the customer. (That is, the
power influence measurement includes all the CO equipment which normally
makes up the connection.) Figure 7 is as follows:
[GRAPHIC] [TIFF OMITTED] TR02MY97.029
(5) Test equipment. (i) Loop checking equipment which is available
from several manufacturers may be used for these measurements. The
equipment
[[Page 500]]
should have the capability of measuring loop current, insertion loss,
circuit noise (NM) and power influence (PI). The test equipment
manufacturer's operating instructions shall be followed.
(ii) There should be no measurable transmission loss when testing
through loop extenders.
(6) Applicable results--(i) Insertion loss. (A) For D66 loaded
cables (a specific loading scheme using a 66 millihenry inductor spaced
nominally at 4,500 ft [1,371 m] intervals) measured at a point one-half
section length beyond the last load point, the measured nonrepeated
insertion loss shall be within 10% at 1000, 1700, 2300, and
2800 Hz, 15% at 3400 Hz and 20% at 4000 Hz of
the calculated insertion loss at the same frequencies and temperature.
(B) For H88 loaded cables (a specific loading scheme using an 88
millihenry inductor spaced nominally at 6,000 ft [1,829 m] intervals)
measured at a point one-half section length beyond the last load point,
the measured nonrepeatered insertion loss shall be within
10% at 1000, 1700, and 2300 Hz, 15% at 2800 Hz,
and 20% at 3400 Hz of the calculated insertion loss at the
same frequencies and temperature.
(C) For nonloaded cables, the measured insertion loss shall be
within 10% at 1000, 1700, 2300, and 2800 Hz, 15%
at 3400 Hz and 20% at 4000 Hz of the calculated insertion
loss at the same frequencies and temperature.
(D) For loaded cables, the calculated loss at each desired frequency
shall be computed as follows:
(1) Multiply the length in miles (km) of each different gauge in the
loaded portion of the loop (between the office and a point one-half load
section beyond the furthest load point) by the applicable decibel (dB)/
mile (dB/km) value shown in Table 4 or 5. This loss represents the total
loss for each gauge in the loaded portion of the loop;
(2) Multiply the length in miles (km) of each different gauge in the
end section or nonloaded portion of the cable (beyond a point one-half
load section beyond the furthest load point) by the applicable dB/mile
(dB/km) value shown in Table 6. This loss represents the total loss for
each gauge in the nonloaded portion of the loop; and
(3) The total calculated insertion loss is computed by adding the
individual losses determined in paragraphs (e)(6)(i)(D)(1) and
(e)(6)(i)(D)(2) of this section.
(E) For nonloaded cables, the calculated loss at each desired
frequency shall be computed by multiplying the length in miles (km) of
each different gauge by the applicable dB/mile (dB/km) value shown in
Table 6 and then adding the individual losses for each gauge to
determine the total calculated insertion loss for the nonloaded loop.
(F) The attenuation information in Tables 4, 5, and 6 are based on a
cable temperature of 68 deg.F (20 deg.C). Insertion loss varies
directly with temperature. To convert measured losses for loaded cables
to a different temperature, use the following value for copper
conductors: For each 5 deg.F ( 2.8 deg.C)
change in the temperature from 68 deg.F (20 deg.C), change the
insertion loss at any frequency by 1%. To convert measured
losses for nonloaded cables to a different temperature, use the
following value for copper conductors: For each 10 deg.F
(5.6 deg.C) change in the temperature from 68 deg.F (20
deg.C), change the insertion loss at any frequency by 1%.
Tables 4, 5, and 6 are as follows:
Table 4--Frequency Attenuation @ 68 deg.F (20 deg.C) D66 Loaded Exchange Cables 83 nanofarad (nF)/mile (52 nF/
km) (See Note)
----------------------------------------------------------------------------------------------------------------
Attenuation dB/mile (dB/km) AWG
Frequency (Hz) -------------------------------------------------------------------
19 22 24 26
----------------------------------------------------------------------------------------------------------------
200......................................... 0.41 (0.26) 0.67 (0.42) 0.90 (0.56) 1.21 (0.75)
400......................................... 0.43 (0.26) 0.77 (0.48) 1.09 (0.68) 1.53 (0.95)
600......................................... 0.44 (0.27) 0.80 (0.49) 1.17 (0.73) 1.70 (1.06)
800......................................... 0.44 (0.27) 0.81 (0.50) 1.21 (0.75) 1.80 (1.12)
1000........................................ 0.44 (0.27) 0.82 (0.51) 1.23 (0.76) 1.86 (1.15)
1200........................................ 0.45 (0.28) 0.83 (0.52) 1.24 (0.77) 1.91 (1.19)
1400........................................ 0.45 (0.28) 0.83 (0.52) 1.26 (0.78) 1.94 (1.20)
1600........................................ 0.45 (0.28) 0.84 (0.52) 1.26 (0.78) 1.96 (1.22)
1800........................................ 0.45 (0.28) 0.84 (0.52) 1.27 (0.78) 1.98 (1.23)
[[Page 501]]
2000........................................ 0.46 (0.29) 0.85 (0.53) 1.28 (0.79) 1.99 (1.24)
2200........................................ 0.46 (0.29) 0.85 (0.53) 1.29 (0.80) 2.01 (1.25)
2400........................................ 0.47 (0.29) 0.86 (0.53) 1.30 (0.81) 2.02 (1.26)
2600........................................ 0.47 (0.29) 0.87 (0.54) 1.31 (0.81) 2.04 (1.27)
2800........................................ 0.48 (0.30) 0.88 (0.55) 1.32 (0.82) 2.07 (1.29)
3000........................................ 0.49 (0.30) 0.89 (0.55) 1.34 (0.83) 2.10 (1.30)
3200........................................ 0.50 (0.31) 0.91 (0.57) 1.36 (0.84) 2.13 (1.32)
3400........................................ 0.52 (0.32) 0.93 (0.58) 1.40 (0.87) 2.19 (1.36)
3600........................................ 0.54 (0.34) 0.97 (0.60) 1.45 (0.90) 2.26 (1.40)
3800........................................ 0.57 (0.35) 1.02 (0.63) 1.52 (0.94) 2.36 (1.47)
4000........................................ 0.62 (0.38) 1.10 (0.68) 1.63 (1.01) 2.53 (1.57)
----------------------------------------------------------------------------------------------------------------
Note: Between end-section lengths of 2,250 ft (686 m) for D66 loading.
Table 5--Frequency Attenuation @ 68 deg.F (20 deg.C) H88 Loaded Exchange Cables 83 nF/ mile (52 nF/km) (See
Note)
----------------------------------------------------------------------------------------------------------------
Attenuation dB/mile (dB/km) AWG
Frequency (Hz) -------------------------------------------------------------------
19 22 24 26
----------------------------------------------------------------------------------------------------------------
200......................................... 0.40 (0.25) 0.66 (0.41) 0.90 (0.56) 1.20 (0.75)
400......................................... 0.42 (0.26) 0.76 (0.47) 1.08 (0.67) 1.53 (0.95)
600......................................... 0.43 (0.27) 0.79 (0.49) 1.16 (0.72) 1.70 (1.06)
800......................................... 0.43 (0.27) 0.80 (0.50) 1.20 (0.75) 1.80 (1.12)
1000........................................ 0.43 (0.27) 0.81 (0.50) 1.23 (0.76) 1.86 (1.15)
1200........................................ 0.44 (0.27) 0.82 (0.51) 1.24 (0.77) 1.91 (1.19)
1400........................................ 0.44 (0.28) 0.82 (0.51) 1.25 (0.78) 1.94 (1.20)
1600........................................ 0.44 (0.27) 0.83 (0.52) 1.26 (0.78) 1.97 (1.22)
1800........................................ 0.45 (0.28) 0.84 (0.52) 1.28 (0.79) 1.99 (1.24)
2000........................................ 0.46 (0.29) 0.85 (0.53) 1.29 (0.80) 2.02 (1.26)
2200........................................ 0.47 (0.29) 0.86 (0.53) 1.31 (0.81) 2.06 (1.28)
2400........................................ 0.48 (0.30) 0.89 (0.55) 1.34 (0.83) 2.10 (1.30)
2600........................................ 0.50 (0.31) 0.92 (0.57) 1.39 (0.86) 2.18 (1.35)
2800........................................ 0.53 (0.33) 0.97 (0.60) 1.47 (0.91) 2.29 (1.42)
3000........................................ 0.59 (0.37) 1.07 (0.66) 1.60 (0.99) 2.48 (1.54)
3200........................................ 0.71 (0.44) 1.26 (0.78) 1.87 (1.16) 2.86 (1.78)
3400........................................ 1.14 (0.71) 1.91 (1.19) 2.64 (1.64) 3.71 (2.30)
3600........................................ 4.07 (2.53) 4.31 (2.68) 4.65 (2.90) 5.30 (3.29)
3800........................................ 6.49 (4.03) 6.57 (4.08) 6.72 (4.18) 7.06 (4.39)
4000........................................ 8.22 (5.11) 8.27 (5.14) 8.36 (5.19) 8.58 (5.33)
----------------------------------------------------------------------------------------------------------------
Note: Between end-section lengths of 3,000 ft (914 m) for H88 loading.
Table 6--Frequency Attenuation @ 68 deg.F (20 deg.C) Nonloaded Exchange Cables 83 nF/ mile (52 nF/km) AWG
----------------------------------------------------------------------------------------------------------------
Attenuation dB/mile (dB/km) AWG
Frequency (Hz) -------------------------------------------------------------------
19 22 24 26
----------------------------------------------------------------------------------------------------------------
200......................................... 0.58 (0.36) 0.82 (0.51) 1.03 (0.64) 1.30 (0.81)
400......................................... 0.81 (0.51) 1.15 (0.71) 1.45 (0.90) 1.84 (1.14)
600......................................... 0.98 (0.61) 1.41 (0.87) 1.77 (1.10) 2.26 (1.40)
800......................................... 1.13 (0.70) 1.62 (1.01) 2.04 (1.27) 2.60 (1.61)
1000........................................ 1.25 (0.78) 1.80 (1.12) 2.28 (1.42) 2.90 (1.80)
1200........................................ 1.36 (0.84) 1.97 (1.22) 2.50 (1.55) 3.17 (1.97)
1400........................................ 1.46 (0.91) 2.12 (1.32) 2.69 (1.67) 3.42 (2.12)
1600........................................ 1.55 (0.96) 2.26 (1.40) 2.87 (1.78) 3.65 (2.27)
1800........................................ 1.63 (1.01) 2.39 (1.48) 3.04 (1.89) 3.87 (2.40)
2000........................................ 1.71 (1.06) 2.51 (1.56) 3.20 (1.99) 4.08 (2.53)
2200........................................ 1.78 (1.11) 2.62 (1.63) 3.35 (2.08) 4.27 (2.65)
2400........................................ 1.85 (1.15) 2.73 (1.70) 3.49 (2.17) 4.45 (2.76)
2600........................................ 1.91 (1.19) 2.83 (1.76) 3.62 (2.25) 4.63 (2.88)
2800........................................ 1.97 (1.22) 2.93 (1.82) 3.75 (2.33) 4.80 (2.98)
3000........................................ 2.03 (1.26) 3.02 (1.88) 3.88 (2.41) 4.96 (3.08)
3200........................................ 2.08 (1.29) 3.11 (1.93) 4.00 (2.48) 5.12 (3.18)
3400........................................ 2.13 (1.32) 3.19 (1.98) 4.11 (2.55) 5.27 (3.27)
3600........................................ 2.18 (1.35) 3.28 (2.04) 4.22 (2.62) 5.41 (3.36)
[[Page 502]]
3800........................................ 2.22 (1.38) 3.36 (2.09) 4.33 (2.69) 5.55 (3.45)
4000........................................ 2.27 (1.41) 3.43 (2.13) 4.43 (2.75) 5.69 (3.53)
----------------------------------------------------------------------------------------------------------------
(G) For loaded subscriber loops, the 1 kHz loss shall be
approximately 0.45 dB per 100 ohms of measured dc loop resistance. This
loss shall be the measured loss less the net gain of any voice frequency
repeaters in the circuit. Testing shall also be conducted to verify that
the loss increases gradually as the frequency increases. The loss on H88
loaded loops should be down only slightly at 2.8 kHz but drop rapidly
above 2.8 kHz. The loss on D66 loaded loops shall be fairly constant to
about 3.4 kHz and there shall be good response at 4.0 kHz. When voice
frequency repeaters are in the circuit there will be some frequency
weighting in the build-out network and the loss at the higher
frequencies will be greater than for nonrepeatered loops.
(H) For nonloaded subscriber loops, the 1 kHz loss shall be
approximately 0.9 dB per 100 ohms of measured dc loop resistance.
Testing shall also be conducted to verify that the loss is approximately
a straight line function with no abrupt changes. The 3 kHz loss should
be approximately 70% higher than the 1 kHz loss.
(ii) Noise. The principal objective related to circuit noise (noise-
metallic) and the acceptance of new plant is that circuit noise levels
be 20 dBrnc or less (decibels above reference noise, C-message weighted
(a weighting derived from listening tests, to indicate the relative
annoyance or speech impairment by an interfering signal of frequency (f)
as heard through a ``500-type'' telephone set)). For most new, properly
installed, plant construction, circuit noise will usually be
considerably less than 20 dBrnc unless there are unusually long sections
of telephone plant in parallel with electric power facilities and/or
power influence of paralleling electric facilities is abnormally high.
When circuit noise is 20 dBrnc or less, the loop plant shall be
considered acceptable. When measured circuit noise is greater than 20
dBrnc, loop plant shall still be considered acceptable providing circuit
balance (power influence reading minus circuit noise readings) is 60 dB
or greater and power influence readings are 85 dBrnc or greater. When
circuit noise is greater than 20 dBrnc and circuit balance is less than
60 dB and/or power influence is less than 85 dBrnc, loop plant shall not
be considered acceptable and the loop plant shall be remedied to make
circuit balance equal to or greater than 60 dB.
(7) Data record. Measurement data shall be recorded. A suggested
format similar to Format I for subscriber loops in Sec. 1755.407 or a
format specified in the applicable construction contract may be used.
(8) Probable causes for nonconformance--(i) Insertion loss. Some of
the more common causes for failing to obtain the desired results may be
due to reversed load coil windings, missing load coils, bridge taps
between load coils, load coil spacing irregularities, excessive end
sections, cables having high or low mutual capacitance, load coils
having the wrong inductance, load coils inadvertently installed in
nonloaded loops, moisture or water in cable, split pairs, and improperly
spliced connections. The above factors can occur singularly or in
combination. Experience to date indicates that the most common problems
are missing load coils, reversed load coil windings or bridge taps.
(ii) Noise. Some of the common causes for failing to obtain the
desired results may be due to high power influence from paralleling
electrical power systems, poor telephone circuit balance, discontinuous
cable shields, inadequate bonding and grounding of cable shields, high
capacitance unbalance-to-ground of the cable pairs, high dc loop
resistance unbalance, dc loop current less than 20 milliamperes, etc.
The
[[Page 503]]
above factors can occur singularly or in combination. See TE&CM Section
451, Telephone Noise Measurement and Mitigation, for steps to be taken
in reducing telecommunications line noise.
(f) One-person open circuit measurement (subscriber loops). (1) When
specified by the borrower, open circuit measurements shall be made on
all loaded and nonloaded subscriber loops upon completion of the cable
work to verify that the plant is free from major impedance
irregularities.
(2) For loaded loops, open circuit measurements shall be made using
one of the following methods:
(i) Impedance or pulse return pattern, with cable pair trace
compared to that of an artificial line of the same length and gauge. For
best results, a level tracer or fault locator with dual trace capability
is required;
(ii) Return loss using a level tracer, with cable pair compared to
an artificial line of the same length and gauge connected in lieu of a
Precision Balance Network (PBN). This method can be made with level
tracers having only single trace capability; or
(iii) Open circuit structural return loss using a level tracer. This
method can be made with level tracer having only single trace
capability.
(3) Of the three methods suggested for loaded loops, the method
specified in paragraph (f)(2)(ii) of this section is the preferred
method because it can yield both qualitative and quantitative results.
The methods specified in paragraphs (f)(2)(i) and (f)(2)(iii) of this
section can be used as trouble shooting tools should irregularities be
found during testing.
(4) For nonloaded loops, open circuit measurements shall be made
using the method specified in paragraph (f)(2)(i) of this section.
(5) Method of measurement. Open circuit measurements shall be made
at the CO on each loaded and nonloaded pair across the tip and ring
terminals of the pair under test. All CO equipment shall be disconnected
at the MDF for this test. For loaded loops containing voice frequency
repeaters installed in the CO or field mounted, the open circuit
measurement shall be made after the repeaters have been disconnected.
Where field mounted repeaters are used, the open circuit measurement
shall be made at the repeater location in both directions.
(i) Impedance or pulse return pattern. The step-by-step measurement
procedure using the impedance or pulse return pattern for loaded and
nonloaded loops shall be as shown in Figure 8. An artificial line of the
same makeup as the cable to be tested shall be set up. The traces of the
impedance or pulse return pattern from the cable pair and the artificial
line shall be compared and should be essentially identical. If the
impedance or pulse return traces from the cable pair are different than
the artificial line trace, cable faults are possible. When the cable
pair trace indicates possible defects, the defects should be identified
and located. One method of identifying and locating defects involves
introducing faults into the artificial line until its trace is identical
with the cable trace.
(ii) Return loss balanced to artificial line. The step-by-step
measurement procedure using the return loss balanced to artificial line
for loaded loops shall be as shown in Figure 9. An artificial line of
the same makeup as the cable to be tested shall be set up. The
artificial line is connected to the external network terminals of the
test set. The cable pair under test is compared to this standard. When
defects are found, they should be identified and located by introducing
faults into the artificial line. This is more difficult than with the
method referenced in paragraph (f)(5)(i) of this section since this
measurement is more sensitive to minor faults and only a single trace is
used.
(iii) Open circuit structural return loss using level tracer. The
step-by-step measurement procedure using the level tracer for loaded
loops shall be as shown in Figure 10. The cable pair is compared to a
PBN.
(6) Test equipment. Equipment for performing these tests is shown in
Figures 8 through 10. For loaded loops, artificial loaded lines must be
of the same gauge and loading scheme as the line under test. For
nonloaded loops, artificial nonloaded lines must be of the same gauge as
the line under test. Artificial lines should be arranged using
[[Page 504]]
switches or other quick connect arrangements to speed testing and
troubleshooting. Figures 8 through 10 are as follows:
[GRAPHIC] [TIFF OMITTED] TR02MY97.030
[[Page 505]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.031
[[Page 506]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.032
(7) Applicable results. (i) For loaded and nonloaded loops, the two
traces in the pulse return pattern or impedance method (paragraph
(f)(5)(i) of this section) shall be essentially identical. The degree of
comparison required of the two traces is to be determined by experience.
(ii) For loaded loops, results for return loss measurements using a
level tracer, with artificial line, in lieu of a PBN (paragraph
(f)(5)(ii) of this section) shall meet the following requirements:
(A) For D66 and H88 loaded cables the structural return loss (SRL)
values shall range between 28 and 39 dB, respectively, at the critical
frequency of structural return loss (CFSRL) within the pass band of the
loading system being used. The minimum SRL value for uniform gauge shall
be 25 dB CFSRL. These SRL values apply for loaded cables of uniform
gauge for the
[[Page 507]]
entire length of the subscriber loop circuit. Subscriber loop circuits
shall meet the loading spacing deviations and the cable mutual
capacitance requirements in the applicable RUS cable specifications;
(B) For mixed gauge loaded cables the SRL values shall be 25 and 27
dB CFSRL, respectively, and the minimum SRL value shall be 22 dB CFSRL;
and
(C) The two traces in the pulse return pattern should be essentially
identical. The degree of comparison required of the two traces is
determined by experience.
(iii) For loaded loops, the results of open circuit structural
return loss measurements using a level tracer (paragraph (f)(5)(iii) of
this section) shall meet the following requirements. For D66 and H88
loaded cables with uniform or mixed gauges, the worst value allowed for
measured open circuit structural return loss between 1,000-3,500 Hz and
1,000-3,000 Hz, respectively, shall be approximately 0.9 dB (round trip)
for each 100 ohms outside plant dc loop resistance including the
resistance of the load coils. The value of 0.9 dB per 100 ohms for the
round trip loss remains reasonably accurate as long as:
(A) The subscriber end section of the loaded pair under test is
approximately 2,250 ft (685 m) for D66 loading or 3,000 ft (914 m) for
H88 loading in length; and
(B) The one-way 1,000 Hz loss does not exceed 10 dB.
(iv) For loaded loops, the measured value of open circuit structural
return loss can only be as accurate as the degree to which the dc loop
resistance of the loaded pair under test is known. Most accurate results
shall be obtained when the dc loop resistance is known by actual
measurements as described in paragraph (d) of this section. Furthermore,
where the dc loop resistance is measured at the same time as the open
circuit structural return loss, no correction for temperature is needed
because the loss is directly proportional to the loop resistance. Where
it is not practical to measure the dc loop resistance, it shall be
calculated and corrected for temperature as specified in paragraph
(d)(6)(ii) of this section. When measuring existing plant, care shall be
taken to verify the accuracy of the records, if they are used for the
calculation of the dc loop resistance. For buried plant, the temperature
correction shall be based at the normal depth of the cable in the
ground. (Temperature can be measured by boring a hole to cable depth
with a ground rod, placing a thermometer in the ground at the cable
depth, and taking and averaging several readings during the course of
the resistance measurements.) For aerial cable it shall be based on the
temperature inside the cable sheath.
(v) For loaded loops, the best correlation between the measured and
the expected results shall be obtained when the cable is of one gauge,
one size, and the far end section is approximately 2,250 ft (685 m) for
D66 loading or 3,000 ft (914 m) for H88 loading. Mixing gauges and cable
sizes will result in undesirable small reflections whose frequency
characteristics and magnitude cannot be accurately predicted. In
subscriber loop applications, cable gauge may be somewhat uniform but
the cable pair size most likely will not be uniform as cable pair sizes
taper off toward the customer access location and a downward adjustment
of 1 dB of the allowed value shall be acceptable. ``Long'' end sections
(as defined in TE&CM Section 424, ``Guideline for Telecommunications
Subscriber Loop Plant'') lower the expected value, a further downward
adjustment of 3 dB in the allowed value shall be acceptable.
(vi) For loaded loops, the limiting factor when making open circuit
structural return loss measurements is when the 1,000 Hz one-way loss of
the loaded cable pair under test becomes 10 dB or greater; it becomes
difficult to detect the presence of irregularities beyond the 10 dB
point on the loop. To overcome this difficulty, loaded loops having a
one-way loss at 1,000 Hz greater than 10 dB shall be opened at some
convenient point (such as a pedestal or ready access enclosure) and loss
measurements at the individual portions measuring less than 10 dB one-
way shall be made separately. When field mounted voice frequency
repeaters are used, the measurement shall be made at the repeater
location in both directions.
(8) Data record.(i) When performing a pulse return pattern or
impedance open
[[Page 508]]
circuit measurement on loaded and nonloaded loops, a ``check mark''
indicating that the pair tests good or an ``X'' indicating that the pair
does not test good shall be recorded in the SRL column. A suggested
format similar to Format I for subscriber loops in Sec. 1755.407 or a
format specified in the applicable construction contract may be used.
(ii) When performing open circuit return loss measurements using the
return loss balanced to an artificial line or return loss using a level
tracer on loaded loops, the value of the poorest (lowest numerical
value) SRL and its frequency in the proper column between 1,000 and
3,500 Hz for D66 loading or between 1,000 and 3,000 Hz for H88 loading
shall be recorded. A suggested format similar to Format I for subscriber
loops in Sec. 1755.407 or a format specified in the applicable
construction contract may be used.
(9) Probable causes for nonconformance. Some of the more common
causes for failing to obtain the desired results may be due to reversed
load coil windings, missing load coils, bridge taps between load coils,
load coil spacing irregularities, excessive end sections, cables having
high or low mutual capacitance, load coils inadvertently installed in
nonloaded loops, moisture or water in the cable, load coils having the
wrong inductance, split pairs, and improperly spliced connectors. The
above can occur singularly or in combination. Experience to date
indicates that the most common problems are missing load coils, reversed
load coil windings or bridge taps.
(g) Cable insertion loss measurement (carrier frequencies). (1) When
specified by the borrower, carrier frequency insertion loss measurements
shall be made on cable pairs used for T1, T1C, and/or station carrier
systems. Carrier frequency insertion loss shall be made on a minimum of
three pairs. Select at least one pair near the outside of the core unit
layup. If the three measured pairs are within 10% of the calculated loss
in dB corrected for temperature, no further testing is necessary. If any
of the measured pairs of a section are not within 10% of the calculated
loss in dB, all pairs in that section used for carrier transmission
shall be measured.
(2) Method of measurement. The step-by-step method of measurement
shall be as shown in Figure 11.
(3) Test equipment. The test equipment is shown in Figure 11 as
follows:
[[Page 509]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.033
(4) Applicable results. (i) The highest frequency to be measured is
determined by the type of carrier system. For T1 type carrier, the
highest frequency is normally 772 kHz. For T1C type carrier, the highest
frequency is normally 1576 kHz. The highest frequency to be measured for
station carrier is 140 kHz.
(ii) The measured insertion loss of the cable shall be within
10% of the calculated loss in dB when the loss is corrected
for temperature.
(iii) The calculated insertion loss is computed as follows:
[[Page 510]]
(A) Multiply the length of each different gauge by the applicable dB
per unit length as shown in Table 7 or 8 as follows:
Table 7.--Cable Attenuation @ 68 deg.F (20 deg.C) Filled Cables--Solid Insulation
----------------------------------------------------------------------------------------------------------------
Frequency (kHz) Attenuation dB/mile (dB/km) Gauge (AWG)
----------------------------------------------------------------------------------------------------------------
19 22 24 26
----------------------------------------------------------------------------------------------------------------
10.......................................... 2.8 (1.7) 4.8 (2.9) 6.4 (3.9) 8.5 (5.3)
20.......................................... 3.2 (2.0) 5.8 (3.6) 8.2 (5.1) 11.2 (6.9)
40.......................................... 3.6 (2.2) 6.5 (4.0) 9.6 (6.0) 13.9 (8.6)
60.......................................... 4.0 (2.5) 6.9 (4.2) 10.3 (6.4) 15.2 (9.4)
80.......................................... 4.5 (2.8) 7.3 (4.5) 10.7 (6.6) 16.0 (9.9)
100......................................... 4.9 (3.0) 7.7 (4.7) 11.1 (6.8) 16.5 (10.2)
112......................................... 5.2 (3.2) 8.0 (4.9) 11.3 (7.0) 16.8 (10.5)
120......................................... 5.4 (3.3) 8.1 (5.0) 11.5 (7.1) 17.0 (10.6)
140......................................... 5.8 (3.6) 8.6 (5.3) 11.9 (7.4) 17.4 (10.8)
160......................................... 6.2 (3.8) 9.0 (5.6) 12.3 (7.6) 17.8 (11.1)
180......................................... 6.6 (4.1) 9.5 (5.9) 12.7 (7.9) 18.2 (11.3)
200......................................... 7.0 (4.3) 10.0 (6.2) 13.2 (8.2) 18.6 (11.5)
300......................................... 8.7 (5.4) 12.2 (7.5) 15.4 (9.6) 20.6 (12.8)
400......................................... 10.0 (6.2) 14.1 (8.8) 17.7 (11.0) 22.9 (14.2)
500......................................... 11.2 (6.9) 15.9 (9.8) 19.8 (12.3) 25.2 (15.6)
600......................................... 12.2 (7.5) 17.5 (10.9) 21.8 (13.6) 27.4 (17.0)
700......................................... 13.2 (8.2) 19.0 (11.8) 23.6 (14.7) 29.6 (18.4)
772......................................... 13.8 (8.5) 19.9 (12.4) 24.8 (15.4) 31.4 (19.5)
800......................................... 14.2 (8.8) 20.1 (12.5) 27.4 (17.1) 31.7 (19.7)
900......................................... 14.8 (9.2) 21.6 (13.4) 29.0 (18.0) 33.8 (21.0)
1000........................................ 15.8 (9.8) 22.7 (14.1) 31.1 (19.3) 35.9 (22.3)
1100........................................ 16.4 (10.2) 23.8 (14.8) 32.7 (20.3) 38.0 (23.6)
1200........................................ 17.4 (10.8) 24.8 (15.4) 34.3 (21.3) 40.0 (24.9)
1300........................................ 17.9 (11.1) 25.9 (16.1) 35.4 (22.0) 41.7 (25.9)
1400........................................ 19.0 (11.8) 26.9 (16.7) 37.0 (23.0) 43.3 (26.9)
1500........................................ 19.5 (12.1) 28.0 (17.4) 38.0 (23.6) 44.3 (27.6)
1576........................................ 20.1 (12.4) 29.0 (18.0) 39.0 (24.3) 44.4 (28.2)
----------------------------------------------------------------------------------------------------------------
Table 8.--Cable Attenuation @ 68 deg.F (20 deg.C) Filled Cables--Expanded Insulation
----------------------------------------------------------------------------------------------------------------
Attenuation dB/mile (dB/km) Gauge (AWG)
Frequency (kHz) -------------------------------------------------------------------
19 22 24 26
----------------------------------------------------------------------------------------------------------------
10.......................................... 3.0 (1.8) 4.9 (3.0) 6.5 (4.0) 8.6 (5.3)
20.......................................... 3.5 (2.1) 6.0 (4.1) 8.5 (5.2) 11.5 (7.1)
40.......................................... 4.0 (2.5) 7.0 (4.3) 10.2 (6.3) 14.4 (8.9)
60.......................................... 4.5 (2.8) 7.5 (4.6) 11.1 (6.8) 16.0 (9.9)
80.......................................... 5.2 (3.3) 7.9 (4.9) 11.3 (6.9) 16.2 (10.1)
100......................................... 5.8 (3.6) 8.4 (5.2) 11.6 (7.2) 16.4 (10.2)
112......................................... 6.0 (3.8) 8.8 (5.4) 11.9 (7.4) 16.6 (10.3)
120......................................... 6.2 (3.9) 9.0 (5.6) 12.1 (7.5) 16.9 (10.5)
140......................................... 6.6 (4.1) 9.5 (5.9) 12.7 (7.9) 17.2 (10.7)
160......................................... 6.9 (4.3) 10.0 (6.2) 13.2 (8.2) 17.4 (10.8)
180......................................... 7.4 (4.6) 10.6 (6.6) 13.7 (8.5) 17.9 (11.1)
200......................................... 7.9 (4.9) 11.1 (6.9) 14.2 (8.8) 18.5 (11.5)
300......................................... 9.5 (5.9) 13.2 (8.2) 16.8 (10.5) 21.6 (13.4)
400......................................... 11.1 (6.9) 15.3 (9.5) 19.5 (12.1) 24.3 (15.1)
500......................................... 12.1 (7.5) 17.9 (11.1) 22.2 (13.8) 27.4 (17.1)
600......................................... 13.7 (8.5) 19.5 (12.1) 24.3 (15.1) 29.6 (18.4)
700......................................... 14.8 (9.2) 21.1 (13.1) 26.4 (16.4) 32.2 (20.0)
772......................................... 15.3 (9.5) 21.6 (13.4) 27.4 (17.1) 33.8 (21.90)
800......................................... 15.8 (9.8) 22.2 (13.8) 28.0 (17.4) 34.4 (21.3)
900......................................... 17.0 (10.5) 23.8 (14.8) 29.6 (18.4) 36.4 (22.6)
1000........................................ 17.4 (10.8) 24.8 (15.4) 31.1 (19.3) 38.5 (23.9)
1100........................................ 17.9 (11.1) 26.4 (16.4) 33.3 (20.7) 40.6 (25.3)
1200........................................ 19.0 (11.8) 27.4 (17.1 34.3 (21.3) 42.2 (26.2)
1300........................................ 19.5 (12.1) 28.5 (17.7) 35.9 (22.3) 43.8 (27.2)
1400........................................ 20.1 (12.5 29.6 (18.4) 37.0 (23.0) 45.9 (28.5)
1500........................................ 20.6 (12.8) 30.6 (19.0) 38.5 (23.9) 47.5 (29.5)
1576........................................ 21.6 (13.4) 31.1 (19.3) 39.1 (24.3) 48.6 (30.2)
----------------------------------------------------------------------------------------------------------------
[[Page 511]]
(B) Add the individual losses for each gauge to give the total
calculated insertion loss at a temperature of 68 deg.F (20 deg.C);
(C) Correct the total calculated insertion loss at the temperature
of 68 deg.F (20 deg.C) to the measurement temperature by the following
formulae:
At=A68x[1+0.0012x(t-68)] for English Units
At=A20x[1+0.0022x(t--20)] for Metric Units
Where:
At=Insertion loss at the measurement temperature in dB.
A68=Insertion loss at a temperature of 68 deg.F in dB.
A20=Insertion loss at a temperature of 20 deg.C in dB.
t=Measurement temperature in deg.F or ( deg.C); and
(D) Compare the calculated insertion loss at the measurement
temperature to the measured insertion loss to determine compliance with
the requirement specified in paragraph (g)(4)(ii) of this section.
(Note: Attenuation varies directly with temperature. For each
10 deg.F (5.6 deg.C) change in temperature increase or
decrease the attenuation by 1%.)
(iv) If the measured value exceeds the 10% allowable
variation, the cause shall be determined and corrective action shall be
taken to remedy the problem.
(5) Data record. Results of carrier frequency insertion loss
measurements for station, T1, and/or T1C type carrier shall be recorded.
Suggested formats similar to Format III, Outside Plant Acceptance Tests-
-T1 or T1C Carrier Pairs, and Format IV, Outside Plant Acceptance Tests-
-Station Carrier Pairs, in Sec. 1755.407 or formats specified in the
applicable construction contract may be used.
(6) Probable causes for nonconformance. If the measured loss is low,
the cable records are likely to be in error. If the measured loss is
high, there may be bridge taps, load coils or voice frequency build-out
capacitors connected to the cable pairs or the cable records may be in
error. Figures 12 and 13 are examples that show the effects of bridge
taps and load coils in the carrier path. Figures 12 and 13 are as
follows:
[[Page 512]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.034
[[Page 513]]
[GRAPHIC] [TIFF OMITTED] TR02MY97.035
[62 FR 23962, May 2, 1997]