7 C.F.R. §§ 1755.400–1755.407

For the CO and RST, the resistance after the bond has been made to the MGB electric service ground shall not exceed 5 ohms. Where the measured ground resistance exceeds 5 ohms, the borrower shall determine what additional grounding, if any, shall be provided.

For electronic equipment, the ground resistance shall not exceed 25 ohms. Where the measured ground resistance exceeds 25 ohms, the borrower shall determine what additional grounding, if any, shall be provided.

When ground resistance measurements exceed the ground resistance requirements of paragraphs (e)(1) and (e)(2) of this section, refer to RUS Bulletin 1751F-802, “Electrical Protection Grounding Fundamentals,” for suggested methods of reducing the ground resistance.

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.

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.

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.

Probable causes for nonconformance. Among probable causes for nonconformance are broken or damaged shields or shield/armors, bad bonding harnesses, poorly connected bonding clamps, loose bonding lugs, etc.

IR measurements shall be made on completed lengths of insulated cable and wire plant.

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 § 1755.407 or formats specified in the applicable construction contract may be used.

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.

Dc loop resistance and dc resistance unbalance measurements shall be made on all cable pairs used as subscriber loop circuits when:

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.

Method of measurement. The method of measurement shall be as detailed in Figures 4 and 5.

Test equipment. The test equipment is shown in Figures 4 and 5 as follows:

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 circuits in § 1755.407 or formats specified in the applicable construction contract may be used.

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.).

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.

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.

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.

Data record. Measurement data shall be recorded. A suggested format similar to Format I for subscriber loops in § 1755.407 or a format specified in the applicable construction contract may be used.

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.

For loaded loops, open circuit measurements shall be made using one of the following methods:

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.

For nonloaded loops, open circuit measurements shall be made using the method specified in paragraph (f)(2)(i) of this section.

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.

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 switches or other quick connect arrangements to speed testing and troubleshooting. Figures 8 through 10 are as follows:

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.

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.

Method of measurement. The step-by-step method of measurement shall be as shown in Figure 11.

Test equipment. The test equipment is shown in Figure 11 as follows:

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 § 1755.407 or formats specified in the applicable construction contract may be used.

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:

Tests and measurements shall be made to ensure that the armor of fiber optic cables is continuous. There are two areas of concern. The first is armor bonding within a splice and the second is armor continuity between splices.

Measurement techniques outlined here for verification of armor continuity are applicable to buried fiber optic cable plant. Measurements of armor continuity between splices in aerial, armored, fiber optic cable 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.

Method of measurement. Armor continuity within 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.

Test equipment. A cable shield splice continuity tester shall be used to measure armor continuity within splices.

Applicable results. When utilizing shield continuity testers to measure armor continuity within splices, refer to the manufacturer's published information covering the specific test equipment to be used and for anticipated results.

Data record. Measurement data from armor continuity tests shall be recorded together with anticipated values in an appropriate format to permit comparison. The recorded data shall include specific location, cable size, and cable type, if known, etc.

Probable causes for nonconformance. Among probable causes for nonconformance are broken or damaged armors, bad bonding harnesses, poorly connected bonding clamps, loose bonding lugs, etc.

After placement of all fiber optic cable plant has been completed and spliced together to form a continuous optical link between end termination points, splice loss measurements shall be performed on all field and central office splice points.

Test equipment. The test equipment is shown in Figures 14 and 15. The optical time domain reflectometer (OTDR) used for the testing should have dual wave length capability. Figures 14 and 15 are as follows:

Data record. The measurement data shall be recorded. A suggested format similar to Format V, Outside Plant Acceptance Test—Fiber Optic Telecommunications Plant, in § 1755.407 or a format specified in the applicable construction contract may be used.

Probable causes for nonconformance. When the results of the splice loss measurements exceed the specified limits the following factors should be checked:

After placement of all fiber optic cable plant has been completed and spliced together to form a continuous optical link between end termination points, end-to-end attenuation measurements shall be performed on each optical fiber within the cable.

Method of measurement. For single mode fibers, the end-to-end attenuation measurements of each optical fiber at 1310 and/or 1550 nanometers in each direction between end termination points shall be performed in accordance with Figure 16.

Test equipment. The test equipment is shown in Figure 16 as follows:

Applicable results. The end-to-end attenuation of each single mode optical fiber at 1310 and/or 1550 nanometers shall not exceed the limits specified in the applicable construction contract.

Data record. The measurement data shall be recorded. A suggested format similar to Format V for fiber optic telecommunications plant in § 1755.407 or on a format specified in the applicable construction contract may be used.

Probable causes for nonconformance. Failure of each optical fiber to meet the end-to-end attenuation limit could be attributed to the following:

After placement of all fiber optic cable plant has been completed and spliced together to form a continuous optical link between end termination points, end-to-end fiber signature testing shall be performed on each optical fiber within the cable.

Method of measurement. For single mode fibers, the end-to-end fiber signature measurement of each optical fiber in each direction shall be performed between end termination points at 1310 and/or 1550 nanometers in accordance with Figure 17.

Test equipment. The test equipment is shown in Figure 17 as follows:

Applicable results. The appearance of each optical fiber between end termination points.

Data record. Plot the trace of each optical fiber and retain as a permanent record for future comparison if needed.

Probable causes for nonconformance. None.

When specified by the borrower, S/CNN measurements shall be made on trunk circuits and nonloaded subscriber loops. For trunk circuits, the measurement shall be made between CO locations. For nonloaded subscriber loops, the measurement shall be made from the CO to the station protector of the NID at the customer's access location.

S/CNN is the logarithmic ratio expressed in dB of a 1,004 Hz holding tone signal compared to the C-message weighted noise level. S/CNN is one of the most important transmission parameters affecting the performance of data transmission because proper modem operation requires low noise relative to received power level. Since modulated carriers are used in data communication systems, noise measurements need to be performed with power on the connection to activate equipment having signal-level-dependent noise sources. For 4 kHz channels, a 1,004 Hz holding tone is used to activate the signal-dependent equipment on the channel or connection.

Method of measurement. The S/CNN measurement shall be made using a 1,004 Hz holding tone at −13 dBm0 (decibels relative to one milliwatt, referred to a zero transmission level point) and performed in accordance with American National Standards Institute (ANSI) T1.506-1990, American National Standard for Telecommunications—Network Performance—Transmission Specifications for Switched Exchange Access Network including supplement ANSI T1.506a-1992, and American National Standards Institute/Institute of Electrical and Electronics Engineers (ANSI/IEEE) 743-1984, IEEE Standard Methods and Equipment for Measuring the Transmission Characteristics of Analog Voice Frequency Circuits. The ANSI T1.506-1990, American National Standard for Telecommunications—Network Performance—Transmission Specifications for Switched Exchange Access Network is incorporated by reference in accordance with 5 U.S.C. 522(a) and 1 CFR part 51. Copies of ANSI T1.506-1990 are available for inspection during normal business hours at RUS, room 2845, U.S. Department of Agriculture, STOP 1598, Washington, DC 20250-1598, or at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030, or go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html. Copies are available from ANSI, Customer Service, 11 West 42nd Street, New York, New York 10036, telephone number (212) 642-4900. The ANSI/IEEE 743-1984, IEEE Standard Methods and Equipment for Measuring the Transmission Characteristics of Analog Voice Frequency Circuits is incorporated by reference in accordance with 5 U.S.C. 522(a) and 1 CFR part 51. Copies of ANSI/IEEE 743-1984 are available for inspection during normal business hours at RUS, room 2845, U.S. Department of Agriculture, STOP 1598, Washington, DC 20250-1598, or at the National Archives and Records Administration. Copies are available from ANSI, Customer Service, 11 West 42nd Street, New York, New York 10036, telephone number (212) 642-4900.

Test equipment. The equipment for performing the measurement shall be in accordance with ANSI/IEEE 743-1984.

Applicable results. The S/CNN for both trunk and nonloaded subscriber loop circuits shall not be less than 31 dB.

Data record. The measurement data shall be recorded. Suggested formats similar to Format VI, Voiceband Data Transmission Tests—Nonloaded Subscriber Loops, and Format VII, Voiceband Data Transmission Tests—Trunk Circuits, in § 1755.407 or formats specified in the applicable construction contract may be used.

Probable causes for nonconformance. Some of the causes for failing to obtain the desired results may be due to excessive harmonic distortion, quantizing noise, phase and amplitude jitter, and loss in digital pads used for level settings.

When specified by the borrower, S/IMD measurements shall be made on trunk circuits and nonloaded subscriber loops. For trunk circuits, the measurement shall be made between CO locations. For nonloaded subscriber loops, the measurement shall be made from the CO to the station protector of the NID at the customer's access location.

S/IMD is a measure of the distortion produced by extraneous frequency cross products, known as intermodulation products, when a multi-tone tone signal is applied to a system.

Intermodulation distortion (IMD) is caused by system nonlinearities acting upon the harmonic frequencies produced from an input of multiple tones. The products resulting from IMD can be more damaging than noise in terms of producing data transmission errors.

IMD is measured as a signal to distortion ratio and is expressed as the logarithmic ratio in dB of the composite power of four resulting test frequencies to the total power of specific higher order distortion products that are produced. The higher order products are measured at both the 2nd order and 3rd order and are designated R2 and R3, respectively. The four frequency testing for IMD is produced with four tones of 857, 863, 1,372, and 1,388 Hz input at a composite power level of −13 dBm0.

Method of measurement. The S/IMD measurement shall be performed in accordance with ANSI T1.506-1990 and ANSI/IEEE 743-1984.

Test equipment. The equipment for performing the measurement shall be in accordance with ANSI/IEEE 743-1984.

Applicable results. The 2nd order (R2) S/IMD for both trunk and nonloaded subscriber loop circuits shall not be less than 40 dB. The 3rd order (R3) S/IMD for both trunk and nonloaded subscriber loop circuits shall not be less than 40 dB.

Data record. The measurement data shall be recorded. Suggested formats similar to Format VI for nonloaded subscriber loops and Format VII for trunk circuits in § 1755.407 or formats specified in the applicable construction contract may be used.

Probable causes for nonconformance. Some of the causes for failing to obtain the desired results may be due to channel nonlinearities, such as compression and clipping, which cause harmonic and intermodulation distortion in a voiceband signal.

When specified by the borrower, EDD measurements shall be made on trunk circuits and nonloaded subscriber loops. For trunk circuits, the measurement shall be made between CO locations. For nonloaded subscriber loops, the measurement shall be made from the CO to the station protector of the NID at the customer's access location.

EDD is a measure of the linearity or uniformity of the phase versus frequency characteristics of a transmission facility. EDD is also known as relative envelope delay (RED).

EDD is specifically defined as the delay relative to the envelope delay at the reference frequency of 1,704 Hz. EDD is typically measured at two frequencies, one low and one high in the voiceband. The low frequency measurement is made at 604 Hz. The high frequency measurement is made at 2,804 Hz.

Method of measurement. The EDD measurement shall be performed in accordance with ANSI T1.506-1990 and ANSI/IEEE 743-1984.

Test equipment. The equipment for performing the measurement shall be in accordance with ANSI/IEEE 743-1984.

Applicable results. The EDD for both trunk and nonloaded subscriber loop circuits at the low frequency of 604 Hz shall not exceed 1,500 microseconds. The EDD for both trunk and nonloaded subscriber loop circuits at the high frequency of 2,804 Hz shall not exceed 1,000 microseconds.

Data record. The measurement data shall be recorded. Suggested formats similar to Format VI for nonloaded subscriber loops and Format VII for trunk circuits in § 1755.407 or formats specified in the applicable construction contract may be used.

Probable causes for nonconformance. Some of the causes for failing to obtain the desired results may be due to nonlinearity of the phase versus frequency characteristic of the transmission facility. This nonlinear phase versus frequency characteristic of the transmission facility causes the various frequency components to travel at different transit times which results in successively transmitted data pulses to overlap at the receive end. The overlapping of the pulses at the receive end results in distortion of the received signal. Excessive EDD on the transmission facility may be reduced using data modems with equalization or by conditioning the transmission line.

When specified by the borrower, AJ measurements shall be made on trunk circuits and nonloaded subscriber loops. For trunk circuits, the measurement shall be made between CO locations. For nonloaded subscriber loops, the measurement shall be made from the CO to the station protector of the NID at the customer's access location.

AJ is any fluctuation in the peak amplitude value of a fixed tone signal at 1,004 Hz from its nominal value. AJ is expressed in peak percent amplitude modulation.

AJ is measured in two separate frequency bands, 4-300 Hz and 20-300 Hz. The 4-300 Hz band is important for modems employing echo canceling capabilities. The 20-300 Hz band is used for modems that do not employ echo cancelers.

Amplitude modulation can affect the error performance of voiceband data modems. The measurement of amplitude jitter indicates the total effect on the amplitude of the holding tone of incidental amplitude modulation and other sources including quantizing and message noise, impulse noise, gain hits, phase jitter, and additive tones such as single-frequency interference.

Method of measurement. The AJ measurement shall be performed in accordance with ANSI T1.506-1990 and ANSI/IEEE 743-1984.

Test equipment. The equipment for performing the measurement shall be in accordance with ANSI/IEEE 743-1984.

Applicable results. The AJ for both trunk and nonloaded subscriber loop circuits in the 4-300 Hz frequency band shall not exceed 6%. The AJ for both trunk and nonloaded subscriber loop circuits in the 20-300 Hz frequency band shall not exceed 5%.

Data record. The measurement data shall be recorded. Suggested formats similar to Format VI for nonloaded subscriber loops and Format VII for trunk circuits in § 1755.407 or formats specified in the applicable construction contract may be used.

Probable causes for nonconformance. Some of the causes for failing to obtain the desired results may be due to excessive S/CNN, impulse noise, and phase jitter.

When specified by the borrower, PJ measurements shall be made on trunk circuits and nonloaded subscriber loops. For trunk circuits, the measurement shall be made between CO locations. For nonloaded subscriber loops, the measurement shall be made from the CO to the station protector of the NID at the customer's access location.

PJ is any fluctuation in the zero crossings of a fixed tone signal (usually 1,004 Hz) from their nominal position in time within the voiceband. PJ is expressed in terms of either degrees peak-to-peak (° p-p) or in terms of a Unit Interval (UI). One UI is equal to 360° p-p.

PJ measurements are typically performed in two nominal frequency bands. The frequency bands are 20-300 Hz band and either the 2-300 Hz band or the 4-300 Hz band. The 20-300 Hz band is important to all phase-detecting modems. The 4-300 Hz band or the 2-300 Hz band is important for modems employing echo canceling capabilities.

Phase jitter can affect the error performance of voiceband data modems that use phase detection techniques. The measurement of phase jitter indicates the total effect on the holding tone of incidental phase modulation and other sources including quantizing and message noise, impulse noise, phase hits, additive tones such as single-frequency interference, and digital timing jitter.

Method of measurement. The PJ measurement shall be performed in accordance with ANSI T1.506-1990 and ANSI/IEEE 743-1984.

Test equipment. The equipment for performing the measurement shall be in accordance with ANSI/IEEE 743-1984.

Applicable results. The PJ for both trunk and nonloaded subscriber loop circuits in the 4-300 Hz frequency band shall not exceed 6.5° p-p. The PJ for both trunk and nonloaded subscriber loop circuits in the 20-300 Hz frequency band shall not exceed 10.0° p-p.

Data record. The measurement data shall be recorded. Suggested formats similar to Format VI for nonloaded subscriber loops and Format VII for trunk circuits in § 1755.407 or formats specified in the applicable construction contract may be used.

Probable causes for nonconformance. Some of the causes for failing to obtain the desired results may be due to excessive S/CNN, impulse noise, and amplitude jitter.

When specified by the borrower, impulse noise measurements shall be made on trunk circuits and nonloaded subscriber loops. For trunk circuits, the measurement shall be made between CO locations. For nonloaded subscriber loops, the measurement shall be made from the CO to the station protector of the NID at the customer's access location.

Impulse noise is a measure of the presence of unusually large noise excursions of short duration that are beyond the normal background noise levels on a facility. Impulse noise is typically measured by counting the number of occurrences beyond a particular noise reference threshold in a given time interval. The noise reference level is C-message weighted.

Method of measurement. The impulse noise measurement shall be performed using a 1,004 Hz tone at −13 dBm0 and in accordance with ANSI T1.506-1990 and ANSI/IEEE 743-1984.

Test equipment. The equipment for performing the measurement shall be in accordance with ANSI/IEEE 743-1984.

Applicable results. The impulse noise for both trunk and nonloaded subscriber loop circuits shall not exceed 65 dBrnC0 (decibels relative to one picowatt reference noise level, measured with C-message frequency weighting, referred to a zero transmission level point). The impulse noise requirement shall be based upon a maximum of 5 counts in a 5 minute period at equal to or greater than the indicated noise thresholds.

Data record. The measurement data shall be recorded. Suggested formats similar to Format VI for nonloaded subscriber loops and Format VII for trunk circuits in § 1755.407 or formats specified in the applicable construction contract may be used.

Probable causes for nonconformance. Some of the causes for failing to obtain the desired results may be due to excessive transient signals originating from the various switching operations.

The shield or armor ground resistance measurement shall be made between the copper cable and wire shield and ground and between the fiber optic cable armor and ground, respectively. The measurement shall be made either on cable and wire lengths before splicing and before any ground connections are made to the cable or wire shields or armors. Optionally, the measurement may be made on cable and wire lengths after splicing, but all ground connections must be removed from the section under test.

The method of measurement using either an insulation resistance test set or a dc bridge type megohmmeter shall be as shown in Figure 18 as follows:

The shield or armor ground resistance measurements may be made using an insulation resistance test set, a dc bridge type megohmmeter, or a commercially available fault locator.

The insulation resistance test set should have an output voltage not to exceed 500 volts dc and may be hand cranked or battery operated.

The dc bridge type megohmmeter, which may be ac powered, should have scales and multipliers which make it possible to accurately read resistance values of 50,000 ohms to 10 megohms. The voltage that is applied to the shield or armor during the test should not be less than “250 volts dc” nor greater than “1,000 volts dc” when using an instrument having adjustable test voltage levels.

Commercially available fault locators may be used in lieu of the above equipment, if the devices are capable of detecting faults having resistance values of 50,000 ohms to 10 megohms. Operation of the devices and method of locating the faults should be in accordance with manufacturer's instructions.

For all new copper cable and wire facilities and all new fiber optic cable facilities, the shield or armor ground resistance levels normally exceed 1 megohm-mile (1.6 megohm-km) at 68 °F (20 °C). A value of 100,000 ohm-mile (161,000 ohm-km) at 68 °F (20 °C) shall be the minimum acceptable value of the shield or armor ground resistance.

Shield or armor ground resistance varies inversely with length and temperature. In addition other factors which may affect readings could be soil conditions, faulty test equipment and incorrect test procedures.

For the resistance test method and dc bridge type megohmmeter, the ohm-mile (ohm-km) value for the shield or armor ground resistance shall be computed by multiplying the actual scale reading in ohms on the test set by the length in miles (km) of the cable or wire under test.

Due to the differences between various jacketing materials used in manufacturing cable or wire and to varying soil conditions, it is impractical to provide simple factors to predict the magnitude of variation in shield or armor to ground resistance due to temperature. The variations can, however, be substantial for wide excursions in temperature from the ambient temperature of 68 °F (20 °C).

When results of resistance measurements are below the 100,000 ohm-mile (161,000 ohm-km) requirement at 68 °F (20 °C), the jacket temperature, soil conditions, test equipment and method shall be reviewed before the cable or wire is considered a failure. If the temperature is approximately 68 °F (20 °C) and soil conditions are acceptable, and a reading of less than 100,000 ohm-mile (161,000 ohm-km) is indicated, check the calibration of the equipment; as well as, the test method. If the equipment was found to be out of calibration, recalibrate the equipment and remeasure the cable or wire. If the temperature was 86 °F (30 °C) or higher, the cable or wire shall be remeasured at a time when the temperature is approximately 68 °F (20 °C). If the test was performed in unusually wet soil, the cable or wire shall be retested after the soil has reached normal conditions. If after completion of the above steps, the resistance value of 100,000 ohm-mile (161,000 ohm-km) or greater is obtained, the cable or wire shall be considered acceptable.

When the resistance value of the cable or wire is still found to be below 100,000 ohm-mile (161,000 ohm-km) requirement after completion of the steps listed in paragraph (f)(1) of this section, the fault shall be isolated by performing shield or armor ground resistance measurements on individual cable or wire sections.

Once the fault or faults have been isolated, the cable or wire jacket shall be repaired in accordance with § 1755.200, RUS Standard for Splicing Copper and Fiber Optic Cables or the entire cable or wire section may be replaced at the request of the borrower.