This standard specifies the test equipment, sample preparation, test steps, test results and calculations for the conductor DC resistance test. This standard is applicable to the measurement of the DC resistance of wire and cable conductors. The measurement range is: double-arm bridge: 1Ω and below; single-arm bridge or double bridge: 1~99.9Ω; single-arm bridge: 100Ω and above. GB/T 3048.4-1994 Test methods for electrical properties of wires and cables Conductor DC resistance test GB/T3048.4-1994 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Test methods for determining electrical properties of electric cables and wires
Conductor DC resistance test
GB/T3048.4-94
Generates GI 3048. 483
Test methods for determining electrical properties of electric cables and wiresMeasurement of DC resistance of conductors1 Subject content and scope of application
This standard specifies the test equipment, sample preparation, test procedures, test results and calculations for the DC resistance test of conductors. This standard is applicable to the measurement of the DC resistance of wire and cable conductors, and its measurement range is: double-arm bridge: less than 10 Ω;
single-arm bridge or double-arm bridge: 1~99.92; single-arm bridge: 1002 and above.
Except as otherwise specified in the product standard, during type tests and sampling tests, measurements should be carried out indoors with an ambient temperature of 15-35C and an air humidity of no more than 85%. www.bzxz.net
This test method is not applicable to measuring the DC resistance of installed wires and cables. The general requirements, definitions and periodic calibration requirements for electrical performance tests of wires and cables are specified in (B/T3048.1. 2 Reference standards
GB/T3048.1 General principles for electrical performance test methods for wires and cables
3 Test equipment
3.1 The wiring schematic diagram of the bridge tree measurement system is shown in Figures 1 and 2. Approved by the State Administration of Technical Supervision on May 19, 1994 and implemented on January 1, 1995
GB/T3048.4-94
Figure 1 Single-arm bridge
Figure 2 Double-arm bridge
E—H-current source; A-ammeter; G—galvanometer; P-shunt; RR,.R..Rz, R—bridge arm resistance; Rn standard resistor R variable resistor tR—resistance to be measured, 5 galvanometer switch: S—DC power switch: —cross-line resistance
3.2 The bridge and its accessories should be assembled according to their technical specifications. 3.3 As long as the measurement accuracy is sufficient, it is allowed to use other resistance measuring instruments besides the bridge, and their wiring and installation should be carried out according to the instrument manual. .
3.4 ​​Four-terminal measuring fixture: When the measured resistance is less than 1, a special four-terminal measuring fixture should be used for wiring as much as possible. The outer pair of the four terminals are current electrodes. The inner pair is the potential electrode, and its contact width with the sample should not be greater than (.2% of the sample measurement length. The distance between the potential electrode and the current electrode clamp should not be less than 1.5 times the circumference of the cross-section of the test sample. 4 Sample preparation
4.1 Cut a sample of not less than 1m in length from the test wire and cable, or use a coiled () Cables and wires are used as test specimens. Remove the insulation, sheath or other coverings on the outer surface of the test conductor. You can also remove only the covers at both ends of the test specimen where they are connected to the measuring system to expose the conductor.
Be careful when removing the covers to prevent damage to the conductor. 4.2 Length of test specimens for large-section aluminum conductors
For type tests and bundle tests, it is recommended to use a test specimen length of 3m for cross-sections of 95~185mm2 and 5m for cross-sections of 240mm and above. In case of dispute, 5m for cross-sections of 185mm2 and below and 5m for cross-sections of 240mm and above. mm and above, take 10m4.3 If the sample needs to be straightened, no twisting that causes the cross-sectional area of ​​the sample conductor to change is allowed. It is recommended that the current input terminal of the aluminum stranded wire adopts an aluminum crimping joint (aluminum nose) with the same nominal cross-section as the sample, and is crimped using conventional crimping tools to ensure that the conductor and the joint are integrated after crimping. Its potential electrode should be made of soft copper wire with a diameter of 0.7 to 1.0 mm, tightly wrapped around the stranded wire twice and then tied to prevent loosening.
4.4 Before the sample is connected to the measurement system, the conductor surface of its connection part should be cleaned in advance to remove attachments, dirt and grease. The oxide layer on the surface of the connection should be removed as much as possible.
4.5 During type test and sampling test, the sample should be placed in the test environment for a long enough time to achieve temperature equilibrium. During the sample placement and test process, the change in ambient temperature should not exceed 1°C. When measuring the ambient temperature, the thermometer should be at least 11 from the ground and no more than 1m from the sample, and the two should be roughly at the same temperature. 5 Test steps
5.1 When measuring with a single-arm bridge, connect the sample to be tested with two clamps. GB/T 3048.4-94
When measuring with a double-arm bridge or other resistance instruments, connect the sample to be tested with four clamps. 5.2 Resistance measurement error: It should not be greater than 10% in routine tests and should not be greater than 0.5% in arbitration tests. 5.3 The length of the sample should be measured on the sample between two potential electrodes, and the measurement error should not exceed 0.5%. 5.4 All single wires of the twisted conductor should be reliably connected to the current clamp of the measurement system. For the conductor resistance measurement of finished wires and cables with two cores or more, the two ends of the single-arm bridge or a pair of potential clamps of the effective arm bridge should be connected to the actual marking line for length measurement. 5.5 Close the DC power switch, balance the bridge, read the reading, and record at least four significant digits. When the resistance of the sample is less than 0.12, switch S1 should be reversed, and the current in the opposite direction should be measured again, and the reading should be read. 5.6 When measuring the resistance of a fine conductor, it is necessary to prevent the conductor from heating up due to excessive current. The recommended current density is 0.5A/mm2 for aluminum conductors and 1.0A/mm2 for copper conductors. Two measuring currents with a ratio of 1:1.41 can be used to measure the resistance value of the sample respectively. If the difference between the two does not exceed 0.5%, it is considered that the sample conductor has no temperature rise when measured with a current with a ratio of 1. 6 Test results and calculations
6.1 When measuring with a double-arm bridge, the resistance of the sample is calculated according to the following formula: R = RN·R
Where: R--the resistance value of the sample, a;
the standard resistance value, ;
R,.R2--the resistance value of the bridge arm when the bridge is balanced, 2. 6.2 When measuring with a single-arm bridge, the resistance of the sample is calculated according to the following formula: R
Wu Zhong: R, sample resistance value, 2:
the resistance value of the bridge arm when the bridge is balanced,
If the resistance value of the connecting wire reaches or exceeds 0.2% of the test mouse resistance value, the resistance value R of the sample should be corrected according to the following formula: R,RR
Where: R,-the resistance value calculated according to formula (2), R:-the total resistance of the connecting wire when the two ends of the sample are short-circuited, Q. 6.3 The resistance value per kilometer at 20℃ is calculated as follows: R.
Rz = I + aao(t - 20)
Where: RgpThe resistance value per kilometer at 20℃.2/km, L-the measured length of the sample m:
-the ambient temperature during measurement,
The resistance temperature coefficient of the conductor material at 20℃.1/℃. The resistivity of the conductor at 20℃ is calculated as follows: 1000
GB/T 3048.4-94
-[1 + g(t ~ 20)]
Where: P%—the resistivity of the conductor at -20℃, 0·mm2/mA—the nominal cross-section of the conductor, mm;
6.4 The number of significant digits in the calculation result should be consistent with the product standard. Additional notes:
This standard is proposed by the Ministry of Machinery and Electronics Industry of the People's Republic of China. This standard is under the jurisdiction of Shanghai Cable Research Institute of the Ministry of Machinery and Electronics Industry. This standard was drafted by Shanghai Cable Research Institute of the Ministry of Machinery and Electronics Industry and others. The main drafters of this standard are Zhu Zhongzhu and Jin Biaoyi. This standard was first issued in 1965, revised for the first time in November 1983, and revised for the second time in May 1994.
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