- Conductor Resistance Test Definition: The conductor resistance test measures the DC resistance of copper or aluminum conductors to determine how easily they allow current flow.
- Importance of Resistance: Higher resistance in a conductor results in less current flow, which is crucial for efficient power transmission.
- Test Equipment: The test uses a Kelvin Double Bridge or Wheatstone Bridge to measure resistance accurately.
- Testing Procedure: Involves connecting the conductor to a resistance measuring bridge, measuring resistance, and adjusting for temperature and length.
- Conclusion: The test results indicate if the conductor meets specified resistance standards, ensuring reliability in electrical power cables.
The conductor resistance test measures the DC resistance of copper or aluminium conductors. IS 10810-5 reports that value in ohms per kilometre at 20°C. For a given voltage, higher resistance means less current. Conductor size, construction, temperature and resistivity all change the reading. Cable standards compare the corrected value with a maximum in ohms per kilometre.
IS 10810-5 uses a Kelvin Double Bridge, 0.2% accuracy, or a Wheatstone Bridge, 0.5% accuracy. For measured resistance up to 1 Ω, only the Kelvin double bridge is allowed.
Choose the specimen length as follows.
- All solid circular conductors: drum length or 1 m
- All stranded or sector shaped solid conductors up to and including 25 mm2: drum length or 5 m
- All stranded or sector shaped solid conductors greater than 25 mm2: drum length or 10 m
Note – Specimen length is the length between the potential terminals.
Procedure of Conductor Resistance Test
Connect the specimen to the bridge so contact resistance stays low.
Measure the resistance and record the ambient temperature. Use a current that does not heat the specimen.
Convert the reading to 20°C and to one kilometre.
Observation and Report
| Sample no | Nominal conductor size in mm2 | Length (m) | Material Al/Cu | Class of conductor | Temperature oC | Observed Resistance | Specified Resistance |
| – | – | – | – | – | – | – | – |
| – | – | – | – | – | – | – | – |
| – | – | – | – | – | – | – | – |
Calculation
Convert the observed resistance at temperature t as
where
Rt = observed resistance
K = temperature correction factor from IS 10810-5 Table 1
L = specimen length in m
Conclusion: the sample meets or does not meet the specified maximum at 20°C.
