FED-STD-228A
Method 6021.1
18 APRIL 2014
RESISTANCE, ELECTRICAL, CONDUCTOR
1. SCOPE
1.1 This method is intended for use in determining the electrical resistance of solid and stranded
conductors.
2. SPECIMEN
2.1 The specimen shall be free of splices, surface cracks, or other visible defects and shall be at least 36
inches in length.
3. APPARATUS
3.1 Resistance shall be measured with a Kelvin bridge, or a suitable four-terminal test method alternate if
the resistance is below one ohm. Measurement accuracy shall be within 0.1 percent of reading:
3.2 Resistance may be measured with a Wheatstone bridge, or a suitable alternate if the resistance is
above one ohm. Measurement accuracy shall be within one percent of reading.
3.3 Temperature measuring equipment shall be used that will determine the temperature of the
conductor to within ±0.5°C (0.9 °F).
3.4 A rule shall be used to measure the length of the specimen to an accuracy of ± 0.2 percent.
4. PROCEDURE
4.1 If a Wheatstone bridge is used, the resistance of the leads connecting the bridge to the specimen
shall be obtained with the leads short-circuited on themselves and the result subtracted from the
measured resistance of the specimen.
4.2 If a Kelvin bridge is used, separate current and potential leads shall be used. The current leads shall
be attached in such a manner as to give assured contact with all the strands of the conductor. The
potential lead clamps shall be such as to encircle the conductor and of small enough width so that the
tested length can be assured within the ±0.2 percent accuracy. The distance between the current and
potential lead contact shall be greater than three times the diameter of the specimen.
4.3 The test specimen should be allowed to come to the same temperature as the surrounding medium
to ensure a correct reading.
4.4 In all resistance measurements, the measuring current raises the temperature of the conductor.
Therefore, care should be taken to keep the magnitude of current low, and the time of its use short
enough so that the change in resistance cannot be detected.
4.5 To eliminate errors due to contact potential, two readings, one direct and one with current reversed,
may be taken in direct succession and the results averaged.
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