UL 2556-2021 pdf free download.Wire and Cable Test Methods.
3.3.6 Report
The report shall include, as a minimum, the cross-sectional area of the conductor.
3.4 DC resistance
3.4.1 Scope
This test establishes the method for determining the DC resistance of a conductor.
3.4.2 Apparatus
The apparatus shall consist of the following:
a) a 4-terminal measuring device for specimens of resistance of 1 Ω or less, with an accuracy of ±0.5 percent;
b) a 4- or 2-terminal measuring device for specimens of resistance greater than 1 Ω, with an accuracy of ±0.5 percent;
c) a temperature-measuring device with an accuracy of ±1 °C; and
d) a length-measuring device accurate to 0.1 percent of length measured.
3.4.3 Preparation of specimens
3.4.3.1 The specimen shall be a length taken from a wire, cable, or cord, finished or during manufacture,and shall have the following characteristics:
a) a resistance of at least 0.000 01 Ω (10 µΩ) in the test length between voltage contacts;
b) no surface cracks or defects visible with NORMAL VISION , and substantially free from surface oxide, dirt, and grease; and
c) no joints or splices.
d) a test length of at least 1 m (3.3 ft).
3.4.3.2 The test equipment and the test specimen shall be allowed to come to the same temperature as the surrounding medium.
3.4.4 Procedure
3.4.4.1 The electrical resistance of the conductor shall be determined using the measuring device described in 3.4.2. When a 4-terminal measuring device is used, the distance between each voltage contact and the corresponding current contact shall be at least 4.7 times the diameter of the specimen.
Care shall be taken to keep the magnitude of the current low and to minimize measurement time to avoid a change in resistance.
3.4.4.2 The test temperature, which shall be in the range of 10 – 35 °C, shall be recorded at the time the resistance measurement is taken.
3.4.4.3 The length of the specimen under test, between the voltage contact points, shall be recorded.
3.4.5 Results and calculations
3.4.5.1 The resistance of a specimen measured at a temperature other than 20 ° C (or 25 ° C), as determined by the product standard, shall be corrected to the resistance at 20 °C (or 25 °C) by means of the applicable multiplying factor from Table 1.UL 2556 pdf download.