Standard Test Method for Resistivity of Electrical Conductor


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Designation: B193 − 16

Standard Test Method for Resistivity of Electrical Conductor Materials1
This standard is issued under the fixed designation B193; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.

1. Scope
1.1 This test method covers the determination of the electrical resistivity of metallic electrical conductor material. It provides for an accuracy of 60.30 % on test specimens having a resistance of 0.00001 Ω (10 µΩ) or more. Weight resistivity accuracy may be adversely affected by possible inaccuracies in the assumed density of the conductor.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:2 A111 Specification for Zinc-Coated (Galvanized) “Iron”
Telephone and Telegraph Line Wire A326 Specification for Zinc-Coated (Galvanized) High Ten-
sile Steel Telephone and Telegraph Line Wire (Withdrawn 1990)3 B9 Specification for Bronze Trolley Wire B105 Specification for Hard-Drawn Copper Alloy Wires for Electric Conductors B298 Specification for Silver-Coated Soft or Annealed Copper Wire B355 Specification for Nickel-Coated Soft or Annealed Copper Wire B415 Specification for Hard-Drawn Aluminum-Clad Steel Wire B498/B498M Specification for Zinc-Coated (Galvanized)
1 This test method is under the jurisdiction of ASTM Committee B01 on Electrical Conductors and is the direct responsibility of Subcommittee B01.02 on Methods of Test and Sampling Procedure.
Current edition approved April 1, 2016. Published April 2016. Originally approved in 1944. Last previous edition approved in 2014 as B193 – 02 (2014). DOI: 10.1520/B0193-16.
2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [email protected] For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website.
3 The last approved version of this historical standard is referenced on www.astm.org.

Steel Core Wire for Use in Overhead Electrical Conductors B566 Specification for Copper-Clad Aluminum Wire B606 Specification for High-Strength Zinc-Coated (Galvanized) Steel Core Wire for Aluminum and AluminumAlloy Conductors, Steel Reinforced B800 Specification for 8000 Series Aluminum Alloy Wire for Electrical Purposes—Annealed and Intermediate Tempers B802 Specification for Zinc-5% Aluminum-Mischmetal Alloy-Coated Steel Core Wire for Aluminum Conductors, Steel Reinforced (ACSR)[Metric](Discontinued 1998Replaced by B 802/B802M) B0802_B0802M B803 Specification for High-Strength Zinc–5 % AluminumMischmetal Alloy-Coated Steel Core Wire for Use in Overhead Electrical Conductors B957 Specification for Extra-High-Strength and Ultra-HighStrength Zinc-Coated (Galvanized) Steel Core Wire for Overhead Electrical Conductors B958 Specification for Extra-High-Strength and Ultra-HighStrength Class A Zinc–5% Aluminum-Mischmetal AlloyCoated Steel Core Wire for Use in Overhead Electrical Conductors 2.2 NIST Document: NBS Handbook 100 —Copper Wire Tables4
3. Resistivity
3.1 Resistivity (Explanatory Note 1) is the electrical resistance of a body of unit length, and unit cross-sectional area or unit weight.
3.2 Volume Resistivity is commonly expressed in ohms for a theoretical conductor of unit length and cross-sectional area; in inch-pound units in Ω·cmil/ft and in acceptable metric units in Ω· mm2/m. It may be calculated by the following equation:
ρv 5 ~A/L!R
where: ρv = volume resistivity, Ω·cmil/ft or Ω·mm2/m, A = cross-sectional area, cmil or mm2,
4 Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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B193 − 16

L = gage length, used to determine R, ft or m, and R = measured resistance, Ω.
3.3 Weight Resistivity is commonly expressed in ohms for a theoretical conductor of unit length and weight. The method for calculating weight resistivity, based on resistance, length, and weight measurements, of a test specimen is given in Explanatory Note 2.
4. Apparatus
4.1 Resistance shall be measured with a circuit configuration and instrumentation that has a resistance measurement capability of 60.15 % accuracy.
5. Test Specimen
5.1 The test specimen may be in the form of a wire, strip, rod, bar, tube, or shape. It shall be of uniform cross section throughout its length within 60.75 % of the cross-sectional area. Wherever possible it shall be the full cross section of the material it represents, if the full cross section is such that the uniformity of the cross-sectional area can be accurately determined.
5.2 The test specimen shall have the following characteristics:
5.2.1 A resistance of at least 0.00001 Ω (10 µΩ) in the test length between potential contacts,
5.2.2 A test length of at least 1 ft or 300 mm, 5.2.3 A diameter, thickness, width, or other dimension suitable to the limitations of the resistance measuring instrument, 5.2.4 No surface cracks or defects visible to the unaided normal eye, and substantially free from surface oxide, dirt, and grease, and 5.2.5 No joints or splices.
6. Procedure
6.1 Make all determinations of the dimensions and weight of the test specimen using instruments accurate to 60.05 %. In order to assure this accuracy in measuring the length between potential contacts, the surface in contact with the test specimen shall be a substantially sharp knife-edge when using a Kelvintype bridge or a potentiometer.
6.2 The cross-sectional dimensions of the specimen may be determined by micrometer measurements, and a sufficient number of measurements shall be made to obtain the mean cross section to within 60.10 %. In case any dimension of the specimen is less than 0.100 in. and cannot be measured to the required accuracy, determine the cross-section from the weight, density, and length of the specimen.
6.3 When the density is unknown, determine the density by weighing a specimen first in air and then in a liquid of known density at the test temperature, which shall be room temperature to avoid errors due to convection currents. Exercise care in removing all air bubbles from the specimen when weighing it in the liquid. Calculate the density from the following equation:
δ 5 ~Wa 3d!/~Wa 2 Wl!

where:
δ= Wa = Wl = d=

density of the specimen, g/cm3;
weight of the specimen in air, g;
weight of the specimen in the liquid, g; and density of the liquid at the test temperature, g/cm3.

6.4 When potential leads are used, make sure the distance between each potential contact and the corresponding current contact is at least equal to 11⁄2 times the cross-sectional perimeter of the specimen. Make sure the yoke resistance (between reference standard and test specimen) is appreciably smaller than that of either the reference standard or the test specimen unless a suitable lead compensation method is used, or it is known that the coil and lead ratios are sufficiently balanced so that variation in yoke resistance will not decrease the bridge accuracy below stated requirements.

6.5 Make resistance measurements to an accuracy of 60.15 %. To ensure a correct reading, allow the reference standard and the test specimen to come to the same temperature as the surrounding medium. (If the reference standard is made of manganin it is possible to obtain correct readings with the test specimen at reference temperatures other than room temperature). In all resistance measurements, the measuring current raises the temperature of the medium. Therefore, take care to keep the magnitude of the current low, and the time of its use short enough so that the change in resistance cannot be detected with the galvanometer. To eliminate errors due to contact potential, take two readings, one direct and one with current reversed, in direct succession. Check tests are recommended whereby the specimen is turned end for end, and the test repeated. Surface cleaning of the specimen at current and potential contact points may be necessary to obtain good electrical contact.

7. Temperature Correction
7.1 When the measurement is made at any other than a reference temperature, the resistance may be corrected for moderate temperature differences to what it would be at the reference temperature, as follows:
Rt
RT 5 11αT~t 2 T!
where:
RT = resistance at reference temperature T, Rt = resistance as measured at temperature t, αT = known or given temperature coefficient of resistance of
the specimen being measured at reference temperature T, T = reference temperature, and t = temperature at which measurement is made.
NOTE 1—The parameter αT, in the above equation, varies with conductivity and temperature. For copper of 100 % conductivity and a reference temperature of 20°C, its value is 0.00393. Values at other conductivities and temperatures will be found in NBS Handbook 100.4Table 1 lists temperature coefficients for the common electrical conductor materials.

8. Report
8.1 For referee tests, report the following information: 8.1.1 Identification of test specimen, 8.1.2 Kind of material,

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B193 − 16

TABLE 1 Resistivity and Conductivity Conversion

NOTE 1—These factors are applicable only to resistivity and conductivity values corrected to 20°C (68°F). They are applicable for any temperature when used to convert between volume units only or between weight units only. Values of density, δ, for the common electrical conductor materials, are listed in Table 2.

Given N→ Perform indicated
operation to obtain ↓
Ω·cmil/ft
Ω·mm2/m
µΩ·in.
µΩ·cm
Ω·lb/mile2
Ω·g/m2
% IACS (volume basis)
% IACS (weight basis)

Ω·cmil/ft
... N × 0.0016624 N × 0.065450
N × 0.16624
N × 9.4924 × δ N × 0.0016624
×δ (1/N) × 1037.1 (1/N) × 9220.0
× (1/δ)

Volume Resistivity at 20°C

Weight Resistivity at 20°C

Ω·mm2/m N × 601.52
... N × 39.370 N × 100.00
N × 5710.0 × δ

µΩ·in.

µΩ·cm

Ω·lb/mile2

Volume Resistivity at 20°C

N × 15.279

N × 6.0153 N × 0.10535 ×

(1/δ)

N × 0.025400 N × 0.010000 N × 0.00017513

× (1/δ)

...

N × 0.39370 N × 0.0068950

× (1/δ)

N × 2.5400

...

N × 0.017513 ×

(1/δ)

Weight Resistivity at 20°C

N × 145.03 × δ N × 57.100 × δ

...

Ω·g/m2
N × 601.53 × (1/δ)
N × (1/δ)
N × 39.370 × (1/δ)
N × 100.00 × (1/δ)
N × 5710.0

N×δ
(1/N) × 1.7241 (1/N) × 15.328
× (1/δ)

N × 0.025400 N × 0.010000

×δ

×δ

Conductivity at 20°C

(1/N) × 67.879 (1/N) × 172.41

(1/N) × 603.45 × (1/δ)

(1/N) × 1532.8 × (1/δ)

N × 0.00017513
(1/N) × 9844.8 ×δ
(1/N) × 87520

...
(1/N) × 1.7241 ×δ
(1/N) × 15.328

Conductivity at 20°C

% IACS

% IACS

(Volume Basis) (Weight Basis)

(1/N) × 1037.1 (1/N) × 1.7241 (1/N) × 67.879 (1/N) × 172.41
(1/N) × 9844.8 ×δ
(1/N) × 1.7241 ×δ ...
N 8.89 × (1/δ)

(1/N) × 9220.0 × (1/δ)
(1/N) × 15.328 × (1/δ)
(1/N) × 603.45 × (1/δ)
(1/N) × 1532.8 × (1/δ)
(1/N) × 87520
(1/N) × 15.328
N × 0.11249 ×δ ...

8.1.3 Test temperature, 8.1.4 Test length of specimen, 8.1.5 Method of obtaining cross-sectional area: 8.1.5.1 If by micrometer, the average values of micrometer readings, or 8.1.5.2 If by weighing, a record of length, weight, any density determinations that may be made, and calculated cross-sectional areas. 8.1.6 Weight, if used, 8.1.7 Method of measuring resistance, 8.1.8 Value of resistance, 8.1.9 Reference temperature, 8.1.10 Calculated value of resistivity at the reference temperature, and 8.1.11 Previous mechanical and thermal treatments. (Since the resistivity of a material usually depends upon them, these shall be stated whenever the information is available.)
8.2 For routine tests, only such of the items in 8.1 as apply to the particular case, or are significant, shall be reported.

9. Precision and Bias
9.1 Precision—This test method has been in use for many years. No statement of precision has been made and no work has been planned to develop such a statement.
9.2 Bias—This test method has no bias because the value for resistivity is determined solely in terms of this test method.
10. Keywords 10.1 conductivity; electrical conductor materials; resistivity;
resistivity of electrical conductor; volume resistivityweight resistivity

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B193 − 16

TABLE 2 Density and Temperature Coefficient of Resistance for Electrical Conductor Materials

Material

Approximate Density, δ, at 20°C, g/cm3

Temperature Coefficient of Resistance, α, at
20°C

Material

Approximate Density, δ, at 20°C, g/cm3

Copper, % 101 100 98.40 98.16 97.80 97.66 97.40 97.16 96.66 96.16 94.16 93.15

IACS:

Silver Coated Copper, Specification B298:
Class A Class B Class C Class D Class E

Nickel Coated Copper, Specification B355:
Class 2 Class 4 Class 7 Class 10 Class 27

Bronze, Specification B9: Alloy 40 Alloy 55 Alloy 80

Aluminum Alloy 8000,

8.89

0.00397

Specification B800, % IACS:

8.89

0.00393

61.8

2.71

8.89

0.00387

61.5

2.71

8.89

0.00386

61.4

2.71

8.89

0.00384

61.3

2.71

8.89

0.00384

61.2

2.71

8.89

0.00383

61.0

2.71

8.89

0.00382

60.9

2.71

8.89

0.00380

60.8

2.71

8.89

0.00378

60.7

2.71

8.89

0.00370

60.6

2.71

8.89

0.00366

Aluminum Alloy 6101,

% IACS:

59.5

2.70

8.91

0.00393

59.0

2.70

8.93

0.00393

57.0

2.70

8.95

0.00394

56.5

2.70

8.99

0.00394

56.0

2.70

9.05

0.00395

55.0

2.70

54.0

2.70

53.0

2.70

8.89

0.00395

Aluminum Alloy, % IACS:

8.89

0.00397

5005-H19

53.5

2.70

8.89

0.00400

6201-T81

52.5

2.69

8.89

0.00404

8.89

0.00422

Aluminum Clad Steel,

% IACS:

20.3

6.59

27

5.91

30

5.61

40

4.64

8.89

0.00157

Copper Clad Steel:

8.89

0.00224

Grade 30 A, HS, EHS

8.15

8.89

0.00322

Grade 40 A, HS, EHS

8.25

Temperature Coefficient of Resistance, α, at
20°C
0.00408 0.00406 0.00406 0.00405 0.00404 0.00403 0.00402 0.00402 0.00401 0.00400
0.00393 0.00390 0.00377 0.00373 0.00370 0.00363 0.00357 0.00350
0.00353 0.00347
0.0036 0.0036 0.0038 0.0040
0.00378 0.00378

Copper Alloy, B105:
Grade 8.5 Grade 13 Grade 15 Grade 20 Grade 30 Grade 40 Grade 55 Grade 74 Grade 80 Grade 85

Specification

Aluminum 1350, % IACS: 61.8 61.5 61.4 61.3 61.2 61.0

8.78 8.78 8.54 8.89 8.89 8.89 8.89 8.89 8.89 8.89
2.705 2.705 2.705 2.705 2.705 2.705

0.00042 0.00063 0.00072 0.00079 0.00118 0.00157 0.00224 0.00299 0.00322 0.00342
0.00408 0.00406 0.00406 0.00405 0.00404 0.00403

Galvanized Steel (Telephone and Telegraph), Specification A111:
Class A Coating: Grade EBB (Non cu-brg) Grade BB (Cu-brg) Grade BB (Non cu-brg)
Class B Coating: Grade EBB (Non cu-brg) Grade BB (Cu-brg) Grade BB (Non cu-brg)
Class C Coating: Grade EBB (Non cu-brg) Grade BB (cu-brg) Grade BB (Non cu-brg)
Copper Clad Aluminum, Specification B566:
Class 10A and 10H Class 15A and 15H

7.83

0.0056

7.83

0.0046

7.83

0.0042

7.80

0.0056

7.80

0.0046

7.80

0.0042

7.77

0.0056

7.77

0.0046

7.77

0.0042

3.32

0.00405

3.63

0.00404

Galvanized Steel, Specification A326:
Class A Coating: Grade 85 Grade 135 and 195
Class B Coating: Grade 85 Grade 135 and 195
Class C Coating: Grade 85 Grade 135 and 195

7.83

0.0046

7.83

0.0042

7.80

0.0046

7.80

0.0042

7.77

0.0046

7.77

0.0042

4

Material

Approximate Density, δ, at 20°C, g/cm3

B193 − 16

TABLE 2 Continued

Temperature Coefficient of Resistance, α, at
20°C

Material

Galvanized Steel and Zn-5 % Aluminum Coated Steel (for ACSR, ACSS) Specifications B498/B498M, B606, B802, B803, B957, B958

Approximate Density, δ, at 20°C, g/cm3
7.78

Temperature Coefficient of Resistance, α, at
20°C
0.00360

TABLE 3 Equivalent Resistivity Values for CopperA Conductivity at 20°C (68°F)
percent IACS
Volume Resistivity

100.0

Ω·cmil/ft Ω·mm2/m µΩ·in. µΩ·cm

10.371 0.017241 0.67879 1.7241

Weight Resistivity

Ω·lb/mile2 Ω·g/m2

875.20 0.15328

A The equivalent resistivity values for 100 % IACS (soft copper) were each computed from the fundamental IEC value (1/58 Ω·mm2/m) using conversion factors each accurate to at least seven significant figures. Corresponding values for other conductivities (aluminum, etc.) may be derived from these by multiplying by the reciprocal of the conductivity ratios and where applicable also by the density ratios, both accurate to at least seven significant figures.

EXPLANATORY NOTES

NOTE 1—Volume resistivity is used in place of “weight resistivity” and
“percent conductivity.”
Resistivity units are based on the International Annealed Copper Standard (IACS) adopted by IEC in 1913, which is 1/58 Ω·mm2/m at 20°C (68°F) for 100 % conductivity. The value of 0.017241 Ω·mm2/m and the value of 0.15328 Ω·g/m2 at 20°C (68°F) are respectively the international
equivalent of volume and weight resistivity of annealed copper equal (to
five significant figures) to 100 % conductivity. The latter term means that
a copper wire 1 m in length and weighing 1 g would have a resistance of 0.15328 Ω. This is equivalent to a resistivity value of 875.20 Ω·lb/mile2,
which signifies the resistance of a copper wire 1 mile in length weighing
1 lb. It is also equivalent, for example, to 1.7241 µΩ/cm of length of a copper bar 1 cm2 in cross section. A complete discussion of this subject is contained in NBS Handbook 100.4 The use of five significant figures in
expressing resistivity does not imply the need for greater accuracy of
measurement than that specified in Test Method B193. The use of five
significant figures is required for reasonably accurate reversible conver-
sion from one set of resistivity units to another. The equivalent resistivity
values in Table 3 were derived from the fundamental IEC value (1/58 Ω·mm2/m) computed to seven significant figures and then rounded to five
significant figures.
NOTE 2—Weight resistivity is expressed in U.S. customary units in

Ω·lb/mile2 and in metric units in Ω·g/m2. It may be calculated as follows:

ρw 5 ~W/L1L2!R

where:
ρw = W= L2 = L1 = R=

weight resistivity, Ω·lb/mile2 or Ω·g/m2, weight of the test specimen, lb or g, length of the test specimen, miles or m, gage length, used to determine R, miles or m, and measured resistance, Ω.

NOTE 3—Resistivity and Conductivity Conversion—Conversion of the various units of volume resistivity, weight resistivity, and conductivity, may be facilitated by employing the formulas and factors shown in Table 1. The factors given therein are applicable to all metallic electrical conductor material. Table 2 lists values of density, δ, for the common electrical conductor materials.

NOTE 4—Density—For the purpose of resistivity and conductivity conversion, the density of the various conductor materials may be taken as shown in Table 2, based on a temperature of 20°C (68°F).
However, if the conversion is for specification acceptance purposes, the density used shall be that specified in the product specification involved.

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Standard Test Method for Resistivity of Electrical Conductor