ASTM D257-99(2005)
(Test Method)Standard Test Methods for DC Resistance or Conductance of Insulating Materials
Standard Test Methods for DC Resistance or Conductance of Insulating Materials
SCOPE
1.1 These test methods cover direct-current procedures for the determination of dc insulation resistance, volume resistance, volume resistivity, surface resistance, and surface resistivity of electrical insulating materials, or the corresponding conductances and conductivities.
1.2 These test methods are not suitable for use in measuring the electrical resistivity/conductivity of moderately conductive materials. Use Test Method D 4496 to evaluate such materials.
1.3 The test methods and procedures appear in the following sections:
1.4 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. For a specific hazard statement, see .
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An American National Standard
Designation: D 257 – 99 (Reapproved 2005)
Standard Test Methods for
DC Resistance or Conductance of Insulating Materials
This standard is issued under the fixed designation D 257; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 2. Referenced Documents
1.1 These test methods cover direct-current procedures for 2.1 ASTM Standards:
the determination of dc insulation resistance, volume resis- D 150 Test Methods for AC Loss Characteristics and Per-
tance, volume resistivity, surface resistance, and surface resis- mittivity Dielectric Contant of Solid Electrical Insulation
tivity of electrical insulating materials, or the corresponding D 374 Test Methods for Thickness of Solid Electrical Insu-
conductances and conductivities. lation
1.2 These test methods are not suitable for use in measuring D 618 Practice for Conditioning Plastics for Testing
the electrical resistivity/conductivity of moderately conductive D 1169 Test Method for Specific Resistance (Resistivity) of
materials. Use Test Method D 4496 to evaluate such materials. Electrical Insulating Liquids
1.3 The test methods and procedures appear in the follow- D 1711 Terminology Relating to Electrical Insulation
ing sections: D 4496 Test Method for DC Resistance or Conductance of
Moderately Conductive Materials
Test Method or Procedure Section
Calculation 13
D 5032 Practice for Maintaining Constant Relative Humid-
Choice of Apparatus and Test Method 7
ity by Means of Aqueous Glycerin Solutions
Cleaning Solid Specimens 10.1
E 104 Practice for Maintaining Constant Relative Humidity
Conditioning of Specimens 11
Effective Area of Guarded Electrode Appendix
by Means of Aqueous Solutions
X2
Electrode Systems 6
3. Terminology
Factors Affecting Insulation Resistance or Conductance Appendix
Measurements X1
3.1 Definitions—The following definitions are taken from
Humidity Control 11.2
Terminology D 1711 and apply to the terms used in these test
Liquid Specimens and Cells 9.4
methods.
Precision and Bias 15
Procedure for the Measurement of Resist- 12
3.1.1 conductance, insulation, n—the ratio of the total
ance or Conductance
volume and surface current between two electrodes (on or in a
Referenced Documents 2
Report 14 specimen) to the dc voltage applied to the two electrodes.
Sampling 8
3.1.1.1 Discussion—Insulation conductance is the recipro-
Significance and Use 5
cal of insulation resistance.
Specimen Mounting 10
3.1.2 conductance, surface, n—the ratio of the current
Summary of Test Methods 4
Terminology 3
betweentwoelectrodes(onthesurfaceofaspecimen)tothedc
Test Specimens for Insulation, Volume, and Surface 9
voltage applied to the electrodes.
Resistance or Conductance Determination
Typical Measurement Methods Appendix 3.1.2.1 Discussion—(Some volume conductance is un-
X3
avoidably included in the actual measurement.) Surface con-
ductance is the reciprocal of surface resistance.
1.4 This standard does not purport to address all of the
3.1.3 conductance,volume,n—theratioofthecurrentinthe
safety concerns, if any, associated with its use. It is the
volume of a specimen between two electrodes (on or in the
responsibility of the user of this standard to establish appro-
specimen) to the dc voltage applied to the two electrodes.
priate safety and health practices and determine the applica-
3.1.3.1 Discussion—Volume conductance is the reciprocal
bility of regulatory limitations prior to use. For a specific
of volume resistance.
hazard statement, see 6.1.8.
These test methods are under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and are the direct responsibility of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Subcommittee D09.12 on Electrical Tests. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Sept. 1, 2005. Published October 2005. Originally Standards volume information, refer to the standard’s Document Summary page on
approved in 1925. Last previous edition approved in 1999 as D 257 – 99. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 257 – 99 (2005)
3.1.4 conductivity, surface, n—the surface conductance 4. Summary of Test Methods
multiplied by that ratio of specimen surface dimensions (dis-
4.1 The resistance or conductance of a material specimen or
tance between electrodes divided by the width of electrodes
of a capacitor is determined from a measurement of current or
defining the current path) which transforms the measured
of voltage drop under specified conditions. By using the
conductance to that obtained if the electrodes had formed the
appropriate electrode systems, surface and volume resistance
opposite sides of a square.
or conductance may be measured separately. The resistivity or
3.1.4.1 Discussion—Surface conductivity is expressed in
conductivity can then be calculated when the required speci-
siemens. It is popularly expressed as siemens/square (the size
men and electrode dimensions are known.
of the square is immaterial). Surface conductivity is the
5. Significance and Use
reciprocal of surface resistivity.
3.1.5 conductivity, volume, n—the volume conductance 5.1 Insulatingmaterialsareusedtoisolatecomponentsofan
electrical system from each other and from ground, as well as
multiplied by that ratio of specimen volume dimensions
(distance between electrodes divided by the cross-sectional to provide mechanical support for the components. For this
area of the electrodes) which transforms the measured conduc- purpose, it is generally desirable to have the insulation resis-
tance to that conductance obtained if the electrodes had formed tance as high as possible, consistent with acceptable mechani-
the opposite sides of a unit cube. cal, chemical, and heat-resisting properties. Since insulation
resistance or conductance combines both volume and surface
3.1.5.1 Discussion—Volume conductivity is usually ex-
resistance or conductance, its measured value is most useful
pressed in siemens/centimetre or in siemens/metre and is the
when the test specimen and electrodes have the same form as
reciprocal of volume resistivity.
is required in actual use. Surface resistance or conductance
3.1.6 moderately conductive, adj—describes a solid mate-
changes rapidly with humidity, while volume resistance or
rial having a volume resistivity between 1 and 10 000 000
conductance changes slowly although the final change may
V-cm.
eventually be greater.
3.1.7 resistance, insulation, (R), n—the ratio of the dc
i
5.2 Resistivity or conductivity may be used to predict,
voltage applied to two electrodes (on or in a specimen) to the
indirectly, the low-frequency dielectric breakdown and dissi-
total volume and surface current between them.
pation factor properties of some materials. Resistivity or
3.1.7.1 Discussion—Insulation resistance is the reciprocal
contivity is often used as an indirect measure of moisture
of insulation conductance.
content, degree of cure, mechanical continuity, and deteriora-
3.1.8 resistance,surface,(R ),n—the ratio of the dc voltage
s
tion of various types.The usefulness of these indirect measure-
applied to two electrodes (on the surface of a specimen) to the
ments is dependent on the degree of correlation established by
current between them.
supporting theoretical or experimental investigations. A de-
3.1.8.1 Discussion—(Some volume resistance is unavoid-
crease of surface resistance may result either in an increase of
ably included in the actual measurement.) Surface resistance is
the dielectric breakdown voltage because the electric field
the reciprocal of surface conductance.
intensity is reduced, or a decrease of the dielectric breakdown
3.1.9 resistance,volume,(R ),n—the ratio of the dc voltage
voltage because the area under stress is increased.
v
applied to two electrodes (on or in a specimen) to the current
5.3 All the dielectric resistances or conductances depend on
in the volume of the specimen between the electrodes.
the length of time of electrification and on the value of applied
3.1.9.1 Discussion—Volume resistance is the reciprocal of voltage (in addition to the usual environmental variables).
Thesemustbeknowntomakethemeasuredvalueofresistance
volume conductance.
or conductance meaningful.
3.1.10 resistivity, surface, (r ), n—the surface resistance
s
5.4 Volume resistivity or conductivity can be used as an aid
multiplied by that ratio of specimen surface dimensions (width
in designing an insulator for a specific application. The change
of electrodes defining the current path divided by the distance
of resistivity or conductivity with temperature and humidity
between electrodes) which transforms the measured resistance
may be great (1, 2, 3, 4), and must be known when designing
to that obtained if the electrodes had formed the opposite sides
for operating conditions. Volume resistivity or conductivity
of a square.
determinations are often used in checking the uniformity of an
3.1.10.1 Discussion—Surface resistivity is expressed in
insulatingmaterial,eitherwithregardtoprocessingortodetect
ohms.Itispopularlyexpressedalsoasohms/square(thesizeof
conductive impurities that affect the quality of the material and
thesquareisimmaterial).Surfaceresistivityisthereciprocalof
that may not be readily detectable by other methods.
surface conductivity.
21 19
5.5 Volume resistivities above 10 V·cm (10 V·m), ob-
3.1.11 resistivity, volume, (r ), n—the volume resistance
v
tained on specimens under usual laboratory conditions, are of
multiplied by that ratio of specimen volume dimensions
doubtful validity, considering the limitations of commonly
(cross-sectional area of the specimen between the electrodes
used measuring equipment.
divided by the distance between electrodes) which transforms
5.6 Surface resistance or conductance cannot be measured
the measured resistance to that resistance obtained if the
accurately,onlyapproximated,becausesomedegreeofvolume
electrodes had formed the opposite sides of a unit cube.
3.1.11.1 Discussion—Volume resistivity is usually ex-
pressed in ohm-centimetres (preferred) or in ohm-metres.
The boldface numbers in parentheses refer to the list of references appended to
Volume resistivity is the reciprocal of volume conductivity. these test methods.
D 257 – 99 (2005)
resistance or conductance is always involved in the measure-
ment. The measured value is also affected by the surface
contamination. Surface contamination, and its rate of accumu-
lation, is affected by many factors including electrostatic
charging and interfacial tension. These, in turn, may affect the
surface resistivity. Surface resistivity or conductivity can be
considered to be related to material properties when contami-
nation is involved but is not a material property in the usual
sense.
6. Electrode Systems
6.1 The electrodes for insulating materials should be of a
materialthatisreadilyapplied,allowsintimatecontactwiththe
specimen surface, and introduces no appreciable error because
of electrode resistance or contamination of the specimen (5).
The electrode material should be corrosion-resistant under the
conditions of test. For tests of fabricated specimens such as
feed-through bushings, cables, etc., the electrodes employed
are a part of the specimen or its mounting. Measurements of
insulationresistanceorconductance,then,includethecontami-
nating effects of electrode or mounting materials and are
generally related to the performance of the specimen in actual
use.
6.1.1 Binding-Post and Taper-Pin Electrodes, Fig. 1 and
Fig. 2, provide a means of applying voltage to rigid insulating
materials to permit an evaluation of their resistive or conduc-
tive properties. These electrodes simulate to some degree the
actual conditions of use, such as binding posts on instrument
panels and terminal strips. In the case of laminated insulating
FIG. 2 Taper-Pin Electrodes
materials having high-resin-content surfaces, somewhat lower
insulation resistance values may be obtained with taper-pin
than with binding posts, due to more intimate contact with the
body of the insulating material. Resistance or conductance
values obtained are highly influenced by the individual contact
between each pin and the dielectric material, the surface
roughness of the pins, and the smoothness of the hole in the
dielectric material. Reproducibility of results on different
specimens is difficult to obtain.
6.1.2 Metal Bars in the arrangement of Fig. 3 were prima-
rily devised to evaluate the insulation resistance or conduc-
tance of flexible tapes and thin, solid specimens as a fairly
simple and convenient means of electrical quality control. This
arrangement is somewhat more satisfactory for obtaining
FIG. 3 Strip Electrodes for Tapes and Flat, Solid Specimens
approximate values of surface resistance or conductance when
the width of the insulating material is much greater than its
thickness.
6.1.3 Silver Paint, Fig. 4, Fig. 5, and Fig. 6, is available
commercially with a high conductivity, either air-drying or
low-temperature-baking varieties, which are sufficiently po-
FIG. 1 Binding-Post Electrodes for Flat, Solid Specimens rous to permit diffusion of moisture through them and thereby
D 257 – 99 (2005)
trodes may be obtained with a fine-bristle brush. However, for
circular electrodes, sharper edges can be obtained by the use of
arulingcompassandsilverpaintfordrawingtheoutlinecircles
of the electrodes and filling in the enclosed areas by brush. A
narrow strip of masking tape may be used, provided the
pressure-sensitive adhesive used does not contaminate the
surface of the specimen. Clamp-on masks also may be used if
the electrode paint is sprayed on.
6.1.4 Sprayed Metal, Fig. 4, Fig. 5, and Fig. 6, may be used
if satisfactory adhesion to the test specimen can be obtained.
Thin sprayed electrodes may have certain advantages in that
they are ready for use as soon as applied. They may be
sufficientlyporoustoallowthespecimentobeconditioned,but
this should be verified. Narrow strips of masking tape or
clamp-on masks must be used to produce a gap between the
guarded and the guard electrodes.The tape shall be such as not
to contaminate the gap surface.
6.1.5 Evaporated Metal may be used under the same
...
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