ASTM D495-22

Standard Test Method for High-Voltage, Low-Current, Dry Arc Resistance of Solid Electrical Insulation

SIGNIFICANCE AND USE
4.1 The high-voltage, low-current type of arc resistance test is intended to simulate only approximately such service
conditions as exist in alternating current circuits operating at high voltage, but at currents limited to units and tens of milliamperes.  
4.2 In order to distinguish more easily among materials that have low arc resistance, the early stages of this test method are mild, and the later stages are successively more severe. The arc occurs intermittently between two electrodes resting on the surface of the specimen, in normal or inverted orientation. The severity is increased in the early stages by successively decreasing to zero the interval between flashes of uniform duration, and in later stages by increasing the current.  
4.3 Four general types of failure have been observed:  
4.3.1 Many inorganic dielectrics become incandescent, whereupon they are capable of conducting the current. Upon cooling, however, they return to their earlier insulating condition.  
4.3.2 Some organic compounds burst into flame without the formation of a visible conducting path in the substance.  
4.3.3 Others are seen to fail by “tracking,” that is, a thin wiry line is formed between the electrodes.  
4.3.4 The fourth type occurs by carbonization of the surface until sufficient carbon is present to carry the current.  
4.4 Materials often fail within the first few seconds after a change in the severity stage. When comparing the arc resistance of materials, much more weight shall be given to a few seconds that overlap two stages than to the same elapsed time within a stage. Thus, there is a much greater difference in arc resistance between 178 and 182 s than between 174 and 178 s.
Note 4: Some investigators have reported attempts to characterize the remaining insulating value of the damaged area after failure by allowing the specimen to cool to room temperature, without disturbance of the original position of the electrodes, and then either (1) measuring the insu...
SCOPE
1.1 This test method covers, in a preliminary fashion, the differentiation of similar materials’ resistance to the action of a high-voltage, low-current arc close to the surface of insulation, when a conducting path is formed causing the material to become conducting due to the localized thermal and chemical decomposition and erosion.  
1.2 The usefulness of this test method is very severely limited by many restrictions and qualifications, some of which are described in the following paragraphs and in Section 5. Generally, this test method shall not be used in material specifications. Whenever possible, alternative test methods shall be used, and their development is encouraged.  
1.3 This test method will not, in general, permit conclusions to be drawn concerning the relative arc resistance rankings of materials that are potentially subjected to other types of arcs: for example, high voltage at high currents, and low voltage at low or high currents (promoted by surges or by conducting contaminants).  
1.4 The test method is intended, because of its convenience and the short time required for testing, for preliminary screening of material, for detecting the effects of changes in formulation, and for quality control testing after correlation has been established with other types of simulated service arc tests and field experience. Because this test method is usually conducted under clean and dry laboratory conditions rarely encountered in practice, it is possible that the prediction of a material's relative performance in typical applications and in varying “clean to dirty” environments will be substantially altered (Note 1). Caution is urged against drawing strong conclusions without corroborating support of simulated service tests and field testing. Rather, this test method is useful for preliminary evaluation of changes in structure and composition without the complicating influence of environmental conditions, espe...

General Information

• Status: Published
• Publication Date: 14-Jan-2022
• ICS: 29.035.01 - Insulating materials in general
• Technical Committee: D09 - Electrical and Electronic Insulating Materials
• Drafting Committee: D09.12 - Electrical Tests

Relations

• Refers: ASTM D1711-24 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Mar-2024
• Refers: ASTM D2132-12(2018) - Standard Test Method for Dust-and-Fog Tracking and Erosion Resistance of Electrical Insulating Materials
• Effective Date: 01-Nov-2018
• Refers: ASTM D1711-15 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Nov-2015
• Refers: ASTM D1711-14a - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Nov-2014
• Refers: ASTM D1711-14 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-May-2014
• Refers: ASTM D1711-13 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Nov-2013
• Refers: ASTM D2132-12 - Standard Test Method for Dust-and-Fog Tracking and Erosion Resistance of Electrical Insulating Materials
• Effective Date: 01-Jan-2012
• Refers: ASTM D1711-11a - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-Aug-2011
• Refers: ASTM D2132-11 - Standard Test Method for Dust-and-Fog Tracking and Erosion Resistance of Electrical Insulating Materials
• Effective Date: 15-Apr-2011
• Refers: ASTM D1711-08 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 01-May-2008
• Refers: ASTM D3638-07 - Standard Test Method for Comparative Tracking Index of Electrical Insulating Materials
• Effective Date: 01-Jun-2007
• Refers: ASTM D2303-97(2004) - Standard Test Methods for Liquid-Contaminant, Inclined-Plane Tracking and Erosion of Insulating Materials (Withdrawn 2013)
• Effective Date: 01-Mar-2004
• Refers: ASTM D2132-03 - Standard Test Method for Dust-and-Fog Tracking and Erosion Resistance of Electrical Insulating Materials
• Effective Date: 01-Oct-2003
• Refers: ASTM D1711-02 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 10-Mar-2002
• Refers: ASTM D1711-99 - Standard Terminology Relating to Electrical Insulation
• Effective Date: 10-Oct-1999

Overview

ASTM D495-22 is the Standard Test Method for High-Voltage, Low-Current, Dry Arc Resistance of Solid Electrical Insulation, developed by ASTM International. This test method provides a preliminary procedure for differentiating the resistance of similar electrical insulating materials to the action of a high-voltage, low-current arc occurring near the surface. The standard is chiefly intended for initial screening, formulation changes, and quality control in environments where alternating current circuits operate at high voltage yet carry limited current, typically in the range of units to tens of milliamperes. While valuable for assessing the arc resistance of solid insulation, its use is limited by certain restrictions and should generally not be used as the sole basis for material specifications.

Key Topics

• Purpose: Simulates service conditions for high-voltage, low-current arc exposure on solid electrical insulating materials.
• Test Method: Involves generating an arc between electrodes placed on the specimen surface, exposing the material to increasing severity by reducing intervals between arcs and increasing current.
• Types of Failures:
  • Incandescence in inorganic dielectrics, leading to temporary conductivity.
  • Flaming in organic compounds absent a clear conductive path.
  • “Tracking” where a thin conductive line forms.
  • Surface carbonization that develops enough carbon for current flow.
• Assessment: Short failure times following changes in severity are weighted more heavily, as these indicate significant differences in arc resistance between materials.
• Restrictions: Not generally suitable for determining arc resistance under other arc conditions (e.g., high current or contaminated environments).

Applications

ASTM D495-22 is best used for:

• Preliminary screening: Quickly comparing similar insulating materials for relative arc resistance in clean, dry conditions.
• Quality control: Ensuring consistency of insulation properties between production batches, especially after correlation with service conditions has been established.
• Material development: Monitoring the effects of formulation changes on arc resistance performance, free from environmental contaminants.

It is important to note that test results from ASTM D495-22 may not directly predict material performance in actual installations, where moisture, dust, or other contaminants and different voltage or current conditions may prevail. For more representative service assessments, other standards utilizing wet or contaminated surfaces are recommended.

Related Standards

ASTM D495-22 references several important related standards that address different arc resistance scenarios or provide supporting terminology:

• ASTM D1711: Terminology Relating to Electrical Insulation.
• ASTM D2132: Test Method for Dust-and-Fog Tracking and Erosion Resistance of Electrical Insulating Materials.
• ASTM D2303: Test Methods for Liquid-Contaminant, Inclined-Plane Tracking and Erosion of Insulating Materials.
• ASTM D3638: Test Method for Comparative Tracking Index of Electrical Insulating Materials.
• IEC 61621: Dry Solid Insulating Materials - Resistance Test To High-Voltage, Low-Current Arc Discharges (technically equivalent to D495).
• ASTM D6054: Practice for Conditioning Electrical Insulating Materials for Testing (Withdrawn).

Practical Value

• High-voltage insulation testing using ASTM D495-22 helps identify electrical insulation materials that may fail early under high-voltage stress, thus supporting safer and more reliable component selection.
• Short testing times allow for rapid preliminary evaluation without the complicating effects of environmental variables.
• Quality control tool for manufacturers looking to detect formulation changes or ensure process consistency between batches of insulating materials.

Caution: Always corroborate findings from ASTM D495-22 with additional testing under simulated service and environmental conditions for a comprehensive assessment of material suitability. This test is primarily for comparative screening in controlled laboratory conditions, not final qualification for field applications.

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Keywords: ASTM D495-22, high-voltage arc resistance, dry arc resistance, electrical insulation testing, quality control, insulating materials, high-voltage insulation, arc tracking, IEC 61621, electrical safety standards.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D495 − 22
Standard Test Method for
High-Voltage, Low-Current, Dry Arc Resistance of Solid
Electrical Insulation
This standard is issued under the fixed designation D495; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber 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* without the complicating influence of environmental
conditions, especially dirt and moisture.
1.1 This test method covers, in a preliminary fashion, the
differentiation of similar materials’resistance to the action of a
NOTE 1—By changing some of the circuit conditions described herein
it has been found possible to rearrange markedly the order of arc
high-voltage,low-currentarcclosetothesurfaceofinsulation,
resistance of a group of organic insulating materials consisting of
when a conducting path is formed causing the material to
vulcanized fiber and of molded phenolic and amino plastics, some
become conducting due to the localized thermal and chemical
containing organic, and some inorganic, filler.
decomposition and erosion.
1.5 While this test method uses dry, uncontaminated speci-
1.2 The usefulness of this test method is very severely
men surfaces, Test Method D2132, Test Methods D2303, and
limited by many restrictions and qualifications, some of which
Test Method D3638 employ wet, contaminated specimen
are described in the following paragraphs and in Section 5.
surfaces. Their use is recommended for engineering purposes
Generally, this test method shall not be used in material
and to assist in establishing some degree of significance to this
specifications. Whenever possible, alternative test methods
test method for quality control purposes.
shall be used, and their development is encouraged.
1.6 This test method is not applicable to materials that do
1.3 Thistestmethodwillnot,ingeneral,permitconclusions
not produce conductive paths under the action of an electric
to be drawn concerning the relative arc resistance rankings of
arc, or that melt or form fluid residues that float conductive
materials that are potentially subjected to other types of arcs:
residues out of the active test area thereby preventing forma-
for example, high voltage at high currents, and low voltage at
tion of a conductive path.
low or high currents (promoted by surges or by conducting
1.7 Thevaluesstatedininch-poundunitsaretoberegarded
contaminants).
as standard. The values given in parentheses are mathematical
1.4 The test method is intended, because of its convenience
conversions to SI units that are provided for information only
and the short time required for testing, for preliminary screen-
and are not considered standard.
ing of material, for detecting the effects of changes in
1.8 This standard does not purport to address all of the
formulation,andforqualitycontroltestingaftercorrelationhas
safety concerns, if any, associated with its use. It is the
been established with other types of simulated service arc tests
responsibility of the user of this standard to establish appro-
and field experience. Because this test method is usually
priate safety, health, and environmental practices and deter-
conducted under clean and dry laboratory conditions rarely
mine the applicability of regulatory limitations prior to use.
encountered in practice, it is possible that the prediction of a
For specific precautionary statements, see 6.1.14, 6.1.19, Sec-
material’s relative performance in typical applications and in
tion 7, and 10.1.1.
varying “clean to dirty” environments will be substantially
altered (Note 1). Caution is urged against drawing strong NOTE 2—Due to the deficiencies covered in Section 1, Committee D09
has proposed that without significant proposed improvements this stan-
conclusionswithoutcorroboratingsupportofsimulatedservice
dard be withdrawn in 2027 during its next 5 year review. This notice is
tests and field testing. Rather, this test method is useful for
provided so that referencing standards can transition.
preliminaryevaluationofchangesinstructureandcomposition
1.9 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
This test method is under the jurisdiction of ASTM Committee D09 on
Electrical and Electronic Insulating Materials and is the direct responsibility of
Subcommittee D09.12 on Electrical Tests. Also helpful is Test Method D2302 for Wet Tracking Resistance of Electrical
Current edition approved Jan. 15, 2022. Published January 2022. Originally Insulating Materials with Controlled Water-to-Metal Discharges. This test method
approved in 1938. Last previous edition approved in 2014 as D495– 14. DOI: waswithdrawnandlastappearedinthe 1982 Annual Book of ASTM Standards,Part
10.1520/D0495-22. 39.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D495 − 22
Development of International Standards, Guides and Recom- conditions as exist in alternating current circuits operating at
mendations issued by the World Trade Organization Technical high voltage, but at currents limited to units and tens of
Barriers to Trade (TBT) Committee. milliamperes.
4.2 In order to distinguish more easily among materials that
2. Referenced Documents
havelowarcresistance,theearlystagesofthistestmethodare
2.1 ASTM Standards:
mild,andthelaterstagesaresuccessivelymoresevere.Thearc
D1711Terminology Relating to Electrical Insulation
occurs intermittently between two electrodes resting on the
D2132Test Method for Dust-and-Fog Tracking and Erosion
surface of the specimen, in normal or inverted orientation.The
Resistance of Electrical Insulating Materials
severity is increased in the early stages by successively
D2303Test Methods for Liquid-Contaminant, Inclined-
decreasing to zero the interval between flashes of uniform
Plane Tracking and Erosion of Insulating Materials
duration, and in later stages by increasing the current.
D3638Test Method for Comparative Tracking Index of
4.3 Four general types of failure have been observed:
Electrical Insulating Materials
4.3.1 Many inorganic dielectrics become incandescent,
D6054Practice for Conditioning Electrical Insulating Mate-
whereupon they are capable of conducting the current. Upon
rials for Testing (Withdrawn 2012)
cooling, however, they return to their earlier insulating condi-
2.2 IEC Standard:
tion.
IEC61621Dry Solid Insulating Materials—Resistance Test
4.3.2 Some organic compounds burst into flame without the
To High-Voltage, Low-Current Arc Discharges
formation of a visible conducting path in the substance.
NOTE 3—IEC 61621 is technically equivalent to D495, and is directly
4.3.3 Others are seen to fail by “tracking,” that is, a thin
based upon Test Method D495. IEC 61621 describes only the tungsten
wiry line is formed between the electrodes.
electrodes, and does not include the stainless steel electrodes.
4.3.4 Thefourthtypeoccursbycarbonizationofthesurface
3. Terminology
until sufficient carbon is present to carry the current.
3.1 Definitions:
4.4 Materials often fail within the first few seconds after a
3.1.1 For definitions of terms used in this test method, refer
change in the severity stage. When comparing the arc resis-
to Terminology D1711.
tance of materials, much more weight shall be given to a few
3.2 Definitions of Terms Specific to This Standard:
seconds that overlap two stages than to the same elapsed time
3.2.1 arc resistance, n—the total elapsed time in seconds
within a stage. Thus, there is a much greater difference in arc
from the start of this test procedure until failure occurs (see
resistance between 178 and 182 s than between 174 and 178 s.
Section 14).
NOTE 4—Some investigators have reported attempts to characterize the
3.2.2 failure, n—the end-point of the test procedure em-
remaining insulating value of the damaged area after failure by allowing
ployed in this test method (see Section 14). the specimen to cool to room temperature, without disturbance of the
original position of the electrodes, and then either (1) measuring the
3.2.3 normal orientation, n—a test condition in which the
insulation resistance between the electrodes or (2) determining the
electrodes are located on the upper surface of the specimen.
percentageofbreakdownvoltageremainingrelativetothatobtainedonan
undamagedareaofthespecimen.Arecommendedcircuitarrangementand
3.2.4 inverted orientation, n—a test condition in which the
test procedure for carrying out the second of these two means of
electrodes are located on the under surface of the specimen.
characterizing the remaining insulating value of the damaged area is
3.2.4.1 Discussion—Tests made with inverted orientation
described in Appendix X1. Still another, and obvious, method of reevalu-
are more severe than tests made with normal orientation.
atingthedamagedareaafterfailureistorepeatthearcresistancetestafter
the specimen has cooled, with the electrodes undisturbed from their
Reduced data dispersion has been encountered when testing
originalpositions.However,keepinmindthatnoneofthesemethodswill
certain materials using inverted orientation. With other
beuniversallyapplicablebecauseoftheseverephysicaldamagetothetest
materials, increased data dispersion has been encountered,
area in many instances.
especially with materials that evolve considerable gas during
test.
5. Interferences
3.3 Abbreviations:
5.1 Changes in both the timing of the intermittent arc and
3.3.1 The stainless steel strip electrodes are referred to as
the current, as well as other changes affecting the nature of the
s.s.s. electrodes.
discharge, has the potential to affect the duration of a test of
most specimens taken from a group of dissimilar materials.
4. Significance and Use
Any of these changes have the potential to drastically alter a
4.1 The high-voltage, low-current type of arc resistance test
material’s position in order of rank. Regardless of the condi-
is intended to simulate only approximately such service
tions of anticipated use, do not use data obtained by this test
method to infer that the materials examined occupy an un-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
changing quality relationship to each other.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
5.2 Thistestmethoddescribestwoelectrodesystems:stain-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
less steel strip and tungsten rod. When testing materials with
The last approved version of this historical standard is referenced on
poor to moderate arc resistance (up to 180 s), use the stainless
www.astm.org.
steelstripelectrodesasthepreferredtechnique.Thistechnique
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. decreases the variability often associated with the use of rod
D495 − 22
electrodesonmaterialshavingpoorormoderatearcresistance. 6.1.1 Transformer, T —A self-regulating transformer (non-
v
All of the factors that affect the disparate behavior of rod powerfactorcorrected)witharatedprimarypotentialof115V
electrodes on such materials have not yet been fully reported. at 60 Hz ac, a rated secondary potential (on open circuit) of
Itispermissibletomakeadditionaltestswithrodelectrodes,so 15000 V, and a rated secondary current (on short circuit) of
as to provide a basis for comparison with other data obtained 0.060 A.
with such electrodes. For values of arc resistance greater than
6.1.2 Variable Autotransformer, T , An autotransformer
a
180 s, the use of the tungsten rod electrodes is recommended
rated at 7 A or more, and nominally adjustable up to 135 V.
because the corners of the stainless steel strip electrodes erode
6.1.3 Voltmeter, V —An ac voltmeter, readable to 1Vin the
appreciably under such conditions. It is possible that results
range 90 to 130 V, is permanently connected across the output
obtained with the use of the tungsten rod electrode system will
of the autotransformer to indicate the voltage supplied to the
be different from those obtained with the use of the stainless
primary circuit.
steel strip electrode system.
NOTE 5—A constant primary voltage supply is recommended. Com-
mercially available line voltage stabilizers that do not distort the voltage
6. Apparatus
wave form are suitable.
6.1 The apparatus (see Fig. 1 for electrical circuit) is
6.1.4 Milliammeter, A—An ac milliammeter capable of
specified to maximize data reproducibility among different test
reading from 10 to 40 mA with an error of not over 65%.
sets. The arc obtained will be relatively quiet, rather than the
Before use, this meter shall be calibrated in a test circuit
crackly blue spark characteristic of a condenser discharge.
containing no arc gap. Since this milliammeter is used only
Primary voltage control is made by a variable transformer
when setting up or making changes in the circuit, it is to be
rather than by a variable inductance because of its proved
shorted out by a by-pass switch when not in use.
deleterious effect on the performance of the arc.
NOTE 6—Although provision has been made for the suppression of
radio-frequencycomponentsofcurrentinthearc,itwilloftenbedesirable
to check for their presence when the apparatus is first constructed.This is
done by use of a suitable thermocouple-type r-f milliammeter temporarily
inserted in series with the milliammeter.
6.1.5 Current Control Resistors, R ,R ,R ,R —Four
10 20 30 40
resistors are required in series with the primary of T but in
v
parallel with each other. These resistors must be adjustable to
permit exact settings of the currents during calibration. R is
always in the circuit to provide a 10 mA current. Its value is
approximately 60 Ω, with a current rating of at least 1 ⁄4 A.
Closingswitch S ,toadd R inparallelwith R ,willprovide
20 20 10
a 20 mAarc current. R is about 50Ω with a current rating of
atleast1 ⁄4A.Similarly, R and R havevaluesofabout30Ω
30 40
and 15Ω respectively, with associated current ratings of 2 and
5A.These resistors, when switched in, provide arc currents of
30 mA and 40 mA respectively.
6.1.6 Suppressing Resistor, R —Rated at 15000Ω and at
least 24 W. This resistor, along with the inductors in 6.1.7,is
used to suppress parasitic high frequency in the arc circuit.
6.1.7 Air Core Inductors—Inductance totaling from 1.2 to
1.5 H is obtained from about 8 coils of No. 30 cotton- or
enamel-covered wire.Asingle coil of this inductance must not
be used. Each coil consists of 3000 to 5000 turns of wire
wound or insulating nonmetallic cores of about ⁄2 in.
(12.7mm) diameter and ⁄8 in. (15.9mm) inside length.
6.1.8 Interruptor, I—This motor-driven device is used to
give the required cycles for the three lower steps of the test by
opening and closing the primary circuit according to the
schedule in Table 1, with an accuracy of 6 ⁄120 s or better. A
synchronous motor driving three appropriate sets of cams
which actuate the contactor switches has been found useful.
6.1.9 Timer, TT—A stop watch or electric interval timer
operating at 115 V ac, accurate to 1 s.
6.1.10 Indicator Lamp, IL—A6 W, 115 V lamp with a
NOTE 1—Switches S to S are aligned in the sequence of their
M 40
2000Ω resistor, R , in series.This lamp indicates the interrupt-
closing, from bottom to top, during a test.
FIG. 1 Arc-Resistance Test Circuit ing cycle being used and permits the operator to start the first
D495 − 22
TABLE 1 Sequence of 1-min Current Steps
6.1.14 High Voltage Switch, S —Asingle-pole,single-throw
A
Step Current, mA Time Cycle Total Time, s switch insulated for 15000 V ac. This switch must be isolated
1 3
⁄8 10 10 s on, 1 ⁄4soff 60 from the operator by a suitable enclosure through which
1 3
⁄4 10 10 s on, ⁄4 s off 120
projects an insulating handle of sufficient length to ensure
1 1
⁄2 10 10 s on, ⁄4 s off 180
operator safety.
10 10 continuous 240
20 20 continuous 300 6.1.15 Wiring—All wiring in the arc circuit must be of
30 30 continuous 360
ignitionwireratedat15kVorhigher,andmustbesodisposed
40 40 continuous 420
that it and any circuit components are not readily accessible
A
In the earlier steps an interrupted arc is used to obtain a less severe condition
when energized.
than the continuous arc; a current of less than 10 mA produces an unsteady
(flaring) arc.
6.1.16 Sharpening Jig for Tungsten Rod Electrodes—Asteel
jig for securing the electrodes during sharpening to ensure
finishing the pointed tips to the proper geometry (see Fig. 2).
6.1.17 Stainless Steel Strip Electrodes— Cut 0.006 in.
cycle of each test in a uniform manner by closing S ⁄8 just after
the lamp is extinguished. (0.15mm) thick stainless steel into ⁄2 by 1 in. (12.7 by 25.4
mm) strips. (The edges must be free of burrs.) Bend each strip
6.1.11 Control Switches—Toggle switches are convenient.
Allshallbeofthesizeratedat3Aand110to125Vac,except slightly in the middle of the long dimension to form an angle
of approximately 160° (see Fig. 3).
S and S , which require 10 A ratings.
1 40
6.1.12 Safety Interlocking Contactor, C —Ratedat10Aand 6.1.18 Tungsten Rod Electrodes (see 5.2 for restrictions)—
S
110 to 125 V ac, this interlocking contactor is installed so that Make the electrodes from ⁄32 in. (2.4 mm) diameter tungsten
raisingthedraftshieldaroundtheelectrodeassemblywillopen rod (tungsten welding rod has been found suitable) which is
the contactor and thus remove high voltage from the elec- free of cracks, pits, or rough spots. Use rods about 1 ⁄4 in.
trodes. (45mm) long in the electrode assembly, or use shorter rod
1 1 1
6.1.13 Interruptor Contactors, C ⁄8 , C ⁄4 , C ⁄2 —Normally- lengths fastened into a square shank (see Fig. 4) by swaging,
open spring contactors, rated at 1 ⁄4A(or better) and 125Vac. brazing,orsilversoldering,leavinganexposedlengthofabout
These contactors are operated by the interrupted cams, thus ⁄4 in. (19 mm). The shank ensures correct orientation of the
closing and opening the primary circuit and providing the electrode point after sharpening (see 9.2.2), although correct
intermittent arc cycles listed in Table 1. orientation of the simple rod electrode will be obtained by
FIG. 2 Grinding and Polishing Block with Tungsten Rod Electrode in Place
D495 − 22
FIG. 3 Strip Electrodes and Holders
FIG. 4 Top and Side Views of Tungsten Rod Electrode
adjustment of the rod in the electrode assembly. In either type space the tips 0.250 6 0.003 in. (6.35 6 0.08 mm) apart. The
of rod electrode, grind the end of the rod at a 30° angle to the proper orientation will automatically be obtained if the follow-
axis (see Fig. 4) to achieve a flat elliptical face. Exercise care ing factors are controlled: (a) axis of tungsten rod is perpen-
in grinding to prevent cracking or chipping. dicular to the axis of the support rod, (b) support rods are
6.1.19 Electrode Assemblies—These assemblies provide a gripped in the pivot blocks in a position such that the axis of
means of holding the electrodes and specimen and of applying each electrode is inclined at 35° when the support rods are
the arc to the top surface of the specimen. Construct each horizontal, (c) electrodes are mounted in square shanks and
assembly, whether for stainless steel strip electrodes or for sharpened in a correctly made jig, and (d) the spacing between
tungsten rod electrodes, so that the top surface of each electrode tips is adjusted with the support rods in a horizontal
specimen is at the same level height. Provide ample air space position.Ifelectrodesarenotmountedinsquareshanks,obtain
belowthespecimen,especiallyintheregiondirectlybelowthe properorientationbyadjustingandrotatingtheelectrodesafter
test area. Adjust each electrode so that it rests independently they are inserted in the appropriate electrode assembly.
with a force of 50 6 5 g on the top of the specimen. Provide
7. Safety Precautions
a transparent shield around the assembly to protect the speci-
menfromairdrafts,and allow venting of combustionproducts 7.1 Warning—It is possible that lethal voltages will be
in c
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D495 − 14 D495 − 22
Standard Test Method for
High-Voltage, Low-Current, Dry Arc Resistance of Solid
Electrical Insulation
This standard is issued under the fixed designation D495; 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 Scope*
1.1 This test method covers, in a preliminary fashion, the differentiation of similar materials’ resistance to the action of a
high-voltage, low-current arc close to the surface of insulation, when a conducting path is formed causing the material to become
conducting due to the localized thermal and chemical decomposition and erosion.
1.2 The usefulness of this test method is very severely limited by many restrictions and qualifications, some of which are described
in the following paragraphs and in Section 5. Generally, this test method shall not be used in material specifications. Whenever
possible, alternative test methods shall be used, and their development is encouraged.
1.3 This test method will not, in general, permit conclusions to be drawn concerning the relative arc resistance rankings of
materials that are potentially subjected to other types of arcs: for example, high voltage at high currents, and low voltage at low
or high currents (promoted by surges or by conducting contaminants).
1.4 The test method is intended, because of its convenience and the short time required for testing, for preliminary screening of
material, for detecting the effects of changes in formulation, and for quality control testing after correlation has been established
with other types of simulated service arc tests and field experience. Because this test method is usually conducted under clean and
dry laboratory conditions rarely encountered in practice, it is possible that the prediction of a material’s relative performance in
typical applications and in varying “clean to dirty” environments will be substantially altered (Note 1). Caution is urged against
drawing strong conclusions without corroborating support of simulated service tests and field testing. Rather, this test method is
useful for preliminary evaluation of changes in structure and composition without the complicating influence of environmental
conditions, especially dirt and moisture.
NOTE 1—By changing some of the circuit conditions described herein it has been found possible to rearrange markedly the order of arc resistance of a
group of organic insulating materials consisting of vulcanized fiber and of molded phenolic and amino plastics, some containing organic, and some
inorganic, filler.
1.5 While this test method uses dry, uncontaminated specimen surfaces, Test Method D2132, Test Methods D2303, and Test
Method D3638 employ wet, contaminated specimen surfaces. Their use is recommended for engineering purposes and to assist in
establishing some degree of significance to this test method for quality control purposes.
This test method is under the jurisdiction of ASTM Committee D09 on Electrical and Electronic Insulating Materials and is the direct responsibility of Subcommittee
D09.12 on Electrical Tests.
Current edition approved April 1, 2014Jan. 15, 2022. Published May 2014January 2022. Originally approved in 1938. Last previous edition approved in 20042014 as
D495 – 94 (2004)D495, which was withdrawn in January 2013 and reinstated in April 2014. DOI: 10.1520/D0495-14. – 14. DOI: 10.1520/D0495-22.
Also helpful is Test Method D2302 for Wet Tracking Resistance of Electrical Insulating Materials with Controlled Water-to-Metal Discharges. This test method was
withdrawn and last appeared in the 1982 Annual Book of ASTM Standards, Part 39.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D495 − 22
1.6 This test method is not applicable to materials that do not produce conductive paths under the action of an electric arc, or that
melt or form fluid residues that float conductive residues out of the active test area thereby preventing formation of a conductive
path.
1.7 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.8 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. For specific precautionary statements, see 6.1.14, 6.1.19, Section 7, and 10.1.1.
NOTE 2—Due to the deficiencies covered in Section 1, Committee D09 has proposed that without significant proposed improvements this standard be
withdrawn in 2027 during its next 5 year review. This notice is provided so that referencing standards can transition.
1.9 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1711 Terminology Relating to Electrical Insulation
D2132 Test Method for Dust-and-Fog Tracking and Erosion Resistance of Electrical Insulating Materials
D2303 Test Methods for Liquid-Contaminant, Inclined-Plane Tracking and Erosion of Insulating Materials
D3638 Test Method for Comparative Tracking Index of Electrical Insulating Materials
D6054 Practice for Conditioning Electrical Insulating Materials for Testing (Withdrawn 2012)
2.2 IEC Standard:
IEC 61621 Dry Solid Insulating Materials—Resistance Test To High-Voltage, Low-Current Arc Discharges
NOTE 3—IEC 61621 is technically equivalent to D495, and is directly based upon Test Method D495. IEC 61621 describes only the tungsten electrodes,
and does not include the stainless steel electrodes.
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D1711.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 arc resistance, n—the total elapsed time in seconds from the start of this test procedure until failure occurs (see Section 14).
3.2.2 failure, n—the end-point of the test procedure employed in this test method (see Section 14).
3.2.3 normal orientation, n—a test condition in which the electrodes are located on the upper surface of the specimen.
3.2.4 inverted orientation, n—a test condition in which the electrodes are located on the under surface of the specimen.
3.2.4.1 Discussion—
Tests made with inverted orientation are more severe than tests made with normal orientation. Reduced data dispersion has been
encountered when testing certain materials using inverted orientation. With other materials, increased data dispersion may behas
been encountered, especially with materials that evolve considerable gas during test.
3.3 Abbreviations:
3.3.1 The stainless steel strip electrodes are referred to as s.s.s. electrodes.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
nd
Available from American National Standards Institute, 11 W 42Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036.10036, http://www.ansi.org.
D495 − 22
4. Significance and Use
4.1 The high-voltage, low-current type of arc resistance test is intended to simulate only approximately such service
conditions as exist in alternating current circuits operating at high voltage, but at currents limited to units and tens of milliamperes.
4.2 In order to distinguish more easily among materials that have low arc resistance, the early stages of this test method are mild,
and the later stages are successively more severe. The arc occurs intermittently between two electrodes resting on the surface of
the specimen, in normal or inverted orientation. The severity is increased in the early stages by successively decreasing to zero
the interval between flashes of uniform duration, and in later stages by increasing the current.
4.3 Four general types of failure have been observed:
4.3.1 Many inorganic dielectrics become incandescent, whereupon they are capable of conducting the current. Upon cooling,
however, they return to their earlier insulating condition.
4.3.2 Some organic compounds burst into flame without the formation of a visible conducting path in the substance.
4.3.3 Others are seen to fail by “tracking,” that is, a thin wiry line is formed between the electrodes.
4.3.4 The fourth type occurs by carbonization of the surface until sufficient carbon is present to carry the current.
4.4 Materials often fail within the first few seconds after a change in the severity stage. When comparing the arc resistance of
materials, much more weight shall be given to a few seconds that overlap two stages than to the same elapsed time within a stage.
Thus, there is a much greater difference in arc resistance between 178 and 182 s than between 174 and 178 s.
NOTE 4—Some investigators have reported attempts to characterize the remaining insulating value of the damaged area after failure by allowing the
specimen to cool to room temperature, without disturbance of the original position of the electrodes, and then either (1) measuring the insulation resistance
between the electrodes or (2) determining the percentage of breakdown voltage remaining relative to that obtained on an undamaged area of the specimen.
A recommended circuit arrangement and test procedure for carrying out the second of these two means of characterizing the remaining insulating value
of the damaged area is described in Appendix X1. Still another, and obvious, method of reevaluating the damaged area after failure is to repeat the arc
resistance test after the specimen has cooled, with the electrodes undisturbed from their original positions. However, keep in mind that none of these
methods will be universally applicable because of the severe physical damage to the test area in many instances.
5. Interferences
5.1 Changes in both the timing of the intermittent arc and the current, as well as other changes affecting the nature of the discharge,
can has the potential to affect the duration of a test of most specimens taken from a group of dissimilar materials. Any of these
changes can have the potential to drastically alter a material’s position in order of rank. Regardless of the conditions of anticipated
use, do not use data obtained by this test method to infer that the materials examined occupy an unchanging quality relationship
to each other.
5.2 This test method describes two electrode systems: stainless steel strip and tungsten rod. When testing materials with poor to
moderate arc resistance (up to 180 s), use the stainless steel strip electrodes as the preferred technique. This technique decreases
the variability often associated with the use of rod electrodes on materials having poor or moderate arc resistance. All of the factors
that affect the disparate behavior of rod electrodes on such materials have not yet been fully reported. It is permissible to make
additional tests with rod electrodes, so as to provide a basis for comparison with other data obtained with such electrodes. For
values of arc resistance greater than 180 s, the use of the tungsten rod electrodes is recommended because the corners of the
stainless steel strip electrodes erode appreciably under such conditions. It is possible that results obtained with the use of the
tungsten rod electrode system will be different from those obtained with the use of the stainless steel strip electrode system.
6. Apparatus
6.1 The apparatus (see Fig. 1 for electrical circuit) is specified to maximize data reproducibility among different test sets. The arc
obtained will be relatively quiet, rather than the crackly blue spark characteristic of a condenser discharge. Primary voltage control
is made by a variable transformer rather than by a variable inductance because of its proved deleterious effect on the performance
of the arc.
D495 − 22
NOTE 1—Switches S to S are aligned in the sequence of their closing, from bottom to top, during a test.
M 40
FIG. 1 Arc-Resistance Test Circuit
6.1.1 Transformer, T —A self-regulating transformer (non-power factor corrected) with a rated primary potential of 115 V at 60
v
Hz ac, a rated secondary potential (on open circuit) of 15 000 V, and a rated secondary current (on short circuit) of 0.060 A.
6.1.2 Variable Autotransformer, T , An autotransformer rated at 7 A or more, and nominally adjustable up to 135 V.
a
6.1.3 Voltmeter, V —An ac voltmeter, readable to 1 V in the range 90 to 130 V, is permanently connected across the output of the
autotransformer to indicate the voltage supplied to the primary circuit.
NOTE 5—A constant primary voltage supply is recommended. Commercially available line voltage stabilizers that do not distort the voltage wave form
are suitable.
6.1.4 Milliammeter, A—An ac milliammeter capable of reading from 10 to 40 mA with an error of not over 65 %. Before use,
this meter shall be calibrated in a test circuit containing no arc gap. Since this milliammeter is used only when setting up or making
changes in the circuit, it is to be shorted out by a by-pass switch when not in use.
NOTE 6—Although provision has been made for the suppression of radio-frequency components of current in the arc, it will often be desirable to check
for their presence when the apparatus is first constructed. This is done by use of a suitable thermocouple-type r-f milliammeter temporarily inserted in
series with the milliammeter.
6.1.5 Current Control Resistors, R , R , R , R , R —Four resistors are required in series with the primary of T but in
110 020 2300 3400 40 v
parallel with each other. These resistors must be adjustable to permit exact settings of the currents during calibration. R is
D495 − 22
always in the circuit to provide a 10 mA current. Its value is approximately 60 Ω, with a current rating of at least 1 ⁄4 A. Closing
switch S , to add R in parallel with R , will provide a 20 mA arc current. R is about 50 Ω with a current rating of at
2200 2200 1100 2200
least 1 ⁄4 A. Similarly, R and R have values of about 30 Ω 30Ω and 15Ω respectively, with associated current ratings of 2
3300 4400
and 5 A. These resistors, when switched in, provide arc currents of 30 mA and 40 mA respectively.
6.1.6 Suppressing Resistor, R —Rated at 15 000 Ω 15 000Ω and at least 24 W. This resistor, along with the inductors in 6.1.7, is
used to suppress parasitic high frequency in the arc circuit.
6.1.7 Air Core Inductors—Inductance totaling from 1.2 to 1.5 H is obtained from about 8 coils of No. 30 cotton- or
enamel-covered wire. A single coil of this inductance must not be used. Each coil consists of 3000 to 5000 turns of wire wound
1 5
or insulating nonmetallic cores of about ⁄2 in. (12.7 mm) (12.7 mm) diameter and ⁄8 in. (15.9)(15.9 mm) inside length.
6.1.8 Interruptor, I—This motor-driven device is used to give the required cycles for the three lower steps of the test by opening
and closing the primary circuit according to the schedule in Table 1, with an accuracy of 6 ⁄120 s or better. The interruptor can be
a A synchronous motor driving three appropriate sets of cams which actuate the contactor switches. switches has been found useful.
6.1.9 Timer, TT—A stop watch or electric interval timer operating at 115 V ac, accurate to 1 s.
6.1.10 Indicator Lamp, IL—A6 W, 115 V lamp with a 2000 Ω 2000Ω resistor, R , in series. This lamp indicates the interrupting
cycle being used and permits the operator to start the first cycle of each test in a uniform manner by closing S ⁄8 just after the lamp
is extinguished.
6.1.11 Control Switches—Toggle switches are convenient. All shall be of the size rated at 3 A and 110 to 125 V ac, except S and
S , which require 10 A ratings.
6.1.12 Safety Interlocking Contactor, C —Rated at 10 A and 110 to 125 V ac, this interlocking contactor is installed so that raising
S
the draft shield around the electrode assembly will open the contactor and thus remove high voltage from the electrodes.
1 1 1
6.1.13 Interruptor Contactors, C ⁄8, C ⁄4, C ⁄2—Normally-open spring contactors, rated at 1 ⁄4 A (or better) and 125 V ac. These
contactors are operated by the interrupted cams, thus closing and opening the primary circuit and providing the intermittent arc
cycles listed in Table 1.
6.1.14 High Voltage Switch, S —A single-pole, single-throw switch insulated for 15 000 V ac. This switch must be isolated from
the operator by a suitable enclosure through which projects an insulating handle of sufficient length to ensure operator safety.
6.1.15 Wiring—All wiring in the arc circuit must be of ignition wire rated at 15 kV or higher, and must be so disposed that it and
any circuit components are not readily accessible when energized.
6.1.16 Sharpening Jig for Tungsten Rod Electrodes—A steel jig for securing the electrodes during sharpening to ensure finishing
the pointed tips to the proper geometry (see Fig. 2).
6.1.17 Stainless Steel Strip Electrodes— Cut 0.006 in. (0.15 mm) (0.15 mm) thick stainless steel into ⁄2 by 1 in. (12.7 by 25.4 mm)
strips. (The edges must be free of burrs.) Bend each strip slightly in the middle of the long dimension to form an angle of
approximately 160° (see Fig. 3).
6.1.18 Tungsten Rod Electrodes (see 5.2 for restrictions)—Make the electrodes from ⁄32 in. (2.4 mm) diameter tungsten rod
TABLE 1 Sequence of 1-min Current Steps
A
Step Current, mA Time Cycle Total Time, s
1 1 3
⁄8 10 10 ⁄4 s on, 1 ⁄4 s off 60
1 1 3
⁄4 10 10 ⁄4 s on, ⁄4 s off 120
1 1 1
⁄2 10 10 ⁄4 s on, ⁄4 s off 180
10 10 continuous 240
20 20 continuous 300
30 30 continuous 360
40 40 continuous 420
A
In the earlier steps an interrupted arc is used to obtain a less severe condition
than the continuous arc; a current of less than 10 mA produces an unsteady
(flaring) arc.
D495 − 22
FIG. 2 Grinding and Polishing Block with Tungsten Rod Electrode in Place
FIG. 3 Strip Electrodes and Holders
(tungsten welding rod has been found suitable) which is free of cracks, pits, or rough spots. Use rods about 1 ⁄4 in. (45 mm)
(45 mm) long in the electrode assembly, or use shorter rod lengths fastened into a square shank (see Fig. 4) by swaging, brazing,
or silver soldering, leaving an exposed length of about ⁄4 in. (19 mm). The shank ensures correct orientation of the electrode point
after sharpening (see 9.2.2), although correct orientation of the simple rod electrode will be obtained by adjustment of the rod in
the electrode assembly. In either type of rod electrode, grind the end of the rod at a 30° angle to the axis (see Fig. 4) to achieve
a flat elliptical face. Exercise care in grinding to prevent cracking or chipping.
6.1.19 Electrode Assemblies—These assemblies provide a means of holding the electrodes and specimen and of applying the arc
to the top surface of the specimen. Construct each assembly, whether for stainless steel strip electrodes or for tungsten rod
D495 − 22
FIG. 4 Top and Side Views of Tungsten Rod Electrode
electrodes, so that the top surface of each specimen is at the same level height. Provide ample air space below the specimen,
especially in the region directly below the test area. Adjust each electrode so that it rests independently with a force of 50 6 5
g on the top of the specimen. Provide a transparent shield around the assembly to protect the specimen from air drafts, and allow
venting of combustion products in cases where specimens give off toxic smoke or gases during the test. Protect the operator from
inadvertent contact with the electrodes, and provide a clear view of the arc from a position slightly above the plane of the specimen.
6.1.19.1 Stainless Steel Strip Electrode Assembly (see Fig. 3, Fig. 5, Fig. 6, and Fig. 7)—Place two stainless steel strip electrodes
on the top of the specimen surface with the corners down and spaced 0.250 6 0.003 in. (6.35 6 0.08 mm) apart, and at angles
of 45° to a line joining the corners. Either use an electrode holder such as the one in Fig. 3, Fig. 6, and Fig. 7, or use the rod
electrode assembly with the rods separated and resting on the stainless steel strip ele
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