ASTM D5288-97

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An American National Standard
Designation: D 5288 – 97
Standard Test Method for
Determining the Tracking Index of Electrical Insulating
Materials Using Various Electrode Materials (Excluding
Platinum)
This standard is issued under the fixed designation D 5288; 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.
1. Scope D 1898 Practice for Sampling of Plastics
D 3638 Test Method for Comparative Tracking Index of
1.1 This test method was developed using copper electrodes
Electrical Insulating Materials
to evaluate the low-voltage (up to 600 V) tracking resistance of
2 2.2 IEC Publication:
materials in the presence of aqueous contaminants.
IEC 112, Recommended Method for Determining the Com-
NOTE 1—At this time, only industrial laminates have been examined
parative Track Index of Solid Insulating Materials Under
using this method which was developed at the National Manufacturers
Moist Conditions, 1971 Second Edition
Electrical Association (NEMA) laboratory located at the University of
Cincinnati. It was found that a closer end point (less scatter) was obtained
3. Terminology
than with platinum electrodes, and materials tested tended to be ranked by
3.1 In addition to the definitions listed below, terminology
resin system.
as defined in Terminology D 1711 is assumed.
1.1.1 Other electrode materials may be considered for use
3.2 Definitions:
with this test method depending upon the application of the
3.2.1 track, n—a partially conducting path of localized
insulating material.
deterioration on the surface of an insulating material.
1.2 This test method is similar to Test Method D 3638,
3.2.2 tracking, n—the process that produces tracks as a
which determines the comparative tracking index of materials
result of the action of electric discharges on or close to an
using platinum electrodes to produce the tracking on the
insulation surface.
specimen surface.
3.2.3 tracking, contamination, n—tracking caused by scin-
1.3 The values stated in metric (SI) units are the standard.
tillations that result from the increased surface conduction due
The inch-pound equivalents of the metric units are approxi-
to contamination.
mate.
3.2.4 tracking index, TI, n—an index for electrical insulat-
1.4 This standard does not purport to address all of the
ing materials which is arbitrarily defined as the numerical value
safety concerns, if any, associated with its use. It is the
of that voltage which will cause failure by tracking when the
responsibility of the user of this standard to establish appro-
number of drops of contaminant required to cause failure is
priate safety and health practices and determine the applica-
equal to 50.
bility of regulatory limitations prior to use.
3.2.4.1 Discussion—This value is obtained from a plot of
the number of drops required to cause failure by tracking
2. Referenced Documents
versus the applied voltage.
2.1 ASTM Standards:
3.2.5 tracking index–copper electrodes, TI-Cu, n—a track-
D 618 Practice for Conditioning Plastics and Electrical
3 ing index test using copper electrodes.
Insulating Materials for Testing
4 3.2.5.1 Discussion—This test is comparable to comparative
D 1711 Terminology Relating to Electrical Insulation
tracking index, Test Method D 3638, with the following
exceptions: (1) copper electrodes are used instead of platinum,
and (2) the electrodes may have to be re-ground after every test
This test method is under the jurisdiction of ASTM Committee D-9 on
Electrical and Electronic Insulating Materials and is the direct responsibility of
because of the softness of copper.
Subcommittee D09.12 on Electrical Tests.
Current edition approved Sept. 10, 1997. Published December 1997. Originally
published as D 5288 – 92. Last previous edition D 5288 – 92.
Mathes, K. N., Chapter 4, “Surface Failure Measurements,” Engineering
Dielectrics, Vol IIB, Electrical Properties of Solid Insulating Materials, Measure-
ment Techniques, R. Bartnikas, Editor, ASTM STP 926, ASTM, Philadelphia, 1987. Annual Book of ASTM Standards, Vol 10.02.
3 6
Annual Book of ASTM Standards, Vol 08.01. Available from the International Electrotechnical Commission, Geneva, Swit-
Annual Book of ASTM Standards, Vol 10.01. zerland.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 5288
3.2.6 tracking resistance, n—the quantitative expression of platinum electrodes in the same type of test. It is a fact that
the voltage and the time required to develop a track under copper is more widely used than platinum for electrical
specified conditions. conductors.
6. Apparatus
4. Summary of Test Method
6.1 The simplified electrical circuitry used in this test is
4.1 The surface of a specimen of electrical insulating
illustrated in Fig. 1. For necessary information on the cleanli-
material is subjected to a low-voltage alternating stress com-
ness of apparatus, see Annex A1. The essential components
bined with a low current which results from an aqueous
are:
contaminant (electrolyte) which is dropped between two op-
6.1.1 Variable Power Source, consisting of a transformer
posing copper electrodes every 30 s. The voltage applied across
type supply, such as the combination T and T in Fig. 1, with
1 2
these electrodes is maintained until the current flow between
a variable output of 0 to 1000 V, 60 Hz capable of maintaining
them exceeds a predetermined value which constitutes failure.
a current of 1 A (1 kVA).
Additional specimens are tested at other voltages so that a
6.1.2 Voltmeter (V ), capable of measuring the varying ac
relationship between applied voltage and number of drops to
output of the power source. A0 to 600-V voltmeter with an
failure can be established through graphical means. The
accuracy of at least 60.5 % of full scale.
numerical value of the voltage which causes failure with the
6.1.3 Ammeter (A ), with a range of 0 to 1 A ac and an
application of 50 drops of the electrolyte is arbitrarily called
accuracy of at least 610 % of full scale.
the tracking index. This value provides an indication of the
6.1.4 Current Limiting Resistor (R ), continuously vari-
relative track resistance of the material.
able, wire wound, rated at greater than 1 A.
6.1.5 Shorting Switch (S ), single-pole single-throw rated
5. Significance and Use
at 1000 V and greater than 1 A.
5.1 Electrical equipment may fail as a result of electrical
NOTE 2—The need for a shorting switch is optional. It is possible to
tracking of insulating material that is exposed to various
couple the variable resistor with the autotransformer which gives an
contaminating environments and surface conditions. There are
automatic setting of the current throughout the range of the instrument.
a number of ASTM and other tests designed to quantify
Then whenever it is necessary to check the calibration of the instrument,
behavior of materials, especially at relatively high voltages.
the shorting action can be accomplished by a jumper wire placed across
This method is an accelerated test which at relatively low test the electrodes. This coupling of the autotransformer with the variable
resistor is another option.
voltages, provides a comparison of the performance of insu-
lating materials under wet and contaminated conditions. The
6.1.6 Over-Current Relay (R ), shall not trip at currents up
Tracking Index—Copper Electrodes test is not related directly
to 0.1 A and the tripping time on short circuit shall be a
to the suitable operating voltage in service.
minimum of 0.5 s (the current shall be limited on short circuit
5.2 When organic electrical insulating materials are sub-
to 1 A with a tolerance of6 10 % at a power factor of 0.9 to
jected to conduction currents between electrodes on their
1.0).
surfaces, many minute tree-like carbonaceous paths or tracks
NOTE 3—Some instruments have used a Heinemann breaker, which is
are developed near the electrodes. These tracks are oriented
probably the closest standard commercial breaker to that described in the
randomly, but generally propagate between the electrodes
IEC Method. Also the tripping action can be accomplished with elec-
under the influence of the applied potential difference. Even-
tronic circuitry.
tually a series of tracks spans the electrode gap, and failure
occurs by shorting of the electrodes.
Middendorf, W. H. and Vemuri, R., “Report on Copper vs. Platinum Elec-
5.3 As in other tracking test methods, for example, IEC 112
trodes”, 1990, Available from National Electrical Manufacturer’s Association, 2101
and Test Method D 3638, this test method specifies test
L St. N.W., Suite 300, Washington, D.C. 20037-8400.
procedures that are intended to promote the formation of
Heinemann Model Series JA, Curve 2.
surface discharges which will produce carbon tracks in a
reproducible manner. Since these conditions rarely reproduce
the actual conditions encountered in service, the results of
tracking tests cannot be used to infer either direct or relative
service behavior of a material in a specific design application.
Tracking tests can be used for screening purposes only.
Suitability is verified through testing of the material in actual
end use or under conditions that closely simulate actual end
use.
5.4 The use of copper electrodes in this type of test was
developed at the University of Cincinnati, NEMA laboratory. It
is felt by the members of the Industrial Laminates Section of
NEMA that using copper electrodes gives a more realistic
value for a tracking index, related to the resin system used to
reinforce the substrate of a laminate. In general, tracking tests
made with copper electrodes tend to give lower values than FIG. 1 Electrical Circuit Components
D 5288
6.1.7 Testing Fixture (J )—adjustable platform which sup- 8. Test Specimens
ports the specimen and electrode setup.
8.1 Samples should be selected in accordance with Practice
6.1.8 Copper Electrodes, of electrolytic copper having a
D 1898.
rectangular cross section measuring 5 by 2 mm (0.2 by 0.08
8.2 Typical test specimens are 50 mm (2 in.) or 100 mm (4
in.), extending 20 mm (0.8 in.) minimum from suitable
in.) diameter disks or any other similar shape. The minimum
mounting shanks (Fig. 2). The end of each electrode is
thickness i
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