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ASTM D 495 Document Information:
Title
Standard Test Method for High-Voltage, Low-Current, Dry Arc Resistance of Solid Electrical Insulation
ASTM International
Publication Date:
Mar 10, 1999
Scope:
This test method covers, in a preliminary fashion, the differentiation
among similar materials with
respect to their resistance to the action of a high-voltage,
low-current are close to the surface
of insulation, intending to form a conducting path therein or in
causing the material to become
conducting due to the localized thermal and chemical decomposition and
erosion.
The usefulness of this test method is very severely limited by many
restrictions and qualification,
some of which are described in the following paragraphs and in Section
5. Generally, this test
method should not be used in material specifications. Whenever
possible, alternative test methods
should be used, and their development is encouraged.
This test method will not, in general, permit conclusions to be drawn
concerning the relative are
resistance rankings of materials that may be 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).
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 are tests and field experience. Because this test method is
usually conducted under clean
and dry laboratory conditions rarely encountered in practice, the
prediction of a material's
relative performance in typical applications and in varying "clean to
dirty" environments may 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.
While this test method uses dry, uncontaminated specimen surfaces,
Test Method D 2132, Test Methods
D 2303, and Test Method D 3638 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.(Footnote 2)
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.
The values stated in inch-pound units are to be regarded as the
standard.
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
specific precautionary statements, see 6.1.14, 6.1.19, Section 7, and
10.1.1.
Footnote 2 - Also helpful is Test Method D 2302 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.
Keywords:
- arc resistance
- dry are resistance
- high voltage
- low current
- stainless steel electrodes
- tungsten rod electrodes
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