Safety Information
3"
The HWI test indicates a material's resistance to ignition when exposed to abnormally high
temperatures resulting from a component failure, such as a conductor carrying far more than its
rated current HWI performance is expressed as the mean number of seconds required to ignite a
specimen when wrapped with an energized ni-chrome resistive wire that dissipates a specified
level of energy.
The HAI test determines the material's ability to withstand electrical arcing either directly on or
just above the surface of the plastic material. This can occur in the presence of open switch
contacts or in the event of the failure of an electrical connection. HAI performance is expressed
as the number of arc rupture exposures -- using standardized electrode materials, geometry and
electrical supply circuit -required to ignite a specimen when the arc occurs directly on the surface
or a specified distance above the test specimen.
The HVTR for a material is expressed as the rate (in inches per minute) that a tracking path can
be produced on the surface of the material under standardized test conditions. This test relates to
establishment of an electrically conductive path on the surface of a solid, insulated material as a
result of electrical stress.
Another ignition test can be applied to measure a material's resistance to ignition property. This
test is the Glow-Wire Ignitability Test and is also described in UL 746A and 746C, Polymeric
Materials - Use in Electrical Equipment Evaluations. The method is based on a test procedure
that is documented in IEC 60695 and specified in numerous IEC end-product specifications,
including IEC 60335-1. The test is somewhat similar to the HWI test in that it measures a
material's resistance to ignition on application of a heated non-flaming source.