UL 746A UL 498 Polymeric Materials Flammability Test Chamber High Current Arc Ignition Test

Test Procedure:
 

The test is to be conducted on five specimens. Each specimen, in turn, is to be clamped flat so that the longitudinal axis of the sample is normal to the common vertical plane of the electrodes. The fixed electrode is to be secured in place such that the chisel edge is in firm contact with the top surface of the specimen with sufficient force to ensure the electrode remains stationary during the test, but does not cause significant physical damage to the specimen. The point of contact of the fixed electrode is not to be less than 4 mm from any edge of the sample. The moveable electrode is to be adjusted such that it contacts the fixed electrode between 0.75 to 1.00mm above the surface of the specimen. The movable electrode is to be secured in position. The equipment is to be adjusted to provide a dwell time of 100±20ms before electrode withdrawal breaks the circuit and the timing of the arcs is to be adjusted to a rate of 40 complete arcs per minute. The circuit is to be energized and the cyclic arcing started. The test is to be continued until ignition of the sample occurs, a hole is burned through the sample, or until a total of 150 cycles has elapsed.

If ignition or a hole through any specimen occurs, an optional above-surface test may be conducted. This optional test is conducted on an additional set of three samples tested with the electrodes making contact a maximum of 1.6mm above the surface of the specimen. Should ignition or a hole occur within 150 cycles, an additional set of three samples may optionally be tested with the electrodes making contact a maximum of 3.2mm above the surface of the specimens. A hole caused by the fixed electrode impinging on the sample or initiating a tear is to be excluded from the test results. Or holes caused by combusting the sample, as a result of arcing, are to be recorded and included in the report.

The following is to be recorded as applicable:

a) The number of arcs to cause ignition.

b) The number of arcs to cause a hole through the sample

c) The maximum number of cycles, 150.

d) Observations regarding meltning, charring, or the like.