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Hot-Wire Ignition (HWI) - UL 746 Test Standard Explained

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Hot-Wire Ignition (HWI) - UL 746

Test specimens are wrapped with resistance wire that dissipates a specified level of energy. HWI is the time it takes to either ignite or burn through a specimen.

Performance Level Categories (PLC) were introduced to avoid excessive implied precision and bias.

HWI Mean Ignition Time (sec)	PLC
120 and longer	0
60 through 119	1
30 through 59	2
15 through 29	3
7 through 14	4
<7	5

Property information for specific grades of resin are available in the Prospector Plastics Database.