The H in THW probably designates it as 75°C insulation, versus TW being 60°C. In a number of areas, it was the default industrial building wire before THWN/THHN was popular. Earlier, THW aced out RHW with improved ease of handling.
[No hepcat electrician would use solid TW if he could get stranded THW.] At one time, TW was available in solid up to 6AWG.
[This message has been edited by Bjarney (edited 03-30-2003).]
