The difference between hard usage and extra-hard usage able is simply in the
jacket thickness and the
conductor insulation thickness. In aggregate, these increased thicknesses provide additional resistance to cuts, abrasion, and flexing damage that might expose the
conductor.
Now, you might ask "How much better is extra-hard usage?" That is very hard to quantify, since the UL62 standard for Flexible Cords and Cables does not contain
performance standards, only
construction standards specifying the thicknesses. A few years ago, I asked UL whether a specific custom 12-conductor
flat cable would meet the extra-hard usage performance requirements. They replied that they would be happy to test some extra hard usage cables to failure in order to
determine performance, and then see if the
flat cable could meet that number of test cycles. If I recall correctly, that was a $50,000 science experiment.
BTW, the end result was this change in the
NEC:
520.40 Stage Lighting Hoists.
Where a
stage lighting
hoist is listed as a complete assembly and contains an integral cable-handling
system and cable to connect a moving wiring device to a fixed
junction box for connection to permanent wiring, the extra-hard usage requirement of
520.44(C)(1) shall not apply.
ST