(Probably for Tony)
I've got here an Australian HPM power plug. Looks like the following link.
The HPM design seems to have included a method to clamp the sheath (screw up thing at the rear top that radially bites into the plastic) and three plastic hooks (to wind the individual wires about to reduce movement near the screw terminals).
But as I say, no consumer instructions how joe public should attempts to assemble it correctly - so one could just ignore the strain relief and have flying earth wires contacting everything else just before it breaks, or the user does :-(