The original ERC -Manufacturers, 500/550 kV Cable Research test schedule was successfully completedl in August 1972 and most of the basic data has been presented. 2 A follow-on program designed to search for end9oints has run its course and it is now appropriate to describe the events and consider their significance in EHV system design. Cyclic thermal loading has been postulated as a cause of EHV cable system problems.This paper relates specifically to test specimen Aand its performance in a high thermal load study at the Waltz Mill test facility. 3 The end point was reached but the failure mode appeared to be one of mechanical origin and will require further tests.