From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Table of breakdown voltage tests for various types of electrical cables.
| Identifier | ExFiles\Box 167\3\ img139 | |
| Date | 19th January 1939 | |
| (3) ATTACHED TO Rm{William Robotham - Chief Engineer}/RC.{R. Childs}8/JH.19.1.39. TYPE OF CABLE. | BREAKDOWN VOLTAGE. Complete cable. | Rubber only. Standard Helsby - 14/36. Overall diameter .150 inches. Diameter over rubber .110 inches. No breakdown at 18,900 | 15,200. Standard Helsby - 23/36. Overall diameter .158 inches. Diameter of rubber .105 inches. 15,000 | 10,000. Standard Helsby - 40/36. Overall diameter .145 inches. Diameter of rubber .136 inches. No break-down. 18,600 | Breakdown. 18,600. Standard Helsby - 90/36. Overall diameter .190 inches. Diameter of rubber .150. No break-down at 19,400 | 18,600. Standard Horn cable, Thiokol cotton braided 2 x 23/36. Overall diameter .285 inches. Breakdown voltager taken core to core. No break-down at 19,200 volts. * Slight variation in dielectric strength in test pieces. Sufficient length not available for an average figure to be given. | ||