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).
Investigation into a fuse failure after a short circuit incident in a car.
| Identifier | ExFiles\Box 166\7\ img108 | |
| Date | 8th March 1940 | |
| 6071 To Rm{William Robotham - Chief Engineer}/FD.{Frank Dodd - Bodies} from Rm{William Robotham - Chief Engineer}/RC.{R. Childs} c. Ev.{Ivan Evernden - coachwork} c. Jnr.{Charles L. Jenner} Re Fuses. It was reported by Lp.{Mr Lappin}, 10.11.39 that he had met with a slight accident in car 11.B.V., in which the tail lamp was knocked off. This caused a short circuit to develop at the lamp terminals, and he complained that the fuse in this circuit did not "blow", and that consequently the battery was run down. It was known that the fuse, which was of 28.SWG. tinned copper wire, melted at about 47 to 50 amperes; it having been continued on the five-terminal board from the days of the long type board, when it was necessary to have a heavy fuse in the armature circuit. A number of observations have been made using car 2.B.50. A carbon resistance was connected in the place of the tail lamp, and the current in the circuit gradually increased until, finally, the carbon resistance was out out, thus establishing a short circuit at the cable ends. Readings of current were taken at intervals, and these readings together with remarks concerning the heating of the fuse wire, are given below. 28 SWG. WIRE. Condition of Circuit. Condition of Fuse. Current raised to 25 amps. Fuse found to be warm. " " " 30 " " " " hot. Carbon resistance cut out, i.e. short circuit at cable ends. Current 45 amperes, battery terminal volts 11.65, resistance of circuit .295 ohms in a warm condition. Fuse glowed brightly. The above result shows that the 28 SWG wire fuse affords no protection to a circuit of this type. Continued. | ||