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).
Technical discussion on the implications of extra electrical fittings and the appropriate fusing currents for car electrical systems.
| Identifier | ExFiles\Box 61\2\ scan0485 | |
| Date | 14th March 1927 | |
| 1 Copy W/S. to H.R. V'ID 3 Copies To CWH. q'from EFC. 1 Copy C. to EFC. X207 EFC/2/14.3.27. X4629 EXTRA ELECTRICAL FITTINGS ON CARS. With reference to your CWHB/CM2.3.27. addressed to 'Hs{Lord Ernest Hives - Chair}', the actual fusing current of the 30 SWG. copper wire in position on the distribution board is about 30 amperes, (N.B. This is greater than the tabulated value of the fusing current for this size of wire because the length is shorter.) Taking into account the fact that we do not want to have too many different sizes of fuse - we have to have a large size 90 ampere (3 strands of 30 SWG. for the emergency fuse) and a small one of about 5 or 6 amperes for the field fuse - the size chosen for the remainder of the fuses is that considered to be most suitable in one size to serve every position, and we consider it would not be wise either to increase (or reduce, see later) the size of any one of these fuses because of the increased complication, as we should have to make some dissimilarity in the mounting, as we have done in the cases of the two fuses which are different. There is not much objection to the addition to the electrical equipment of apparatus of the type which is only intermittently in action, in which category the apparatus you mention largely falls. In the very unlikely event of the momentary demand exceeding the fusing current of the fuse wire, we consider it better that the fuse should go and draw attention to the fact that the system is being overloaded. There is much more objection to the addition of apparatus taking moderate current only, which current may be on continuously and really make a seriously increased demand on the system. In answer to your last question it would scarcely be safe, even if advisable in other respects, to increase the fusing current, because the size of the fuse would then be approaching that of some of the distributing conductor wires. Curiously enough, only yesterday we had a complaint that this very fuse was too heavy and allowed some of the body wires or flexes to get too hot and smoke on the occurrence of a short circuit, probably on one of the lamp points. The query was raised as to whether the fuse could not be smaller. The logical answer to that was that the conductor wires should be heavier or alternatively that another and finer fuse should be provided for a distributing circuit in which the conductors are of finer section, the fuse on the distribution board being looked upon as a main fuse. I should be pleased if you would note that in any matter concerning the electrical equipment of the chassis, | ||