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).
Advantages of a semi-earthed electrical system for a chassis.
| Identifier | WestWitteringFiles\J\December1922\ Scan61 | |
| Date | 5th December 1922 | |
| To R & E.{Mr Elliott - Chief Engineer} from EFC. c. C.J. & PN.{Mr Northey} c. Hy.{Tom Haldenby - Plant Engineer} & EP.{G. Eric Platford - Chief Quality Engineer} c. Rg.{Mr Rowledge} & Ds. ORIGINAL EFC1/T5.12.22. X.3374 - CHASSIS ELECTRICAL SYSTEMS. We think there is a good deal to be said for what might be called a semi-earthed electrical system for a chassis. Such a system is shown in an electrically simple way on the diagram herewith from which it will be seen that the lighting, ignition and other distributing circuits are shown with an earth return but that the dynamo and starter motor circuits have insulated returns. There is a main negative fuse for the distributing circuits between the battery main negative and earth, the remainder of the system being as usual. The points in favour of such a system are :- (1) Single pole lamps, lamp fittings and connections may be used, thus introducing an element of simplicity. (2) As compared with the entirely earthed system, the system is protected by the negative fuse against earths on those live positive wires which are not protected by the distributing fuses. (3) In the event of the main negative fuse going, this still does not disconnect the dynamo from the battery, possibly leaving it on the lights, in such a way that over-voltage could do damage to the dynamo or the lights, (including or excluding from the test the dynamo as desired, according to the position of the charging switches and (switch (4) By turning off the distributing switches and removing the said negative fuse - a test can be done on the rest of the system for insulation resistance or leakage. The 40/50 system is, of course this to some extent, the difference being that the lamp currents are returned to the battery without having to pass through the negative earthing fuse; in fact, on the 40/50 system, there are-no-fuses-in- | ||