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).
Evolution and arrangement of the S.S. Switchbox positions and functionality.
| Identifier | ExFiles\Box 59\1\ Scan351 | |
| Date | 8th July 1929 | |
| X4008 By.{R.W. Bailey - Chief Engineer} from EFC. c. By/RD? EFC2/AD8.7.29. X7730 X4040 X4008 S.S. SWITCHBOX. The arrangement of S.S. switchbox which finally evolved as standard after passing through several modifications, is the one in which the four positions are - M & C M B & C M & B OFF the red underline signifying that the two M's underlined are capable of being switched off by the auxiliary switch. This arrangement was evolved as being suitable for working in conjunction with the green lamp scheme, in which case it was not possible to have the dynamo armature contact extended to the first "on" position (M & B) of the switch. Where however, there is no green lamp switch and unit (as present standard), the arrangement of the S.S. switchbox as originally instructed and made, namely M & C M B & C M & B (& A) OFF which you will note only differs from the standardised arrangement in incorporating the extended armature (A) contact, would be quite suitable, and in fact more appropriate. Though we have formed the conclusion as a result of test that the green lamp scheme can never be satisfactory, we do not suggest an immediate reversion to this type of switchbox, but we do suggest that we should have one or two switchboxes made to this original S.S. standard for running on the experimental cars, the idea being to have a direct comparison in actual running as to whether any advantage is apparent in the burning of the switch contacts by having a longer delay between the field break and armature break. Further to the above the switchbox arrangement most suited to the long distribution board with incorporated auto switch is - M & C M B & C B (& A) OFF | ||