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).
General table and a table of suggested limits for main switch gaps.
| Identifier | ExFiles\Box 64\3\ scan0212 | |
| Date | 9th March 1926 | |
| x7650 9.3.26. GENERAL TABLE FOR MAIN SWITCH GAPS. (Main and relay switch unit). Position. | Gap between pole core and armature stop. | Copper gap. | Carbon gap. --- | --- | --- | --- Off. | A + C/2 | C | 1/2(C-B) Carbons just making. | A + B/2 | B | O Coppers in contact. | A | O | O TABLE OF SUGGESTED LIMITS ACCORDING TO THE ABOVE RELATIONS. Position. | Gap between pole core and armature stop. | Copper gap. | Carbon gap. --- | --- | --- | --- Off. | .057"+-5 | .065+-5 | .062+-10 Carbons just making. | .032"+-5 | .020+10-5 | O Coppers in contact. | .030" | O | O EFC. | ||