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).
The overload specifications for a chassis ammeter, requiring it to withstand 90 amperes.
| Identifier | ExFiles\Box 70\3\ scan0034 | |
| Date | 25th January 1928 | |
| X8783a To BY/Cgh.{W Clough} EFC2/T25.1.28. RE OVERLOAD OF AMMETER. X 1162 (struck through) X.8783a A chassis ammeter in proper condition will stand momentarily a current of 90 amperes. It has got to do this because it takes 90 amperes to blow the emergency fuse. if there is an earth beyond the ammeter to the battery. An ammeter which will not do this ought to be returned to the makers for correction. We have tested ammeters with 90 amperes e for three seconds each way without doing any harm, and we always specify this on any new ammeter proposed. If the ammeter is going to be damaged by the load of two cigar lighters, it is certainly going to be damaged by an earth, as described. That is to say, the ammeter should easily stand the cigar lighter load without damage. If there are cases of instruments which will not stand this load, we should take the matter up with Messrs. Weston with a view to getting them to make the above specified 90 ampere test. Attached please find copy of a Production Specification of Inspection and test, which we think might be applied to, say, one in every 12 ammeters. EFC. | ||