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 operation of a circuit breaker with a shunt coil and an earth indicator lamp.
| Identifier | Morton\M1.7\ img007 | |
| Date | 13th December 1921 | |
| Contd. -3- EFC/T3.12.21. the circuit breaker with the shunt coil would not remake the circuit when the earth were removed unless the lamps were first switched off. This second case would offer the possibility of putting in a little red earth indicator lamp in series with the shunt coil. This would indicate the existence of an earth visually instead of audibly and take very much less current for the indication. Then if the danger lamps were burnt out, the instrument would merely act as a buzzer without any harm. It might be thought that the dynamo would be capable in this instance of over-exciting in the case where the earth were removed and some lamps left on, as the contacts would be still apart, but when the dynamo had run up and its voltage was equal to that of the battery, there would be no current through the shunt coil for the moment and the contacts would make, thus not giving the dynamo a chance of running up to excess voltage. EFC. R.{Sir Henry Royce} R.{Sir Henry Royce} 136A. 100 (T) (S. E.{Mr Elliott - Chief Engineer} 798, 10-12-30) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 3847 | ||