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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).
Description of Circuit 4 (Hold off) detailing the operation of a relay switch, current, resistance and voltage.

Identifier  ExFiles\Box 64\3\  scan0037
Date  1st March 1924 guessed
  
-4- Contd.

Circuit 4. Hold off.

Immediately the main current circuit is made and the relay switch pulled over, circuit 1 is broken and circuit 4 is made.

Circuit 4 supplies a current through the push button switch to the bottom contacts of the relay switch and through the fine wire coil of the relay switch to earth. The resistance of this fine wire coil is 3.06 ohms. The current through it at 11.0 volts is 3.6 amperes. 11 VOLTS.

The condition of correct operation as regards this circuit is that a current of 3.0 amperes through its coil must easily be capable of holding the relay switch lever down unassisted by the main current coil, the main current being switched off so soon as the engine kicks over the toggle of the actuator box and so opens the operating circuit of the main switch.

EFC.
  
  


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