Hawkins electrical guide ... : questions, answers & illustrations : a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications ; a practical treatise (1914)
Hawkins, N. (Nehemiah), 1833-1928 · New York : T. Audel & Co. · leaf 315
tact switches areall connected in parallel. The door switches may be like that shown in fig. 3,309 inwhich the insertion of a key closes switch contacts in the lock. The battery and bellsare connected in parallel to the main wires going to the battery and switches. The backstoop has a floor tread… … Fig. 3,314.—Burglar alarm trap. This trap is so constructed that when the contact leveris off the bridge it cannot be returned to its original position except by hand. Whenset, a pull on the string draws the lever from the bridge on to the contact points. Ifthe string be cut, broken or burned…
Electrical engineering
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