Ques. What is the difference between a single-break and a double-break switch?
Ans. The distinction is that the one breaks the circuit at one point only, while the other breaks it at two points.
Ques. What is the advantage of a double-break?
Ans. If the circuit be opened at two points in series at the same instant, the electromotive force is divided between the two breaks and the length to which the current will maintain an arc at either break is reduced to one-half; thus there is less chance of burning the metal of the switch. Another reason for providing two breaks is to avoid using the blade pivot as a conductor, the contact at this point being too poor for good conductivity.
Figs. 455 to 457.—Adam's single-throw knife switches without fuse connections. Fig. 455, single-pole switch; fig. 456, double-pole switch; fig. 457, three-pole switch.
Figs. 458 to 460.—Adam's single-throw knife switches with fuse connections at the handle end. Fig. 458, single-pole switch; fig. 459, double-pole switch; fig. 460, three-pole switch.
Ques. When should a knife switch be used?
Ans. When the capacity of the circuit in which it is to be placed exceeds 10 amperes.
Ques. Describe a knife switch.