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Large switches.

The switch Fig. 101 is called a single-throw switch, because the blade can only be thrown in one direction to close the circuit. The design shown in Fig. 102 is called a double throw switch from the fact that the blade will close the circuit if thrown in either direction. If the switch has but one blade it can only open or close the

Figure 111. Switch for heavy current.

circuit in one wire, and is, therefore, called a single-pole switch; but if S consists of two blades, as shown in Fig 103, which is a plan of Fig. 102, then if the two blades are insulated from each other, each can open or close the

Quick break switches.

circuit through one wire. Switches of this latter type are called double-pole, and if S consists of three insulated blades the switch is three-pole.

In Fig. 102, as well as in Fig. 101, the current passes through A, therefore there must be a perfect fit between A and S. In Fig. 104 the current does not enter through A, hence a loose fit will answer as well as a tight one. In this last figure the current passes through the blade S

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from N to N; therefore at these points a good fit is required, and N must exert a considerable pressure against S. It can be readily seen that if the blade S is raised in Fig. 104 it will produce two breaks in the circuit. On

How they work.

this account switches of this construction are called double-break switches.

If the two sides of S in Fig 103, are not insulated from each other, the switch cannot be used as a doublepole. If the voltage of the current that passes through the two sides of a double-pole switch is low, the insulation need not be very heavy, but for an electro-motive

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force greater than 110 volts the most substantial insulation must be provided. When a two-pole switch is used to connect a generator with the switchboard, the outgoing current passes through one of the blades S and the returning current passes through the other, and since it is much easier for the current to jump across from one side of the switch to the other than to make the journey through a

Carbon break switches.

weak point in the insulation. To properly insulate the sides of a multiple pole switches several types of construction are resorted to, one of which is shown in Fig.

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103. This consists in providing a block, which is made of hard rubber, fiber or hard wood, the former being used for the higher grade of switches and for higher volt

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