Still other modifications.

tributing switch si is connected with these busses; hence it is supplied with current from generator GI. Generator G2 connects, through switch B, with busses 6, 5 and 1; hence it will feed into switch s4, which is connected with busses 5 and 1.

In the same way as described in the foregoing, it will be found that generator G3 feeds into the distributing circuit controlled by switch s2, and that generator G4 supplies the circuit controlled by switch s3. If it is desired to connect two of the generators, as, for example, G1 and G2, with the same distributing circuit-say with the one controlled by switch s3-then the four-point switches, A and B, are set with their levers covering contact 3. In the same way any of the generators can be set so as to feed into any of the busses. Hence, we have in this construction of switchboard an arrangement whereby any one, or all, of the generators can be connected with any one of the distributing circuits, but we cannot connect any one generator with more than one circuit at a time. If we desire to so modify the arrangement as to render it possible for the generators to feed into more than one circuit at the same time, all we have to do is to provide switches that will enable us to connect the various busses. Thus, if by means of a switch we connect busses I and 2, then generator G4, with the lever of the D switch set as in the diagram, would feed into the circuit controlled by the switches $3 and s4. Switches used to connect the bus bars are called tie switches, and, as can be readily seen, it is a simple matter to so arrange them as to make any connections desired. By means of one tie switch we can connect busses 1 and 2, and by means of another we can connect busses 2 and 3, while a third tie switch will con

Independent distributing systems.

nect busses 3 and 4. Thus, by the use of three tie switches we can connect all the busses from 1 to 4, and then we will have an arrangement that will be precisely the same as those shown in previous figures, with only three busses, under these conditions, for the four connected busses would virtually act the same as one.

If we desire to make the bus-tying arrangement more complete, so as to be able to tie and 3, or 1 and 4, or so as to be able to connect any pair without connecting the others, then the switches will have to be more than threeproviding two-pole switches are used-and their connection will involve more complication. By using three-point switches of the same type as A, B, etc., and providing one for each bus bar, we can connect the bars in any order desired; for suppose we provide four such switches and connect the center of each one with one of the busses, then, by placing the lever over any one of the three outside contacts, we can connect with any one of the other busses.

There is one objection to the arrangement of Fig. 21, and that is that the several distributing systems are not entirely independent, but, on the contrary, all are connected through busses 6 and 5. Now, it is desirable, when the external circuits are divided into several systems, to have these entirely independent, so that if anything goes wrong with one set of circuits it will not interfere with the operation of the others. When the several systems are partially connected, as by the busses 5 and 6 in this figure, it is possible for a ground or short circuit in one to interfere with the operation of the others; hence, if each system is so arranged as to be disconnected entirely, the operation will be more satisfactory.

Twelve switches here.

Fig. 22 shows an arrangement whereby four generators are connected so as to feed into four entirely independent distributing systems; but in this case none of the generators can connect with all the bus bars. Two of them can be connected with three sets of busses, but the others can only connect with two sets. It will be seen that generator GI connects with switch S1 running to the center row of contacts, which is marked k. This switch is of the double throw type, and when turned to the right connects with the center row of contacts of Switch S2. The right-side row of contacts of this switch connect with the busses C. Thus, with the switches in the position shown, generator GI is connected with busses C. If switch S2 were turned to the left, the generator would be connected with the B busses. If switch S1 were turned to the left, the generator would be connected with the D busses. By means, therefore, of the two switches S1 and S2, generator GI can be connected with either one of three sets of busses—namely, B, C, D. In like manner generator G2 can be connected with busses A B C by means of switches S4 and S5.

Generator G3 is connected with switch S6, and when the latter is turned to the left, the generator is connected with the B busses, and when turned to the right, it is connected with the A busses. By means of switch S3, generator G4 can be connected with the C and D busses, it being connected with the C set as drawn.

With the arrangement of Fig. 22 it would be necessary to have twelve switches to be able to connect each generator with any one of the busses, and to tie the busses all together four more switches would be required. To be able to connect any set of busses with any other set, or with all of them these tie switches would

Comparing the two plans.

have to be of the same type as A C D in Fig. 21; but, as they would have to connect three busses with three others, they would require three times the number of contacts, and on that account would be of a much more complicated construction.

Suppose that generator GI were connected with the center row of contacts of switch S2, instead of with SI, and that the right-side contact of S2 were connected with the center of S3 and the left-side row with the center of S1, then by turning switch S2 in opposite directions generator GI could be connected with the center of either SI or S3. If the right and left hand sides of switch SI were connected with busses C and D respectively, and the sides of S3 were connected with busses A and B, by means of these three switches, generator GI could be connected with any one of the four sets of busses, but only with one set at a time. From this explanation it will be seen that three switches are required to connect one generator with the four sets of busses; hence for the four machines twelve switches would be necessary.

Comparing Figs. 21 and 22 we see that in the first only eight switches, four S and four four-point, are required, and only six bus bars, while to effect the same combinations with Fig. 22 twelve switches and twelve bus bars are necessary. From this fact it would at first thought be inferred that the arrangement of Fig. 21 is better than the other, but such is not necessarily the case. It depends wholly upon what we want to accomplish. Fig. 22 is more complicated and more expensive than Fig. 21, but to compensate for the greater expense and complication we have the fact that the four sets of busses are entirely