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 CD 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 S1, 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

Connecting ammeters.

disconnected from each other, and no possible disorder of one set could affect the other three. In order to obtain the greater simplicity of Fig. 21 we are compelled to adopt a type of connection in which the four sets of busses are merged into one, and, although by means of it we are able to feed into four separate distributing systems, these are not entirely disconnected, but, on the contrary, all have the busses 5 and 6 in common, and on that account a disarrangement of one set of circuits might result in disabling the whole system.

When the location of the circuit wires is such that the liability of disarrangement is slight, the plan of Fig. 21 can be used, and it is particularly desirable if we wish to reduce the cost of construction to the lowest point. If the circuit wires are so located that there is more or less danger of their becoming crossed, short-circuited, etc., then the construction of Fig. 22 is the proper one, even if we desire to practice economy.

The connection of the measuring instruments, ammeters and voltmeters with the generators is not shown in Figs. 21 and 22, as it would lead to unnecessary confusion; but from the illustrations of instrument connections furnished in other figures, the manner in which the wires should be run can be readily understood when the office of each instrument is explained, as we propose to do in the following lines:

In Fig. 21 the four ammeters-marked Am1, Am2, Am3, Am4-are to be connected with the four corresponding generators, and so are the four voltmeters. The ammeters can be connected in series in the e wires or in the d wires of generators GI and G2, and the f and e wires of the other two machines. The voltmeters

Measuring instruments.

are connected to the d and e wires in the two first generators and to e and f in the third and fourth machines. The ammeter marked Am G is intended to be used when all the circuits are connected by means of tie switches into one system, and the voltmeter V G is used under the same conditions.

With the latter arrangement of circuit-that is, with busses 1, 2, 3 and 4 tied together-the voltmeter V G is connected with one side to bus 5 and the other side to any one of busses 1, 2, 3, 4. The ammeter AmG cannot be connected in the circuit with the connections shown in the diagram, for there is no way in which it can be arranged so as to be traversed by the entire current of the four machines. To be able to connect it, it is necessary to provide a seventh bus, to which the wires leading from the generators to bus 5 are attached, or else those leading from the S switches to this same bus. The ammeter is then connected between the seventh bus and bus 5, and thus all the current generated by the four machines has to pass through it to reach the distributing circuits.

In Fig. 22 there are four ammeters, one for each generator, and four voltmeters, just as in Fig. 21; but we have no general ammeter and voltmeter, and, as will be seen, it would complicate the circuits to a considerable extent to provide them, for then we would require busses to which one of the wires of the generators could lead, so that between these and the main busses the ammeter could be placed, and also so that the voltmeter could span across from one side of the general system to the other. The circuits could be arranged so as to use a single instrument to indicate the voltage when all the busses are connected into one system, and another in