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Bars often better than wires.

electro-chemical operations. If we estimate the cross section of the conductors at the rate of i square inch per 1,000 amperes, then the range of cross sections for the switchboards of industrial installations will be from i to 15 or. 20 square inches. Unless the current is used for chemical processes the cross sections will not very often run beyond four or five inches, for when the power transmitted is very great the yoltage is increased, and thus the current strength reduced.

For any size of conductor greater than one-half of a square inch, flat bars can be used to better advantage than round wires, and they are more desirable from an electrical point of view, as they present a greater radiating surface for the same cross section, and therefore will not heat up to the same extent with a given current strength. The general arrangement of these connecting bars is shown in Fig. 27, which represents the back of a switchboard arranged for four generators, each one having a capacity of 1,000 amperes, making 4,000 amperes as the total capacity of the board. The connections between the generators and the board are shown in single lines, but these are made with cables, or bars, whichever may be the most convenient. The conductors I 2, of each generator, run to the lower terminals of circuit breakers, which are marked C B, C B.,, etc. The conductors marked 3 are the equalizer connections, and run to the lower center terminals of the switches marked S1, S., S3, St. The bar D is the equalizing bus, and the bars C and E are the positive and negative busses, and to these the current passes from the outside terminals of the switches, these being connected with the center and top terminals of the circuit breakers by the bars b b. This board is How bus bars are arranged.

d

arranged so as to distribute the current of the generators, or to obtain a supply from the street mains. The switch S, is for the purpose of connecting the bars E2, E3, C2, which are the main distributing busses, either with the generator busses C ED or with the street mains, which come to the three terminals in the vertical row marked SS. The switch S, is double throw, and when thrown to the left connects the generators and the main busses, and when thrown to the right connects the street mains with the main busses. The main busses, at both ends, connect with secondary busses Ed E, C; by means of the bars marked d d d and d d d'. From these secondary busses the current passes by means of the distributing switches S' to the external circuits L L L.

The ammeters are of the shunt type and derive current from the top and bottom terminals of the ammeter shunts marked St. The voltmeters are connected with the lower terminals of the circuit breakers or with any convenient points on the wires i 2 leading from the generator. As the ammeters and voltmeters take very small cur

Figure 28. rents, the connecting wires are small Cross section showing flexible cables.

bus bars.

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