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102 HANDBOOK OF PROJECTION FOR
nected to the neutral and the right hand feeder bar, so that it is on the right hand "side" of the three wire cuicuit. The neutral and the left hand bar is connected to the upper circuit, so that circuit is on the left hand "side." We thus have one circuit connected to each "side," and if both circuits use the same number of amperes the load will be "balanced."
This forms the keynote to the connections of your big house switchboard. It is a bit puzzling for the novice to trace these connections, but look at it for a while and you will find that in all individual circuits one side is connected to the neutral and the other to one or the other of the main switchboard feeder bars, except in the possible case of the use of a 220 volt motor circuit, which would connect to the two outside bars or wires. It will be understood that where there is no screw head there is no connection between the feeder bars and circuit bars. Thus: The left hand feeder bar, Fig. 14, crosses the lower second and third bars without electrical connection and makes electrical connection to the top bar at the screw head. Where copper bars of this kind are used instead of wires they are commonly called "bus bars," though the term correctly applies to the copper bars which connect the power house generators to their circuits.
Fig. 15 is a photograph of a moderately large and somewhat complicated switchboard. On the right side the individual circuits are indicated by X. Study the contacts and you will be able to trace out the connections. Taking the next-to-the-top right hand circuit for example, we find it leaves the main bus bars in the form of a three-wire circuit, and that there are three plug fuses which protect the three-wire circuit as a whole. Just beyond the fuses is the handle of the T. P. S. T. switch, beyond which the upper bar connects to the upper wire of the upper two-wire circuit, the neutral connects to both the lower wire of the upper circuit and the upper wire of the lower circuit, and the lower bar connects to the lower wire of the lower circuit.
We thus have the three-wire circuit split up into two twowire circuits, at the beginning of which are the individual circuit fuses which must be present on all individual circuits. To the left this circuit starts off and ends as a plain threewire circuit. Above this circuit, at the very top of the bars, are two two-wire circuits, the neutral bar (see Screw Head) connecting to the lower circuit bar, the left hand bus bar to the upper left hand circuit bar and the right hand bus bar to the upper right hand circuit bar, and thus by a little care in observing the screw heads, which mean electrical