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498 HANDBOOK OF PROJECTION FOR
<;.umstances be installed without their sub-base, if they be of the type which uses a sub-base.
Where a motor and generator are carried on a single subbase or base, it is not necessary that they be bolted to the floor, nor is it necessary to build any special foundation for them.
CORK, FELT OR RUBBER.— Motor generator sets in which both elements are carried on a single base or sub-base require no base, but between them and the floor should be one of three things, viz. : a thick pad of cork, a thick pad of felt or a thick pad of fairly resilient rubber. These pads serve two purposes. They absorb any possible vibration, which would otherwise be communicated to the floor, and they serve to deaden the noise of the machine.
Cork is best, but the pad should be two or three inches thick. It need not extend all the way under the machine if the machine be of the horizontal type. If it be of the vertical type it will be just as well to use a pad or mat the full size of the machine, and two or three inches more. If the pad be of felt it should be of the kind J4 to one inch thick, and four or five thicknesses should be used. We can give no advice with regard to the rubber pad, because it will depend upon the kind of rubber you are able to get, but in any event a sufficient thickness should be used to absorb all the vibration.
It is imperatively necessary that the armature of horizontal type motor generator sets be perfectly level endwise, else it will not "float" (have end play), and failure to float will probably produce grooved bearings and commutator. For this reason it is necessary, after the machine has been set on its pad for a week, that it be tested, and if necessary levelled by slipping sheets of paper or metal under the low end. See Page 524, Figure 155.
CAUTION. — In the case of motor generators the armatures of which are joined by a coupling and which are not mounted on a single, rigid iron base, the pad method does not apply. Such machines must be bolted down to a solid, rigid foundation, the top of which is, of course, perfectly level.
ELECTRICAL CONNECTIONS.— Wiring diagrams and instructions should accompany each machine. It is hardly to be expected that the projectionist will be able to make the electrical connections for a motor generator, since there not only are several different makes, but more than one type of some makes ; also there are single two and three-phase current complications. It is, therefore, to be expected that the