(5) Damage to commutators can reduce the power output or cause short circuiting in direct-current motors: Loosen or remove commutator holding rings. Sprinkle carbon, graphite, or metal dust on commutators. Put a little grease or oil at the contact points of commutators. Where commutator bars are close together bridge the gaps between them with metal dust, or sawtooth their edges with a chisel so that the teeth on adjoining bars meet or nearly meet and current can pass from one to the other.
(6) Put a piece of finely grained emery paper half the size of a postage stamp in a place where it will wear away rotating brushes. The emery paper—and the motor—will be destroyed in the resulting fire.
(7) Sprinkle carbon, graphite or metal dust on slip-rings so that the current will leak or short circuits will occur. When a motor is idle, nick the slip-rings with a chisel.
(8) Cause motor stoppage or inefficiency by applying dust mixed with grease to the face of the armature so that it will not make proper contact.
(9) To overheat electric motors, mix sand with heavy grease and smear it between the stator and rotor, or wedge thin metal pieces between them. To prevent the efficient generation of current, put floor sweepings, oil, tar, or paint between them.
(10) In motors using three-phase current, deeply nick one of the lead-in wires with a knife or file when the machine is at rest, or replace one of the three fuses with a blown-out fuse. In the first case, the motor will stop after running awhile, and in the second, it will not start.
(f) Transformers
(1) Transformers of the oil-filled type can be put out of commission if you pour water, salt
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