The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Practical Electricity And House Wiring
Other examples could be given but this will suffice to show the extreme importance of proper grounding. High voltage wires do not fall across low voltage wires every day, nor do people often touch live wires, but when these things do happen, grounding is insurance that the actual danger be reduced to a minimum.
All this covers the theory of grounding; the actual methods employed will be covered in another chapter.
Equipment Grounding.—In addition to grounding the neutral wire in a system, it is customary on electrical machinery such as motors, generators, etc., to ground the metal frames and other parts which ordinarily do not carry electricity. The object of this is safety. Assume that a motor is located in a dry spot, but above damp ground. Assume further that a defect occurs inside the motor, so that part of the bare copper of the windings touches the metal framework of the motor. The motor will continue to operate normally, if the frame is not grounded.
If the frame is not grounded, anyone standing on the damp ground and touching the frame of the defective motor will complete the circuit through his own body and will have 115 or 230 volts impressed upon it, a definitely dangerous situation.
If, however, the frame is grounded and the motor is protected by the proper size of fuse, the fuse will blow when the windings become grounded. If it did not blow, anyone touching the frame and standing also on the damp ground would not be in danger—the ground and the frame of the motor would be at the same voltage.
Make it a practice to ground the frames of all electric motors, heaters, and similar equipment in general, especially on farms or other locations where, in touching the equipment, one would be standing on moist floors or the ground. Use a white wire at least as heavy as the wires serving the device, connect it to ground, using a ground rod or pipe, as will be explained later. Protect the ground wire well mechanically so that it cannot accidentally get knocked off.
Continuity of Ground.—In conduit and armored cable wiring, it is a definite object of the conduit and the metal armor not only to protect the wires from mechanical injury, but to completely encircle the "hot" wires with a grounded metal sheath. If then a black wire, for example, had its insulation frayed, and touched the conduit or pipe, it would be the same as a direct short circuit between the black wire and the white wire (because the white wire and conduit or armor are connected to each other through ground). Upon the wires short-circuiting, a fuse would blow disconnecting that wire from the source of electricity.
