Chapter 8 Basic Electricity For example, suppose the insulation on the wire inside a burner motor cracks and the wire is touching the motor case. If you kneel down on a damp floor to work on the burner and you touch the motor with your hand, the current could flow through your body into the floor, and over to the ground rod from the house service—a complete circuit. This is a dangerous situation. To stop this from happening, run a ground (bare copper or green) wire from the burner back to the ground rod. This pathway will offer much less resistance to the electricity than your body and the cellar floor and the current will go that way. Electricity is lazy; it will always go the easiest way, the path of least resistance. Figure 8-26. All electric codes including the NEC— National Electrical Code®—call for careful grounding. Connections from one wire to another must be enclosed in insulation. Every switch, outlet, and appliance must be protected. All these devices should be connected to each other by grounding wires connected to a rod driven 10 feet into the earth. The ground wire is the third prong on plug-in devices. To protect us, the ground wire must go from the load back to the panel without any breaks. The best way to check this is to touch one lead from your voltmeter to the either the hot or neutral wire and one to the ground wire. If the ground is good you will get the same reading as you would from hot to neutral. Stay on the lookout for potential problems When troubleshooting a circuit, electric junction boxes often must be opened. This can be dangerous. Sometimes wires from more than one circuit might be hiding in a 8-24 Basic Electricity box. If you can, try to trace all the wires going into the box to see if more than one goes back to the service panel. The goal is to shut off all the electric wires going to that box before removing the cover. If this is not possible then treat the wires in the box as if they were hot. While holding the cover plate, use an insulated screwdriver to carefully loosen the screws and ease off the plate. To test for power, use only one hand to gently pull out the wires so all connections are at least an inch apart. Unscrew the wire nuts and use your meter to test for voltage. Watch out for overcrowded junction boxes Too many wires jammed into too small a box can cause shorts. • Check for old and cracked insulation. • Confirm polarization. White wires go to silver terminals. Black goes to brass. Be sure there is only one wire hooked to each terminal. • Check armored cable connectors. The cut end of the metal cable can be sharp. To prevent the wire insulation from being cut be sure protective plastic bushings are installed at the cable ends. Safety tips The Occupational Safety and Health Administration’s (OSHA) electric safety regulations require that anyone doing electrical repairs must receive safety training. They also require that employers must adopt safe electrical work practices and that a lock out tag out must be used for hard-wired equipment that is de-energized. The key to safety is to know the dangers of electricity and how to avoid hazards.
NORA Oilheat Technicians Manual
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