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NORA Oilheat Technicians Manual

Chapter 8 Basic Electricity Broken Load You Wanted Figure 8-24: Common ohmmeter reading error, isolate the load to be tested Figure 8-25: Safely discharging a capacitor L1 L2 Load Actually Tested to Test putting out 10,000 volts and that can give you a dangerous and serious shock. Always use proper test equipment. Be sure to verify that all capacitors are fully discharged before touching or working on them. To safely discharge a capacitor you will need a 20,000 ohm 5 watt resistor, two insulated screwdrivers and two jumper wires with alligator clips on both ends. Figure 8-25. Connect one jumper wire clip to one wire of the resistor and clip the other jumper wire to the other resistor wire. Connect the clips on the Chapter 8—Basic Electricity 8-21 being tested from other paths back to the source. Do this in case there is a capacitor (a device that stores electricity) in the circuit. The ohmmeter must be zero adjusted before every test. Just touch the two test leads together creating a short circuit with zero resistance and use the zero adjustment dial. Most digital meters automatically zero adjust. If your meter will not read zero, the battery is too weak and must be replaced. To test for resistance, disconnect L1 and L2 (H and N wires) from the power source and touch the two leads on either side of the component to be tested. If there is no resistance the reading will be zero. If there is no connection between the two points the resistance will be infinity. The digital meter will read OL (overload). A reading between zero and the maximum scale setting is the resistance between the connected points. Not only must you isolate the circuit to be tested from the source, it must also be isolated from the rest of the circuit. Otherwise, you will get a false reading from the resistance of another load in a branch parallel circuit. Figure 8-24. Electrical safety Electricity can be dangerous. It can create three hazards: fire, skin burns, and shock. Shock can cause muscle spasms, unconsciousness and even death. Proper installation of all electrical equipment is essential. The National Electric Code® sets the standards. Local communities can make this code law, and in addition, they can make their own codes even more restrictive. A common, but dangerous practice, is testing the oilburner ignition transformer with a screwdriver. The transformer is


NORA Oilheat Technicians Manual
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