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NORA Oilheat Technicians Manual

Figure 8-17: Simple relay Movable Contact Load Fixed Contact L2 L1 Chapter 8—Basic Electricity 8-15 Spring Electromagnet To Control Circuit— Power Supply and Switches Chapter 8 Basic Electricity magnet is used to open or close a switch that is held in its normal position by a spring, see Figure 8-17. The nice thing about this kind of automatic switch is that low voltage wiring can be used for the electric magnet and the switch that sends electricity through the coil that can make or break a line voltage switch. When the low voltage remote switch (thermostat) opens, the magnetism immediately stops and the spring quickly returns the switch to its normal position. This snap action reduces arcing as the switch opens or closes. The biggest problem with relays is the contacts. Dirty or corroded contacts add resistance to the circuit, resulting in reduced voltage to the load, which can create arcing that shortens the life of the contacts. The good news is that most new relays are enclosed in plastic to keep them clean. A properly working relay will not cause any voltage drop when closed. Relays are represented in wiring diagrams as the coil of wire and the switch. The coil is usually energized by low voltage. The switch can control either a high or low voltage circuit. The working limit of the switch is determined by the amperage draw of the circuit it is controlling. Many relays are single pole double throw switches, so you might have a low voltage switch and a line voltage switch. The way to keep track of all this is to label the coil with a number and a letter like 1K. Then label the switch contacts controlled by that coil 1K1 and 1K2. Transformers Transformers use electric power at one voltage to produce an almost equal power at another voltage. In our industry transformers operate on alternating current (AC); they are made of an iron core with two separate wire coils wrapped around two sides. The coil where the electricity goes in is the primary coil, and the coil where the electricity comes out is the secondary coil. Figure 8-18. Thanks to AC, the electric field in the primary coil pulses back and forth, causing the magnetic field it creates to pulse back


NORA Oilheat Technicians Manual
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