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NORA Oilheat Technicians Manual

Chapter 8 Basic Electricity Figure 8-11: L1 and L2 point to the power source the electricity cycles 60 times a second, 120 changes of direction. The current delivers power to the load no matter which way it is flowing. The voltage goes from and returns to zero 120 times a second. A light bulb in an AC circuit glows dim and bright in just this rhythm. In a DC system, there are two kinds of electrical charges—positive and negative. Positive is also referred to as “hot” and negative as “neutral”. In an AC system, the switched line is referred to as “hot” (H) or L1 and the unswitched side is referred to as “neutral” (N) or L2. (Be careful: L2 is also labeled as the second hot leg in most electric distribution panels. The L2 referred to here is the neutral wire.) Separating electricity into two wires is called polarization. It is a way of making sure the electricity goes where it is wanted. You have probably noticed that most small appliances have a wide blade and a thin blade on their plug. There is only one way you can plug these things in. This way the appliance’s switch will control the hot wire, not the neutral wire allowing for a safe shut-off of current. If polarization is reversed in heating systems, some controls will appear to function normally, but the limit control will be interrupting the neutral. This is dangerous. 8-10 Basic Electricity Wiring diagrams Wiring diagrams are sort of like road maps or blueprints that show us how a circuit is designed. To install or service electrical equipment, you must be able to read the wiring diagram. One of the confusing things about wiring diagrams is that a complete circuit is always needed, and then the diagram starts right out with a big space between the two wires feeding the circuit. These two wires are labeled + (positive or hot) and - (negative or neutral), or as mentioned previously, they are now called L1 and L2 (line 1 and 2). All three names mean the same thing. When you see these labels, it means there is a complete circuit—without actually drawing it. If you follow L1 and L2 off to the left off the page, they go back to the circuit breaker, the main breaker, and all the way to the big transformer hanging on the pole in front of the building. From there they go all the way back to the power plant. Just remember, the arrows on L1 and L2 are pointing at the power plant, and they represent a complete circuit. Figure 8-11. L1 is the electrically charged line that causes electrical flow and L2 is the return line home. The direction of flow is from L1 to L2—from charged to uncharged— pressurized to unpressurized. Wires Wire comes in many different sizes. Wire sizes run from 0000 (4 naught, the largest) to 40 (the smallest); the lower the number, the fatter the wire. To size a wire, consider the maximum voltage rating of the wire and the amperage draw of all the loads in the circuit. The number of wires bundled together in the wire sheathing (insulating jacket) is printed on the sheathing after the wire


NORA Oilheat Technicians Manual
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