What are two advantages to a single-phase, three-wire system?
What will be an ideal response?
1. The system provides two different voltages. The lower voltage supplies lighting and small-appliance loads, and the higher voltage supplies heavy-appliance and single-phase motor loads.
2. There are 240 V across the outside wires. Thus, the current for a given kilowatt load can be reduced by nearly half if the load is balanced between the neutral and the two outside wires. Because of the reduction in the current, the voltage drop in the circuit conductors is reduced, and the voltage at the load is more nearly constant. In addition, the following problems are minimized: dim lights, slow heating, and unsatisfactory appliance performance.
3. A single-phase, three-wire, 120/240-V system uses 37% less copper as compared to a 120-V, two-wire system having the same capacity and transmission efficiency. Problem 6 shows why less copper is needed in such a single-phase, three-wire circuit.
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Explain what the weathering index (WI) means and how it relates to building construction.
What will be an ideal response?
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