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VOLTAGE DROP IN DIRECT CURRENT CIRCUITS A voltage drop is produced when a Current is forced through a Conductor . The conductor may be a copper Wire , or a Resistor . Passing current through a conductor, will generate heat and change the conductivity of most conductors. An increase in voltage causes an increase in current. The difference in the voltage measured across the conductor is called voltage drop. The longer the conductor, the greater the voltage drop. The greater the Resistance of the conductor, the greater the voltage drop because more voltage is required to force a given current through the conductor. Voltage is measured in “ Volt s”, current in “ Ampere s” and resistance in “ Ohms .” This relationship of the values in Direct Current circuits is expressed in the formula: VOLTAGE DROP IN ALTERNATING CURRENT CIRCUITS Alternating current is a current that continually reverses direction in a circuit. The current used in the distribution systems of the United States alternates (reverses direction)at 60 cycles per second (60 Hertz). The voltage drop in an Alternating Current (AC) circuit is the product of the current flowing through the Impedance (''Z'') of the circuit. Electrical impedance is expressed in ohms, and opposes current flow in a circuit and increases the voltage drop. Electrical impedance is a combination, (actually the vector sum) of Electrical Resistance , Capacitive Reactance , and Inductive Reactance . The voltage drop occurring in an alternating current circuit is the product of the current flowing through the impedance of the circuit and is expressed by the formula VOLTAGE DROP MEANS POWER LOSS Voltage drop in electrical wiring is not a good thing. It represents a power loss. The power loss can be substantial as the voltage drop increases. With a fixed resistance, inherent in the wire used, the power loss increases as the square of the current. This is shown mathematically by the formula: , where ''W'' is the power loss in Watt s. For this reason architects and engineers are careful to select conductors of the proper size to minimize power loss. MINIMIZING VOLTAGE DROP IN POWER TRANSMISSION Great distances often occur in Electric Power Transmission . Power is lost in the conductors all along the way. One way of reducing the lost power is to increase the conductor size and thereby reducing resistance. Another way to minimize power lost because of voltage drop is to increase the voltage. This reduces the current for a given power transmission when the resistance of the conductor remains essentially constant. When we compare the two formulae for power: and it becomes evident that for a given amount of power transmitted, the voltage drop and power loss is reduced when the voltage is decreased while the resistance remains constant. Voltage drop in household wiring In household wiring good design requires that wire size be sufficient to keep voltage drop within limits so that the wiring will not be overheated. The circuits are protected by Circuit Breakers or Fuses to prevent overheating. The National Electric Code In the United States the National Electric Code (NEC) addresses voltage drop and specifies the electrical conductor (wire) Size for a variety of conditions. SEE ALSO
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