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Ensure all the applicable requirements of the National and Local Electrical Codesare met.
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If the voltage drop is over the desired limit, select a larger cable and repeat. Alternatively, use parallel runs of smaller cable, calculating voltage drop on the reduced current carried by each.
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For fire pump motors, check that the voltage drop does not exceed 5% @ 115% rated current; and does not equal or exceed 15% at locked rotor current, including the drop in the motor/generator.
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These calculated voltage drops represent line to line voltage drop in a 3-phase system. To estimate the single phase voltage drop, simply multiply the 3 phase line to line voltage drop by 1.16.
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In the rare instances where line to neutral voltage drop in a three phase system is required, multiply the 3 phase line to line voltage drop by 0.58.
Use the calculated load (not the fuse or breaker rating) to determine voltage drop.
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Select a cable size based on the fuse or breaker rating.
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Load current is used for voltage drop calculations, but conductor size must be chosen based on calculated ampacity with safety factors as required by code.
Conductor size must be chosen based on calculated ampacity with safety factors as required by code.
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