Calculos Electricos

Section 16
Application Data
Contents Reference Guide Table 1: Ampacities of Insulated Conductors Table 2: Correction Factors for Ambient Temperatures Table 4A: Motor Full-Load Currents of Three Phase AC Induction Type Motors Table 4B: Motor Full-Load Currents in Amperes, Single Phase AC Table 4C: Motor Full-Load Currents in Amperes, DC Table 4D: Conversion Table of Polyphase Design Table 5:Normal-Load and Fault Currents of Three Phase Transformers Table 6: Electrical Formulas for Finding Amperes, Horsepower Kilowatts, and kVA Table 7: Grounding Electrode Conductor for AC Systems Table 8: Minimum Size Grounding Conductors for Grounding Raceways and Equipment Conversion Table 16-5 16-6 16-5 16-5 16-4 16-4 16-4 16-4 16-4 16-3 16-3 16-2

16

Application Data
REFERENCE GUIDE GeneralIn the application of fusible switches and circuit breakers, consideration should be given to the following factors: 1. Voltage of circuit. 2. Ampacity of circuit. 3. Frequency of power source. 4. Operating conditions. 5. Fault current available. Voltage of Circuit — The system voltage should not exceed the listed voltage rating of the circuit breaker, fuse or switch. Ampacity of Circuit — Thelisted continuous current rating of the fuse or circuit breaker should not exceed the allowable ampacity of the conductors. Where the allowable ampacity of the conductor does not correspond to listed current ratings for fuses or circuit breakers, the next larger rating of fuse or circuit breaker is permitted providing it does not exceed the conductor ampacity by more than 25%. An exception to thisrule is permitted for motor circuits or other circuits where high inrush currents may persist for an appreciable time. Frequency of Power Source — Circuit breakers and fusible switches are calibrated for use on direct current or 48–68-Hertz alternating current. For frequencies above 62-Hertz, some fuses, switches and circuit breakers must be derated. The derating varies with each type and size ofprotective device. Consult your local representative for specific information. Operating Conditions — Molded case circuit breakers and fuses are calibrated without any enclosure as specified by the Underwriters’ Laboratories, Inc. Sound engineering practice dictates that continuous loads should not exceed 80% of the breaker or fuse current rating for most types of enclosures. Electrical Connections— Molded Case Circuit Breakers are to be connected with 60 or 75°C wire for breakers having a rated ampacity of 125 amperes or less. For circuit breakers having a rated ampacity greater 125 amperes, only 75°C cable shall be used unless otherwise indicated on the circuit breaker label. Note: Exceptions to this rule are outlined in Article 110-14-C(1) and C(2) of the 2002 National Electric Code.Conductors should be derated in accordance with the National Electrical Code for both ambient temperature and continuous loading. Table 2 on page 16-3 lists the correction factors to be applied to the allowable current-carrying capacities of conductors for application in temperatures above 30°C. Conductors which are loaded continuously should be derated to 80% of their allowable currentcarryingcapacity except when supplied by an assembly including its overcurrent device that is listed for continuous operation at 100% of its rating. When the type of load is unusual, intermittent, or one which involves momentary peak currents such as motor loads, consideration should be given to the heating effect on the protective device over a period of time. The duty cycle of a motor which is started andstopped frequently may require a circuit breaker or fuses with a higher rating than an infrequently started motor. The presence of excessive dust, moisture, corrosive fumes, or explosive atmosphere requires the use of enclosures suitable for such atmospheres. For applications in regions where fungus growth may occur, some circuit breakers should be treated with a fungus and moisture resistant...