EC&M’s Electrical Calculations Handbook - Chapter 16 ppsx

Conversion Calculations Temperature Conversion Calculations While almost all ambient temperatures in electrical engi- neering are given in degrees Fahrenheit, almost all tem- peratures of equipment operation are stated in degrees Celsius. Therefore, it is important that a quick and easy conversion method be available. Figure 16-1 shows how to make these conversions and provides a quick cross-refer- ence tool from which the conversion can be derived instantly in either direction. Frequently Used Conversion Calculations For work in the electrical industry, many other conversion calculations are encountered repeatedly. Figure 16-2 pro- vides the conversion formulas for these common conver- sions, and Fig. 16-3 is a set of typical sample calculations showing how to use the conversion formulas correctly. Each of these conversion calculations has been changed into a simple one-step calculation for ease of use. Multiple Conversion Calculations Sometimes it is necessary to multiply an item in one set of units by another item to determine an answer in a completely Chapter 16 425 v Copyright 2001 by The McGraw-Hill Companies, Inc. Click here for Terms of Use. Figure 16-1 Use these formulas and values to solve for degrees Celsius given degrees Fahrenheit or for degrees Fahrenheit given degrees Celsius. Figure 16-2 Commonly used conversion formulas. Figure 16-2 (Continued) Figure 16-2 (Continued) different set of units. When this is necessary, it is frequently expedient to multiply by “one” in the calculation to make the units come out as desired. For example, the rental cost of a diesel generator is quoted at $10 per gallon of diesel fuel used, and it is stated that the diesel engine consumes one 55- gallon (gal) barrel of fuel per 1-hour (h) running period. Determine the rental cost of the diesel generator for a 72-h running period. The cost equals the dollar rate per hour times the quantity of hours in operation: Cost ϭ $ rate per hour ϫ quantity of hours in operation 430 Chapter Sixteen Figure 16-3 Use these calculation methods with the conversion formulas of Fig. 16-2. The problem is that the dollar rate per hour is unknown and must be resolved so that the main equation can be solved. This is done simply by inserting into the main equation what is known, as follows: Cost/hour ϭϫ ϫ By setting up the equation in this manner, unwanted units cancel as shown: Cost/hour ϭϫ ϫ Thus the final rental cost of the diesel generator is deter- mined to be $550 per hour of operation. Therefore, the rental cost of the machine becomes Cost ϭ $ rate per hour ϫ quantity of hours in operation ϭ $550/h ϫ 72 h of operation ϭ $39,600 The rental cost of the machine is calculated to be $39,600. The key to this type of conversion calculation is to multiply by “one.” Multiplying anything by “one” does not change its value at all. In this calculation, the cost per hour was multi- plied by 55 gal/barrel, which is “one” because there are 55 gal in one barrel of fuel. Just as correctly, it could have been mul- tiplied by 1 barrel/55 gal, but this would not have helped with the unit manipulation in this specific equation. Other exam- ples of “one” that can be used in other equations are ■ 24 hours/day ■ 60 minutes/hour ■ 2000 pounds/ton The entire key is to insert the units that resolve the problem at hand and then determine the correct coefficients to pre- cede each unit value. 1 barrel ᎏ hour 55 gal ᎏ barrel $10 ᎏ gal 1 barrel ᎏ hour 55 gal ᎏ barrel $10 ᎏ gal Conversion Calculations 431 NOTES Ambient temperature, 165 Ampacity, cable, 154, 172 Ampere, definition, 3 Autotransformers, 275 Batteries, 8 Battery output, 14 Battery voltage, 4 Bill, electrical utility, 90 Box sizing, pull, 357 Bus bars, 132 Capacitance and voltage, 100 Capacitor bank, 103 Capacitor bank detuning, 108 Capacitors, 46, 100 Circuit breakers, 323 Clearance, working, 358 Conductors, equipment-grounding, 214 Conduit cross-sectional area, 315 Conduit fill, 314 Conduit types, 311 Conversion, units, 425 Current: alternating, 5 definition, 3 direct, 5 through impedance, 75 motor locked-rotor, 298 motor running, 295 motor starting, 291 true rms, 111 Current flow: harmonic, 111 through resistance, 16 Damage, thermal, to cable, 159 dc offset, 180 Delta systems, 60 Dirt depreciation, 235 Economics, engineering calculations, 411 Efficiency, motor, 290 Electron flow, 3 Enclosure types, 317 Expense, project, 409 Fault, 180 Filters, harmonic, 117 Footcandles, 221 Frequency, 5 Fuse curve, 320 Fuses, 321 Ground rod resistance, 208 Grounding electrode conductors, 213 Grounding functions, 205 Grounding method, 216, 218 Harmonic-related problems, troubleshooting solutions for, 120 Harmonics, 104, 114, 116 Heat flow, from cable, 168 Heat loss, from conductor, 143 Illuminance, 221, 231 Impedance, 31, 52 cable, 133, 139 Inductive reactance as function of conductor spacing, 136 Index 433 v Copyright 2001 by The McGraw-Hill Companies, Inc. 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Inrush current, motor, 293 Insulation: cable, 153, 161, 176 motor, 290 Insulators, 3 Interrupting rating, 181 Jacket, cable, 163 Kilowatthour, 80 Knockout spacing, 364 Labor, installation, 374 Lamps, 234 Lighting: indoor, 229 outdoor, 221 Load calculations: commercial building, 347 industrial facility, 349 Luminaire quantity, gross calculation, 222 Motor design code letters, 288 Motor operating characteristics, 292 Motor speed, 286 Motor voltage, 286 Motors, 285, 308 NEMA enclosures, 317 Neutral point, in wye systems, 58 Ohm’s law, 3, 15 Overcurrent devices, 319 Overcurrent protection: motor circuit, 296 transformer, 265, 276 Personnel-hour tables, installation labor, 374 Phase angle, 26 Polar-to-rectangular conversion, 70 Polarity, 6 Power, 29, 33, 79 apparent, 30, 84 in three-phase circuit, 33 true, 30 Power factor, 26, 75 Power factor correction, 87, 90, 93, 104 Power rating, resistor, 18 Q, of a reactor, 117 Raceways, 311 Reactance: cable, 139 capacitive, 46 inductive, 30, 42 Reactor, 42, 188 Reflectance, 230 Reflections, veiling, 232 Relay protective schemes: for feeder circuit breaker, 328 for large generator, 330 for large induction motor, 333 for large transformer, 331 for small generator, 329 Relays, 326 Resistance: conductor, 125, 129 definition, 4 of a ground rod, 212 internal, 8 series, 15 Resistance grounding, 217 Resistivity: conductor, 133 soil, 210 Resistor, power rating, 18 Resonant frequency, 104 rms values, 6, 23 rpm, and number of poles, 60 Service factor, motor, 289 Short-circuit current sources, 182 Short circuits, 179, 190 Skin effect, 131 Spacing, knockout, 361 Speed, motor, 286 Subtransient reactance, generator, 184 Switching, capacitor bank, 104 434 Index [...]... Temperature, ambient, 165 Temperature effect on conductor resistance, 135 Terminal, wire, 169 Thermal damage, cable, 159 Three-phase systems, 57 Torque, motor, 288 Total harmonic current distortion (THCD), 110 Total harmonic voltage distortion (THVD), 110, 116 Transformer ratings, 256 Transformers, 251 impedance % rating, 187 K-rated, 114 Transient voltage surge suppressors, 208 Trigonometry for electrical solutions,... AUTHOR John M Paschal, Jr., P.E., is a Senior Technical Electrical Engineering Specialist with Bechtel, and has held a master electrician’s license for three decades He has worked in all facets of the electrical industry He has worked “with the tools” in the electrical construction trade, as an electrical construction project manager, as chief electrical estimator for national and international construction... assistant professor, and as an electrical engineer of some of the largest and most demanding commercial, health care, and industrial electrical systems throughout the world Mr Paschal is the author of many books on practical electrical engineering and construction methods, and books dealing with the National Electrical Code He is the technical editor of EC&M Books and an author for Electrical Construction... dealing with the National Electrical Code He is the technical editor of EC&M Books and an author for Electrical Construction & Maintenance magazine Electrical Construction & Maintenance magazine, established in 1901, is the electrical industry’s premier magazine for electrical design, construction, and maintenance ... electrical solutions, 32 Triplen harmonic currents, 116 435 Vector addition, 70 Vector multiplication, 74 Vectors, 69 Voltage: definition, 1 effective, rms, 6, 23 system, 56, 271 Voltage distortion, 107 Voltage drop: cable, 140, 144 in series circuit, 17 Wire characteristics, 125 Wire size, square millimeter, 130 Wires, quantity of in raceway or cable, 165 Wiring methods, 175, 313 Withstand rating, 181 . work in the electrical industry, many other conversion calculations are encountered repeatedly. Figure 1 6-2 pro- vides the conversion formulas for these common conver- sions, and Fig. 1 6-3 is a set. Figure 1 6-1 shows how to make these conversions and provides a quick cross-refer- ence tool from which the conversion can be derived instantly in either direction. Frequently Used Conversion Calculations For. Conversion Calculations Temperature Conversion Calculations While almost all ambient temperatures in electrical engi- neering are given in degrees Fahrenheit, almost all tem- peratures of