Electrical Design
Most pipe line facilities are electrical equipment of some sort or another, ranging from simple power circuits of a few amperes capacity to sophisticated supervisory control and data acquisition systems. it is beyond the scope of this manual to provide a complete section on electrical information for pipe line facilities. This section is intended to
provide some basic data that will prove useful to field personnel responsible for electrical installations.
Electric Motor Selection
Based on known facts and calculations, the best selection is made after a close study of the installation, operation and servicing of the motor. Basic steps in proper selection are numbered 1 through 8 and are briefly described.
1. Power Supply
(a) Voltage - NEMA has recommended the following standards.
Nominal Power System Volts Motor Nameplate Volts 240 230 480 460 600 575
(b) Frequency - Motors rated 200 horsepower or less can vary not to exceed 5 percent above or below its rated frequency.
(c) Phases - Three-phase power supplies are found in most industrial locations; for most residential and rural areas, only single-phase power is available.
2. HP and Duty Requirements
(a) Continuous duty - means constant load for an indefinite period (about 90 percent of all motor applications).
(b) Intermittent duty - means alternate periods of load and no-load, or load and rest. (c) Varying duty - means both the load and time operation vary to a wide degree.
3. Speeds - Single speed motors are the most common, but when a range of speeds is
required multispeed motors will give 2, 3 or 4 fixed speeds.
4. Service Factors - Open, general purpose motors have a service factor depending upon
the particular rating of the motor (usually between 1.15 and 1.25).
5. Selection of Motor Type
There are three main types:
(a) DC motors are designed for industrial drives requiring a controlled speed range and constant torque output on adjustable voltage control systems. Because the speed of rotation controls the flow of current in the armature, special devices must be used for starting DC motors.
(b) Single phase alternating-current motors also require some auxiliary arrangement to start rotation.
(c) Polyphase motors are alternating-current types (squirrel cage or wound rotor). Applications - Some driven machines require a low-starting torque which gradually increases to full-load speed; others require higher-staring torque. NEMA code letters A, B, C, D, etc., on the motor nameplate designate the locked-rotor kVaper horsepower of that particular motor design. The diagram shows representative speed-torque curves for polyphase and single-phase NEMA design motors Types A through D.
6. Torque Definitions
(a) Locked rotor torque, or "starting torque" is the minimum-torque which the motor will develop at rest for all angular positions of the rotor.
(b) Breakdown torque is the maximum-torque at rated voltage and frequency without abrupt speed drop.
(c) Full-load-torque is the torque necessary to produce rated horsepower at full-load speed.
(d) Locked-rotor current is the steady-state current of the motor with the rotor locked at rated voltage and frequency.
Code Ltr Locked RotorkVA/hP
A 0 - 3.14 B 3.15 - 3.54 C 3.55 - 3.99 D 4.0 - 4.49 E 4.5 - 4.99 F 5 - 5.59
7. Selection of Enclosure - The two general classifications are open, which permits
passage of air over and around the windings; and totally-enclosed, which prevents exchange of air between inside and outside of frame (but is not strictly airtight).
(a) Open Drip-Proof - means that liquid or solid particles falling on the motor at an angle not greater than 15 degrees from vertical cannot enter the motor.
(b) NEMA Type 1 - A weather protected machine with its ventilating passages
constructed to minimize the entrance of rain, snow and airborne particles to the electric parts and having its ventilating openings so constructed to prevent the passage of a cylindrical rod 3/4 in. in diameter.
(c) NEMA Type II - A weather protected machine which has in addition to the enclosure defined for a Type I weather-protected machine, its ventilating passages at both intake and discharge so arranged that high velocity air and airborne particles blown into the machine by storms or high winds can be discharged without entering the internal
ventilating passages leading directly to the electric parts of the machine itself. The normal path of the ventilating air which enters the electric parts of the machine shall be so
arranged by baffling or separate housings as to provide at least three abrupt changes in direction, none of which shall be less than 90 deg. In addition, an area of low velocity, not exceeding 600 ft/min., shall be provided in the intake air path to minimize the possibility of moisture or dirt being carried into the electric parts of the machine.
(d) Totally Enclosed Non-Vent means that a motor is not equipped for cooling at external means.
(e) Totally Enclosed Fan-Cooled means the motor has a fan integral with the motor but not external to the enclosed parts.
(f) Explosion-Proof means the enclosure is designed to withstand an explosion of a specified gas which may occur within the motor and to prevent the ignition of gas around the motor.
8. End Shield Mountings - Three types of end shields with rabbets and bolt holes for
mounting are standard in the industry:
(a) Type C Face provides a male rabbet and tapped holes.
(b) Type D Flange has a male rabbet with holes for through bolts in the flange.
(c) Type P base has a female rabbet and through bolts for mounting in the flange (used for mounting vertical motors).
Hazardous Locations
Definition of Class Locations
Reprinted with permission from NFPA 70-1990, the National Electrical Code®, Copyright© 1989, National Fire Protection Association, Quincy, MA 02269. This
reprinted material is not the complete and official position of the National Fire Protection Association, on the referenced subject which is represented only by the standard in its entirety.
The National Electrical Code and NEC are registered trademarks of the NFPA.
500-5. Class I Locations. Class I locations are those in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures. Class I locations shall include those specified in (a) and (b) below.
(a) Class I, Division 1. A Class I, Division 1 location is a location: (1) in which ignitable concentrations of flammable gases or vapors can exist under normal operating conditions; or (2) in which ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or (3) in which breakdown or faulty operation of equipment or processes might release ignitable
concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment.
(FPN): This classification usually includes locations where volatile flammable liquids or liquefied flammable gases are transferred from one container to another; interiors of
spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used; locations containing open tanks or vats of volatile
flammable liquids; drying rooms or compartments for the evaporation of flammable solvents; locations containing fat and oil extraction equipment using volatile flammable solvents; portions of cleaning and dyeing plants where flammable liquids are used; gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape; inadequately ventilated pump rooms for flammable gas or for volatile flammable liquids; the interiors of refrigerators and freezers in which volatile flammable materials are stored in open, lightly stoppered, or easily ruptured containers; and all other locations where ignitable concentrations of flammable vapors or gases are likely to occur in the course of normal operations.
(b) Class I, Division 2. A Class I, Division 2 location is a location: (1) in which volatile flammable liquids or flammable gases are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems, or in the case of abnormal operation of equipment; or (2) in which ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operation of the ventilating equipment; or (3) that is adjacent to a Class I, Division 1 location, and to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.
(FPN No. 1): This classification usually includes locations where volatile flammable liquids or flammable gases or vapors are used, but which, in the judgment of the authority having jurisdiction, would become hazardous only in case of an accident or of some unusual operating condition. The quantity of flammable material that might escape in case of accident, the adequacy of ventilating equipment, the total area involved, and the record of the industry or business with respect to explosions or fires are all factors that merit consideration in determining the classification and extent of each location. (FPN No. 1): Piping without valves, checks, meters, and similar devices would not ordinarily introduce a hazardous condition even though used for flammable liquids or gases. Locations used for the storage of flammable liquid or of liquefied or compressed gases in sealed containers would not normally be considered hazardous unless subject to other hazardous conditions also.
Group A: Atmospheres containing acetylene.
Group B: Atmospheres containing hydrogen, fuel and combustible process gases
containing more than 30 percent hydrogen by volume, or gases or vapors of equivalent hazard such as butadiene,* ethylene oxide,** propylene oxide,** and acrolein.**
Group C: Atmospheres such as cyclopropane ethyl ether, ethylene, or gases or vapors of
equivalent hazard.
Group D: Atmospheres such as acetone, ammonia,*** benzene, butane, ethanol,
gasoline, hexane, methanol, methane, natural gas, naphtha, propane or gases of vapors of equivalent hazard.
* Group D equipment may be used for this atmosphere if such equipment is isolated in accordance with Section 501-5(a) by sealing all conduit 1/2-inch or larger.
** Group C equipment may be used for this atmosphere if such equipment is isolated in accordance with Section 501-5(a) by sealing all conduit 1/2-inch or larger.
*** For classification of areas involving ammonia atmosphere, see Safety Code for Mechanical Refrigeration, ANSI/ASHRAE 15-1978, and Safety Requirements for the Storage and Handling of Anhydrous Ammonia, ANSI/CGA G2.1-1981.
NEMA Enclosure Types
1Nonhazardous Locations
Type Intended Use and Description
1 Enclosures are intended for indoor use primarily to provide a degree of protection against limited amounts of falling dirt.
2 Enclosures are intended for indoor use primarily to provide a degree ofprotection against limited amounts of falling water and dirt. 3 Enclosures are intended for outdoor use primarily to provide a degree ofprotection against rain, sleet, and damage from external ice formation. 3R Enclosures are intended for outdoor use primarily to provide a degree ofprotection against rain, sleet, and damage from external ice formation.
3S
Enclosures are intended for outdoor use primarily to provide a degree of protection against rain, sleet, windblown dust,
and to provide for operation for external mechanisms when ice laden. 4 Enclosures are intended for indoor or outdoor use primarily to providea degree of protection against windblown dust and rain, splashing water,
hose-directed water and damage from external ice formation.
4X Enclosures are intended for indoor or outdoor use primarily to providea degree of protection against corrosion, windblown dust and rain,
5 Enclosures are intended for indoor use primarily to providea degree of protection against settling airborne dust, falling dirt, and dripping noncorrosive liquids.
6
Enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against hose-directed water, the entry of water during occasional temporary submersion at a limited depth, and damage from external ice formation.
6P
Enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against hose-directed water, the entry of water during prolonged submersion at a limited depth, and damage
from external ice formation. 12
Enclosures are intended for indoor use primarily to provide a degree of protection against circulating dust,
falling dirt, and dripping noncorrosive liquids. 12K
Enclosures with knockouts are intended for indoor use primarily to provide a degree of protection against circulating dust, falling dirt,
and dripping noncorrosive liquids. 13
Enclosures are intended for indoor use primarily to provide a degree of protection against dust, spraying of water, oil and noncorrosive coolant.
Hazardous (Classified Locations)
7 Enclosures are intended for indoor use in locations classifiedas Class I, Groups A, B, C or D, as defined in the National Electrical Code. 8 Enclosures are intended for indoor use in locations classifiedas Class I, Groups A, B, C, or D, as defined in the National Electrical Code. 9 Enclosures are intended for indoor use in locations classifiedas Class II, Groups E, F, or G, as defined in the National Electrical Code. 10Enclosures are constructed to meet the applicable requirementsof the Mine Safety and Health Administration.
Reference NEMA Standards Publications/No. 250-119
Used with permission - National Electrical Manufacturer's Association.
A power plant must be properly sized for the required load. Electric motors are
particularly difficult for portable plants since they require 2 to 3 times motor nameplate amps or wattage.
A portable power plant's surge capacity is limited by engine horsepower and inertia of its rotating parts. Thus, a current surge of short duration can be supplied by a power plant, but a current demand of longer duration such as a heavily loaded motor starting at a high inertia load, can overload the power plant and possibly damage the power plant and the motor. A 3450 rpm air compressor is a prime example of this type of load.
Example:
Load Requirements:
Electric Heater - 1,000 watts 11 - 100 watt lamps - 1,100 watts Motor - 600 watts
Total motor load = 600 x 3 = 1,800 watts Total other load = 2,100 watts
Total load = 3,100 watts
Add 25% for future = 975 watts
Total load for sizing power plant = 4,875 watts
A generator capable of supplying 5,000 watts continuously will be adequate.
When more than one motor is connected to a power plant, always start the largest motor first. If the total load is connected to one receptacle on the power plant, be sure the ampere rating of the receptacle is not exceeded.
Typical Wattages for Tools and Appliances
1/2" drill 1,000 1" drill 1,100 6" circular saw 800 10" circular saw 2,000 14" chain saw 1,100 Radio 50 to 200 Television 200 to 500 Toaster, coffeemaker 1,200
Water heater (storage type) 1,100 to 5,500 Hot plate or range (per burner) 1,000
Range oven 10,000 Skillet 1,200 Fan 50 to 200 Floodlight 1,000 Water pump 500 Vacuum cleaner 200 to 300 Refrigerator (conventional) 200 to 300 Refrigerator (freezer-combination) 250 to 600 Furnace fan (blower) 500 to 700
Knockout Dimensions
Size Dia. Ins. Ins. Min. Nominal Max. 1/2 0.859 0.875 0.906 3/4 1.094 1.109 1.141 1 1.359 1.375 1.406 1-1/4 1.719 1.734 1.766 1-1/2 1.958 1.984 2.016 2 2.433 2.469 2.500 2-1/2 2.938 2.969 3.000 3 3.563 3.594 3.625 3-1/2 4.063 4.125 4.156 4 4.563 4.641 4.672 5 5.625 5.719 5.750 6 6.700 6.813 6.844 Reference NEMA Standards Publications/No. 250-1991
Used with permission - National Electrical Manufacturer's Association.
Table 430-150. Full Load Current*
Three-Phase Alternating Motors Induction Type
Squirrel-Cage and Wound-Rotor Amperes
Synchronous Type **Unity Power Factor
Amperes HP 115V 200V 208V 230V 460V 575V 2300V 230V 460V 575V 2300V 1/2 4 2.3 2.2 2 1 0.8 --- --- --- --- --- 3/4 5.6 3.2 3.1 2.8 1.4 1.1 --- --- --- --- --- 1 7.2 4.1 4.0 3.6 1.8 1.4 --- --- --- --- --- 1-1/2 10.4 6.0 5.7 5.2 2.6 2.1 --- --- --- --- --- 2 13.6 7.8 7.5 6.8 3.4 2.7 --- --- --- --- --- 3 --- 11.0 10.6 9.6 4.8 3.9 --- --- --- --- --- 5 --- 17.5 16.7 15.2 7.6 6.1 --- --- --- --- --- 7-1/2 --- 25.3 24.2 22 11 9 --- --- --- --- --- 10 --- 32.2 30.8 28 14 11 --- --- --- --- --- 15 --- 48.3 46.2 42 21 17 --- --- --- --- --- 20 --- 62.1 59.4 54 27 22 --- --- --- --- --- 25 --- 78.2 74.8 68 34 27 --- 53 26 21 --- 30 --- 92 88 80 40 32 --- 63 32 26 --- 40 --- 119.6 114.4 104 52 41 --- 83 41 33 --- 50 --- 149.5 143.0 130 65 52 --- 104 52 42 --- 60 --- 177.1 169.4 154 77 62 16 123 61 49 12 75 --- 220.8 211.2 192 96 77 20 155 78 62 15 100 --- 285.2 272.8 248 124 99 26 202 101 81 20 125 --- 358.8 343.2 312 156 125 31 253 126 101 25 150 --- 414 396.0 360 180 144 37 302 151 121 30 200 --- 552 528.0 480 240 192 49 400 201 161 40 * These values of full-load current are for motors running at speeds usual for belted motors and motors with normal torque characteristics. Motors built for especially low speeds or high torques may require more running current, and multispeed motors will have full-load current varying with speed, in which case the nameplate current rating shall be used.
** For 90 and 80 percent power factor the above figures shall be multiplied by 1.1 and 1.25 respectively
The voltages listed are rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 to 120, 220 to 240, 440 to 480, and 550 to 600 volts.
Table 310-16. Ampacities of Insulated Conductors Rated 0-2000 Volts, 60° to 90° C (140° to 194° F)
Not More Than Three Conductors in Raceway or Cable or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F)
Size Temperature Rating of Conductor Size
60°C (140°F) 75°C (167°F) 85°C (185°F) 90°C (194°F) 60°C (140°F) 75°C (167°F) 85°C (185°F) 90°C (194°F) AWG kcmii Types *TW, *UF Types *FEPW, *RF, *RHW, *THHW, *THW, *THWN, *XHHW, *USE, *ZW Type V TA, TBS, Types SA, S/S, *FEP, *FEPB, IRHH, *THHN, *THHW, *XHHW Types *TW, *UF Types *RH, *RHW, *THHW, *THW, *THWN, *XHHW, *USE Type V TA, TBS, Types SA, S/S, *RHH, *THHW, *THHN, *XHHW AWG kcmii
Copper Aluminum or Copper-Clad Aluminum
18 --- --- --- 14 --- --- --- --- --- 16 --- --- 18 18 --- --- --- --- --- 14 20* 20* 25 25* --- --- --- --- --- 12 25* 25* 30 30* 20* 20* 25 25* 12 10 30 35* 40 40* 25 30* 30 35* 10 8 40 50 55 55 30 40 40 45 8 6 55 65 70 75 40 50 55 60 6 4 70 85 95 95 55 65 75 75 4 3 85 100 110 11 65 75 85 85 3 2 95 115 125 130 75 90 100 100 2 1 110 130 145 150 85 100 110 115 1 1/0 125 150 165 170 100 120 130 135 1/0 2/0 145 175 190 195 115 135 145 150 2/0 3/0 165 200 215 225 130 155 170 175 2/0 4/0 195 230 250 260 150 180 195 205 4/0
250 215 255 275 290 170 205 220 230 250 300 240 285 310 320 190 230 250 255 300 350 260 310 340 350 210 250 270 280 350 400 280 335 365 380 225 270 295 305 400 500 320 380 415 430 260 310 335 350 500 600 355 420 460 475 285 340 370 385 600 700 285 460 500 520 310 375 405 410 700 750 400 475 515 535 320 385 420 435 750 800 410 490 535 555 330 395 430 450 800 900 435 520 565 585 355 425 465 480 900 1000 455 545 590 615 375 445 485 500 1000 1250 495 590 640 665 405 485 525 545 1250 1500 520 625 680 705 435 520 565 585 1500 1750 545 650 705 735 455 545 595 615 1750 2000 560 665 725 750 470 560 610 630 2000
AMPACITY CORRECTION FACTORS Ambient
Temp. °C
For ambient temperatures other than 30°C (86°F), multiply the ampacities shown above by the appropriate factor shown below.
Ambient Temp. °F 21-25 1.08 1.05 1.04 1.04 1.08 1.05 1.04 1.04 70-77 26-30 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 79-86 31-35 0.91 0.94 0.95 0.96 0.91 0.94 0.95 0.96 88-95 36-40 0.82 0.88 0.90 0.91 0.82 0.88 0.90 0.91 97-104 41-45 0.71 0.82 0.85 0.87 0.71 0.82 0.85 0.87 106-113 46-50 0.58 0.75 0.80 0.82 0.58 0.75 0.80 0.82 115-122 51-55 0.41 0.67 0.74 0.76 0.41 0.67 0.74 0.76 124-131 56-60 --- 0.58 0.67 0.71 --- 0.58 0.67 0.71 133-140 61-70 --- 0.33 0.52 0.58 --- 0.33 0.52 0.58 142-158 71-80 --- --- 0.30 0.41 --- --- 0.30 0.41 160-176
*Unless otherwise specifically permitted elsewhere in this Code, the overcurrent protection for conductor types marked with an asterisk (*) shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG copper; or 15 amperes for 12 AWG and 25 amperes for 10 AWG aluminum and copper-clad aluminum after any correction factors for ambient temperature and number of conductors have been applied.
Reprinted with permission from NFPA 70-1990, The National Electrical Code®, Copyright© 1988, National Fire Protection Association, Quincy, MA 02269. This
reprinted material is not the complete and official position of the National Fire Protection Association, on the referenced subject which is represented only by the standard in its entirety.
Tables 4 and 5 give the nominal size of conductors and conduit or tubing for use in computing size of conduit or tubing for various combinations of conductors. The
dimensions represent average conditions only, and variations will be found in dimensions of conductors and conduits of different manufacture.
Electrical Formulas
Single Phase kVA = VA/1,000 hp = (VA x eff x PF) / 746 kw = (VA x PF) / 1,000 PF = kW / kVA Torque (ft-lb) = hp x 5,250 / rpm Motor kVA = (hp x 0.746) / eff x PF Motor kW = (hp x 0.746) / eff where:V = Line-to-line volts A = Amperes
eff = Efficiency (decimal) PF = Power Factor (decimal) kVA = Kilovolt amperes kW = Kilowatts
hp = Horsepower
rpm = Revolutions per minute
Three Phase
(31/2 V x A) / 1,000 (31/2 VA x PF x eff) / 746 (31/2 VA x PF) / 1,000 (kW x 1,000) / 31/2 x VA
Motor Controller Sizes
Polyphase Motors
Maximum Horsepower Full Voltage Starting NEMA Size 230 Volts 460-575 Volts
00 1.5 2 0 3 5 1 7.5 10 2 15 25 3 30 50 4 50 100 5 100 200 6 200 400 7 300 600
Single Phase Motors
Maximum Horsepower Full Voltage Starting (Two Pole Contactor) NEMA Size 115 Volts 230 Volts
00 1.3 1
0 1 2
1 2 3
2 3 7.5
3 7.5 15
Voltage Drop on Circuits Using 600 V. Copper
Conductors in Steel Conduit
To determine the voltage drop, multiply the length in feet of one conductor by the current in amperes and by the number listed in the table for the type of system and power factor and divide the result by 1,000,000 to obtain the voltage loss. This table takes into
consideration reactance on AC circuits and resistance of the conductor. Unless otherwise noted, the table is based on 60 Hz.
Determine the Most Economical Size for Electric Power
Conductors
To calculate quickly the most economical size copper wire for carrying a specified current load, use the formula:
where
A = Conductor cross-sectional area (circular mils) I = Current load amperes
Ce = Cost of electrical power (cents per KWH) Cc = Cost of copper (cents per lb)
t = Hours of service per year
F = Factor for fixed charges (amortization, insurance, taxes, etc.)
Selection of the proper size electric conductor will depend on the load to be carried and the mechanical strength required, as well as economics. Once these are considered, the most economical size conductor is that for which the annual energy cost equals the copper cost. This method can be used for other metallic conductors.
Example. Determine the most economical size copper conductor for an installation
operating 365 days a year, 8 hours per day, with a 100 ampere load. Energy costs are $0.00875 per KWH. Fixed charges are 23 percent, considering a five-year amortization with 3 percent for insurance and taxes. Copper costs $0.46 per lb.
= 92,500 circular mils
How to Find the Resistance and Weight of Copper
Wires
It is easy to calculate mentally the approximate resistance and weight of standard sizes of copper wires, by remembering the following rules:
Rule 1: Number 10 wire has a resistance of 1 ohm per thousand ft. Number 2 wire weighs 200 lb per thousand ft.
Rule 2: An increase of ten numbers in the size is an increase of ten times in the resistance, and a decrease to one-tenth of the weight.
Rule 3: An increase of three numbers in the size doubles the resistance and halves the weight.
Rules 4: An increase of one number in the size multiples the resistance by 5/4 and the weight by 4/5.
Always proceed from the known value (No. 10 for resistance, No. 2 for the weight) in the smallest number of jumps; that is, go by tens, then by threes, and finally by ones; the jumps do not all have to be in the same direction.
Example. What is the weight and resistance of 200 ft of No. 18? Apply the rules in order,
as follows; resistance first:
Number 10 wire has a resistance of 1 ohm per thousand ft. (Rule 1) Number 20 wire has a resistance of 10 ohms per thousand ft (Rule 2) Number 17 wire has a resistance of 5 ohms per thousand ft. (Rule 3) Number 18 wire has a resistance of 6.25 ohms per thousand ft. (Rule 4) Number 18 wire has a resistance of 1.25 ohms per 200 ft. Answer. Number 2 wire weighs 200 lb per thousand ft. (Rule 1)
Number 12 wire weighs 20 lb per thousand ft. (Rule 2) Number 22 wire weighs 2 lb per thousand ft. (Rule 2) Number 19 wire weighs 4 lb per thousand ft. (Rule 3) Number 18 wire weighs 5 lb per thousand ft. (Rule 4) Number 18 wire weighs 1 lb per 200 ft. (Answer)
The weight determined by the above rules is that of bare copper wire. Weight of insulated wire varies widely according to the type of insulation. Resistance values are correct for
bare or insulated wire, and for solid or stranded. Errors resulting from the use of the rules will rarely exceed 2 percent.
What You Should Remember About Electrical
Formulas
Ohm's Law
Easily Remember It, or E = RI Power
DC Power Is Easy, or P = IE
It Really Is, or P = IRI = I2R
Other Facts
The number of watts in a hp is equal to the year Columbus discovered American divided by two, or 1492/2 = 746 watts/hp.
The horsepower of a reciprocating engine necessary to drive a three phase, 60 cycle
electric generator can be determined by multiplying KW by 1.5.
Rule. Excluding obstructions such as hills, etc., the microwave (line-of-sight) distances
between two towers will be twice the distance from the transmitter to the horizon. The line-of-sight distance in miles from the top of the tower to the horizon can be found by adding the square root of the tower height to the square root of the first square foot (the latter of course is the fourth root).
Example. How far apart can 100-foot-high towers be spaced to provide line-of-sight
transmission if there are no obstructions between them? X = sqrt(100) + sqrt(10)
X = 10 + 3 + or 13 miles
Distance between towers can be 2X or 26 miles.
This same formula can be used to estimate distances in an airplane.
Example. How far the line-of-sight distance to the horizon in an airplane flying at an
altitude of 4,900 ft? (sqrt(4,900) = 70)
X = sqrt(4,900) + sqrt(70) X = 70 + 8
Distance to horizon is 78 miles.
For Quick Determination of the Horsepower per
Ampere for Induction Motors (3 phase) at Different
Voltages.
Voltage hp per ampere
480 1
2,400 5
Chart Gives Electric Motor Horsepower for Pumping
Units
This chart provides a means of determining the power requirements for a beam pumping installation powered by an electric motor based on a fluid with a specific gravity of one, with fluid at the pump. The power requirement determined by the chart includes a mechanical efficiency factor of 0.45 and a cyclic factor of 0.75, which factors are frequently applied to motors used in sucker rod pumping service.
An arrangement is available for correcting the power requirement in the case of an underloaded pumping unit. The example shown in the chart is self-explanatory. After the power requirements are determined from the chart the next higher size of commercially available motor is used.
Pumping Stations
Table gives capacitor multipliers for kilowatt loads for different desired power factor improvements.
Original Power Factor, Percent Desired Power Factor-Percent 100 95 90 85 80 50 1.732 1.403 1.248 1.112 0.982 51 1.687 1.358 1.203 1.067 0.937 52 1.643 1.314 1.159 1.023 0.893 53 1.600 1.271 1.116 0.980 0.850 54 1.559 1.230 1.075 0.939 0.809 55 1.518 1.190 1.035 0.898 0.769 56 1.480 1.151 0.996 0.860 0.730 57 1.442 1.113 0.958 0.822 0.692 58 1.405 1.076 0.921 0.785 0.655 59 1.369 1.040 0.885 0.749 0.619 60 1.333 1.004 0.849 0.713 0.583 61 1.299 0.970 0.815 0.679 0.549 62 1.266 0.937 0.782 0.646 0.516 63 1.233 0.904 0.749 0.613 0.483 64 1.201 0.872 0.717 0.581 0.451 65 1.169 0.840 0.685 0.549 0.419 66 1.138 0.809 0.654 0.518 0.388 67 1.108 0.779 0.624 0.488 0.358 68 1.078 0.749 0.594 0.458 0.328
69 1.049 0.720 0.565 0.429 0.299 70 1.020 0.691 0.536 0.400 0.270 71 0.992 0.663 0.508 0.372 0.242 72 0.964 0.635 0.480 0.344 0.214 73 0.936 0.607 0.452 0.316 0.186 74 0.909 0.580 0.425 0.289 0.159 75 0.882 0.553 0.398 0.262 0.132 76 0.855 0.526 0.371 0.235 0.105 77 0.829 0.500 0.345 0.209 0.079 78 0.802 0.473 0.318 0.182 0.052 79 0.776 0.447 0.292 0.156 0.026 80 0.750 0.421 0.266 0.130 --- 81 0.724 0.395 0.240 0.104 --- 82 0.698 0.369 0.214 0.078 --- 83 0.672 0.343 0.188 0.052 --- 84 0.646 0.317 0.162 0.026 --- 85 0.620 0.291 0.136 --- --- 86 0.593 0.264 0.109 --- --- 87 0.567 0.238 0.083 --- --- 88 0.540 0.211 0.056 --- --- 89 0.512 0.183 0.028 --- --- 90 0.484 0.155 --- --- --- 91 0.456 0.127 --- --- --- 92 0.426 0.097 --- --- --- 93 0.395 0.066 --- --- --- 94 0.363 0.034 --- --- --- 95 0.329 --- --- --- --- 96 0.292 --- --- --- --- 97 0.251 --- --- --- --- 98 0.203 --- --- --- --- 99 0.143 --- --- --- ---
Example: Assume total plant load is 100 kw at 60 percent power factor. Capacitor kvar
rating necessary to improve power factor to 80 percent is found by multiplying kw (100) by multiplier in table (0.583), which gives kvar (58.3). Nearest standard rating (60 kvar) should be recommended.
Floodlighting Concepts
Terms
Candela or Candlepower - Light sources do not project the same amount of light in every direction. The directional characteristic of a lamp is described by the candlepower in specific directions. This directional strength of light or luminous intensity is measured in candelas.
Lumin - Light quantity, irrespective of direction, is measured in lumens. Lamp lumens are the quantity of light produced by a lamp. Average light level calculations use total lamp lumens as a basis and then adjust for all factors that lower this quantity. The amount of useful light in a floodlight beam is measured in beam lumens.
Footcandle, fc - Specifications are usually based on density of light or level of
illumination which is measured in footcandles. Footcandles are the ratio of quantity of light in lumens divided by the surface area in square feet on which the lumens are falling. A density of one lumen per square foot is one footcandle. One footcandle is equal to 10.76 lux.
Lux, lx - The SI unit of illuminance. This metric measurement is based upon the density of lumens per unit surface area similar to footcandle, except one lux is one lumen per square meter. One lux is equal to 0.09 footcandle.
Light Loss Factor, LLF - These factors are used to adjust lighting calculations from laboratory test conditions to a closer approximation of expected field results. The I.E.S. Lighting Handbook, 1984 Reference Volume, defines LLF as follows: "a factor used in calculating illuminance after a given period of time and under given conditions. It takes into account temperature and voltage variations, dirt accumulations on luminaire and room surfaces, lamp depreciation, maintenance procedures and atmosphere conditions."
Floodlighting encompasses many variations. Since the location of the floodlight relative to the object to be lighted can be in any plane and at any distance from the source ... floodlighting application is often considered the most complex and difficult of all light techniques.
The most commonly used systems for floodlight calculations are the point-by-point method and the beam-lumen method.
Point-by-point Method
The point by point method permits the determination of footcandles at any point and orientation on a surface and the degree of lighting uniformity realized for any given set of conditions.
In such situations, the illumination is proportional to the candlepower of the source in a given direction, and inversely proportional to the square of the distance from the source. See Figure 1.
Footcandles on Plane (Normal to Light Ray) = Candlepower of Light Ray / Distance in Feet from Source to Point-Squared
E = I / D2
When the surface on which the illumination to be determined is tilted, the light will be spread over a greater area, reducing the illumination in the ratio of the area of plane A to the area of plane B as shown in Figure 2. This ratio is equal to the cosine of the angle of incidence; thus:
Footcandles on Plane B = Candlepower of Light Ray / Distance in Feet from Source to Point-Squared
x Cosine of Angle beta E = (I / D2) x Cosine(beta)
Then beta equals the angle between the light ray and a perpendicular to the plane at the point.
Beam-lumen Method
The beam-lumen method is quite similar to the method used for interior lighting except that the utilization factors must take into consideration the fact that floodlights are not usually perpendicular to the surface and therefore not all of the useful light strikes the surface.
Beam lumens are defined as the quantity of light that is contained within the beam limits as described as "beam spread." Beam lumens equal the lamp lumens multiplied by the beam efficiency of the floodlight.
Coverage. It is recommended that sufficient point-by-point calculations be made for each job to check uniformity and coverage.
Light Loss Factor (LLF). The maintenance or light loss factor is an allowance for
depreciation of lamp output with age and floodlight efficiency due to the collection of dirt on lamp, reflector, and vover glass. The total factor may vary from 0.65 to 0.85
depending on the type of lamp and luminaire used and may include losses due to lamp orientation, or "tilt."
Beam-lumen Method
Step 1 - Determine the level of illumination. See Table 1 for some typical levels of illumination (fc). The basic formula is:
fc = (N x BL x CBU x LLF) / A where
N = quantity of luminaires A = area in square feet BL = beam lumens
CBU = Coefficient of beam utilization LLF = Light loss factor
Step 2 - Determine type and location of floodlights. Regardless of light source there are industry standards on beam spreads. See Table 2.
Step 3 - Determine the coefficient of beam utilization. This factor, CBU, written as a decimal fraction, is expressed in the following ratio:
The exact CBU can be determined graphically by projecting the outline of the are to be lighted upon the photometric data and totaling the utilized lumens. This procedure is detailed in the I.E.S. Lighting Handbook. See Table 3.
As an approximation, the average CBU of all the floodlights in an installation should fall within the range of 0.6 to 0.9. If less than 60% of the beam lumens are utilized, a more economical lighting plan should be possible by using different locations or narrower beam floodlights. If the CBU is over 0.9, it is probable that the beam spread selected is too narrow and the resultant illumination will be spotty. An estimated CBU can be determined by experience, or by making calculations for several potential aiming points and using the average figure thus obtained.
Step 4 - Determine the quantity of floodlights (N) required. Rearrange the basic formula in Step 1 as follows:
