Questions and Answers of Electrical Systems For Buildings

Using your location, estimate the total electricity generate from a PV system per unit of roof area using a single crystal technology with a rated efficiency of 13.5%. You may use PV Watts or any
Compare the electricity generated by a rooftop PV system for various tilt angle for your specific house location. You can use PV Watts or a similar tool. Conclude on the optimal tilt angle.
Determine the wire size needed to maintain the voltage drop below 2% for a 48-V PV array located 200 ft away from the electrical panel. The short-circuit current for the array is estimated at 36.5 A.
Design the specifications and the layout for the following standalone PV system made up of six, 12 V, 51 W module. Each module has the following characteristics: ISC = 2.85 A and VOC =18.2 V.• A
Design the specifications and the layout for a grid-connected PV system made up of 12, 50 V, 200 W modules. Each module has a short-circuit current of 4.5 A and open circuit voltage of 58 V. The
Provide the actual efficiency and the PURPA efficiency for 10 MW cogeneration system with an electrical efficiency of 30% and thermal efficiency of 40%.
A small cogeneration system rated at 100 kW rated at 80% overall efficiency and 30% electrical efficiency. Estimate the potential cost-effectiveness of deploying this system for a building that
Determine the efficiency of 500 kVA, three-phase transformer if the open test indicates a loss of 0.900 kW, and the short-circuit test provides a loss of 2.550 KW.
Determine the percent regulation of a three-phase 480 Y/277-V transformer if the secondary voltage for full-load conditions is measured to be 269 V.
Determine the percent impedance of a 480 Y/277–208 Y/120 V transformer if the short-circuit test provides a primary voltage of 25 V.
Determine the change in the size of the service entrance including the main feeder and panel rating required to electrify an 800-ft2 (74 m2) apartment unit served by 208Y/120-V with the following
Determine the circuit breaker and the feeder size using THW(Cu) for a 480Y/277 V lighting panelboard serving 100-kW load with a power factor of 0.95 for a commercial building.
Determine the circuit breaker and the feeder size using THW(Cu) for a 208Y/120 V power panelboard serving 100 receptacles in an office building. The power factor for the load associated with the
Determine the breakeven costs for installing a 1,000-kVA transformer for a new building with an efficiency of 99.28% rather than 98.90%. If the annual load factor is 80%, the average building’s
A building has an electrical load of 500 kVA at 0.70 power factor, lagging.Among the load is a 50 HP induction motor with an efficiency of 0.93 and a power factor 0.90 (lagging). It has been decided
A one-phase motor rated at 5-hp and 240-V with an efficiency of 0.90, and a power factor of 0.85, lagging. Determine the equivalent impedance for the motor.
A three-phase motor rated at 100-hp and 460-V with an efficiency of 0.92, and a power factor of 0.90, lagging. Determine the equivalent impedance for the motor.
A coil of # 12 AWG copper wire wound in a single layer on a cylindrical form so that the mean diameter of each turn is 6.0 in., and it has a resistance of 4.0 Ω. How many turns of wire are there in
Consider the following circuit setup shown below. Determine the voltage drop across the 7 Ω resistor. 120 V DC 12 www 5 H 402 www 50 70 V
An automobile generator with an internal resistance of 0.5 Ω develops an open-circuit emf of 9.0 V. The storage battery has an internal resistance of 0.03 Ω and open- circuit emf of 7.0 V. Both
A 5 A current flows when a neon lighting fixture is supplied by a 120 V power source. If the current lags the voltage by 75°, determine the power factor and the real power consumed by the fixture.
Determine the rating of a generator in kVA for a home in order to ensure that the following systems and appliances can be operated in case of a long-term power outage:(a) Air conditioner rated at 9.5
A 240 V, single-phase load has a resistance of 3 Ω and an inductive reactance of 4 Ω. Calculate(a) The impedance of the load(b) The power factor of the load(c) The power consumed by the load
For a single-phase circuit served by an AC power source:(a) Determine the total impedance at 60 Hz of a circuit consisting of a 0.25 H inductor with a 100 Ω resistance and a 50 μF capacitor, all
A 1 horsepower motor is connected to 120 V, 60 Hz AC source and has a pf = 0.80 (lagging) and an efficiency of 0.90. A capacitor is connected in parallel with the motor in order to correct its pf
A motor for a blender can be modeled as a resistance of 10 Ω and an inductance of 25 mH connected in a series and supplied by a 120 V, 60 Hz source. Determine(a) The real power consumed by the
A single-phase induction motor draws 250 W at a power factor of pf = 0.80 (lagging) when connected to 120 V, 60 Hz source. Find the capacitance needed to correct the pf of the motor to unity (i.e.,
Find the real power and the power factor for a load whose impedance is 60 Ω < 60° when connected to an AC source of 120 V and 60 Hz.
Determine the capacitance that can increase the overall power factor to 95% lagging when connected in parallel with a load that draws 1.0 kW at a 70% lagging power factor from a 240 V, 60 Hz source.
Find the capacitance that minimizes the source current when connected in parallel with a single-phase induction motor drawing 10 A at a power factor of pf = 0.80 (lagging) when connected to 120 V, 60
A synchronous motor capable of operating with a leading power factor draws 10 kW from a transformer while driving a fan. The remainder load on the transformer consists of 100 kW with 0.80 lagging
Consider a motor rated 840 W with 70% power factor operating from a 120 V, 60 Hz, one-phase source. Determine(a) The source current if a 308 μF capacitor is added to the motor in series(b) The value
A 200 HP induction motor with a power factor of 0.65 and an efficiency of 90% is supplied by a 3-ϕΔ-connected 480 V AC source.(a) Show the power triangle for the motor.(b) Determine the impedance
A manufacturing plant has an electrical load of 5000 kW at 0.80 power factor, lagging. It has been decided to replace a 500 HP induction motor that drives a pump. This motor operates at an efficiency
For one-phase 10 kVA transformer, determine the turns ratio if the primary and secondary voltages are 120 and 240 V, respectively. Estimate the primary and secondary currents.
A one-phase transformer has 220 V in the primary and 110 V and 125 A in the secondary. Assuming it as an ideal transformer (i.e., 100% efficient), determine the rating of the transformer in kVA.
If the secondary phase current of a 480Y/277–208Y/120 V transformer, a three-phase transformer, is 10 A, estimate the primary line current and the total primary power used by the transformer in kW
A three-phase transformer 13.6 kV–480Y/277 V serves a building. Determine the primary and secondary line currents if the rating of the transformer is 500 kV. Estimate the turns ratio of the
A three-phase transformer in a large building steps down the primary voltage of 13.8 kV (line-to-line) to a secondary voltage of 208 V (line-to-line). The transformer rating is 5000 kVA. Specify the
A one-phase 500 kVA 240/120 V transformer is reconnected as an autotransformer:(a) Calculate the currents in each part of the autotransformer and determine its power rating if it is reconnected as a
In a building, it is found that 60 fluorescent luminaires are needed as well as 90 receptacle outlets. Each receptacle has a load of 180 VA and operates at 120 V with a power factor of 0.90 while
Estimate the cost savings for replacing a 750 kVA transformer of an efficiency of 99.2 % by an energy-efficient transformer of 99.6 % if the average power factor of the transformer load is 85% and
A 200 HP induction motor with a power factor of 0.65 and an efficiency of 90% is supplied by a three-phase Δ-connected 480 VAC source.(a) Show the power triangle for the motor.(b) Determine the
A commercial building has an electrical load of 2000 kW at 0.80 power factor, lagging. It has been decided to replace a 100 HP induction motor that drives a pump. This motor operates at an efficiency
Determine the motor speed in rpm and rad/s for an induction motor with a 2% slip and six pole for two cases of voltage source frequency(a) f = 60 Hz and(b) f = 50 Hz.
A four-pole squirrel-cage motor has the following characteristics:• Power input at a rated load is 4200 W with a power factor of 0.60.• Rated speed is 1150 rpm.• Resistance of each stator
Consider a 50 HP induction motor with a nameplate rated energy efficiency of 92% and a power factor of 0.85.Determine the required size in kVAR of a capacitor to be installed in parallel with the
A commercial building is subject to an electricity rate schedule that requires a demand charge of $2.50 per kVA per month. The electrical load of the building consists of (a) a group of ten (10)
The load in a building panel is 120 kW at 480 V and is three-phase with a low power factor of 0.75 lagging. This power factor is to be corrected to 0.95 lagging. A motor rated at 60 Hz, 70 HP, 1200
A building has a total load of 150 kVA and a power factor of 0.85 (lagging). Among the electrical load, there is a 40 HP, three-phase, 60 Hz, 480 V induction motor with an efficiency of 0.92 and a
For a 20 HP three-phase induction motor with a nameplate rated voltage of 208 V energy efficiency of 90.5 % and a power factor of 0.87. Determine the impact of 5% overvoltage on the energy
A supply fan motor for an air handling unit of a variable air volume system is rated at 20 HP with 88% energy efficiency. The fan is operated during 5500 h/year according to the following load
A 50 HP motor is to operated 4500 h/year at 80% load. A premium-efficiency motor has an energy efficiency of 93.4 %, compared to 91.2 % for the standard-efficiency motor. Calculate the annual energy
An induction motor is rated 60 HP, three-phase, 60 Hz, 460 V, 1760 rpm, and a power factor of 90%.(a) Estimate the efficiency of each motor if its line current is 70 A.(b) Determine the number of
A motor control center (MCC) has three induction motors each rated at 40 HP and 480 V and four induction motors each rated at 30 HP and 480 V. Each 40 HP motor has an energy efficiency of 0.92 , a
For a series R–L circuit, it can be shown that the rms (I.E., effective value) of the asymmetrical fault current is given by the following equationwhere θ = f × t is time in cycles X = L/ω = 2π
A dwelling unit is supplied by a single-phase, 120/240 V service. The electric load of the unit includes.(1) 7000 VA water heater, 240 V; (2) 800 VA vent fan, 120 V;(3) 1200 VA compactor, 120 V; (4)
Determine the size of molded-case circuit breakers and associated number of poles for the following loads in a dwelling served by 120/240 V system: 1.8 kVA dishwasher, 120 V; 1.2 kVA compactor, 120
Consider a panelboard for a commercial building supplied by a 480Y/277 V, threephase feeder. The panel has the following loads:• A lighting system of a total power 45 kVA with a power factor of
Consider the distribution system of a commercial building shown in the following diagram. Select the frames and trip ratings for all the power circuit breakers for the various panels and motors as
Determine the size of the equipment grounding copper conductors for a panel that is served by 2/0 THW (Cu) and 400 A circuit breaker.
Consider a 480Y/277 V panelboard that serves the following loads for an office building:• Lighting: 15.0kVA at pf = 0.95• Resistance Heater: 9.0 kVA at pf =1.00(a) Select the proper circuit
For an office building, a 208Y/120 V power panel has the following loads:• Receptacles with a total load of 30.00 kVA at PF = 0.90• Heaters with a total load 12.00 kVA at PF = 1.00(a) Determine
Determine the copper service grounding conductor required for a service entrance with 3 parallel 300 MCM copper feeders.
Determine the potential damages incurred by an electrical distribution system when 2000 A ground-fault current occurs for 10 cycles.
Determine the ampacity rating of each of the 12 #4 THW (Cu) conductors placed in the same conduit.
Determine the ampacity of each of 5 #8 THHN (Cu) conductors installed in an area with a surrounding ambient temperature is 45°C.
Check if a #12 THW (Cu) conductor can supply power to 10 fluorescent lighting fixtures each rated at 1.8 A.
Determine the size of THHN (Cu) conductors needed to supply eight rows of fluorescent lighting fixtures with seven fixtures in each row with each fixture rated at 1.5 A. If only 20 A circuits are
Determine the symmetrical short-circuit current a #1/0 XHHW (Cu) conductor protected by a circuit breaker rated at 480 V.
Estimate the maximum asymmetrical short-circuit current that #1/0 THW (Cu) conductors can handle if circuit breakers are used as overcurrent protection devices.
Calculate the voltage drop in percent for a feeder that serves a load of 100 kW, 480 V, three-phase, power factor of 85%, and length of 300 ft. The feeder is #1 XHHW copper conductors in an aluminum
Calculate the percent voltage drop of a 240 V, 1-phase feeder consisting of 150 ft one way of #10 THW copper conductors in steel EMT conduit carrying a load of 20 A, 90% PF.
Calculate the percent voltage drop of a 120 V, 1-phase branch circuit consisting of 25 m one way of 2 #12 THHN copper conductors in EMT conduit carrying a load of 16 A, 85% PF.
Calculate the percent voltage drop of a 240 V, 3-phase feeder consisting of 190 ft one way of 2 #4 THW copper conductors in steel EMT conduit carrying a load of 40 A, 85% PF.
A building is supplied by 750 ft, three-wire, 480 V, three-phase feeder. The total load of the building is 250 kVA with a power factor of 0.8. Determine(a) The size of the feeder and conduit using
Three 120/240 V panelboards are supplied with three subfeeders: A, B, and C. A is 50 ft, B is 100 ft, and C is 50 ft in length. The load on A is 15 kVA with a pf of 1.0; load B is 25 kVA with a pf of
Select the size of conductors and conduit for a feeder that services a lighting panel with the following features:• Load is 275 kW with a power factor of 90% and is continuous.• More than 50% of
A 208Y/120 V panelboard for an office building has the following loads:• Receptacles with a total load of 30.00 kVA at pf = 0.90• Lighting with a total load of 20.00kVA at pf = 0.95• One Motor
A panelboard for a commercial building is supplied by 250 ft, four-wire, 480Y/277 V, three-phase feeder. The panel has the following loads:• A lighting system of a total power 30 kVA with a power
Calculate the motor circuit conductors for a 30 HP, 460 V, 3-phase squirrel cage motor; use copper, 75°C THW.
Determine the size of the disconnecting means for a 50 HP, 230 V, 3-phase squirrel cage motor.
Size the branch circuit for an induction motor rated at 50 HP, three-phase, 60 Hz, 460 V, 1175 rpm, a service factor of 1.15, and a power factor of 90%. The motor is protected by time-delay fuses.
Determine the size of THHN copper branch circuit conductors required to supply a 20 kVA, single-phase, 240 V heating unit (continuous duty) with a 10 A blower motor.
Estimate the size of THW copper conductors that are required to supply a group of three-phase, 230 V motors 230 V rated at 7.5, 15, and 25 HP.
An MCC serves 9 identical motors, each motor is rated 50 HP, three-phase, 60 Hz, 460 V, 1175 rpm, a service factor of 1.00, and a power factor of 90%. All the motors are protected by time-delay fuses
A motor control center has three induction motors each rated at 40 HP and 480 V and four induction motors each rated at 30 HP and 480 V. Each 40 HP motor has an efficiency of 0.92 , 1772 rpm, and a
Determine the size of the service entrance THW (Cu) conductors required for phases A and B and the neutral of a 310 m2 (3200 ft2) dwelling with the following loads: 12.0 kVA range; 6.0kVA dryer; 30.0
A dwelling unit is supplied by a single-phase, 120/240 V service. The electric load of the unit includes:(1) 7000 VA water heater, 240 V; (2) 500 VA vent fan, 120 V;(3) 1200 VA compactor, 120
Determine the size of the service entrance THW (Cu) conductors required for phases A and B using the optional method of a 310 m2 (3200 ft2) dwelling with the following loads: 12.0 kVA range; 6.0 kVA
A 274 m2 (2950 ft2) dwelling is supplied by a single-phase, 120/240 V service and has the following loads: 1.8 kVA dishwasher, 120 V; 1.2 kVA compactor, 120 V; 1.0 kVA disposal, 120 V; 0.5 kVA vent
Determine the size of the service entrance conductors required for phases A and B and the neutral of a 186 m2 (2000 ft2) residence having the following load: 15 kVA space heating (five electric
A 348 m2 (3750 ft2) house has the following loads: 12 kVA range, 240 V; 15 kVA air conditioning unit, 240 V; and 8 kVA water heater, 240 V.(a) Using the standard method, size the THW service entrance
A 316 m2 (3400 ft2) house has the following loads: 1.5 kVA compactor, 120 V; 1.2 kVA ceiling fan, 120 V; 14 kVA range, 240 V; 30 kVA heating unit, 240 V; 40 A air conditioning unit, 240 V; and 10 kVA
Determine the size of the service entrance conductors required for phases A and B and the neutral for twenty (20) 83.5 m2 (900 ft2) units in a multifamily dwelling. The units have the following
A 480Y/277 V lighting panelboard has the following loads:• Lighting (4 circuits at 277 V) with a total load of 16.0kVA at PF = 0.95 (continuous load)• Appliances (2 circuits at 277 V) with a
A 208Y/120 V panelboard for an office building has the following loads:• Receptacles with a total load of 50.00 kVA and a power factor of 0.90• Lighting with a total load of 80.00 kVA and a power
A panel for a commercial building is supplied by a 500 ft four-wire 208Y/120-V three-phase feeder. The panel serves three major loads:• A lighting system of a total power of 70 kVA with a power
A panel for an office building is supplied by a 200 ft four-wire and a 480Y/277 V feeder. The loads of the panel include• A lighting system of a total power of 10 kVA with a power factor of 0.8•
A 208Y/120 V panelboard for an office building has the following loads:• Receptacles with a total load of 30.00 kVA at PF = 0.90• Lighting with a total load of 20.00 kVA at PF = 0.95• One motor

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