Maryland Journeyperson Electrician Exam, Electrical Calculations: all 120 questions

All questions from the Electrical Calculations section for Maryland Journeyperson Electrician Exam, each with the correct answer.

13001A resistive heating element has a resistance of 15 ohms and is connected to 120 volts. What current does it draw?
13002A 4,800 watt resistive water heater is connected to a 240 volt single-phase circuit. What is the current?
13003What is the resistance of a 1,500 watt, 120 volt space heater element at its rated operating point?
13004A heater rated 4,000 watts at 240 volts is connected to a 208 volt supply. Assuming constant resistance, about how much power will it produce?
13005A current of 10 amperes flows through a conductor path with a total resistance of 0.5 ohm. How much power is lost as heat in the conductors?
13006A balanced three-phase 480 volt resistive load is rated 50 kW. What is the line current?
13007What is the full-load line current of a balanced 30 kVA three-phase load supplied at 208 volts?
13008A single-phase 240 volt resistive load draws 32 amperes. What is the load in kilowatts?
13009A three-phase 480 volt motor draws 40 amperes per line at a power factor of 0.85. What is the true power input?
13010A load consumes 72 kW at a power factor of 0.80. What is the apparent power?
13011A load has an apparent power of 100 kVA and a power factor of 0.80. What is its reactive power?
13012A motor delivers 10 horsepower at the shaft while drawing 8.5 kW of electrical input. What is its efficiency?
13013A motor takes 20 kW of electrical input and operates at 90 % efficiency. What is its output in horsepower?
13014A three-phase 460 volt motor delivers 25 hp with an efficiency of 92 % and a power factor of 0.86. What is the actual line current (not the NEC table value)?
13015A single-phase 240 volt load draws 50 amperes, and a wattmeter reads 10.2 kW. What is the power factor?
13016A 5 kW resistance heater runs 8 hours per day. At $0.12 per kWh, what does one day of operation cost?
13017A 15 kW balanced three-phase resistive heater is connected to 208 volts. What is the line current?
13018A 120/240 volt single-phase 3-wire feeder carries 40 A on one ungrounded conductor and 25 A on the other. Assuming linear loads, what current flows in the neutral?
13019A 3-phase 4-wire wye feeder has linear loads of 50 A on phase A, 40 A on phase B and 30 A on phase C. What is the approximate neutral current?
13020What is the line-to-neutral voltage of a 480Y/277 volt system, calculated from the 480 volt line-to-line value?
13021Each winding of a balanced delta-connected load carries 20 amperes. What is the line current?
13022What is the apparent power of a three-phase 480 volt load drawing 100 amperes per line?
13023A plant load of 100 kW operates at 0.80 power factor. About how much capacitor kVAR is needed to raise the power factor to 0.95?
13024Resistors of 6, 3 and 2 ohms are connected in parallel. What is the total resistance?
13025A 10 ohm and a 15 ohm resistor are connected in parallel. What is the equivalent resistance?
13026A 4 ohm resistor is connected in series with a parallel group of 6 ohms and 12 ohms, and the circuit is supplied at 120 volts. What is the total current?
13027Four identical 40 ohm heating elements are connected in parallel. What is the combined resistance?
13028Resistors of 5, 10 and 15 ohms are connected in series across 120 volts. What is the voltage across the 10 ohm resistor?
13031A 120 volt single-phase branch circuit uses 12 AWG copper (6,530 circular mils), runs 100 feet one way and carries 16 A. Using K = 12.9, what is the voltage drop?
13032A 240 volt single-phase circuit of 10 AWG copper (10,380 circular mils) supplies 24 A at 150 feet one way. What is the voltage drop as a percentage of the supply voltage?
13033A three-phase 480 volt load draws 50 A over 6 AWG copper conductors (26,240 circular mils), 200 feet one way. What is the line-to-line voltage drop?
13034A 240 volt single-phase feeder uses 4 AWG aluminum conductors (41,740 circular mils), 175 feet one way, carrying 60 A. Using K = 21.2 for aluminum, what is the voltage drop?
13035A 240 volt single-phase load of 40 A is located 180 feet from the panel. What is the smallest copper conductor that keeps voltage drop at or below 3 %?
13036A three-phase 208 volt load of 90 A is 150 feet from the source. Ignoring ampacity, what is the smallest copper conductor that limits voltage drop to 3 %?
13037A three-phase 480 volt load of 100 A is 300 feet away. Ignoring ampacity, what is the smallest aluminum conductor that holds voltage drop to 3 %?
13038What is the maximum one-way length for a 120 volt circuit of 12 AWG copper (6,530 circular mils) carrying 16 A if voltage drop must not exceed 3 %?
13039A 240 volt single-phase circuit of 8 AWG copper (16,510 circular mils) runs 120 feet one way. What is the maximum load current that keeps voltage drop at 3 %?
13040A 240 volt single-phase load draws 50 A through 6 AWG copper (26,240 circular mils) that is 200 feet long one way. What voltage is available at the load?
13041On a single-phase circuit, the length of the run is doubled and the load current is cut in half, with the same conductor. What happens to the voltage drop?
13042What voltage corresponds to a 3 % voltage drop on a 208 volt branch circuit?
13043In the common voltage drop formula VD = 2KIL / CM, what K value is normally used for aluminum conductors?
13044A three-phase 208 volt circuit of 10 AWG copper (10,380 circular mils) supplies 25 A per phase at 120 feet one way. What is the percent voltage drop?
13045A 120 volt, 20 A load is 150 feet from the panel. What is the smallest copper conductor that keeps voltage drop at or below 3 %?
13046What is the allowable ampacity of 6 AWG THHN copper (90 °C column) with three current-carrying conductors in a raceway at an ambient temperature of 40 °C?
13047Six current-carrying 10 AWG THHN copper conductors share one raceway at 30 °C ambient. What is the adjusted ampacity from the 90 °C column?
13048Nine current-carrying 12 AWG THHN copper conductors are installed in one conduit at 30 °C ambient. What is the adjusted ampacity of each conductor based on the 90 °C column?
13049Eight current-carrying 12 AWG THHN copper conductors run through an area with a 45 °C ambient. What is the allowable ampacity using the 90 °C column?
13050What is the ampacity of 4 AWG THWN copper (75 °C insulation) with three current-carrying conductors at an ambient of 45 °C?
13051Four current-carrying 3/0 AWG THWN-2 copper conductors are installed in a raceway where the ambient is 50 °C. What is the derated ampacity from the 90 °C column?
13052Six current-carrying 8 AWG THHN copper conductors are in one raceway at 30 °C ambient, and all terminations are rated 75 °C. What is the maximum ampacity that may be used for each conductor?
13053Three current-carrying 2 AWG THHN copper conductors are installed at 35 °C ambient and terminate on 75 °C rated lugs. What is the maximum load current the conductors may be used for?
13054A raceway contains two 3-phase, 4-wire wye circuits, and the loads are mainly electronic (nonlinear), so the neutrals count as current-carrying. Equipment grounding conductors are also present. What adjustment factor applies?
13055A raceway holds three 120 volt, 2-wire branch circuits, each with its own neutral, plus one equipment grounding conductor per circuit. How many current-carrying conductors are counted for adjustment?
13056A raceway contains three 120/240 volt, single-phase 3-wire multiwire circuits. The neutrals carry only unbalanced current. What adjustment factor applies to the conductors?
13057What is the allowable ampacity of 4/0 AWG XHHW aluminum conductors in the 75 °C column at 30 °C ambient with not more than three current-carrying conductors?
1305812 AWG copper UF cable (60 °C rated) is installed where the ambient temperature is 40 °C. What is its corrected ampacity?
13059A 50 A noncontinuous load is supplied by one of six current-carrying THHN copper conductors in a raceway at 30 °C. Terminations are rated 75 °C. What is the smallest conductor size permitted?
13060Twenty current-carrying 12 AWG THHN copper conductors are in one raceway at 30 °C ambient. What is the adjusted ampacity based on the 90 °C column?
13061What adjustment factor applies when 25 current-carrying conductors are installed in a single raceway longer than 24 inches?
13062What ambient temperature correction factor applies to a 75 °C rated conductor at an ambient of 38 °C (tables based on 30 °C)?
13063A device box contains four 12 AWG insulated conductors, two 12 AWG equipment grounding conductors and one receptacle on a yoke. What minimum box volume is required?
13064A box has internal cable clamps, six 14 AWG insulated conductors, two 14 AWG equipment grounding conductors and a single-pole switch. What minimum volume does 314.16 require?
13065A box has a marked volume of 18.0 cubic inches and will contain only 12 AWG conductors with no fittings, devices or grounding conductors. What is the maximum number of conductors permitted?
13066A box contains four 12 AWG and two 14 AWG insulated conductors, 12 AWG equipment grounding conductors and a receptacle connected to the 12 AWG conductors. What minimum volume is required?
13067What is the volume listed in 314.16(A) for a 4 inch by 2-1/8 inch square metal box?
13068A 4 inch by 1-1/2 inch square box (21.0 cu in) has a plaster ring marked 3.6 cu in. What is the maximum number of 12 AWG conductors permitted if nothing else is in the box?
13069A box contains three 14 AWG insulated conductors that are spliced and terminated, two 14 AWG pigtails that originate and end inside the box, and one 14 AWG equipment grounding conductor group. What minimum volume is required?
13070Which volume allowance does 314.16(B) assign to each 6 AWG conductor?
13071A 4 inch by 1-1/2 inch octagonal box (15.5 cu in) will contain a fixture stud, four 14 AWG insulated conductors and one 14 AWG equipment grounding conductor. What volume is required, and does the box comply?
13072A 3 inch by 2 inch by 3-1/2 inch device box is rated 18.0 cu in. It holds a switch, two 14 AWG cables with grounds (4 insulated conductors) and internal clamps. How many additional 14 AWG insulated conductors may be added?
13073A conductor runs unbroken through a box without being spliced or terminated and is not looped. How is it counted for box fill?
13074What is the maximum fill percentage for a raceway that contains three or more conductors, other than a short nipple?
13075What maximum fill percentage applies when exactly two conductors are installed in a raceway?
13076A raceway nipple not exceeding 24 inches long between enclosures may be filled to what percentage?
13077Using a 40 % fill area of 0.213 sq in for 3/4 inch EMT and an area of 0.0133 sq in for 12 AWG THHN, how many 12 AWG THHN conductors are permitted?
13078How many 10 AWG THHN conductors (0.0211 sq in each) may be installed in 1/2 inch EMT, which has a 40 % fill area of 0.122 sq in?
13079Three 4 AWG THHN (0.0824 sq in each) and one 8 AWG THHN (0.0366 sq in) are to be installed in EMT. Which is the smallest trade size permitted? (40 % areas: 3/4 in 0.213, 1 in 0.346, 1-1/4 in 0.598 sq in)
13080What is the total cross-sectional area of six 10 AWG THHN (0.0211 sq in each) and three 8 AWG THHN (0.0366 sq in each) conductors?
130813/4 inch EMT has a 40 % fill area of 0.213 sq in and 14 AWG THHN has an area of 0.0097 sq in. How many 14 AWG THHN conductors are permitted when all conductors are the same size?
130821 inch EMT has a total internal area of 0.864 sq in. What is the maximum cross-sectional area of a single conductor installed in it?
13083A 25 hp, 460 volt, three-phase induction motor has a table full-load current of 34 A. What is the minimum ampacity of its branch-circuit conductors?
13084What minimum conductor ampacity is required for a 5 hp, 230 volt, single-phase motor? (Table full-load current 28 A.)
13085What is the full-load current from Table 430.250 for a 10 hp, 208 volt, three-phase induction motor, and the resulting minimum conductor ampacity?
13086A 20 hp, 460 volt, three-phase motor has a nameplate current of 26 A. Table 430.250 lists 27 A. What is the minimum branch-circuit conductor ampacity?
13087A 15 hp, 460 volt, three-phase squirrel-cage motor (not Design B energy efficient) has a table full-load current of 21 A. Using an inverse time breaker at its maximum percentage and the next-higher-size allowance, what breaker may be used?
13088A 10 hp, 230 volt, three-phase motor has a table full-load current of 28 A. What is the maximum dual-element time-delay fuse size under the basic percentage of 430.52?
13089A 30 hp, 460 volt, three-phase motor has a table full-load current of 40 A. What is the maximum nontime-delay fuse size, using the next-higher-standard-size allowance?
13090What is the maximum setting, under the basic table percentage, of an instantaneous trip breaker for a 10 hp, 460 volt, three-phase squirrel-cage motor with a table full-load current of 14 A?
13091A motor has a nameplate full-load current of 24 A and a marked service factor of 1.15. What is the maximum rating of a separate overload device under 430.32(A)(1)?
13092A motor has a nameplate current of 40 A, a service factor of 1.0 and a temperature rise of 50 °C. What overload rating is required under the basic rule?
13093A motor with a 1.15 service factor and a nameplate current of 24 A trips its overloads during starting. What is the highest overload rating permitted under 430.32(C)?
13094A feeder supplies three 460 volt, three-phase motors with table full-load currents of 14 A, 21 A and 34 A. What is the minimum feeder conductor ampacity?
13095A 1 hp, 115 volt, single-phase motor has a table full-load current of 16 A. What minimum branch-circuit conductor ampacity is required?
13096A feeder supplies three 460 volt motors: 25 hp (34 A) protected by a 90 A inverse time breaker, 15 hp (21 A) and 10 hp (14 A). What is the maximum rating of the feeder overcurrent device?
13097What is the Table 430.250 full-load current for a 50 hp, 230 volt, three-phase induction motor?
13098A 7.5 hp, 460 volt, three-phase motor has a table full-load current of 11 A. What minimum branch-circuit conductor ampacity is required?
13099Why does the full-load current from Table 430.250, rather than the motor nameplate current, determine motor branch-circuit conductor ampacity for a general-purpose motor?
13100A 25 kVA single-phase transformer has a 480 volt primary and a 240 volt secondary. What are the full-load primary and secondary currents?
13101What is the full-load secondary current of a 75 kVA, three-phase transformer with a 208Y/120 volt secondary?
13102What is the full-load primary current of a 75 kVA, three-phase transformer with a 480 volt delta primary?
13103A 45 kVA, three-phase, 480 volt primary transformer (1,000 volts or less) is protected on the primary side only. What is the maximum primary overcurrent device, using the next-higher-standard-size note?
13104A single-phase transformer steps 480 volts down to 120 volts. If the primary current is 10 A, what is the secondary current (ignoring losses)?
13105A transformer has a turns ratio of 20 to 1 and a primary voltage of 2,400 volts. What is the secondary voltage?
13106A balanced three-phase load draws 150 A per phase at 208 volts. What is the minimum transformer kVA required?
13107A transformer delivers 48.5 kW to its load while its input is 50 kW. What is its efficiency?
13108A 15 kVA, single-phase transformer with a 240 volt primary is protected on the primary side only. Which statement about its primary current is correct?
13109A branch circuit supplies a 36 A continuous load and nothing else. What is the minimum overcurrent device rating?
13110A 40 A continuous load is supplied with THWN copper conductors terminating on 75 °C rated equipment. What is the minimum conductor size?
13111A branch circuit supplies 30 A of continuous load and 20 A of noncontinuous load. What is the minimum standard overcurrent device rating?
13112What is the maximum continuous load permitted on a 20 A branch circuit protected by a standard (not 100 % rated) breaker?
13113What is the maximum continuous lighting load in volt-amperes on a 277 volt, 20 A branch circuit?
13114How many 277 volt LED luminaires drawing 0.75 A each may be connected to a 20 A branch circuit if they operate continuously?
13115A three-phase feeder supplies 120 A of continuous load and 40 A of noncontinuous load. What is the minimum standard overcurrent device rating?
13116A 24 A continuous load is supplied by a branch circuit. What is the minimum overcurrent device rating and minimum copper conductor size with 60 °C terminations?
13118A single-phase 240 volt, 10 kW heater operates for 3 hours. How many kilowatt-hours does it use, and what is its current?
13119What is the circular mil area of a 10 AWG conductor as listed in Chapter 9 Table 8?
13120A 240 volt, single-phase, 2 hp motor has a table full-load current of 12 A at 230 volts. What is the minimum branch-circuit conductor ampacity?
13121Three-phase 460 volt motors are rated 5 hp (7.6 A) and 3 hp (4.8 A). What is the minimum ampacity of a feeder supplying only these two motors?
13122A 9 kW, 480 volt, three-phase resistive heater is a continuous load. What is the minimum standard overcurrent device rating?
13123What is the inverse time breaker maximum for a 3 hp, 230 volt, single-phase motor (table FLC 17 A), allowing the next higher standard size?

Maryland Journeyperson Electrician Exam, Electrical Calculations: all 120 questions

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