Chapter 10 Unit 27,28,29
What is the current flow in amperes through a 6.50kw heatstrip rated 480V when connected to a 480V power source? (a) 13.5A (b) 19.4A (c) 21.3A (d) 23.2A
I = P/E 6,5000/480 = 13. 5 A
What is the current flow in amperes through a 9.50kw heatstrip rated 208V when connected to a 208V power source? (a) 35A (b) 39A (c) 46A (d) 55A
I = P/E 9,500/208V =46A
Wire dc resistance is determined by the __________. (a) material type (b) cross-sectional (c) wire length and operating temp (d) all of these
all of these
Multiwire branch circuits have _______ wires for a given number of circuits, which requires the use of a smaller raceway. (a) fewer (b) more (c) bigger (d) smaller
fewer
A_________ circuit is a circuit consisting of two or more phase wires that have a voltage between them, and an equal voltage between each phase wire and the neutral. (a) series (b) parallel (c) multiwire (d) series-parallel
multiwire
The ______ wire is connected to the neutral point of a system and is intended to carry current under normal conditions. (a) neutral (b) phase (c) copper (d) none of these
neutral
What is the direct-current resistance of a 3 AWG aluminum wire that is 1,000 ft long? (a) 0.231 ohms (b) .313 ohms (c) .403 ohms (d) .422 ohms
(.403/1000) x 1,000 = .403
What is the direct-current resistance of a 3 AWG aluminum wire that is 500 ft long? (a) 0.0231 ohms (b) 0.1614 ohms (c) 0.2015 ohms (d) 0.233 ohms
(.403/1000) x 500 = .2015 ohms
what is the direct-current resistance of a 6 AWG copper wire that is 400 ft long? (a) .20 ohms (b) .30 ohms (c) .40 ohms (d) .50 ohms
(.491ohms/1000 ft) x 400ft = .20 ohms
What is the direct-current resistance of a 1 AWG copper wire that is 100 ft long? (a) 0.0154 ohms (b) 0.1620 ohms (c) 0.2330 ohms (d) 0.5610ohms
(0.154ohms/1000) x 100 ft = 0.0154 ohms
***Added from Unit 27 What is the operating voltage of a single-phase, 12A, 230V rated load wired with 10 AWG if it is located 250 ft from the power supply, and has a nominal circuit voltage of 240V? Answer 1: 200.40V Answer 2: 216.60V Answer 3: 232.56V Answer 4: 238.80V
10 AWG = 1.26 (1.26 1,000/1,000) x Answer 3: 232.56V
According to chapter 9, table 8, what is the cross-sectional area circular for a 3/10 AWG aluminum wire? (a) 83,690 cmil (b) 105,600 cmil (c) 167,800 cmil (d) 211,600 cmil
167,800 cmil
What is the power loss at a terminal having a resistance of 0.20 ohms when carrying 40A? (a) 100W (b) 210W (c) 320W (d) 430W
P = I^2 x R 40^2 x .20 = 320W
What is the voltage of a circuit carrying 7.5A supplying a 37 ohms resistor? (a) 120V (b) 277V (c) 360V (d) 520V
V = I x R 7.5 x 37 = 277V
What is the voltage of a circuit carrying 4.6A supplying a 52ohms resistor? (a) 110W (b) 120V (c) 230V (d) 240V
V= I x R 4.6 x 52 = 240V
What is the direct-current resistance of a 1 / 10 AWG aluminum wire that is 800 ft long? (a) 0.08 ohms (b) 0.16 ohms (c) 0.23 ohms (d) 0.56 ohms
1 / 10 AWG = 0.201 (0.201/1,000) x 800 = .16 ohms
According to Chapter 9, Table 8, what is the cross-sectional area in circular mils for a 4 AWG wire? (a) 41,740 cmil (b) 63,360 cmil (c) 70,380 cmil (d) 96,510 cmil
41, 740
What is the cross sectional area in circular mils for a 2 AWG wire? (a) 41, 740 cmil (b) 66,360 cmil (c) 70,380 cmil (d) 83, 690 cmil
66,360 cmil
What is the voltage of a circuit carrying 20.8A supplying a 10 ohms resistor? (a) 110V (b) 208V (c) 460V (d) 500V
V = I x R 20.8 x 10 = 208V
What is the voltage of a circuit carrying 4.8A supplying a 100 ohms resistor? (a) 110V ( b) 220V (c) 360V (d) 480V
V = I x R 4.8 x 100 = 480V
What is the direct current resistance of a 1 AWG copper wire that is 200 ft long? (a) 0.0308 ohms (b) 0.0311 ohms (c) 0.0423 ohms (d) 0.0564 ohms
.Resistance of 1 AWG = (.1.54 ohms/1000) x 200 = .0308
A 240V, single phase load is located 100 ft from the panelboard and is wire 10 AWG wires. What is the voltage drop of the circuit wires? (a) 3V (b) 4 V (c) 5 V (d) 6V
1.26/1,000 = .00126 .00126 x 100 x 2 = .252 .252 x 20A = 5 V
What is the current flow in amperes through a 9.5 kw heat strip rated 230V when connected to a 230V power source? (a) 25A (b) 39A (c) 41A (d) 230A
I = P/E 9.5 kw x 1,000 = 9,500 9,500/230V = 41 A
What is the current flow in amperes through a 6.50kw heatstrip rated 460V when connected to a 460V power source? (a) 14A (b) 21A (c) 27A (d) 30A
I = P/E 6,500/460 = 14A
The ______ lists the resistance and area in circular mils for both direct-current and alternating current circuit wires. (a) NEC (b) CEC (c) IEC (d) none
NEC
What is the power loss at a terminal having a resistance of .70 ohms when carrying 10A? (a) 10W (b) 40W (c) 70W (c) 100W
P = 10^2 x.70 = 70W
What is the power loss at a terminal having a resistance of 0.50 ohms when carrying 15A? (a) 112.5W (b) 200.4W (c) 230.2W (d) 340.3W
P = I^2 x R 15^ x .50 = 112.5 W
The cross sectional area of a wire is commonly expressed in ________ (a) square inches (b) mils (c) circular mils (d)none
circular mils
Multi-wire branch circuits are more _______ than 2-wire circuits in that they have fewer wires for a given number of circuits, which enables the use of a smaller raceway and result in lower circuit voltage drop. (a) cost effective (b) conductive (c) nicer (d) easier
cost effective
Increased ______ flow will result in greater wire voltage drop (a) resistance (b) voltage (c) current (d) none of these
current
The current flowing in the neutral wire of a 3-wire, 120V/240V, single-phase circuit equals the _________ current flowing in the phase wires. (a) minimum (b) difference in (c) opposition to (d) maximum
difference in
______ currents are small independent currents that are produced as a result of the expanding and collapsing magnetic field. They flow erratically within the wire opposing current flow and consuming power. (a) Lenz (b) Ohms (c) Eddy (d) Kirchhoff's
eddy
The opposition to current flow is greater for alternating current circuits than for direct-current circuits because of ______. (a) eddy currents (b) skin effect (c) eddy currents and skin effect (d) none
eddy currents and skin effect
Smaller wires have _______ resistance and larger wires have lower resistance. (a) lesser (b) greater (c) the same (d) all of these
greater
Aluminum has _____ resistance to the flow of electrons than does copper. (a) higher (b) lower (c) equal (d) none of these
higher
The dc resistance of a wire is directly proportional to its _____ (a) color (b) length (c) weight (d) insulation
length
In dc circuits, the only property that affects current flow is _______. (a) impedance (b) reactance (c) resistance (d) none
resistance
The current on the neutral wire of a 2-wire circuit is the ________ the current on the phase wire. (a) same as (b) different than (c) opposite that of (d) all of these
same as
Eddy currents are strongest in the center of the wires and repel the flowing electrons toward the wire surface. This is known as "_______ effect. (a) inductive (b) skin (c) surface (d) watt
skin
The resistance of a wire is affected by temperature change. This is called the "________." (a) temperature correction factor (b) temperature coefficient (c) ambient temperature factor (d) none of these
temperature coefficient
*****Added from Unit 27 A 240V, 20A, single-phase load is located 100 ft from the panelboard and is wired with 10 AWG wires. What is the voltage drop of the circuit wires? Answer 1: 3V Answer 2: 4V Answer 3: 5V Answer 4: 6V
1.26/1000 = .00126 .00126 x 100 x 2 = .252 .252 x 20 = 5.04
According to chapter 9, Table 8, what is the cross sectional area in circular mils. for a 1/ 10 AWG wire? (a) 83,690cmil (b) 105,600 cmil (c) 167,800 cmil (d) 21,600cmil
105,600 cmil
According to chapter 9, Table 8, what is the cross sectional area in circular mils for a 1 AWG wire? (a) 41700 cmil (b) 63,360 cmil (c) 70,380cmil (d) 83,690 cmil
83,690 cmil
What is the resistance of the circuit wires when the wire voltage drop is 6.24V and the current flow is 40A? (a) .145 ohms (b) .156 ohms (c) .60 ohms (d) 6.41 ohms
R = E/I 6.24V/40 = .156 ohms
What is the circuit voltage drop over each line wire of a balanced 3-wire multi-wire circuit? Each wire is a 12 AWG, 150 ft long, supplying a 20A load. (a) 2V (b) 3V (c) 4V (d) 6V
R= 150 x 3/1,000 = .225 .225 x 20 = 6 V
What is the voltage drop of two 12 AWG wires, each 150 ft long , supplying a 2-wire, 20A load? (a) 6V (b) 10 V (c) 12V (d) 16V
R = 150 x 2/1,000 = .30 20A x .30 = 12V
What is the resistance of the wires when the wire voltage drop is 14.4V and the current flow is 60A? (a) .24 ohms (b) .30 ohms (c) 3.14 ohms (d) 4.2 ohms
R = E/I 14.4/60 = .24 ohms
What is the resistance of the circuit wires when the wire voltage drop is 3.60V and the current flow is 20A? (a) .15 ohms (b) .18 ohms (c) 2 ohms (d) 5.55 ohms
R = E/I 3.6V/20 = .18 ohms
What is the resistance of the circuit wires when the wire voltage drop is 7.20V and the current flow is 50A? (a) 0.14 ohms (b) 0.30 ohms (c) 3 ohms (d) 14 ohms
R = E/I 7.20/50 = .144 ohms
Improper wiring or mishandling of multi-wire circuits can cause _______. (a) better power quality (b) a fire hazard (c) equipment failure (d) a fire hazard/and or equipment failure
a fire hazard/and or equipment failure
A typical 2-wire circuit flow over both the phase and and neutral wires and the circuit voltage drop includes the voltage drop of ________ wire(s) (a) zero (b) one (c) both (d) three
both
The grounded wire is a wire that is intentionally _______ to the Earth. (a) grounded (b) bolted (c) earthed (d) bonded
grounded
The common point of a 4-wire, three phase wye-connected system; the midpoint of a 3 wire, single phase system; or the midpoint of the single phase portion of a three phase, delta-connected system is referred to as the "_______ point." (a) neutral (b) phase (c) copper (d) none
neutral
A balanced 3-wire, single phase or 4-wire three-phase multi-wire branch circuit has current flowing only on the phase circuit wires and the circuit voltage drop includes the voltage drop of _______ wires(s). (a) one (b) two (c) three (d) four
one
Because of the dangers associated with an _______ neutral wire, the continuity of the neutral wire(s) in a multiwire branch circuit cannot depend upon the receptacle. (a) closed (b) open (c) ungrounded (d) grounded
open
The formula wheel is divided into ______ sections with three formulas in each section. (a) two (b) three (c) four (d) five
four
A ______ wire results in greater wire resistance and greater wire voltage drop. (a) wider (b) shorter (c) longer (d) nonen
longer
If the continuity of the ________ wire of a multi-wire circuit is interrupted (opened), there could be a fire and/or destruction of electrical equipment resulting from over voltage or under-voltage. (a) grounding (b) neutral (c) phase (d) all of these
neutral
What is the power loss at a terminal having a resistance of 0.40 ohms when carrying 20A? (a) 100W (b) 160W (c) 250W (d) 300W
P = I^2 x R 20^2 x .40 = 160W
The current on the neutral wire is equal to the difference in phase wire current because at any instant the currents on the two phase wires________ each other. (a) attract (b) oppose (c) equal (d) rely
oppose
Failure to terminate the phase wires to separate phases may cause the neutral wire to become _______ from excessive neutral current, and the insulation may be damaged or destroyed. (a) short circuit (b) grounded (c) overloaded (d) all of these
overloaded
If the number of wires is reduced for a multi-wire circuit, the size of the raceway can often be ________. (a) reduced (b) copper (c) increased (d) aluminum
reduced
For ac circuits, the ac ________ of a wire is greater than the dc resistance because of eddy currents and skin effect. (a) voltage (b) current (c) resistance (d) power
resistance