Download Module 2 Unit 6, 7, 8

Module 2 Unit 6, 7, 8
1. What is the definition of an ideal conductor? Material that will carry the greatest
current with the lowest temperature rise
2. How much does copper weigh compared to aluminum? More than 3 times as
much
3. What is ductility? Ability of a material to be drawn into a wire
4. What is malleability? Ability of a material to be rolled or hammered into thin
sheets
5. What are three problems with aluminum wire? Rapid oxidation, electrolysis, and
cold flow
6. What is cold flow in an aluminum wire? Aluminum can take on a new shape (in a
terminal connection) and reduce the pressure on the connectors
7. How is steel incorporated into electrical systems? Strength member with copper
or aluminum wound around it
8. What is hard-drawn copper wire? Where is it used? Wire that has been “workhardened” by drawing it through dies. Often used for outdoor overhead wiring
9. What is the purpose of an annealing oven for wire? Heat and soften wire so it can
be made in any size
10. Where are bus bars typically used? High current applications (Industrial)
11. What requirement of a stranded conductor will determine the number and size of
the individual strands? Current-carrying capacity
12. What is a compact concentric wire? Tightly compacted wire with smoother
outside edge and minimum diameter
13. What are the four conditions that must be met by conductor insulation? 1. Proper
voltage rating 2. Proper temperature rating 3. Appropriate for the location (wet,
hazardous, etc.) 4. Protected from mechanical damage
14. What are five insulating materials for conductors? 1. Enamel 2. Varnished
cambric 3. Rubber 4. Thermoplastic 5. Minerals
15. What are the two colors for the identified conductor in a circuit? White or natural
grey
16. What are two methods for identifying a ground or bonding wire? Green color or
bare copper
17. Where would the largest conductors be found in a residential installation? Service
equipment
18. What is the most common application for NMD-90 sheathed cable? Residential
branch circuit wiring
19. What are the important features of fixture wire? Stranded, flexible, and hightemperature
20. What is low voltage according to the CEC? 31-750 Volts
21. What is the term used to describe circuits of less than 30V according to the CEC?
Extra-low voltage
22. Give some examples of Class 2 circuits. Door bells, buzzers, thermostats, lowvoltage relays, etc.
23. List three of the most common cable assemblies in residential construction. Nonmetallic sheathed cable, armored cable, aluminum-sheathed cable (MI, Service
entrance, Neutral-support, and flexible cord)
24. What is “loomex”? Non-metallic sheathed cable
25. What is NMW cable? Non-metallic sheathed cable for wet locations
26. What is NMU cable? Non-metallic sheathed cable for underground locations
27. What are two limitations on Non-metallic sheathed cable? Limited to 300 Volts
and wood-frame construction
28. What is another name for Armored Cable? BX
29. What are the voltage ratings for TECK cable? 600V-5000 V
30. How many PVC jackets are on teck cable? 2
31. What is corflex? Aluminum-sheathed cable
32. What is the powder in a mineral-insulated cable? Magnesium-oxide
33. What is the greatest advantage of mineral-insulated cable? Fire rating
34. What is the limitation of light-weight, mineral-insulated cable? 300 Volts max
35. How are terminations made for MIC cable? Termination kits
36. What is NSC (neutral support cable) typically used for? Secondary distribution to
overhead services
37. What are flexible cables typically used for? Portable equipment with attachment
plugs
38. What is the difference between “SJ” and “S” flexible cord? SJ is 300 Volt and S is
600 Volt
39. What is flat-conductor cable used for? Wiring across floors in office areas
(Under-carpet strip)
40. What determines the ampacity of a panel? Size of bus bars
41. How are splitter boxes rated for amperage? Size of bus bars
42. What is busway or busduct? Prefabricated sections (Often with tap offs)
Unit 7
1. What is a “mil”? 1/1000th of an inch
2. What is the cross-sectional area of a conductor? (Physically) Square of the wire
diameter (D2)
3. What is a “circular mil”? Cross-sectional area of a wire with a diameter of one mil
4. What is “KCM”? Metric for 1000 circular mils
5. What is “MCM”? Roman numeral for 1000 circular mils
6. How are rectangular bus bars measured? Square mil area
7. What type of wire is measured with a wire gauge? Solid
8. What is the smallest wire size manufactured? No.50
9. How do you calculate CM for a conductor when you know the diameter in mils?
D2
10. How do you calculate the diameter in mils for a conductor when you know the
CM? D = √CM
11. How do you calculate SMA for a conductor when you know CMA? SMA = CMA
x .7854
12. What is the SMA for a busbar measuring ½” x 1 ½”? 500 mil x 1500 mils =
750,000 SMA
13. What is the CMA for the busbar in question 12? CMA = SMA/.7854 =
750,000/.7854 = 954,927
14. What are the specifications for No.10 wire? (CM, mils, and Resistance) CM =
10,380, Diameter = 102 mils, and Resistance = 1Ω per 1000’
15. What would you estimate the resistance per 1000’ of No.6 wire to be, based on
the values given for #10? .396 Ω per 1000’
16. What would you estimate the CM of #6 wire to be, based on the values given for
No.10? 26,157 CM
17. What happens to the resistance of wire as the gauge number gets larger?
Resistance is higher
18. What factors help determine the material for a conductor? Cost, strength, and ease
of use
19. What is the relationship between resistance and conductance? (Think about it)
They are inversely proportional (If one increases the other decreases)
20. When is resistance in an electric circuit a good thing? Electrical heating devices
(Toaster, iron, and electric heater)
21. What are the four factors that affect conductor resistance? 1. Natural resistance of
the material (K) 2. Length of wire 3. Cross sectional area 4. Temperature
22. What is the formula to find the resistance of a length of wire? R = K x L / CMA
23. What is the resistance of 100’ of No.14 copper wire? R = 10.4 x 100 / 4096 = .254
Ω
24. What is the resistance of 2000’ of No.2 aluminum wire? R = 17 x 2000 / 66,370 =
.512 Ω
25. Which materials have a constant (regardless of temperature change) resistance?
Manganin
26. What factors affect the ampacity rating of conductors? Conductor material, size,
type of insulation, whether in free air or raceway or cable, and surrounding air
temperature (ambient temperature)
27. What is the maximum allowable ampacity for a No.12 TW copper conductor in a
cable according to the CEC? 25 A
28. What is the maximum allowable ampacity for a No.10 TW copper conductor in a
cable according to the CEC? 30 A
29. What is the maximum allowable ampacity for a No.000 TW copper conductor in a
cable according to the CEC? 165 A
30. What is the maximum allowable ampacity for a No.12 TW aluminum conductor
in a cable according to the CEC? 20 A
31. What is the maximum allowable ampacity for a No.8 TW aluminum conductor in
a cable according to the CEC? 35 A
32. What is the maximum allowable ampacity for a No.00 TW aluminum conductor
in a cable according to the CEC? 115 A
33. What is the maximum allowable ampacity for a No.10* R90 aluminum conductor
in free air according to the CEC? 40 A
34. What is the maximum allowable ampacity for a No.2 R90 aluminum conductor in
free air according to the CEC? 150 A
35. What is the maximum allowable ampacity for a No.0000 R90 aluminum
conductor in free air according to the CEC? 315 A
36. What is the maximum allowable ampacity for a No.10 R90 copper conductor in
free air according to the CEC? 55 A
37. What is the maximum allowable ampacity for a No.3 R90 copper conductor in
free air according to the CEC? 165 A
38. What is the maximum allowable ampacity for a No.10 TW copper conductor if
there are 15 in a conduit? 21 A
39. What is the maximum allowable ampacity for a No.3 TW copper conductor if
there are 5 in a conduit? 68 A
40. What is the maximum allowable ampacity for a No.2 R90 aluminum conductor if
there are 10 in a conduit? 70A
41. What is the maximum allowable ampacity for a No.10 TW copper conductor in a
conduit when the ambient temperature will be 40 degrees C? 24.6 A
42. What is the maximum allowable ampacity for a No.4 R90 copper conductor in a
conduit when the ambient temperature will be 40 degrees C? 86.45 A
43. What is the maximum allowable ampacity for a No.10* TW aluminum conductor
in a conduit when the ambient temperature will be 50 degrees C? 14.5A
44. What is the maximum allowable ampacity for a No.8 TW aluminum conductor in
a conduit when the ambient temperature will be 50 degrees C? 20.3 A
45. What is the maximum allowable ampacity for a No.10* R90 aluminum conductor
in a conduit when the ambient temperature will be 40 degrees C? 31.85 A
46. Which CEC table gives allowable ampacity for flexible cords? Table 12
47. Short cables made from a good conductive material have no line loss. True or
False?
48. What are the three formulas for calculating line loss? P = E x I, P = I 2R, and P =
E2/R
49. What is the formula for voltage drop? VD = 2 x K x L x I / CMA
50. What is “K” in the formulas for conductors? Resistivity of material (copper) at
200C
Unit 8
1. What are the advantages of an Edison three-wire circuit? 1. Reduced copper
conductor ampacity requirements 2. Two different voltages (120/240) 3. Line
drop (volts) and line loss (watts) are reduced 4. Improved safety through
grounding the neutral
2. Where is the neutral conductor connected to the transformer in an Edison threewire circuit? Directly to earth
3. At what point is the neutral wire in a three-wire system to be grounded? At the
supply and at the main switch
4. When does it become especially important for a system to be grounded? Fault
occurs
5. What is a bonding conductor used for? Ground all metallic non-current-carrying
parts of a system
6. What is the result of a fault to ground in a piece of equipment that is properly
bonded and grounded? Tripped overcurrent device
7. What is a balanced load condition in a three-wire circuit? Current equal on both
lines
8. Can a circuit with both 120V and 240V loads be balanced? Yes
9. What is the benefit of balanced loading in a three-wire circuit? Reduced line loss
10. What is the phrase that describes the amount of current on the neutral wire of a
three-wire circuit? Unbalanced load
11. What is the result of an open or broken neutral wire in a balanced three-wire
circuit? Loads are connected in series across 240V with no noticeable change in
operation
12. What is the result of an open or broken neutral wire in an unbalanced three-wire
circuit? (See figure 12) Severe voltage imbalance can result in damaged
equipment
13. Is the neutral conductor ever fused? Why? No. Serious problems can occur if it
opens
14. What is Kirchhoff’s voltage law? The sum of voltage drops or rises in any circuit
must equal the supply voltage
Skip to page 232 (Open Neutral Connections)
15. What are three things you never do with a neutral conductor? Never fuse the
neutral, never switch the neutral, and never open the neutral on a live system
16. What is the maximum voltage that can be applied to one of the loads in a 240V
three-wire system when the neutral wire is open? Close to 240 V
17. What is the voltage across an open neutral in a balanced three-wire circuit? Zero