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Michigan Master Electrical > Masters Material Keypoints > Flashcards

Masters Material Keypoints Flashcards

1
Q

An electrical conductor is made up of 19 strands each with a diameter of 0.0837 inches. The approximate circular mil area of the conductor is approximately:

A

133,100 cmil
1 in = 1000 mil
0.0837 inches = 83.7 mil
83.7 mil x 83.7 mil = 7,005.69 cmil per strand
19 strands @ 7,0005.69 cmil = 133,108 cmil
Consulting Chapter 9, Table 8 133,108 cmil is close to 2/0 @ 133,100 cmil

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2
Q

When sizing short circuit and ground fault protection for motor circuits. Under what conditions are you allowed to round down to the next size OCPD?

A

Motor Feeders art 430.62
The maximum rating of overcurrent device for feeder supplying two or more motors is not permitted to be greater than the value determined by 430.62 (A)

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3
Q

When sizing short circuit and ground fault protection for motor circuits. Under what conditions are you allowed to round up to the next size OCPD?

A

Motor Branch Circuits art 430.52
430.52 (C)(1) exception 1 permits the ampere rating determined to be rounded up to the next standard rating of fuse given in 240.6(A).

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4
Q

A run of rigid metal conduit contains (6) size 4/0 AWG copper THW wires and (3) size 1 AWG copper THWN wires. The minimum trade size rigid metal conduit permitted for these wires is:
A. 1 1/4 inch
B. 1 1/2 inch
C. 2 inch
D. 2 1/2 inch
E. 3 inch

A

The cross-sectional area of the conductors must be first determined by using Chapter 9 Table 5.

THWN: 1 awg = 0.1562 sq in x 3 = 0.4868 sq in
THW 4/0awg = 0.3718 sq in x 6 = 2.2308 sq in
___________
Total conductor area 2.6994 sq in

Use Chapter 9 Table 4 to find RMC and the cross-sectional area over 2 wires/40 % to find a conduit larger than 2.6994 sq in. 3” RMC has a cross-sectional area of 3.000 sq in.

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5
Q

A resistance type heating element in an industrial electric space heater rated at not more than 48 amperes is required to be protected from overcurrent with a set of fuses or a circuit breaker with a rating not exceeding

A

48 A x 1.25 = 60 A
Section 424.22(B) requires that any resistance type heating element is required to be subdivided into loads not exceeding 48 amperes which are permitted to have OCPD rated at not more than 60 A. Electric heating loads are considered continuous.

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6
Q

A feeder protected by 800 ampere fuses is run from one part of a building to another under the floor in two parallel set of RMC with size 500kcmil copper RHW wires. The minimum size copper equipment grounding conductor permitted to be run in each conduit is:
A. 4 awg
B. 3 awg
C. 2 awg
D. 1 awg
E 1/0 awg

A

1/0 awg based of the overcurrent device and table 250.122

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7
Q

A service entrance with a 1000 ampere main circuit breaker is supplied with three parallel sets of size 400 kcmil copper THWN wires. A metal underground water pipe entering the building is used as a grounding electrode for the service. The minimum size copper grounding electrode conductor permitted to be run to the water pipe is:

A

3/0 awg based off the largest sum of the cross-sectional areas of the conductors.

3 sets x 400 kcmil = 1200 kcmil

table 250.102 (C)(1) grounding electrode conductor for 1200 kcmil is 3/0 copper

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8
Q

The copper THWN wires for a 480 volt, 3-phase feeder protected by 150 ampere time-delay fuses are increased in size from the minimum required 1/0 awg size to 3/0 awg to compensate for voltage drop. If the feeder is run in rigid nonmetallic conduit (PVC), the minimum size copper equipment conductor permitted to be run for this feeder is:

A

4 awg.
Since the conductor sizes are different, need to find the circulars for each in Chapter 9 Table 8.

3/0 awg = 167,800 cmils
1/0 awg = 105,600 cmils
_____________
1.589
Based off 150 A overcurrent protection, table 250.122 says that a 6 awg is required to be ran. Then the circular mils for 6 awg needs to be found.

6 awg = 26,240 cmils / 1.589 = 41,695 cmils; 4 awg is sized @ 41,740 cmils which would work.

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9
Q

A building served with 208/120 volt, 3-phase electrical system has a demand load or 750 amperes. The service consists of a single 1000 ampere main circuit breaker supplied with three parallel sets of service conductors each in a separate RMC. The neutral does not count as a current carrying conductor. The minimum size copper THWN ungrounded wire permitted for this service is:

A

400 kcmil
Section 240.4(C) requires the conductors to have an ampacity not less than the rating of the overcurrent device when the overcurrent device is rated in excess of 800 amps.

1000 A OCPD / 3 Sets run in Parallel = 333 A

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10
Q

When do you use the 60 Degree, 75 Degree and 90 Degree columns?

A

90 Degree for adjustments for the number of conductors and temperature derating
75 Degree for mostly everything that is terminated - Services, motors
60 Degree for anything less than 100A - Appliances most likely going to be the question

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11
Q

A single family dwelling has 100 amp service. What size feeder will be required to supply a 75 amp electric space heater and a 25 amp air conditioner?

A

An electric space heater is considered a continuous load.

75 A x 1.25 = 93.75 A

Since it is under 100 A, use 60 degree column for 2 awg

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12
Q

If you have 4 sets of 4 inch PVC with 500 kcmil THW copper wire in each pipe. what is the maximum size fused disconnect that can be installed?

A

500 kcmil copper = 380 A
380 A per 500kcmil x 4 sets = 1520 A

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13
Q

What is the expansion rate of 250 feet of PVC that goes from a temperature changed of -20 F to 80 F?

A

Per 352.44 the rate is 4.06 per 100 ft at a temp change of 100 F
250 ft is 2.5 times larger than 100 ft
4.06 x 2.5 = 10.15

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14
Q

What article is Low-Voltage Suspended ceiling power distribution systems?

A

Article 393

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15
Q

Fixed electric space heating equipment shall be rated for how many amps?

A

60 A ; Section 424.22(B)
This is for resistance type heating elements. Do not confuse this with the branch circuit feeding 2 of more fixed heating elements.

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16
Q

What is the maximum surface temperature of T2A?

A

536; Table 500.8(C)

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17
Q

What is the difference between repair garage minor and repair garage minor?

A

Repair garage major is where class 1 liquids or gaseous fuels are transferred or dispersed or where lighter than air gaseous fueled vehicles are repaired or stored. Repair garage minor does not have these class 1 liquids or gaseous fuels not stored or transferred.

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18
Q

What size RMC pipe is needed for the total square inch area (including insulation) of: (4) # 8 THHN and (6) #10 THHN wires?

A

Use Chapter 9 Table 5 for insulated approximate area.

8 awg = 0.0366 sq in
10 awg = 0.0211 sq in

4 conductors x 0.0366 sq in = 0.1464
6 conductors x 0.0211 sq in = 0.1266
______
0.2730 sq in

Chapter 9 Table 4 for RMC conduit larger than 0.2730 sq in. 1” RMC good for 0.355

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19
Q

What is the smallest size conductor you can run in parallel?

A

1/0 awg; 250.24(C)(2)

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20
Q

What is the formula for Voltage drop?

A

Circular Mils = (2 x K x I x D)
____________
(V) x (VD%)

Max voltage drop for feeder = 5%
Max voltage drop for branch = 3%
K for Cu = 12.9
K for Al = 21.2

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21
Q

Convenience outlets must be GFCI and located between _____ and _______ of the inside of the wall of a pool

A

6’ and 20’

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22
Q

Flexible cords must have an equipment grounding conductor no smaller than?

A

12 awg

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23
Q

Pool pump receptacles must be at least ______ from the inside wall of a pool?

A

680.22(A)(1-2)
6’

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24
Q

If the pool pump receptacle is GFCI protected, the pump receptacle may be located as close as ______ from the inside wall of a pool

A

6’; 680.22(A)(1)

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25
Q

Equipotential bonding conductors must be ____________

A

Solid and no smaller than 8 awg

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26
Q

If a fence is located _______ away it would need to be bonded due to fixed metal parts

A

5’

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27
Q

Connectors and Conduit to wet niche must be corrosion resistant

A

Rigid Brass; 680.23

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28
Q

What is the constant for Copper?

A

K= 12.9

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29
Q

What is the constant for Aluminum?

A

K= 21.2

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30
Q

How many Kilowatts will there be for a 3 phase 240V, 40 amp electric welder

A

(1.73 x 240V) x 40 A = 16,6000W/1000 = 16.6 kW

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31
Q

A 20 HP 460V, 3 phase motor has a nameplate kilovolt ampere code letter M. What is the minimum locked rotor current for this motor?

A

Tbl 430.7(B)

Min is 10 x 20 HP = 200
________________
(1.73 x 460V) / 1000
Locked Rotor kVA = 251 A

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32
Q

What is the branch circuit ampacity for a 3 phase 460V 10 HP motor that has a short time duty operation with a 15-minute time rating?

A

Tbl 430.22(E)

14 A x 1.2 = 16.8 A

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33
Q

What is the motor tap rule for 15’?

A

Per 430.28
Over 10’ but less than 25’ must have an ampacity of atleast 1/3 of the feeder conductors.
175 A x 33% = 57.75 A
#6 Wire, less than 25’ you do not have to fuse

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34
Q

Non motor generator arc welders are being served by a branch panel. There are (2) 120A welders with a 70% duty cycle, (1) 90A welder with a 80% duty cycle and (1) 250A welder with a 50% duty cycle. What is the minimum disconnect for this branch panel?

A

Step 1. Step 2. –>tbl 630.11(A)

120A .84 = 100.8A
120A .84 = 100.8A
90A .89 = 80.1A
250A .71 = 177.5A

Step 3. Step 4.–>tbl 630.11(B)

177.5 x 100% = 177.5A
100.8 x 100% = 100.8A
100.8 x 85% = 85.86A
80.1 x 70% = 56.07A
________
420.05 Disconnects must be able to hold this so 500A

35
Q

A motor generator type arc welder has a nameplate primary current rating of 95A and a duty cycle of 80%. What is the minimum ampacity of the branch circuit conductors and the maximum rating of the branch circuit OCPD?

A

95 A x .91 = 86.45 A is the minimum ampacity for the circuit
95 A x 200% = 190A 200A would be the max standard size OCPD

**look for keywords of either nonmotor or motor generator for Arc welder. If not, then it’s a resistance welder.

36
Q

A ______ or __________ can pull a permit and be responsible for the work on a single family dwelling

A

Homeowner or electrical contactor;
ACT 407 339.5737 sec 737 (1) and (3) (G)

37
Q

Master or Journeyman license issued in Michigan expires _________ of each year and must be renewed within _______. Not renewing in this time may result in loss of license and additional fees.

A

December 31st, 60 days
ACT 407

38
Q

A permit issued shall not last longer than ________

A

180 Days
MI Part 8

39
Q

A holder of a master electrical license may qualify ____ electrical contractors licenses

A

1
ACT 407

40
Q

___________ means a person, firm, or corporation, engaged in the business of erecting, installing, altering. repairing, servicing, or maintaining electrical wiring, devices, appliances or equipment.

A

Electrical contractor
ACT 407

41
Q

Feeders or services more than ______ amps and more than ________sq ft require the submission of plans and specifications with the electrical permit application.

A

400 A, 3,500 sq ft
MI Part 8

42
Q

An electrical contractor doesn’t need permit for ____________

A

minor work ($100.00 or less)
ACT 407

43
Q

A Capacitor is rated at 120V and 20 A. What is the watts?

A

460.8(a)

120V x (20 x 1.35) = 3240 W

44
Q

A restaurant has a 15.5’ plug strip for all their television systems which are likely to be used at the same time. What is the VA?

A

220.14(H)(2)
Keywords: Plug strip = fixed multioutlet
Likely = 180 VA per foot
IF it was unlikely, 180 VA per 5 foot
16’ x 180 VA per outlet = 2,880 VA

45
Q

What is the expansion rate of 500’ of type RTRC. That goes from a temperature change of 80 F degrees to 50 F degrees

A

tbl 355.44
Temperature change = 30 F degree
expansion per (in /100’) = 500’ / 100’ = 5 multiplier
For 30 F degree changed = 0.54 (in/100’)

5 multiplier x 0.54 (in / 100’) = 2.7

46
Q

What is the minimum rating for a laundry circuit in a single family dwelling?

A

Tbl 220.50(B)

20 A 1500W

47
Q

18’ of show room window requires home many receptacles above the window?

A

210.62
Installed with 18” of the top of a show window for each 12 linear ft or major fraction thereof
18’ is major fraction over 12’

2 Receptacles

48
Q

A conference room is 250 sq ft and has a 12.5’ wall. How many floor receptacles are needed?

A

210.71(B)(2)

1 recept

49
Q

The conductors of festoon lighting shall be supported by messenger wire in all spans exceeding?

A

225.79(C)
40’

50
Q

Circuit breakers used as switched in 120V fluorescent lighting shall be marked as?

A

240.83(D)

SWD and HID both for fluorescent

51
Q

What is the minimum height of a service entrance conductor above a pedestrian sidewalk?

A

230.24(B)(2)
10’
If voltage was added, it would change to 15 feet. Keep an eye out for this for either the service or pool question

52
Q

What cannot be connected to the supply side of a service disconnect?

A

230.82 (1-9)

53
Q

What is the minimum size main bonding jumper for an 800Kcmil service entrance conductor?

A

Tbl 250.102(C)(1)
2/0 awg

54
Q

What is the minimum size copper grounding electrode for a 200A single phase dwelling copper feeder?

A

Tbl 310.15(B)(16)–>250.66
Services use 75 degree C
Know dwelling services = 83%
200 A x 0.83 = 166A

55
Q

2 of more fixed electrical space heating equipment shall be rated for how many amps?

A

424.3
30 A
Take note of the 2 or more.

56
Q

An outdoors gasoline dispensing device up to 18” above grade level within 20” horizontally of any edge of the enclosure is

A

514.3(B)(1)
Class I Division II

57
Q

Liquid propane indoor storage tank are _________ division ______ within 5’ of tank.

A

514.3(B)(2)
Class I Division I

58
Q

A boat hoist receptacle shall be mounted not less than _____________ above the deck surface of the pier and not below the electrical datum plane of a fixed pier

A

555.19
12 inches

59
Q

Where would I find floor ventilation for commercial garages?

A

511
Tbl 511.3(C) deal with heavier than air fuel
Tbl 511.3(D) deal with lighter than air fuel

60
Q

The receptacle supplying power shall be on a separate circuit serving only the office furnishing and no other loads and shall be located not more than ________ from the office furnishings that is connected to it

A

605.9 (B)
12 inches

61
Q

Where is a portable optional standby source is used as a ______________ it shall be grounded to a grounding electrode.

A

702.11(a-b)
Separately derived system

62
Q

How many inches has to be separated between class 2 and class 3 circuits?

A

725.136(I)
2 inches

63
Q

How many # 8 THHW Compact conductors can be placed inside 1” EMT trade size conduit?

A

Take note: COMPACT CONDUCTORS, the table in the front of Annex C shows all the articles with a * where compact conductors are.
Annex C Tbl C.1(A)
6 conductors

64
Q

Class 3 inherently limited power source circuits are not rated for over how many volts?

A

Ch 9 tbl 11.B
100V

65
Q

How many #8 RHH* conductors can be placed inside 1” EMT trade size conduit?

A

Annex C tbl C.1
6
Pay attention to the * it is not the same as RHH, RHH* are conductors without outer coverings per Note 3

66
Q

Tamper proof receptacles have to be installed where?

A

406.12
There is a tab for this one and think about anywhere that kids may be present.
Elementary Schools/Preschool/Child Care

67
Q

A Car wash receptacle shall be considered what type of location?

A

406.9(B)(1) Exception
Wet Location

68
Q

SERVICES supplying the load to a separate building panel shall be wired how?

A

230.2
Can be taken from the LINE side and installed underground

69
Q

FEEDERS supplying the load to a separate building panel shall be wired how?

A

225.30
Can be taken from the LOAD side and installed underground or above head

70
Q

Where would I find additional ground and bonding requirements?

A

Tbl 250.3

71
Q

What column is used an appliance under 100A

A

60 Degree C

72
Q

Over what ampacity do you go down for a disconnect?

A

Over 800 A, go down
Under 800 A, go up

73
Q

What is the maximum voltage of low voltage suspended ceiling power distribution systems?

A

393.10(1)
30 V or less AC
60 V or less DC

74
Q

SERVICE CONDUCTORS passing through a building are considered outside the building if

A

230.6(1)
They are encased in 2 inches of concrete

75
Q

Electrical wires going over the surface of the pool must be atleast ________ above the waters surface

A

Tbl 680.9(A)
22.5’

76
Q

What is the allowable voltage drop of a circuit

A

Branch and Feeder circuits should not exceed 3% and the combined voltage drop of the feeder and branch circuit should not exceed 5%

77
Q

What is the NEC article for Welders

A

Article 630

78
Q

Determine the true power (Watts) of a 7.5 A load with a power factor of 87% supplied from a three-phase, 208V source

A

Watts = volts x 1.732 x amps x power factor
Watts = (208V x 1.732) x 7.5 A x .87
Watts = 2,350 VA

79
Q

The rating of a branch circuit is determined by the maximum ampere rating of the ____________

A

OCPD

80
Q

OCPD protecting branch circuits are not to be loaded more than ________ of their rated value when protecting continuous loads

A

80%

81
Q

When at 100 A rated circuit breaker is used to protect a branch circuit serving a continuous load, the load shall not exceed

A

80A
100 A x 0.8 = 80 A

82
Q

General lighting loads are to be supplied by:

A

210.23(A)
15 - and 20 A rated branch circuits

83
Q

What is the Volt-Amps/Sq ft for a dwelling without provisions for cooking

A

Tbl 220.12
2 VA
This is the same as hotels and motels

84
Q

What article would you find pull boxes

A

Art 314.28

Michigan Master Electrical (1 decks)

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