Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Local 52 Test > Working with Electricity > Flashcards

Working with Electricity Flashcards

Line loss, power factor

1
Q

Paralleling

A

Increasing the number of conductors (usually 4/0)

cables must match in size, temperature rating, length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

half-million run

A

DOubling the conductors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

750 run

A

Tripling the run

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

million run

A

quadrupling the run

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Three-phase run

A

Five pieces

Doubled run- nine-piece run (ground not doubled)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

two factors in sizing feeder cable

A
  1. control of heat for safety
  2. perservation of voltage to allow for proper functioning of equipment
    must be sized to provide sufficient capacity to carry the full load of the overcurrent decie protecting tha tcircuit upstream, asllowing for exisiting conditions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Existing conditions

A

temperature rating of the overcurrent device,
length of time
temperature conditions
amount of ventilation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

runs longer than 150 ft

A

likely have unacceptable voltage drop if running near capacity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

sizing neutral conductors

A

dependent on the type of load
when loads are resistive- same sizing as the phase wizes
when powering reactive loads- (magnetic ballasts, non PFC electronic ballasts, large numbers of non-PFC fluorescent or LED fixtures)
neutral must by 130% of ampacity of phase conductors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

sizing of ground conductors

A

based on size of overcurrent protection

circuit protection up to 1600A per phase, single piece of 4/0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Sizing grounding electrode and bonding conductors

A

typically conductor is #2 AWG, would never need to be larger than a single-piece of 2/0.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

multiple power sources used in proximity, or in same building

A

grounds must be bonded

eliminates voltage potential between ground of one power souce and ground of another

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

line loss

A

is the erosion of voltage over a long distance caused by the resistance of the feeder cables
severity of line loss increases with the amount of current carried by a particular conductor
can assume 4V per 100 ft when running at 80% capacity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

assumed line loss at 80% capacity

A

4V per 100 ft

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

main causes of line loss

A
  1. length of the run
  2. cross-sectional area (large conductor, less the line loss)
  3. the load (large the amerage, larger the line loss)

(heat)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

other possible causes of line loss (other than amperage, distance, improperly sized conductors)

A

resistance, heat, line loss accours when…
1. connection weak or loose
2.cable is frayed
3. connector only partially inserted
4. loaded beyond its capaicty
5. stacking cables closely together
6.making severe bends in cable creates hotspot
heat increases resistancce
7. circular coils in a single condcutor, current carying cable creates impedance, results in line loss and increased heating.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Allowable voltage drop

A

amount of voltage drop that still allows acceptable performance from the equipment and does not cause harm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

NEC recommendation on acceptable voltage drop as percentage of rated voltage of load

For 120V, 208V, 240V, 480V

A

120V- 3.6V Feeders, 6V Overall
208V- 6.24V Feeders, 10.4V Overall
240V- 7.2V feeders, 12V Overall
480V- 14.4V feeders, 24V overall

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Effect of line loss on tungsten lights

A

light output fallsoff geometrically as voltage decreases
2k lamp at 90% of rated voltage (108V), produces 68% of its normal light output
Kevlin temperature also decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Effect of line loss on Power

A

loss of voltage= loss of power
Power loss in a cable increases as the square of the amperage.
doubling amperage, doubles voltage drop, power less increase fourfold.
Performance of generator is reduced

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Acceptable voltage range for electronic HMI ballasts

A

90-130V or 190-250V

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

result of voltage drop on constant power ballast

A

constant power electronic ballasts will draw more current if the line voltage decreases in order to maintain constant power to the lamp

ex: 4kw HMI is 19A at 240V
22A at 208V
24A at 190V

could overload the connectors on some ballasts

18kw ballast with 100A/240V Stage pin connectors
at 240V, is 80A per phase
at 208V, 93A
at 190V, 102A- overheating connector
most  use camlok connectors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Mitigating line loss by increasing voltage

Drawbacks

A

increasing voltage at the source:
–transformer with tap switch- plus and minus 5% output in 2.5% increments
–generator- increasing field strength of alternator
larger adjustments can harm genny, can destabilize frequency control
HOWEVER- equipment powered upstream wil be over voltage.
voltage drop is porportional to amperage load, so when load is reduced, voltage must be turned down
power source still working harder, loss of efficiency, greater fuel consumption, reduction of maximum power available
must effectively reduce line loss by adding copper- reducing resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Formula to find Voltage Drop for single-phase loads

A

Vd= 2KIL/Cm
or Vd=21.6I*L/Cm

21.6 times current times length/cross-sectional area

K= specific resistance of material composing a conductor. for copper, 10.8 @25 degrees C
I= current carried by the cable
L= the length of the wire in feet. the one-way distance from source to load
Cm= cross-sectional area of a wire in circular mils (cmil). These tend to be pretty big numbers. For example, 4/0 cable has a cross-sectional area of 211,600 cmil
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

1 mil in inches

A

1/1000 in

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

cmil

A

Cross-sectional area

(diameter in mils) squared

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

single-phase load

A

any load, regardless of voltage (120,208, 240) unless equipment requires all three phase wires to operate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

4/0

Cross sectional area and ampacity

A

211,600 cmil

405 A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

2/0

Cross sectional area and ampacity

A

133,100 cmil

300 A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q 
#2
Cross sectional area and ampacity
A

66,360 cmil

190 A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q 
#4
Cross sectional area and ampacity
A

41,740 cmil

140 A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q 
#6
Cross sectional area and ampacity
A

26,240 cmil

105 A

33
Q 
#12
Cross sectional area and ampacity
A

6,530 cmil

20 A

34
Q

4x 4/0

Cross sectional area and ampacity

A

846,400 cmil

1620 A

35
Q

3x4/0

Cross sectional area and ampacity

A

634,800 cmil

1215 A

36
Q

2x4/0

Cross sectional area and ampacity

A

423,200 cmil

810 A

37
Q

Formula for cable gauge for given voltage drop

A

Cm= 2KIL/Vd
Cm=21.6I*L/Vd
finding Cm, using acceptable Vd, divide by cmil of a certain cable and you know how many piece of that cable you need for a given load

38
Q

Formula for maximum current for a given voltage drop

A

I= VdCm/2KL
I=VdCm/21.6L
how many amps you can put through a given length and gauge of cable and remain within a specificed voltage drop

39
Q

Three-phase loads

A

ex: Luminy’s soft sun
three-phase step-down transformer
three-phase xenon power supply

40
Q

Formula, line loss for three-phase load

A

Vd=1.73KI*L/Cm

41
Q

Simple line loss calculation- 4/0

A

1.02 V per 100A per 100 ft

42
Q

Simple line loss calculation 2/0

A

1.62V per 100A per 100 ft

43
Q

Simple line loss calulation #2

A

3.25V per 100 A per 100 ft

44
Q

Weight lbs/ft of cable

A 
4/0- .96 lb/ft
2/0 .68 lbs/ft
4-wire banded #2 1.33 lbs/ft
5-wire banded #2 1.70 lbs/ft
100A #4 .72 lbs/ft
60A #6 .55 lbs/ft
multiconductor (Socapex) .75lbs/ft
45
Q

Formula for weight of a waterfall

A

(number of cables)x(weight per foot)x drop in ft

46
Q

Formula for maximum length given amperag eand voltage drop

A

L=VdCm/2K*I

L= VdCm/21.6I

47
Q

Types of electronics that cause non-linear loads

A

DC rectifiers, tryristors (SCRs), high-freqency switching power supplies (IGBTs) with large capacitors

48
Q

Issues caused by non-linear loads

A

overheating, failing equipment, efficiency losses, circuit breaker trips, excessive current on neutral wire, interference and isntability with generators, noisy or overheating transformers and service equipment, even loosened electrical equipment

49
Q

inductance

A

created by coils in a transformer, motor, or magnetic ballast
as current increases and decreases in acoil carrying AC current, a magnetic field exxpands outward from the center and then collapses back inward
as current increases, the circuit stores energy in the magnetic field, then as the current decreases, the circuit gets the energy back. the energy drawn and released by the magnetic field does not accomplish any actual work, energy just keeps circulating back and forth between the coil and power source
when the lines of flu of the magnInductive reactanceetic field grow and colapse, they sel-induce a voltage in the coil, the counter-e;ectromotive force (counter EMF). has opposite polarity of the applied voltage.

50
Q

unity power factor

A

100% power factor, 1.0 PF

51
Q

inductive reactance

A

opposition to the flow of current, applied voltage must overcome the induced voltage before current can flow through the circuit

52
Q

effect of inductive reactance on waveforms of voltage and current

A

inductive reactanc causes current to ag behind the coltage
the degree to which the two are put out of phase is expressed by the cosine of the phase angle between them. the phase angle depends ont eh relative amount of resistance and inductance offered by the load. the more they are out of phase, the lower the power factor.

53
Q

capactive reactance

A

opposition to the flow of current cause by capacitance.
induces a power factor of less than 100%
causes current to lead voltage

54
Q

power factor correction circuits

A

HMI ballasts have them to erstore the efficiency of a ballast.

55
Q

power factor

A 
the ratio of true power to apparent power.
true power(W)/apparent power(VA)=power factor
the feeder cable must be sufficient to supply the apparaent power, even thoguh only the true power does work
56
Q

apparent power

A

measure the current and the voltage,multiply (voltamps)

the amount of power traveling back and forth in the cables

57
Q

true power

A

the actual amount of energy being converted into real work bythe load- read with wattmeter

58
Q

formula for amperage needed when PF is known

A 
true power/E*pf=I
true power- rated wattage of the equipment
E- voltage
pf-power factor
I- current
59
Q

current waveform made of

A

fundamental frequency 60 Hz, with varying amounts of harmonic frequencies, especially, third-order (180 Hz) and fifth order (300 Hz) harmonics

60
Q

harmonics

A

multiples of the fundamental frequency

create heat in the cables and circuit and power source (transformer coils or generator windings) without doing any work

61
Q

effect of harmonic currents on the neutral wire

A

when an inductive or capacitive load causes current and voltage to be out of phase, or harmonics present, pahse currents no longer cancel when they return on the neutral.

62
Q

NEC requirements for non-linear loads

A

neutral to be able to carry at least 1.3 times the phase current.

63
Q

Mitigating non-linear loads and harmonic distortion

A

over-size (derate) the generator or transformer or use an appropriate K-rated transformer

64
Q

What to measure at the end of a run

A

-if circuit is live
-for proper polarity and ground
-check whether the system voltage is as expected (to be sure feeders connected properly)
check for voltage drop

65
Q

CAT I meter

A

electronics within an appliance or device

66
Q

CAT II

A

branch circuit receptables and commercial loads

67
Q

CAT III

A

permanently installed loads like motors, AC distribution panels or commercial lighting

68
Q

CAT IV

A

service entrance, main panel, and service meter

69
Q

Hazards of using lower category meter

A

possible for meter to short the circuit, arc, or blow-up in the user’s hand

70
Q

CAT IV protection

A

CAT IV meter has thicker insulation on test probes, bigger internal distances between electrical points, a fuse to protect the meter and the user, and a fuse to hel protect against high-energy transient voltages.
electrician required to wear face mask, electrical floves, welders jacket, and fire retardant clothing

71
Q

true RMS vs average responding

A

average responding assumes current is a sine wave, true RMS is needed with non-linear loads

72
Q

precautions when metering

A

hands, shoes, work areas dry
avoid metering in damp, humid conditions, or with dust or sawdust
place meter on stable surface or hook over stable vertical surface
make sure meter leads in good condition, connected to proper meter jack
select type of service and voltage range (start with highest and work down)
accidents caused when meter in amperage reading mode, or resistance or continuity mode when reading live circuit
touch probes to enutral terminal first, and phase terminal second.

73
Q

Circuit tester

A

tests 1) circuit is live 2)polarity is correct 3)grounding wire is present

74
Q

voltage sensor

A

senses magnetic field of electricity
checking if wire is live
prone to false positives

75
Q

Frequency meter

A

especially useful with HMI magnetic ballasts

cinecheck meter reads freq optically, held up to HMI running on magnetic ballast

76
Q

measuring amperage

A

with amp probe or clamp on ammeter
generally AC only
clamp meter measure magnetic field strength
with non-linear loads, need an AC-only RMS meter

77
Q

Continuity testing

A

only when power is not connected to the circuit

can twist wires on one end, and read from only the other end

78
Q

short circuit- testing

A

check continuity between wires
if you find continuity, there is a short, check each combination fo wires
remove bulb before testing for sorts on a light fixture

79
Q

wattmeter/power meter

A

clamp-on device like an ammeter, and probes like a voltmeter
reads true-power in a circuit
can account for the phase diference between curretna dn voltage when there is inductive or capacitive reactance in teh circuit
some require you to turn off power when connecting and disconnect, turn on power to take readsings
reads amperage and voltage separately

Local 52 Test (16 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions