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NABCEP Entry Level > Electricity Basics > Flashcards

Electricity Basics Flashcards

Use this deck to learn about all of the basics of electricity.

1
Q

A 2500-W inverter is used to supply a 120-V AC load of 1500 watts. The ampacity of the wire at the inverter output must be at least how much?

A

26 A

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2
Q

What determines the voltage drop (not voltage drop percentage)?

A

Resistance and current

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3
Q

The duration, path, and path amount of current are all factors that depend on what?

A

The severity of electrical shock

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4
Q

What is a common use for linear current boosters?

A

Direct pumping applications and drop voltage

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5
Q

How does a battery charger work?

A

A battery charger sends an electric current through the battery in an efficient manner

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6
Q

Wire width determines what?

A

Ampacity

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7
Q

What are sealed batteries?

A

Valve-regulated lead-acid batteries

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8
Q

Four 6-volt, 240-Ah batteries are connected in 2 series groups, and there are 120-Ah batteries by another manufacturer available. Under what circumstance is it acceptable to incorporate all of these batteries into a 12-volt PV battery storage bank?

A

There is no acceptable connection of the batteries into a single battery bank

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9
Q

Can the same inverter used for a grid-tied system be used for off-grid with a charge controller?

A

No

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10
Q

A 26 ampacity of the wire at the inverter output with a 2500-W inverter is used to supply what?

A

A 120-V AC load of 1500 watts

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11
Q

If the maximum AC output of an inverter with 120-V AC output is 1500 W, what should be the rating of the circuit breaker at the point-of-utility connection?

A

20A

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12
Q

What is measured in watts per square meter?

A

Irradiance

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13
Q

What is the first step in system checkout?

A

Visually checking the entire system

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14
Q

All else being equal, what happens to temperatue when PV system voltage increases?

A

Since voltage and temperature have an inverse relationship, temperatue will decrease as PV system voltage increases.

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15
Q

What can a bimodal do?

A

It can work as grid-tied or stand-alone

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16
Q

What does low cell temperature do?

A

Increases voltage

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17
Q

What does irradiance proportionally affect?

A

Amperage

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18
Q

If the open circuit voltage (Voc) of a crystalline silicon PV array is 315V at 25 degree Celcius (STC), then according to the NEC (National Electric Code) chart, if the array is operated at -20 degrees Fahrenheit, maximum system voltage must be corrected to?

A

369 V

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19
Q

What is between the inverter and the array?

A

DC disconnect and/or sometimes a charge controller

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20
Q

A crystalline silicon PV array that has bipolar outputs of + 252V and - 252V with a common grounded conductor under Standard Test Condition is selected for a large single-family residence. The lowest expected temperature at the installation site is -25 degrees C. For this system, the maximum system voltage is closest to what?

A

605V

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21
Q

Valve-regulated lead-acid is a type of battery that is between what?

A

Sealed batteries

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22
Q

What can coincide with a loss of power in a 2 phase system?

A

Loss of power in a 3 phase system

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23
Q

What is an advantage of larger wire size?

A

Lower wire temperature, which decreases overall risk of electrical hazards.

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24
Q

What type of measurement do amperes express?

A

Rate of electric charge in circuit (current)

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25
Q

Besides increased ampacity potential, what should wires be oversized in battery interconnections?

A

To keep all battery currents as equal as possible

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26
Q

What factors affect ampacity?

A

Temperature, conductor type, and insulation type

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27
Q

Which of the following exhibits the most distortion: square wave, modified sine wave, and sine wave?

A

Square wave

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28
Q

What is sometimes in a grid-tied system?

A

Charge controllers

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29
Q

If an inverter is at maximum current, 2500W, full rating closest to 129A, and 88% efficiency, what is the input-voltage range at full output?

____V to ____V.

A

22V to 32V

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30
Q

When is a wire better than a conductor?

A

If the gauge is a number below 8

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31
Q

A 12 watt light is working on 12 volts. Approximately how many kilowatt hours does it use in a year if it is on 8 hours a day?

A

12w x 8hrs x 365 days/100 = 35.04 kwh/yr

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32
Q

On an I-V curve, what causes the curve to rise vertically?

A

More sunlight, more panels in series, and/or more amperage

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33
Q

What type of weather causes a voltage drop?

A

Because voltage and temperature have an inverse relationship, hot weather causes voltage to drop.

34
Q

How do you find the wattage at the maximum power point?

A

Multiply the voltage at maximum power by the current at maximum power

35
Q

An over-current protection, fuse, and switch all have the same function as what?

A

Circuit breaker

36
Q

How do you find the value of the current at the maximum power point on the I-V curve?

A

Extend a horizontal line from the curve in order to read the value on the vertical current scale, which represents the Imp

37
Q

If the rating of the circuit breaker at the point-of-utility connections is 20A, then what is the maximum AC output rating of an inverter with 12-V AC?

A

1500 W

38
Q

Ohm’s Law states that an increase in resistance is proportional to what?

A

An increase in voltage

39
Q

On a cloudy day, what effect does Ohm’s law have on PV watts?

A

PV watts decrease because of the relationship of volts to watts

40
Q

Which component of a PV system does NOT require UL or equivalent listing?

A

The concrete anchors

41
Q

Visually inspecting the entire system is the first step to what?

A

System checkout

42
Q

What is the term for what happens when you add small amounts of impurity elements to semiconductors to alter their electrical properties?

A

Doping

43
Q

How is irradiance measured?

A

Watts per square meter

44
Q

A 100 watt light bulb is working on .91 amps. How many volts are there?

A

110 volts

V = P/I = (100/.91) = 110

45
Q

What is the maximum number of series connected Kyocera KC200GT (Vmp = 26.3) modules that would be in the operating range of the SMA 2500 U inverter? Assume STC conditions.

A

22

46
Q

The ___ converts DC at one voltage to AC at the same or another voltage.

A

Inverter

47
Q

How does wire size relate to temperature?

A

Increased wire size prevents wires from over-heating

48
Q

When are charge controllers required?

A

For systems with PV amps that are more than 3% of the battery capacity

49
Q

An AC connect is between what?

A

The panel and the inverter

50
Q

If the gauge is a number below 8, then the wire is what?

A

A better conductor

51
Q

Vmp is horizontal to Imp on what?

A

On an I-V curve

52
Q

What type of inverter can work as grid-tied or stand-alone?

A

Bimodal

53
Q

In terms of voltage, Amps determine what?

A

Voltage drop (not voltage drop percentage)

54
Q

In the event that the utility voltage is lost in a utility-interactive system that has battery backup and an optional standby system AC distribution panel, what happens if the inverter is programmed in the sell mode?

A

The inverter should not supply power to the terminals connected to utility point-of-connection.

55
Q

A crystalline silicon PV array that has bipolar outputs of + 252V and - 252V with a common ground conductor under STC is selected for a large single-family residence. The lowest allowable ambient temperature in which the system can be installed at a single-family dwelling is what?

A

-25 degrees Fahrenheit

56
Q

If the current in one source circuit is significantly lower than the currents in the remaining source circuits of a PV array, and all modules are in full sun, then without disconnecting any conductors, what is an appropriate follow-up test?

A

To measure the individual module voltages in this source circuit

57
Q

A 2500-W inverter with an input-voltage range of 22V to 32V has an efficiency of 88% at full output. What will the maximum inverter input current at full rating be closest to?

A

129 A

58
Q

What converts a high input voltage to a lower output voltage and a low input current to a higher output current?

A

A linear current booster

59
Q

What is the order of wave types from most distorted to least distorted?

A

Square wave, modified sine wave, sine wave

60
Q

What does the order of PV charge controller, battery inverter, and grid accomplish?

A

Utility interconnection

61
Q

Why are sine wave inverters required for connection to utility lines?

A

They are the only inverters that have low enough harmonic distortion

62
Q

What does irradiance NOT affect proportionally?

A

Nominal operating cell temperature (NOCT), air mass, and voltage

63
Q

A 200 watt clothes dryer is working on 220 volts. How many kilowatt hours does it take to dry clothes for 45 minutes with a duty cycle of 50%?

A

200 w = 2kw x .75hr x .5 duty = .75 kwh

64
Q

What is irradiance?

A

Power

65
Q

What is commonly used in direct pumping applications and drop voltage?

A

Linear current boosters

66
Q

Imp is on the vertical y-axis of what?

A

An I-V curve

67
Q

What does the severity of electrical shock depend on?

A

The duration, path, and amount of current

68
Q

If I = V/P then what do V and P equal?

A

V = IR and P = VI

69
Q

The purpose of a linear current booster is to…

A

Convert a high input voltage and low input current to a lower output voltage and a higher output current.

70
Q

The purpose of an inverter is to…

A

Convert DC at one voltage to AC at the same or another voltage.

71
Q

A 100 watt light bulb is working on 110 volts. How many amps are there?

A

0.91

(100/110)

72
Q

What is the order of devices by which utility interconnection is accomplished?

A

PV charger controller, battery inverter, grid

73
Q

What is between the panel and the inverter?

A

An AC disconnect

74
Q

The possibility of using junction boxes (terminal blocks) or switch boxes that are too small to house the large wire is a concern associated with what?

A

A concern with 12-V PV systems that use large wire sizes to minimize voltage drop

75
Q

Keeping all battery currents as equal as possible is a good reason for doing what?

A

A good reason for large wire sizes in battery interconnections even if they are oversized for ampacity

76
Q

Is STC an I-V curve parameter?

A

No

77
Q

Where are functions of linear current boosters commonly used?

A

In grid-tied systems

78
Q

Does an electrolyte freeze if a battery is fully charged?

A

No. Unless the temperature drops to -92 fahrenheit

79
Q

Concrete anchors do NOT require what?

A

UL or equivalent listing

80
Q

What is doping?

A

Adding small amounts of impurity elements to semiconductors to alter their electrical properties

NABCEP Entry Level (7 decks)

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