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Kansas Electrical Prep > Formulas > Flashcards

Formulas Flashcards

1
Q

One kVA is equal to _______

100VA
1000VA
1000 volts
10,000 VA

A

1000 VA

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2
Q

5,000 watts is equal to ______

500 kW
5 kW
.50 kW
50 kW

A

5000/1000=

5 kW

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3
Q

Where a 120-volt microwave oven is rated 1200 watts, how much current, in amperes, will the microwave oven draw?

.10 amperes
5 amperes
10 amperes
15 amperes

A

Current Formula

I = 1200watts/120volts = 10 amperes

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4
Q

When an electric hair dryer draws 6 amperes when connected to a 120 volt source, the rating of the hair dryer is ______

720 watts
750 watts
20 watts
200 watts

A

Power Formula = P/IxE

P = I x E 
Power = Current x Volts
Power = Volts x Amps

P= 6 amperes x 120volts = 720 watts

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5
Q

When a 240 volt, single phase branch circuit has a current flow of 20 amperes, what is the resistance, in ohms, of this branch circuit?

3 ohms
6 ohms
9 ohms
12 ohms

A

Ohms Forumla = E/IxR
R= E/I
Resistance = Volts/Amps
R = 240volts/20amps = 12 ohms

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6
Q

When a 2kW electric baseboard heater is connected to a 240 volt, single phase circuit, the current flow in the circuit is _____

  1. 15
  2. 33
  3. 50
  4. 66
A

Current Formula = I x E/1,000

I =kW x1,000/E
I = 2kW x 1,000 / 240 volts
I = 2,000/240
I = 8.33 amperes

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7
Q

Determine the power consumed, in VA, by lighting load that operates at 115 volts, draws eight amperes and has a power factor of 80 percent.

1150 VA
960 VA
920 VA
736 VA

A

Power Formula =W/VAxPf

Power factor is the ratio between true power expressed (watts,kW) and the apparent power expressed (volt-amps, VA, kVA)

  • *True power is expressed as watts.
  • *True power (watts) equals apparent power (VA) in an electrical circuit or load containing resistance
    • The true power (watts) of a SINGLE PHASE circuit or load that contains inductance can be calculated with this formula:

Watts=volts x amperes x power factor
VA = 8 amperes x 115 volts x .8(pf) = 736 VA

A 3 PHASE formula
Watts = volts x 1.732 x amperes x power factor

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8
Q

A 150 ampere rated, 120/240 volt, single phase residential service will have a volt-ampere rating of ________

180,000 VA
90,000 VA
36, 000 VA
72, 000 VA

A

Power Formula = P/IxE

Power = Current x Volts
Power = Volts x Amps

P = 240volts x 150 amperes = 36,000

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9
Q

What is the power factor of a 6,500 watt load that draws 33 amperes of current when connected to a 240-volt, single phase source?

  1. 21 percent
  2. 0 percent
  3. 0 percent
  4. 04 percent
A 
Power Factor Formula = W/Pf xVA
Pf = W/VA
Pf = 6500watts/ 240volts x 33amps 
Pf = 6500 watts/ 7920 VA = .82
82%
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10
Q

A 15 kW, 208 - volt, single phase heat pump will have a full load current rating of _______

72 amperes
46 amperes
66 amperes
33 amperes

A

Current Formula = kW x 1000/E

I = 15 kW x 1000 / 208volts
I = 15000/208
I = 72amperes
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11
Q

Given: An electric baseboard heater has a total resistance of 22 ohms and is supplied with a 240 volt, single phase power source. Determine the current.

  1. 9 amperes
  2. 8 amperes
  3. 09 amperes
  4. 01 amperes
A

Ohms Forumla = E/IxR

I = 240volts/22ohms

I= 10.90 amperes

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12
Q

The power factor of a 5kW load drawing 30 amperes of current when connected to a 208-volt, single phase source is

92%
46%
80%
83%

A

Power Factor Formula
W/Pf xVA
Pf = W/VA
Pf = 5 kw x 1000 / 208volts x 30amps

= 5000/6240 VA

=.80

80%

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13
Q

A 200 ampere rated, 208Y/120 volt, three phase, 4 wire commercial service will have a VA rating of

360 VA
43,231 VA
41,600 VA
72, 051 VA

A 
Power Formula, 3 phase - 1.732
P/IxE
P = I x E
Power = Current x Volts
Power = Volts x Amps

VA= 208volts x 1.732 x 200A = 72,051

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14
Q

What is the rated secondary current of a 600 VA, single phase transformer at unity power factor, that has a 200 volt input and a 15 volt secondary?

10 amperes
20 amperes
13 amperes
40 amperes

A 
Current Formula
I = P/E
I = Power/Voltage
I = Watts/Volts
I = VA/Volts

I = 600 VA/15 volts = 40 amperes

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15
Q

Ohms Law is a relationship between

current, voltage, amperes
current, voltage, power
voltage, current, resistance
voltage, power, resistance

A

Ohms Law
E / I x R
Volts / current x resistance

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16
Q

Determine the line current, in amperes, on a balanced three phased electrical system with a load of 25 kVA per phase and a line voltage of 208Y/120 volts Total power is 75 kVA

87 amperes
144 amperes
208 amperes
360 amperes

A 
Current Formula
I = P/E
I = Power/Voltage
I = Watts/Volts
I= VA/Volts
I = 75,000 VA / 208volts x 1.732
I = 75,000/360.25
I= 208.20 amperes
17
Q

If an industrial type HID luminaire (lighting fixture) rated at 300 watts is connected to a 120 volt branch circuit and is drawing three amperes of current, the luminaire has a power factor

83 %
93 %
1.2 %
79 %

A

Power Factor Formula

Pf = Watts/VA
Pf = 300 Watts / 120volts x 3 amps
Pf = 300/360
Pf = .83
18
Q

5 horse power is equal to

5kW
3,730 watts
5,000 watts
5 kVA

A

5HP x 746watts = 3,730watts

19
Q

When eight 400 watt metal halide luminaires lighting fixture each have a power factor of .86, are connected to a 277-volt, single phase lighting branch circuit, the full-load current (FLC) of the luminaires will be _______

  1. 55 amperes
  2. 54 amperes
  3. 43 amperes
  4. 68 amperes
A

Current Formula
I = P/E
I = Power/Voltage
I = Watts/Volts

I = 400 watts/ 277 volts x .86
I = 400 / 238.22
I = 1.679 amperes
20
Q

When a 400 amperes rated commercial service supplies with a 480Y/277 volt, three-phase, 4-wire electrical system, the service has a rating of

  1. 10 kVA
  2. 80 kVA
  3. 00 kVA
  4. 50 kVA
A

Power Formula, 3 phase

P = Amps x Volts x 1.732 / 1000
P = 400A x 480V X 1.732 / 1000
P= 332,544 VA / 1000
P= 332.5 kVA

Kansas Electrical Prep (6 decks)

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