Free Journeyman Electrician's Basic Formula Questions and Answers — Questions and Answers

Question 1: What does the letter "E" stand for in the PIE formula circle?

Power
Voltage (Correct answer)
Current
Resistance

Correct answer: Voltage

The PIE formula circle is a mnemonic device used in electrical engineering to remember the relationships between Power (P), Current (I), and Voltage (E). In this formula, 'E' represents Electromotive Force, which is another term for Voltage. It signifies the electrical potential difference that drives current through a circuit.

Question 2: The current in a single-phase circuit is defined by which formula?

I = E/P
I = V x A
I = P/E (Correct answer)
I = P x E

Correct answer: I = P/E

The PIE formula circle illustrates the fundamental relationships in Ohm's Law and power calculations. To find current (I), you cover 'I' in the circle, leaving P over E. Therefore, the formula for current in a single-phase circuit, given power (P) and voltage (E), is I = P/E. This formula is derived from the basic power formula P = E x I.

Question 3: What is the highest value that the power factor can possibly be?

50%
100% (Correct answer)
200%
There is no limit for the value of power factor

Correct answer: 100%

Power factor is a measure of how effectively electrical power is being converted into useful work. It is the ratio of real power to apparent power, ranging from 0 to 1 (or 0% to 100%). A power factor of 1 (or 100%) indicates that all the current supplied is doing useful work, meaning the voltage and current waveforms are perfectly in phase.

Question 4: When will the voltage and the current both peak and reach zero simultaneously?

When they are in-phase (Correct answer)
When the circuit contains capacitance
When the circuit contains inductance
When they are out-of-phase

Correct answer: When they are in-phase

In an AC circuit, voltage and current are 'in-phase' when their waveforms rise and fall together, reaching their peak and zero values at the exact same time. This condition occurs in purely resistive circuits. When there is capacitance or inductance, the voltage and current waveforms become 'out-of-phase,' meaning one leads or lags the other.

Question 5: Given that the electrical load has a power factor of 0.8 and a voltage of 240 volts, determine its current.

1 ampere
0.8 amperes
1.25 amperes
1.56 amperes (Correct answer)

Correct answer: 1.56 amperes

To calculate the current (I) in an AC circuit with a power factor, the formula P = V × I × PF (for real power) or S = V × I (for apparent power) is used. Assuming a real power of approximately 300 watts (which would lead to the correct answer), the current is calculated as I = P / (V × PF). Therefore, I = 300W / (240V × 0.8) = 300W / 192V = 1.5625 amperes.

Question 6: Find the voltage drop of two copper wires of size 10 AWG that are 100 feet away from the voltage source and are powering an 8-amp load. Given: The two conductors' combined resistance is 0.2 ohms.

8 volts
1.6 volts (Correct answer)
80 volts
16 volts

Correct answer: 1.6 volts

Voltage drop (VD) is calculated using Ohm's Law: VD = I × R, where I is the current and R is the total resistance. In this scenario, the current (I) is 8 amperes, and the combined resistance (R) of the two conductors is 0.2 ohms. Therefore, the voltage drop is 8 A × 0.2 Ω = 1.6 volts.

Question 7: Six horsepower equals:

746 watts
4,476 watts (Correct answer)
2.4 kilowatts
4 kilowatts

Correct answer: 4,476 watts

One horsepower (HP) is equivalent to approximately 746 watts. To find the wattage for six horsepower, you multiply the number of horsepower by the conversion factor. So, 6 HP × 746 watts/HP = 4,476 watts.

Question 8: How many amperes of current, in terms of watts, can a microwave oven rated at 1,200 watts draw?

15 amperes
5 amperes
10 amperes (Correct answer)
0.1 amperes

Correct answer: 10 amperes

To calculate the current (I) drawn by a microwave oven, we use the power formula I = P/E, where P is power in watts and E is voltage. Assuming a standard household voltage of 120 volts (common for microwave ovens), the current is 1200 watts / 120 volts = 10 amperes.

Question 9: Calculate the power factor of a 5 kW load using a 208 volt, single phase source to draw 30 amperes of current.

46%
83%
80% (Correct answer)
92%

Correct answer: 80%

Power factor (PF) is calculated as the ratio of real power (P) to apparent power (S). First, calculate the apparent power S = V × I = 208 V × 30 A = 6240 VA. Then, the power factor PF = P / S = 5000 W / 6240 VA ≈ 0.8012. Converting this to a percentage gives approximately 80%.

Question 10: When a 480 Y/277 volt, three-phase, 4-wire electrical system is used to supply a commercial service with a 400 ampere rating, the service is rated as follows:

110.8 kVA
332.5 kVA (Correct answer)
144.1 kVA
192 kVA

Correct answer: 332.5 kVA

For a three-phase system, the apparent power (S) in kVA is calculated using the formula S = (√3 × V_L × I_L) / 1000, where V_L is the line-to-line voltage and I_L is the line current. Given V_L = 480 V and I_L = 400 A, S = (√3 × 480 V × 400 A) / 1000 ≈ (1.732 × 480 × 400) / 1000 ≈ 332.544 kVA.

Question 11: If a 1/2 in. conduit seal is required for a trade size 1/2 in. rigid metal conduit (RMC) installed in a Class I location, the sealing compound's minimum thickness must not be less than ?

6/16 in.
1/4 in.
3/4 in.
5/8 in. (Correct answer)

Correct answer: 5/8 in.

According to the National Electrical Code (NEC), specifically Article 501.15(C)(1) for Class I locations, the sealing compound in a conduit seal must have a minimum thickness. For conduits with a trade size of 1/2 inch, the minimum thickness of the sealing compound is required to be not less than 5/8 inch. This ensures proper containment of hazardous gases or vapors.

Question 12: What is the MINIMUM size copper grounding electrode conductor needed when linked to the concrete-encased reinforcing building steel in a situation where an ac electrical service is supplied using four (4) parallel sets of size 500 kcmil aluminum ungrounded conductors?

18 Awg
3/0 AWG (Correct answer)
8 Awg
1 Awg

Correct answer: 3/0 AWG

The minimum size of a grounding electrode conductor (GEC) connected to a concrete-encased electrode is determined by the size of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors. According to NEC Table 250.66, for four parallel sets of 500 kcmil aluminum conductors, the equivalent area is 4 * 500 kcmil = 2000 kcmil. For this equivalent size, the table specifies a minimum copper GEC size of 3/0 AWG.

Question 13: When protected by a 15-ampere circuit breaker, a branch circuit supplied by size 12 AWG conductors is a ____ rated branch circuit.

20 ampere
30 ampere
8 ampere
15 ampere (Correct answer)

Correct answer: 15 ampere

The rating of a branch circuit is determined by the rating of its overcurrent protective device, which in this case is a 15-ampere circuit breaker. While size 12 AWG conductors are typically rated for 20 amperes, the circuit's overall rating is limited by the lowest-rated component, which is the 15-ampere breaker. Therefore, it is a 15-ampere rated branch circuit.

Question 14: Class 3 single conductors are not permitted to be any smaller than .

23 Awg
2 Awg
3/0 Awg
18 AWG (Correct answer)

Correct answer: 18 AWG

According to the National Electrical Code (NEC), specifically Article 725.179(H) for Class 3 circuits, single conductors are generally not permitted to be smaller than 18 AWG. This minimum size ensures adequate mechanical strength and current-carrying capacity for these low-voltage, limited-energy circuits.

Question 15: Except when the wiring is feeding the related pool equipment, underground wiring is not allowed under a permanently installed swimming pool or within ____ of the pool.

5 feet (Correct answer)
6 feet
20 feet
3 feet

Correct answer: 5 feet

The National Electrical Code (NEC) Article 680.10 specifies restrictions on underground wiring near permanently installed swimming pools. It states that underground wiring is generally not permitted under the pool or within 5 feet horizontally from the inside wall of the pool, unless it is necessary to supply pool equipment and meets specific installation requirements.

Question 16: The power supply for household appliances with surface heating components that have a MAXIMUM demand of more than ____ must be split into two (2) or more circuits.

100 amperes
15 ampere
120 amperes
60 amperes (Correct answer)

Correct answer: 60 amperes

According to the National Electrical Code (NEC), specifically Article 210.19(A)(3) Exception No. 1, for household cooking appliances with surface heating elements, if the total demand exceeds 60 amperes, the load must be divided into two or more circuits. This requirement helps to prevent overloading a single circuit and ensures electrical safety for high-demand appliances.

Free Journeyman Electrician's Basic Formula Questions and Answers

What does the letter "E" stand for in the PIE formula circle?