Must Have Formulas for Your Electrical Exam

Must Have Formulas for the Electrician Exam

Are you ready to tackle the electrical exam with confidence? In this revamped guide, we'll dive into the must-have formulas for your electrical exam, providing examples and tips to help you breeze through test day.

Write these formulas for your electrical exam in your code book, you’ll be glad you did. Most testing centers allow short notes - only write important ones!

Before we go any further, click here to receive our Electrical Formulas Cheat Sheet.

Includes motor calculation steps, box fill, ranges, transformers, conduit fill, PIE, EIR, and more!

Most Common Formulas for Your Electrical Exam

In the test, you'll see questions that will ask you to determine the current of a circuit.  Also, the test will ask you to determine conductor resistance or even voltage drop (and more).  These formulas for your electrical exam are your core formulas. Memorize them but we also strongly suggest you write them in your book.  (Check with your examiner’s bulletin to make sure notes are allowed in your book).

In the off chance that notes are not allowed in your book, then make it a point to know these formulas in your sleep because you will need them.

Here are some core calculations commonly encountered on the electrician exam:

1. Ohm's Law Calculations:

- Calculate Voltage: V = I × R
- Calculate Current: I = V ÷ R
- Calculate Resistance: R = V ÷ I

2. Power Calculations:

- Calculate Power: P = V × I
- Calculate Power (alternative): P = I^2 × R
- Calculate Power (alternative): P = V^2 ÷ R

3. Power Factor Calculations:

- Power Factor: PF = P (watts) / (V (volts) × I (amps))

Download your Electrical Formulas Cheat Sheet for many more advanced formulas and calculations. Remember to practice these calculations regularly to build confidence and proficiency for the exam.

Examples with formulas for your electrical exam

Let's break down some common scenarios you'll encounter on the exam, step by step. Here's a step-by-step guide to answering the sample questions:

Question 1. What is the resistance of the circuit conductors if the conductor voltage drop is 2V and the current flowing in the circuit is 80A?

Step 1. Identify the given values: In this question, you're given the conductor voltage drop (2V) and the current flowing in the circuit (80A).

Step 2. Write down the formula: The formula to calculate resistance (R) is R = V / I, where V is the voltage drop and I is the current.

Step 3. Plug in the given values: Substitute the given values into the formula: R = 2V / 80A.

Step 4. Perform the calculation: Divide the voltage drop by the current: R = 0.025 ohms.

Step 5. Write down the answer: The resistance of the circuit conductors is 0.025 ohms.

• • • • • •

Question2. If the resistance of the circuit conductors is 0.03 ohms and the current flowing in the circuit is 120A, what is the voltage drop across the conductors?

Step 1. Identify the given values: In this question, you're given the resistance of the circuit conductors (0.03 ohms) and the current flowing in the circuit (120A).

Step 2. Write down the formula: The formula to calculate voltage drop (V) is V = R x I, where R is the resistance and I is the current.

Step 3. Plug in the given values: Substitute the given values into the formula: V = 0.03 ohms x 120A.

Step 4. Perform the calculation: Multiply the resistance by the current: V = 3.6V.

Step 5. Write down the answer: The voltage drop across the conductors is 3.6V.

• • • • • •

Question 3. A 120-volt circuit has a power consumption of 600 watts.

What is the current flowing through the circuit?

Step 1. Identify the given values: In this question, you're given the voltage (120 volts) and power consumption (600 watts) of the circuit.

Step 2. Write down the formula for calculating current: The formula to calculate current (I) is I = P / V, where P is power in watts and V is voltage in volts.

Step 3. Plug in the given values: Substitute the given values into the formula: I = 600 watts / 120 volts.

Step 4. Perform the calculation: Divide the power by the voltage to find the current: I = 5 amperes.

Step 5. Write down the answer: The current flowing through the circuit is 5 amperes.

• • • • • •

Question 4. A three-phase motor draws a current of 15 amps per phase.

Calculate the total power consumed by the motor, given that the system voltage is 480 volts.

Step 1. Identify the given values: In this question, you're given the current per phase (15 amps) and the system voltage (480 volts).

Step 2. Write down the formula for calculating power: The formula to calculate power (P) is P = √3 * V * I, where V is voltage in volts, I is current in amps, and √3 is the square root of 3 (approximately 1.73).

Step 3. Plug in the given values: Substitute the given values into the formula: P = 1.73 * 480 volts * 15 amps.

Step 4. Perform the calculation: Multiply the voltage, current, and square root of 3 to find the power: P ≈ 1.73 * 480 * 15 ≈ 124,200 watts.

Step 5. Write down the answer: The total power consumed by the motor is approximately 124,200 watts.

Formulas for Your Electrical Exam - PEMDAS

Finally, technically this isn’t a formula but remember PEMDAS.  I can’t tell you how many students in our electrical exam prep seminars come to class and forget even the most basic order of operations.  Make it funny. Make it memorable. For the love of all you hold dear don’t miss questions for something so basic and elementary.

“Please Excuse My Drunk Aunt Sally”

Here are two sample calculations using PEMDAS:

Calculation 1: Evaluate the expression: 3 + 4 * 2 - 5 ÷ 1

Step 1. Start with parentheses: There are no parentheses in the expression.

Step 2. Exponents: There are no exponents in the expression.

Step 3. Multiplication and Division: Perform multiplication and division from left to right. Start with 4 * 2 = 8 and 5 ÷ 1 = 5.

Step 4. Addition and Subtraction: Perform addition and subtraction from left to right. Start with 3 + 8 = 11 and then 11 - 5 = 6.

Answer: The expression evaluates to 6.

• • • • • •

Calculation 2. Evaluate the expression: (15 - 3) ÷ 2 + 4 * 3

Step 1. Start with parentheses: Perform the operation inside the parentheses first. 15 - 3 = 12.

Step 2. Exponents: There are no exponents in the expression.

Step 3. Multiplication and Division: Perform multiplication and division from left to right. Start with 4 * 3 = 12 and then (12 ÷ 2) = 6.

Step 4. Addition and Subtraction: Perform addition and subtraction from left to right. Start with 12 + 6 = 18.

Answer: The expression evaluates to 18.