Electrical apprentice study guide
Electrical apprentice math and formulas: build the basics first.
Electrical calculations get easier when you recognize the relationship being tested, keep units consistent, write the formula before substituting values, and check whether the result makes physical sense.
Ohm’s law
V = I × R. Rearranged: I = V ÷ R and R = V ÷ I. Keep voltage in volts, current in amperes, and resistance in ohms unless you deliberately convert units.
Basic electrical power
P = V × I for the basic power relationship. Rearranged: I = P ÷ V and V = P ÷ I. Use the formula that matches the known quantities instead of trying to memorize a separate rule for every question.
Common unit conversions
1 kilowatt equals 1,000 watts. 1 milliampere equals 0.001 ampere. Convert units before substituting them into a formula so the numbers represent the same scale.
Write the formula before the numbers
Start with the symbolic relationship, rearrange it if needed, then substitute the values. This makes it much easier to spot whether you multiplied when you should have divided or solved for the wrong quantity.
Carry units through the calculation
Write units beside the values and final answer. Units are an error-checking tool: a result expected in amperes should not quietly end in watts or ohms.
Separate formula knowledge from Code lookup
Some exam calculations require both math and a Code rule or table value. Practice the arithmetic independently first, then practice identifying which values must come from the applicable NEC edition. Do not invent a Code value from memory when the question expects a lookup.
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