Electrical Quick Study Guide: The Cram-Smart Field Companion
No fluff, no engineering degree required — the core electrical concepts apprentices and confident homeowners actually need: Ohm's law, 120/240 service, panels, wire sizes, voltage drop, and the code rules behind them. Fast, plain, and safe.
Jason Mohoska · Owner-Operator, JS Power LLC
Licensed Pennsylvania Home Improvement Contractor · PA HIC #PA166735
20+ years in the trade · Serving Pittsburgh & Western Pennsylvania
Chapter 1
Electricity fundamentals — Ohm's law, Watt's law, series vs. parallel
Everything electrical runs on two little equations. Learn these and half the trade's math is yours.
Ohm's law: V = I × R. Voltage equals current times resistance. Flip it around: I = V ÷ R, R = V ÷ I. A 120 V circuit pushing through 240 Ω of resistance draws 0.5 A. That's it — volts, amps, ohms, one triangle.
Watt's law: P = V × I. Power (watts) equals volts times amps. Flip it: I = P ÷ V. This is the formula that answers "how many amps does this thing draw?" — the question behind breaker and wire sizing.
Worked examples — do these yourself first
60 W bulb on 120 V: I = P ÷ V = 60 ÷ 120 = 0.5 A. R = V ÷ I = 120 ÷ 0.5 = 240 Ω.
1,500 W space heater on 120 V: I = 1,500 ÷ 120 = 12.5 A — more than half of a 15 A circuit's capacity. That's why space heaters dim your lights.
Energy cost: that heater for 3 hours = 1.5 kW × 3 h = 4.5 kWh. At an example rate of 15¢/kWh, that's about 68¢ (rates vary by utility).
Series vs. parallel — the one picture that matters:
Series: one path, everything in a line. The same current flows through each component; the voltage divides across them. Wire two identical bulbs in series on 120 V and each sees 60 V — both glow dim. If one fails open, everything downstream goes dark (old Christmas lights).
Parallel: each component gets its own path to the source. Every branch sees the full voltage; current divides by each branch's resistance. This is how your house is wired — every receptacle sees 120 V whether one thing is plugged in or twelve.
🚨 Safety line
These fundamentals are for understanding, not for experimenting. Everything beyond a battery-powered demo — and anything inside a panel — is licensed-electrician territory. If you're a homeowner reading this, Chapter 3's meter rules apply to you; Chapters 4 and beyond tell you what's happening behind the dead front, not how to work in it.
The other 8 chapters are yours for $13
Chapter 1 is free above. The rest — 120/240 service, multimeter safety, the panel demystified, wire sizes, the 10 home circuits, voltage drop, code-cycle concepts, and the 25-question self-quiz — unlocks when you order.
🔒 Chapter 2: AC vs. DC & what 120/240 really means
🔒 Chapter 3: Reading a multimeter safely
🔒 Chapter 4: The breaker panel demystified
🔒 Chapter 5: Wire sizes & what they're for
🔒 Chapter 6: The 10 circuits every home runs on
🔒 Chapter 7: Voltage drop intuition + the simple rule of thumb
🔒 Chapter 8: Code-cycle concepts in plain English
🔒 Chapter 9: Self-quiz: 25 questions with answers
One-time purchase · Yours to keep
$13 one-time
The complete 9-chapter companion, printable, with worked examples and a 25-question self-quiz — written from 20+ years in the trade. Secure online checkout — instant access after payment.
Jason answers directly · Licensed PA HIC #PA166735
About the author
Need an electrician? Call JS Power LLC.
I'm Jason Mohoska, owner-operator of JS Power LLC (Licensed · PA HIC #PA166735), serving Pittsburgh and Western Pennsylvania. 20+ years in the trade. When you call, you deal directly with me: I quote the job, I do the work, and it's done to code.
Licensed Pennsylvania Home Improvement Contractor · PA HIC #PA166735
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