Electricity Basics: Voltage, Current, and Resistance
Beginner-friendly overview of V, I, and R with simple examples, common mistakes, and next-step tools.
Guides
These guides are written for homeowners, apprentices, and electricians who want the reasoning behind the numbers, not just a result. Each one pairs with a calculator on this site so you can check your work and understand what you are actually solving for.
New here? Start with one of these:
- Electricity Basics: Voltage, Current, and Resistance — the foundation everything else builds on.
- How Circuit Breakers Work — panels, breaker sizes, and wire gauge in plain English.
- Why Does My Breaker Keep Tripping? — the three causes and how to tell them apart.
Downloadable Reference Sheets
These reference sheets are embedded in their guide pages and available to save or print. Each one is a single SVG file that stays readable at any size.
| Reference Sheet | What it covers | Download |
|---|---|---|
| Common Electrical Formulas Cheat Sheet | Power formula, Ohm's Law, energy (kWh), cost, breaker 80% rule, and single-phase power in one reference card. | Download SVG |
| Household Circuit Quick-Reference | Breaker sizes 15A–60A with wire gauges and typical uses, GFCI & AFCI required locations, and common dedicated circuit requirements. | Download SVG |
| Breaker Sizing & Load Planning | 3-step NEC sizing process, standard breaker sizes with 80% continuous limits, worked examples, and key rules. | Download SVG |
Use these quick guides for formula-level checks and practical electrical calculation context.
How to Calculate Voltage
Simple voltage math with step-by-step examples and common pitfalls.
How to Calculate Current
Use Ohm’s Law to estimate amps with quick examples and safety-first context.
How to Calculate Resistance
Learn basic resistance calculations and what the numbers mean.
How Many Amps Does a 1500W Space Heater Draw?
Quick 120V vs 240V current estimates with practical safety-first planning notes.
How Many Watts Is a 15A Circuit at 120V?
Formula-based watts estimate plus a practical planning margin example.
How Many Amps Does a 1000W Microwave Draw?
Fast current estimate guide with label-plate and shared-circuit reminders.
How Many Amps Does a 500W Device Draw at 120V?
Simple amp calculations for small devices and multi-load planning checks.
12V Battery Math: Watts to Amps
Why watts “feel heavier” at 12V, with real examples and wiring/voltage-drop notes.
How Circuit Breakers Work (Home Panel Basics)
Fun beginner guide to 15A vs 20A vs 30A breakers, watt math, and wire safety context.
Can I Use a 20A Outlet on a 15A Circuit?
It looks heavy-duty, but is it safe? Learn what the “T-slot” implies and what to do instead.
50 Amp Subpanel Wire Size
Common wire size starting points for 50A subpanels, plus distance/voltage drop tips and safety notes.
What Wire Size for a Level 2 EV Charger?
Common starting points for 32A, 40A, and 48A home charging, plus the distance checks that can change the wire.
What Wire Size for a 40 Amp Circuit?
Short-run rule of thumb, longer-run caveats, and when a 40A answer grows to the next conductor size.
What Wire Size for a 60 Amp Circuit?
A practical guide to 60A wire sizing for feeders, chargers, and other higher-load homeowner projects.
Wire Size by Distance
Why voltage drop changes wire-size answers on longer runs to garages, sheds, chargers, and workshops.
What Breaker Size for a 40A EV Charger?
The continuous-load rule in plain English, with the common 40A charger to 50A breaker answer.
Can a 100A Panel Handle an EV Charger?
A practical homeowner look at spare capacity, smaller chargers, load management, and upgrade pressure.
How to Convert Watts to Amps
Formula, worked examples at 120V/240V/12V, reference table, and FAQ for converting watts to amps.
How to Convert Amps to Watts
Multiply amps by voltage to get watts, with examples, a reference table, and circuit planning context.
How to Convert kVA to Amps
Single-phase kVA to amps conversion with generator and UPS examples, reference table, and FAQ.
How to Convert kW to Amps
kW to amps with water heater, range, and EV charger examples, plus the 80% continuous load rule.
Why Does My Breaker Keep Tripping?
The three main causes, overload, short circuit, ground fault, with a quick diagnostic table and FAQ.
What Gauge Extension Cord for 15 Amps?
Short-run versus long-run cord choices for real 15A temporary loads, with practical 14 AWG, 12 AWG, and 10 AWG planning ranges.
What Gauge Extension Cord for 20 Amps?
Why 12 AWG is the common short-run answer for 20A loads, and when 10 AWG or a different approach is smarter.
Can You Run a Space Heater on an Extension Cord?
A practical safety-first answer for heater cords, with the rare short heavy-cord exception and the better alternatives.
100 ft Extension Cord Voltage Drop
Why 100-foot runs often change the cord-gauge answer, especially on 120V tools, heaters, and motor loads.
Can I Upgrade a 15A Breaker to 20A?
Why wire gauge matters more than the breaker, and what to check before making any changes.
Single-Pole vs Double-Pole Breaker
120V vs 240V, one slot vs two, and which loads need which type, with a comparison table and FAQ.
How to Find Appliance Wattage
Where to look: nameplate, EnergyGuide label, spec sheet, or plug-in energy monitor, and what to do when the wattage is not listed.
Running Watts vs Starting Watts
Why refrigerators, freezers, sump pumps, and AC units can need much more generator headroom at startup than they do once running.
What Size Generator for a Refrigerator?
Practical fridge-backup starting ranges, compressor startup context, and when a small generator is too tight.
What Size Generator for a Refrigerator and Freezer?
Combined cold-storage planning with startup-overlap risk, comparison table, and generator-sizing next steps.
What Size Generator for a Sump Pump?
Motor-starting reality for basement backup, with practical generator starting points for common pump sizes.
How to Read Your Electric Bill
kWh, rate, fixed charges, and line items explained, plus how to calculate your own bill estimate.
How to Read Your Hydro Bill in Ontario
Ontario-focused bill guide: TOU vs ULO vs Tiered plans, delivery/regulatory lines, and practical bill-estimate workflow.
Why Is My Hydro Bill So High in Ontario?
Ontario high-bill troubleshooting guide: billing days, plan fit, heating, EV charging, and where the extra total usually comes from.
How to Read Your Hydro Bill in British Columbia
BC-focused hydro bill guide: tiered vs flat rate, time-of-day pricing, common line items, and what usually makes the total jump.
How to Read Your Electric Bill in Alberta
Alberta-focused bill guide: retailer vs distributor, Rate of Last Resort, delivery charges, and how to compare one bill to the last one.
How to Read Your Hydro-Quebec Bill (Rate D)
Quebec-focused hydro bill guide: Rate D tier split (40 kWh/day), system access charge, and monthly estimate steps.
Why Is My Hydro Bill So High in Quebec?
Quebec high-bill troubleshooting guide: Rate D threshold pressure, winter heating, billing days, and what usually changes first.
Why Is My Electric Bill So High?
A troubleshooting checklist for high bills: HVAC, water heating, new appliances, standby loads, and rate changes.
How to Calculate Appliance Running Cost
The formula for daily, monthly, and annual cost, with worked examples for a heater, refrigerator, and dryer.
Standby Power & Vampire Loads
Which devices drain power when "off," how much they cost, and the easiest ways to stop the silent drain.
Time-of-Use Rates Explained
How peak and off-peak pricing works, which loads are worth shifting, and whether TOU is right for your household.
Disclaimer: Results are informational estimates for learning and planning only. Always follow the applicable electrical code and consult a qualified licensed electrician for safety-critical work.