Chapter 12 Key Takeaways

The Three Fundamental Concepts

Voltage (volts, V) is electrical pressure — the force that pushes electrons through a conductor. Your home uses 120V for most circuits and 240V for large appliances.
Current (amperes, A) is the flow of electrons. It's what breakers are rated for; it's what causes wires to heat up when too high.
Resistance (ohms, Ω) opposes current flow. Every material has some resistance; the resistance of a toaster's heating element is what converts electrical energy to heat.
Ohm's Law: V = I × R. These three quantities are locked together. Change one, and the others change in response.
Power: P = V × I. Watts measure how fast energy is being used. Kilowatt-hours (kWh) measure how much energy has been used over time — and that's what your utility bills you for.

US household current is 60 Hz AC — it reverses direction 60 times per second.
AC won over DC for distribution because transformers (which only work with AC) allow voltage to be stepped up for efficient long-distance transmission and stepped down for safe household use.
Your home uses AC, but most electronics convert it to DC internally.

Power travels from generating stations → high-voltage transmission lines → substations → distribution lines → the transformer on your street → service entrance → meter → main panel → branch circuits → your outlets.
The utility owns everything up to and including the meter. You own from the meter into the home.
The service entrance conductors and meter are always live. No action you take — including turning off your main breaker — de-energizes the wires entering the top of your panel.

Your home receives split-phase, 120/240V service: two hot legs (Leg A and Leg B), each at 120V to neutral and 240V between them.
120V devices use one hot leg and neutral. 240V devices use both hot legs.
Double-pole breakers occupy two panel slots and connect to both legs — that's how 240V circuits are created.

Grounding provides a fault current path to earth that triggers breakers when a fault occurs, and prevents metal surfaces from becoming energized.
Bonding connects all metallic systems in your home together so they share the same electrical potential — eliminating shock risk between metal objects.
These are not the same thing and not interchangeable terms.
GFCI protection detects 5 milliamps of imbalance and trips in 1/40th of a second — protecting against electrocution even when grounding is intact.

Energy is billed in kilowatt-hours (kWh): 1 kWh = 1,000 watts running for 1 hour.
Average US residential rate is approximately 16 cents/kWh, but varies widely by state.
Rate structures include flat, tiered, and time-of-use. TOU rates reward shifting consumption to off-peak hours.
Secondary refrigerators, aging appliances, and standby loads are common hidden contributors to high bills.
Your bill's consumption history is the best diagnostic tool for identifying changes in your home's energy use.

The service entrance conductors are always live, even with the main breaker off. Never touch them.
Never remove the panel cover. Panel interiors require a licensed electrician.
Understanding electricity does not reduce the danger. Know the rules and follow them.