Electrical Basics Made Easy
Full overview of electrical fundamentals — from atomic electron theory and historical discoveries through Ohm's Law, circuit types, switches, magnetism, wire gauges, and safety.
Notes from watching CaptiveAire — Electrical Basics Made Easy.
Part 1 — Pushing Electrons
Atomic Level Science
All matter is made of atoms. Each atom has a nucleus (protons + neutrons) surrounded by electrons in orbital shells. The outermost shell is called the valence shell.
- Conductors (copper, aluminum) — valence electrons are loosely bound, so they can drift freely between atoms. These free electrons are what carry current.
- Insulators (rubber, plastic, glass) — valence electrons are tightly bound. No free electrons, so current can’t flow.
- Semiconductors (silicon, germanium) — somewhere in between. Conductivity can be controlled, which is what makes transistors possible.
Electric current is simply the coordinated movement of these free electrons through a conductor — pushed along by a voltage source. Electrons actually move slowly (a few mm per second), but the electrical effect propagates at close to the speed of light, because the push travels along the whole wire essentially instantaneously.
A History of Electrical Discoveries
The story of electricity is a series of empirical stumbles over about two centuries:
- Ancient Greeks — noticed that rubbing amber (elektron in Greek) attracted feathers. Static electricity, observed but not understood.
- Benjamin Franklin (1750s) — flew a kite in a thunderstorm, proved lightning is electrical. Coined the terms positive and negative charge. Invented the lightning rod.
- Alessandro Volta (1800) — invented the voltaic pile, the first battery. Stacked zinc and copper discs separated by brine-soaked cloth. Produced the first steady electrical current. The Volt is named after him.
- André-Marie Ampère (1820s) — showed that current-carrying wires exert force on each other, laying the foundations for electromagnetism. The Ampere is named after him.
- Georg Simon Ohm (1827) — published the relationship V = IR. Was initially ridiculed and ignored by the scientific establishment. Vindicated years later. The Ohm is named after him.
- Michael Faraday (1831) — discovered electromagnetic induction: moving a magnet through a coil generates current. This is the operating principle of every generator and transformer.
- Thomas Edison (1880s) — built the first practical DC power distribution system in New York City. Direct current, low voltage, required power stations every mile.
- Nikola Tesla / George Westinghouse (1880s–90s) — championed AC power. High-voltage AC can be transmitted over long distances and stepped down with transformers. AC won the “War of Currents.”
Why Do Lightbulbs Glow?
When electrons are forced through a thin tungsten filament, the filament has high resistance — it fights the flow. That resistance converts electrical energy into heat. Tungsten has an extremely high melting point (~3400°C), so it can get white-hot without melting. Hot enough to emit visible light — this is incandescence.
The bulb is filled with inert gas (or evacuated) to prevent the tungsten from oxidising and burning up. Eventually the filament thins from evaporation and breaks — that’s a blown bulb.
LEDs work on a completely different principle (electroluminescence — electrons dropping energy levels emit photons directly), which is why they’re so much more efficient.
Part 2 — Go With The Flow
Water Analogies
The most useful mental model for DC circuits:
| Electrical | Water |
|---|---|
| Voltage (V) | Pressure (PSI) |
| Current (A) | Flow rate (L/s) |
| Resistance (Ω) | Pipe diameter / restriction |
| Battery / PSU | Pump |
| Wire | Pipe |
High pressure + narrow pipe = some flow. Wide pipe + same pressure = more flow. Increase pump pressure = more flow through same pipe. The analogy holds well for resistive DC circuits. It starts breaking down with capacitors, inductors, and AC.
Ohm’s Law
V = I × R
Three rearrangements:
V = I × R → voltage across a component
I = V / R → current through a component
R = V / I → resistance from measurements
Power:
P = V × I
P = I² × R
P = V² / R
Power is what generates heat. Always check that a component’s wattage rating isn’t exceeded — a resistor dissipating more power than its rating will overheat and fail (or burn).
Series Circuits
One path. Current is the same everywhere. Voltage divides.
R_total = R1 + R2 + R3
V_Rn = Vsupply × (Rn / R_total)
Break the circuit anywhere → current stops everywhere.
Resistors
- Limit current flow
- Value measured in Ohms (Ω), kilohms (kΩ), megohms (MΩ)
- Identified by colour bands (4-band code: band 1 & 2 = digits, band 3 = multiplier, band 4 = tolerance)
- Tolerance typically ±5% (gold band) or ±1% (brown band for precision)
- Power rating (⅛W, ¼W, ½W, 1W) determines how much heat they can safely dissipate
Parallel Circuits
Multiple paths. Voltage is the same across all branches. Current divides.
1/R_total = 1/R1 + 1/R2 + 1/R3
More parallel paths = lower total resistance = more total current drawn from source. Break one branch → others keep working. Household wiring is parallel.
Complex Circuits
Real circuits mix series and parallel sections. Analyse by grouping parallel sections first (find equivalent resistance), then treat the whole thing as series.
Part 3 — Controlling Nature
Manual Switches
A switch physically opens or closes a circuit path. Open = no current. Closed = current flows.
Schematics
Standardised symbols for circuit components. A schematic is a map of how components connect logically — not a physical layout.
Key symbols:
Battery (DC) ──┤ ├── long line = +, short line = −
Resistor (US) ──/\/\/── zigzag = opposition to flow
Capacitor ──┤├── two plates; curved plate = negative (polarised)
LED ──►|── triangle = anode, bar = cathode; arrows leaving = light emitted
↗↗
Switch (SPST) ──o /── open circuit; arm pivots down to close
Relay coil ┌──────┐ current through coil energises the magnet
│ COIL │
└──────┘
Relay contacts ──o o── NO (normally open); shown open at rest
Ground ──┬── reference point: 0V
─
─
─
Motor ──(M)── circle with M; two terminals
Reading a schematic: trace current from + terminal, through components, back to − terminal. Follow each branch.
Switch Poles and Throws
- Pole — how many separate circuits the switch controls simultaneously
- Throw — how many output positions each pole can connect to
| Type | What it does |
|---|---|
| SPST | One circuit, on/off. Simplest switch. |
| SPDT | One input, two outputs. Toggle between two paths. |
| DPST | Two independent circuits, switched together. |
| DPDT | Two independent circuits, each with two output options. |
SPDT is particularly useful — it lets you route a signal to one of two destinations, or use as a “changeover” switch.
Magnetism Basics
All magnets have a north and south pole. Opposite poles attract, like poles repel. Magnetic field lines run from north to south (outside the magnet). The field exerts force on magnetic materials and on moving charges.
Permanent magnets — domains (tiny magnetic regions) are permanently aligned. Can’t be easily switched off. Common materials: ferrite, neodymium (rare earth — extremely strong for their size), alnico.
Electromagnets — wrap a conductor in a coil (solenoid) and pass current through it. The coil generates a magnetic field proportional to current × number of turns. Switch off the current → field collapses. This controllability is what makes relays, contactors, and motors possible.
Electromechanical Switches
Relay — an electromagnet that mechanically moves a set of contacts. A small control current through the coil pulls an armature, which opens or closes the switch contacts. Allows a low-power signal (e.g. from a microcontroller) to switch a high-power load (motor, heater, mains voltage).
Relay contacts are rated for maximum voltage and current — don’t exceed them.
Contactor — a heavy-duty relay, designed for high-current loads like motors and HVAC compressors. Physically larger, with beefier contacts. Same operating principle.
Simple Switch Logic
Contacts can be wired in series or parallel to implement logic:
- Series (AND) — both switches must be closed for current to flow
- Parallel (OR) — either switch closed allows current to flow
- Normally Open (NO) — contacts open at rest, close when coil energised
- Normally Closed (NC) — contacts closed at rest, open when coil energised
NC contacts are useful for fail-safe designs — the default state is “on”, and losing power opens the circuit (e.g. a safety interlock that cuts power if control fails).
Part 4 — Basic Safety
Why Wires Must Be Protected
Bare copper conducting at load current will get hot proportional to resistance and current squared (P = I²R). Insulation:
- Prevents contact with bare conductors (shock hazard)
- Prevents two conductors touching (short circuit)
- Contains the current to the intended path
American Wire Gauge (AWG)
AWG is counterintuitive: lower number = thicker wire = more current capacity.
| AWG | Typical Use | Max Current |
|---|---|---|
| 10 | Heavy appliances, sub-panels | 30A |
| 12 | 20A household circuits | 20A |
| 14 | 15A household circuits | 15A |
| 16 | Extension cords, light fixtures | 13A |
| 18 | Low-voltage signal, lamp cord | 10A |
| 22 | Signal wiring, thermostat wire | 5A |
| 28 | Ribbon cable, PCB jumpers | ~0.5A |
Choosing wire too thin for the current = wire acts as a resistor = heats up = insulation melts = fire. Always upsize wire when in doubt.
Circuit Protection Devices
Two distinct failure modes, two distinct protection mechanisms:
Overload (Slow Trip)
A sustained current slightly above rating — not a dead short, but more than the wire is rated for. The heat builds gradually.
- Thermal breaker / bimetallic strip: excess current heats a bimetallic strip, which bends and mechanically trips the breaker. Slow to respond — designed to match how wire heats up over time. Protects against motors starting cold, or gradual overload conditions.
Short Circuit (Fast Trip)
A sudden, massive current surge — wire shorts to ground, resistance near zero, current spikes instantly.
- Magnetic trip: the large current creates a strong magnetic field in the breaker’s solenoid, which trips the mechanism instantly. This is a separate mechanism from the thermal trip, built into the same breaker.
- Fuse: a thin wire element that melts and opens the circuit when current exceeds rating. One-time use. Faster than a mechanical breaker.
Most modern breakers are dual-action — they incorporate both thermal (overload) and magnetic (short circuit) trip mechanisms.
Ground in Electrical Devices
The ground wire (green or bare copper in US wiring) is a safety conductor — not part of the normal circuit. It connects the metal chassis/enclosure of a device back to the electrical service ground.
If a fault occurs inside a device (e.g. the hot wire touches the metal case), ground provides a low-resistance path for fault current to flow back to the source. This causes a large current spike → breaker trips immediately.
Without a ground, fault current has nowhere to go — until a person touches the case and becomes the path to ground. That’s an electrocution hazard.
Three-prong outlets:
- Hot (black) — carries current to the load
- Neutral (white) — return path, referenced to ground at the panel
- Ground (green/bare) — safety fault path, not normally carrying current
Two-prong devices rely on double-insulation instead of a ground conductor.
Bad Connections
A loose or corroded connection isn’t a clean open — it’s a high-resistance joint. Current still tries to flow, and the excess resistance means:
P = I² × R_joint → heat generated at the joint
Consequences:
- Voltage drop — less voltage reaches the load, equipment underperforms
- Localised heating — insulation chars, connectors melt
- Arcing — intermittent contact causes sparks, which erode contacts and can ignite nearby material
Common causes: loose terminal screws, over-tightened screws that nick conductors, corroded contacts (oxidation increases resistance), mismatched wire gauges in connectors, and wire nuts applied to too few or too many conductors.
Good connections are clean, tight, and mechanically secure. In high-vibration environments (motors, HVAC), connections loosen over time — this is why periodic inspection matters.