Basic Electrical Circuits
Why This Matters
You can build a generator and charge a battery, but electricity sitting in a battery is useless. You need to know how to get it from point A to point B safely — how to wire a light, flip a switch, protect against fire, and connect multiple devices without burning your shelter down. A single short circuit can destroy your only battery, start a fire, or kill you. This article teaches you to make electricity do useful work without any of those things happening.
Understanding Electricity: The Water Analogy
Before you touch a single wire, you need a mental model for what electricity actually is. Forget the physics — think of it as water flowing through pipes. This analogy holds up for everything you will ever need to do in a post-collapse world.
Voltage (V) — Water Pressure
Voltage is the pressure pushing electricity through the wire. A tall water tower creates more pressure than a short one. A 12V car battery pushes harder than a 1.5V AA cell. More voltage means more force driving the current.
Current (A) — Water Flow Rate
Current is how much electricity is flowing, measured in amps. A fire hose carries more water per second than a garden hose. More current means more energy being delivered — and more heat generated in the wires carrying it.
Resistance (R) — Pipe Size
Resistance is how hard it is for electricity to flow, measured in ohms. A thin pipe restricts water flow; a wide pipe lets it flow freely. Thin wire has more resistance than thick wire. A light bulb filament has high resistance — that is what makes it glow hot.
Ohm’s Law: V = I x R
This is the single most important equation in all of electrical work. It ties the three concepts together:
Voltage (V) = Current (I) x Resistance (R)
Rearranged:
I = V / R (how much current flows)
R = V / I (how much resistance you need)
Practical example: You have a 12V car battery and an LED that needs 20 milliamps (0.02A) and has a forward voltage of 2V. How much resistance do you need?
Leftover voltage: 12V - 2V = 10V
R = V / I = 10 / 0.02 = 500 ohms
You need a 500-ohm resistor in series with the LED.
If that math feels complicated, do not worry. For basic wiring — connecting lights, switches, and loads to a battery — you mostly need to understand one thing: thicker wire for more current, and never connect the two battery terminals directly to each other.
Tip
Cover the value you want to find. What remains is the formula. Cover V, and you see I x R. Cover I, and you see V / R. Cover R, and you see V / I.
What You Need
Wire (any of these):
- Copper wire scavenged from house wiring (Romex), extension cords, appliance cords
- Speaker wire, lamp cord, automotive wiring harnesses
- Copper or aluminum wire from electric motors, transformers (unwound)
Power source:
- 12V car battery (most common post-collapse)
- 6V lantern battery
- Homemade cells (see Energy Storage & Batteries)
Loads (things that use electricity):
- LED bulbs (scavenged from flashlights, car dashboards, decorations)
- Incandescent bulbs (car headlights, interior lights, flashlight bulbs)
- Small DC motors, fans, radios
Switches and connectors:
- Scrap metal pieces for knife switches
- Wire nuts, electrical tape, crimp connectors (scavenged)
- Nails, screws, bolts for terminal connections
Protection:
- Thin wire for fuses (strand from a lamp cord)
- Glass or ceramic tube for fuse holder (optional)
- Scrap metal for a grounding rod
Tools:
- Knife or blade for stripping wire
- Pliers (any type)
- Screwdriver
How to Strip Wire
Before you can build anything, you need bare copper at the ends of your wire to make connections.
With a knife:
- Lay the wire on a hard, flat surface.
- Place your blade across the insulation about 2-3 cm from the end, at a shallow angle — you want to cut the plastic, not the copper.
- Press gently and roll the wire under the blade. You should feel the blade bite through the insulation and stop at the copper.
- Pull the insulation sleeve off the end.
Without a knife:
- Burn the insulation off with a flame, then scrape away the char. Works but produces toxic fumes from PVC — do it outdoors.
- Score with a sharp rock and pull the insulation off.
- For enameled magnet wire (from motors/transformers), sand the enamel off with rough stone or sandpaper.
Warning
Never strip wire while it is connected to a power source. Even 12V can produce dangerous sparks and burns if you accidentally short circuit.
Method 1: Simple Circuit — Battery + Wire + Light
This is the most basic circuit possible: one power source, two wires, one load. Every other circuit in this article builds on this.
Step 1 — Strip about 2 cm of insulation from both ends of two pieces of wire, each about 30 cm long.
Step 2 — Connect one wire to the positive (+) terminal of your battery. Wrap the bare copper around the terminal bolt and tighten the nut, or twist it firmly around the terminal clamp.
Step 3 — Connect the other end of that wire to one terminal of your light bulb. For a car bulb, one terminal is the bottom contact point, the other is the metal body/base.
Step 4 — Connect the second wire from the other terminal of the light bulb back to the negative (-) terminal of the battery.
Step 5 — The light turns on. You have a complete circuit.
(+) ----[ wire ]----> LIGHT ----[ wire ]----> (-)
| |
+----------------[ BATTERY ]------------------+
Why it works: Current flows from the positive terminal, through the wire, through the light (which resists the flow and converts the energy to light and heat), through the second wire, and back to the negative terminal. If you break the circuit at ANY point — disconnect a wire, unscrew the bulb — current stops flowing and the light goes out.
Making Connections Without Solder
In a post-collapse situation, you probably do not have a soldering iron. These methods work reliably:
Twist splice (most common):
- Strip 3-4 cm from each wire end.
- Hold the bare sections side by side, overlapping.
- Twist them tightly together — at least 5-6 full turns.
- Fold the twist over on itself for extra security.
- Wrap with electrical tape, cloth tape, or even tree resin on cloth.
Crimp connection:
- Slide a crimp connector (scavenged from automotive wiring) over the bare wire end.
- Squeeze with pliers until the connector bites into the copper.
Bolt terminal:
- Wrap bare wire clockwise around a bolt shaft.
- Sandwich between two washers and tighten the nut.
- Excellent for battery terminals and junction points.
Tip
A bad connection is worse than no connection. Loose joints create resistance, which creates heat, which starts fires. Every connection should be tight enough that you cannot pull it apart by hand.
Method 2: Adding a Switch
A switch is just a deliberate break in the circuit that you can open and close. There is nothing magical about it.
Building a Knife Switch from Scrap Metal
Materials:
- A strip of thin metal (from a can lid, sheet metal, or a large paperclip) — about 8 cm long
- A nail or screw for the pivot point
- A second nail or screw for the contact point
- A small block of wood for a base
Construction:
Step 1 — Punch or drill a hole at one end of the metal strip. Screw it loosely to the wood base so it can pivot up and down.
Step 2 — Drive a second nail or screw into the base about 5 cm away from the pivot, positioned so the metal strip can swing down and touch it firmly.
Step 3 — Connect one wire to the pivot screw (under the metal strip, so it makes contact). Connect another wire to the contact nail.
Step 4 — Wire this switch into your circuit — it goes in series between the battery and the load, on either the positive or negative side.
(+) ---[ wire ]---> SWITCH ---[ wire ]---> LIGHT ---[ wire ]---> (-)
| |
+------------------------[ BATTERY ]-----------------------------+
Switch open (metal strip lifted): Gap in the circuit. No current flows. Light off.
Switch closed (metal strip touching contact nail): Circuit complete. Current flows. Light on.
The Toggle Concept
Any mechanism that opens and closes a gap in a wire is a switch. A clothespin with metal contacts, a bent paperclip, two nails with a metal bar across them — all switches. The concept is universal: make a gap, bridge the gap.
Method 3: Wiring Multiple Lights
Once you can wire one light, you will want to wire several — for a shelter, a workshop, a community building. There are two ways to do it, and one is dramatically better than the other.
Series Wiring: Lights in a Chain
In a series circuit, current flows through one light, then the next, then the next, in a single path.
(+) ----> LIGHT 1 ----> LIGHT 2 ----> LIGHT 3 ----> (-)
Water analogy: Three water wheels on the same stream, one after another. Each wheel slows the water down. By the third wheel, there is barely any flow.
Problems with series:
- The total resistance ADDS UP. Three 12-ohm bulbs in series = 36 ohms total. Each bulb gets only 4V instead of 12V. They all glow dimly.
- If ONE bulb burns out, the entire circuit breaks. All lights go dark. (This is why old Christmas tree lights all went out when one bulb died.)
- Every bulb must be rated for the same current.
Parallel Wiring: Lights Side by Side
In a parallel circuit, each light has its own direct path from positive to negative. They share the same voltage but draw their own current.
+----> LIGHT 1 ----+
| |
(+) ------+----> LIGHT 2 ----+------ (-)
| |
+----> LIGHT 3 ----+
Water analogy: Three separate pipes branching off the same water main, each with its own water wheel, all draining into the same return pipe. Each wheel gets full water pressure.
Why parallel is better for lighting:
- Each bulb gets the full battery voltage (12V from a 12V battery).
- Each bulb burns at full brightness.
- If one bulb burns out, the others stay on — the circuit is not broken for the remaining bulbs.
- You can add or remove lights without affecting the others.
Important
Always wire lights in parallel. The only situation where series wiring is useful is when you need to reduce voltage to a device (for example, wiring two 6V bulbs in series on a 12V battery — each sees 6V).
How to Build a Parallel Circuit
Step 1 — Run two main wires (a “bus”) from your battery — one positive, one negative. These are your power rails.
Step 2 — At each light location, tap into both rails. Connect one wire from the positive rail to the light, and another from the light back to the negative rail.
Step 3 — Continue for each additional light. Each one connects independently to the same two rails.
Calculating Total Load
In parallel, the total current is the sum of all individual currents. This matters because your battery and wires have limits.
Example: Three LED lights, each drawing 0.5A at 12V.
Total current = 0.5A + 0.5A + 0.5A = 1.5A
Total power = Voltage x Current = 12V x 1.5A = 18 watts
A typical car battery can supply 40-60 amps continuously, so three LEDs at 1.5A total is well within limits. But if you wire ten 55W headlight bulbs in parallel, you draw nearly 46A — pushing a car battery to its limit and requiring very thick wire.
Method 4: DC Power and the Inverter Concept
When You Need AC vs DC
In the old world, your wall outlets provided AC (alternating current) at 110V or 220V. Most post-collapse power sources — solar panels, generators, batteries — produce DC (direct current).
Here is the good news: most devices you will actually want to use after collapse run on DC anyway.
- LED lights: DC
- Phones and radios: DC (they have internal converters that accept DC)
- Car accessories: DC (12V)
- Small motors, fans: DC
- USB devices: DC (5V)
AC is mainly needed for:
- Large power tools (drill press, grinder, saw)
- Some refrigeration compressors
- Old-world appliances with AC motors
A Simple Inverter Concept
A true inverter (DC to AC) is complex to build from scratch — it requires switching transistors or a mechanical commutator to alternate the current direction rapidly (50 or 60 times per second). Building one from scavenged parts is covered in Basic Electronics.
For now, understand the concept:
BATTERY (12V DC) ---> INVERTER ---> 110V/220V AC
(switches DC (usable for
back and forth AC devices)
rapidly)
Water analogy: DC is a river flowing in one direction. AC is a tide that sloshes back and forth. An inverter takes a steady river and creates artificial tides.
Practical Advice: Stay With DC
In a post-collapse scenario, avoid AC whenever possible. Here is why:
- AC at 110V+ is far more dangerous than 12V DC. It takes only 30-50 milliamps of AC across the heart to kill. 12V DC cannot push enough current through your body to be lethal under normal conditions.
- DC systems are simpler — no frequency matching, no transformer sizing.
- Car parts, solar panels, and batteries are all natively DC.
- LED lighting, which is the most efficient lighting available, runs on DC.
Wire your shelter and community for 12V DC. Use car light fixtures, LED strips, and 12V appliances. Save AC for the few situations where no DC alternative exists.
Wire Gauge and Capacity Guide
Wire that is too thin for the current it carries will overheat, melt its insulation, and start a fire. This is not a theoretical concern — it is the most common cause of electrical fires.
The rule: More current requires thicker wire. Longer runs also require thicker wire (because resistance increases with length).
| Wire Gauge (AWG) | Approximate Diameter | Max Safe Current | Common Source |
|---|---|---|---|
| 18 AWG | 1.0 mm | 5A | Lamp cord, speaker wire |
| 16 AWG | 1.3 mm | 10A | Extension cords (light duty) |
| 14 AWG | 1.6 mm | 15A | House wiring (lighting circuits) |
| 12 AWG | 2.1 mm | 20A | House wiring (outlet circuits) |
| 10 AWG | 2.6 mm | 30A | Dryer/AC circuits, heavy extension cords |
| 8 AWG | 3.3 mm | 40A | Stove circuits, sub-panels |
| 6 AWG | 4.1 mm | 55A | Large appliances, welding cable |
Warning
If you do not know the gauge of your scavenged wire, measure the bare copper diameter. When in doubt, use a thicker wire than you think you need. An oversized wire wastes nothing. An undersized wire starts a fire.
Without a ruler: Compare the bare copper to known objects:
- Sewing needle diameter: roughly 18 AWG (5A max)
- Thick paperclip wire: roughly 14 AWG (15A max)
- Pencil lead thickness: roughly 12 AWG (20A max)
Long Runs
For every 30 meters (100 feet) of wire run, go up one gauge size. A 12V system is especially sensitive to voltage drop over distance because you are starting with low voltage — losing even 1-2V is significant.
Fuses and Circuit Protection
A fuse is the single most important safety device in any electrical system. It is a deliberate weak point that melts before your wiring does.
How a Fuse Works
A fuse is just a thin piece of wire or metal in the circuit that is rated to carry a specific maximum current. If the current exceeds that rating — due to a short circuit, an overloaded circuit, or a fault — the fuse wire melts first, breaking the circuit before your main wiring overheats.
Water analogy: A fuse is a deliberately fragile section of pipe. If the water pressure gets too high, this section bursts first, stopping the flow before it damages the rest of the plumbing.
Building a Fuse from Scrap
Materials:
- A single thin strand pulled from a multi-strand wire (lamp cord works well)
- Two nails or screws on a non-flammable base (wood, ceramic, glass)
- A small piece of glass tube, ceramic tube, or even a rolled strip of tin (optional housing)
Construction:
Step 1 — Mount two nails about 3 cm apart on a base.
Step 2 — Wrap one thin strand of copper wire between the two nails. The strand should be noticeably thinner than the wire in your main circuit — this is what determines the fuse rating.
Step 3 — Wire the fuse in series on the POSITIVE wire, between the battery and everything else.
(+) ---[ FUSE ]---[ SWITCH ]---[ LOAD ]--- (-)
Rough fuse ratings by strand count (from typical lamp cord):
- 1 strand: blows at approximately 3A
- 2 strands twisted: approximately 5A
- 3 strands twisted: approximately 8A
Test your fuses by intentionally short-circuiting through them (outdoors, safety glasses, keep your face away). Note which strand count blows at what load. Label them.
Important
Always put the fuse between the positive battery terminal and everything else. This is the FIRST thing current flows through. If anything goes wrong downstream, the fuse breaks the circuit before damage occurs. A circuit without a fuse is a fire waiting to happen.
Automotive Fuses
If you are scavenging from cars, pull the fuse box. Automotive fuses are color-coded by rating:
| Color | Rating |
|---|---|
| Orange | 5A |
| Red | 10A |
| Blue | 15A |
| Yellow | 20A |
| Clear/White | 25A |
| Green | 30A |
These are reliable, reusable (if not blown), and clearly rated. Grab every fuse box you find during scavenging runs.
Grounding for Safety
Grounding provides a safe path for electricity to flow into the earth if something goes wrong — like a wire coming loose and touching a metal enclosure.
Why Ground?
Imagine a bare wire comes loose inside a metal lamp housing and touches the housing. Without grounding, the entire housing is now electrified. Touch it, and YOU become the path to ground — current flows through your body.
With a ground wire connected from the housing to a metal rod driven into the earth, the current takes the easy path through the ground wire instead of through you.
Building a Ground
Step 1 — Drive a metal rod (copper pipe, steel rebar, iron pipe) at least 1 meter into the ground, ideally in damp soil.
Step 2 — Run a wire from the ground rod to your electrical system’s negative bus bar or metal enclosures.
Step 3 — Connect the ground wire to any metal housings, frames, or enclosures in your system.
Tip
For a 12V DC system, grounding is less critical for personal safety (12V cannot push lethal current through your body under normal conditions). But it IS critical for lightning protection and for preventing stray currents from corroding your metal structures. Ground your system regardless.
Scavenging Wire and Electrical Components
Knowing where to find wire and parts is as important as knowing how to use them.
Best Sources of Wire
| Source | What You Get | Notes |
|---|---|---|
| Houses (wall wiring) | 14 and 12 AWG solid copper, large quantities | Pull from walls after cutting power. Romex sheathing contains 2-3 conductors plus ground |
| Extension cords | 16-12 AWG stranded copper, flexible | Easy to work with, already insulated |
| Car wiring harness | 18-10 AWG, various colors, connectors included | Cut the entire harness out; sort by color/gauge later |
| Electric motors | Magnet wire (enameled, thin) | Excellent for building coils, generators, radios |
| Transformers | Magnet wire, sometimes heavy gauge | Unwind carefully; the wire is valuable |
| Appliance cords | 18-14 AWG, heavy-duty plugs | Microwave cords are especially thick gauge |
| Telecommunications cable | Many thin conductors, long runs | Low current capacity but useful for signaling |
Useful Components to Scavenge
- Car alternators and batteries — your primary power system
- LED bulbs and strips — efficient lighting
- Switches — light switches, car ignition switches, appliance switches
- Fuses and fuse boxes — from cars and electrical panels
- Resistors, capacitors, diodes — from circuit boards (for later electronics work)
- Connectors — ring terminals, spade connectors, wire nuts
- Electrical tape — grab every roll you find
- Magnets — from speakers, hard drives, motors (for building generators)
Common Mistakes
| Mistake | What Happens | What To Do Instead |
|---|---|---|
| Connecting positive directly to negative (short circuit) | Massive current flow, wire melts, sparks, battery damage, fire | Always have a load (light, motor) in the circuit. Never let bare positive and negative wires touch |
| No fuse in the circuit | When something goes wrong, your wiring catches fire instead of a fuse blowing | Always install a fuse on the positive line, rated below your wire’s capacity |
| Wire too thin for the load | Wire overheats, insulation melts, fire risk | Match wire gauge to current draw. When in doubt, go thicker |
| Reversed polarity on LEDs | LED does not light; may be permanently damaged | LEDs have a long leg (+) and short leg (-). Test briefly before committing |
| Loose connections | Intermittent contact creates arcing, heat, and fire | Twist tightly, crimp, or bolt. Tug-test every connection |
| Bare wire touching metal structures | Unintended short circuits, electrified surfaces | Insulate ALL connections with tape, cloth, or heat-shrink tubing |
| Mixing wire gauges without thinking | Thin section overheats while thick section is fine | The thinnest wire in the circuit sets the current limit for the entire circuit |
| No switch — disconnecting by pulling wires | Sparks at the connection, wear on the wire, eventual failure | Install a switch. Even a crude knife switch is safer than pulling wires |
| Wiring lights in series | Dim lights, all fail if one fails | Wire in parallel. Each light gets its own path to the battery |
| Running wire through heat or pinch points | Insulation damage leads to short circuits | Route wire away from heat sources and sharp edges. Use grommets through holes in metal |
What’s Next
With basic circuit skills, you can now build toward these capabilities:
- Crystal Radio — your first communication device, built from wire coils and scavenged parts
- Basic Electronics — transistors, diodes, and simple amplifier circuits
- DIY Wind Turbine — connect your generator output to a real wiring system
- Hydro Generator — wire a water-powered generator to your shelter
Quick Reference Card
Basic Electrical Circuits — At a Glance
Ohm’s Law: V = I x R (Voltage = Current x Resistance)
Water analogy: Voltage = pressure, Current = flow, Resistance = pipe size
Concept Rule Complete circuit Current must have an unbroken loop from (+) through load to (-) Series wiring Resistances add up, current is same everywhere, one failure kills all Parallel wiring Voltage is same everywhere, currents add up, one failure does not affect others Fuse placement Always on the positive wire, before everything else Wire sizing More current = thicker wire. Check the gauge table Switch placement Anywhere in the circuit loop — breaks the path, stops current The Three Rules That Prevent Fires:
- Always use a fuse rated below your wire’s capacity.
- Never use wire thinner than the current demands.
- Every connection must be tight — no loose twists, no bare wire exposed.
12V DC Safety: Cannot push lethal current through dry skin. Still causes burns and sparks at short circuits. Treat it with respect.
Scavenge priority list: Car batteries, fuse boxes, house wiring, extension cords, LED bulbs, switches, electrical tape.
When in doubt, disconnect the battery first.