Electrical Safety Notice

Last updated: 14 November 2026

Circuits DIY publishes circuits and projects so that people can learn electronics by building things. Most of our projects run from batteries or low-voltage supplies and are safe for beginners. Some do not. This page explains the hazards you may meet when you follow a project, and what you should do about them. Please read it before you build anything that connects to mains electricity, uses lithium batteries, gets hot or produces high voltages.

This notice is general safety information. It is not a substitute for proper training, the manufacturer's documentation for your parts, or the electrical rules that apply where you live.

1. Mains electricity can kill

Household mains (110–120 V in North America, 220–240 V in most other countries) can cause a fatal electric shock, severe burns and fires. A few of our power supply, charger, relay, dimmer, lamp and appliance-control projects connect to mains.

If you are a beginner, do not build mains-powered projects. Use a battery or a commercially made, certified low-voltage adapter instead, and keep your circuit on the low-voltage side.
Never work on a circuit while it is plugged in. Unplug it, and confirm it is dead with a meter before touching anything.
Use a fuse sized for the circuit on the live input, and a properly rated mains switch.
Use a correctly rated, insulated transformer or a certified power module to separate mains from low-voltage parts. Many simple "transformerless" (capacitor-dropper) supplies leave the whole circuit connected to mains, including any part you might touch.
Put mains circuits in a closed, non-conductive enclosure, with cord grip (strain relief), and earth any exposed metal parts.
Keep generous spacing (creepage and clearance) between mains tracks and low-voltage tracks on a PCB or breadboard. Never put mains on a breadboard.
Use an isolation transformer and a residual current device (RCD/GFCI) when testing.
Fixed wiring (anything wired into a building's electrical installation) must be done by a licensed electrician. In Australia and many other countries it is illegal for an unlicensed person to do this work.

2. Capacitors can stay charged

Large electrolytic capacitors in power supplies, inverters, amplifiers, camera flashes and microwave ovens can hold a dangerous charge long after the power is removed. Discharge them through a suitable resistor and check with a meter before you touch the circuit.

3. Batteries store a lot of energy

Lithium-ion and lithium-polymer (Li-ion, LiPo, 18650) cells can catch fire or explode if they are overcharged, over-discharged, short-circuited, punctured or charged with the wrong charger. Use cells with a protection circuit, use a charger IC designed for the chemistry (for example a TP4056 module with protection), never leave lithium cells charging unattended, and charge them on a non-flammable surface.
Lead-acid and car batteries can deliver hundreds of amps into a short circuit, enough to melt wires and tools. Fuse the battery lead close to the battery. Lead-acid batteries give off hydrogen while charging; charge them in a ventilated area away from sparks.
Do not mix old and new cells or cells of different types, and recycle damaged batteries properly.

4. Heat and fire

Regulators, transistors, MOSFETs, power resistors and motor drivers can become hot enough to burn skin or start a fire. Check the power dissipation of each part, fit a heatsink where needed, allow airflow, and never run an untested circuit unattended. Use wire of the correct gauge for the current.

5. Ratings: absolute maximum is not normal operation

Every component has limits for voltage, current, power and temperature. The absolute maximum ratings in a datasheet are the stress levels beyond which the part may be damaged — they are not safe operating conditions. Design to the recommended operating conditions, leave a margin, and check the datasheet for the exact part number you are using. Similar part numbers and different manufacturers' versions can have different ratings and pinouts.

6. Polarity, pinouts and substitutions

Reversing an electrolytic capacitor, a battery, a diode or a supply can destroy parts and make capacitors burst. Check pin numbers against the datasheet for your exact package — the same chip can have different pinouts in different packages. If you substitute a part, confirm that its ratings and pinout are suitable; our circuits are written for the parts listed.

7. Soldering and workshop safety

A soldering iron tip is around 350 °C. Use a stand, and keep the cable away from the hot tip.
Wear eye protection when soldering, cutting leads or working with springs and motors.
Work in a ventilated area; solder flux fumes irritate the lungs. Wash your hands after handling leaded solder, and do not eat at the bench.
Keep liquids away from your work and a suitable fire extinguisher nearby.

8. Motors, relays and inductive loads

Motors, solenoids and relay coils produce voltage spikes when switched off. Fit a flyback diode or suppression network as shown in the project, use drivers rated for the stall current, and keep fingers, hair and clothing away from moving parts.

9. High-voltage projects

Circuits that generate high voltage — such as flyback drivers, ignition coils, Tesla coils, electric fence chargers, CRT or neon drivers and camera flash circuits — can cause shocks, burns, fires and interference even when powered from a small battery. These are for experienced builders only. Never use them on people or animals.

10. Radio transmitters

Transmitters, wireless modules and FM projects must follow your country's radio rules (frequency, power and licensing). Building, owning or using a radio-frequency jammer (for example a mobile-phone, GPS or Wi-Fi jammer) is illegal in Australia, the UK, the EU, the US and most other countries. Infrared projects that interfere with TV remote controls are not radio transmitters, but should only be used on your own equipment.

11. Static electricity (ESD)

MOSFETs, CMOS chips and microcontrollers can be damaged by static. Handle them by the edges, use an anti-static strap or touch earthed metal before handling, and store them in anti-static packaging.

12. Computers and test equipment

A wiring mistake can damage a USB port, laptop or oscilloscope. Check your wiring before connecting a board to a computer, use a powered USB hub or USB isolator where possible, and remember that an oscilloscope's ground clip is connected to earth.

13. Students and young makers

Many of our readers are students. Anyone under 18 should build projects with a parent, teacher or experienced adult, and should stick to battery-powered, low-voltage circuits.

14. Products built from our circuits are not certified

Our circuits are learning examples. A device built from them has not been tested for electrical safety or electromagnetic compatibility and does not carry certification such as RCM, CE, UKCA, FCC or UL. Do not sell, install permanently or rely on such a device for safety-critical, medical or life-support use without professional design, testing and certification.

15. Found something unsafe?

If you think one of our articles contains an unsafe instruction or a dangerous mistake, please tell us through Report a Problem. Safety reports are reviewed first.