Electrical Safety

Introduction

Electricity is useful, and it can also injure or kill. This lesson is the most important in the course. This is general safety education, not a substitute for training or the laws that apply where you live.

The simple explanation

Small batteries are generally safe to practise with. Mains electricity is not.

Low voltage versus mains

• Low-voltage battery and USB circuits (for example 1.5 V to 12 V) are used in these courses. They rarely hurt you, but they can still cause burns or fire if you short-circuit them.
• Mains electricity in a wall socket is much higher voltage, and it can be lethal. Mains voltage differs by country, roughly 100 to 240 V.

The danger comes from the current passing through your body, and mains has enough voltage to push a harmful current through you, especially when skin is wet.

Golden rules

1. Never work on mains wiring, sockets, fuse boxes or appliances unless you are properly qualified. Hire a licensed electrician. Laws in many places require this.
2. Practise only with batteries or a low-voltage power supply. Do not open and tinker with devices that plug into the wall. Some, such as old televisions and power supplies, keep dangerous charge even when unplugged.
3. Keep electricity away from water. Never use electrical items with wet hands or near baths, sinks or outdoors in the rain.
4. Do not overload sockets or use damaged cables. Replace frayed or hot cables and plugs.
5. Use the right protection. Fuses and circuit breakers stop too much current, and residual current devices (RCDs, or GFCIs in some countries) cut power when current leaks, for example through a person. Test them as the maker says.
6. Switch off and unplug before you change anything, and check it is really off.
7. Never bypass or replace a fuse with something stronger or with a wire.

Batteries and heat

• Do not short the terminals of a battery with a wire. It can heat the wire, burn you or damage the battery.
• Lithium batteries, such as in phones and hobby packs, can catch fire if punctured, crushed, overcharged or short-circuited. Use the right charger and never use a damaged battery.
• Resistors and other parts can get hot. Do not touch them right after use.
• If something smells hot or smokes, disconnect power at once.

Tools and soldering

If you later use a soldering iron, work in a ventilated area, keep it in a stand, wear eye protection and never touch the hot tip. Wash your hands after handling solder, especially leaded solder.

In an emergency

• If someone is in contact with electricity, do not touch them. Switch off the power at the source if you can do so safely, and call your local emergency number straight away.
• For a small electrical fire, switch off the power if safe. Never use water on an electrical fire. Use an extinguisher made for it if you know how, or leave and call emergency services.
• Learn where your home's main switch or fuse box is.

Try it yourself

Walk around your home. Find the main switch, check that cables are not damaged, and note any sockets with too many plugs. Write down who to call for electrical work in your area.

Summary

• Practise only with batteries or low-voltage supplies. Never work on mains unless qualified.
• Keep electricity away from water, use fuses and RCDs, and replace damaged cables.
• In an emergency, do not touch the person, switch off the power safely and call for help.