Electrical basics · Lesson 7 of 13

Safety and tools

Electricity doesn’t give second chances. This is the most important lesson in the course: how to protect yourself, how to find the live with a tester screwdriver, how an RCD protects you, and the tools that should be in your bag.

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14 rules before any work

  1. Switch off the breaker for the circuit you will work on (not the light switch!). If you don’t know which breaker, switch off the main one.
  2. Make sure the power is off with a tester screwdriver or a multimeter on the wires themselves. The breaker may be the wrong one, or wrongly labelled.
  3. Hang a note on the panel: "Do not switch on, work in progress", or lock the panel if it has a lock.
  4. Insulated tools and dry hands, and stand on something dry (rubber-soled shoes, not barefoot on a wet floor).
The rule for the whole course: every measurement is done with the appliance disconnected from the supply, except measuring voltage (volts) and measuring current with a clamp meter. Only those two are done with the power on, and carefully.

2The tester screwdriver

A small screwdriver with a neon lamp and a very large resistor inside. You touch the wire with the tip while your finger is on the metal cap at the end. If the wire is live, a tiny current flows through the lamp and your body to earth, and the lamp lights.

Try it: touch the socket with the tester

The tester’s limits: it only lights on the live (AC above about 70V). It doesn’t tell you how many volts, and it doesn’t work on a battery. And if the neutral is broken after a lamp that is switched on, the tester may light on the neutral too (you will see this in lesson 13). For accurate measurement use a multimeter.
Never touch the screwdriver tip while it is on the wire, and don’t use the tester as a heavy-duty screwdriver: if its insulation cracks, it becomes dangerous.

3The ordinary breaker and the RCD

An ordinary MCB breaker
The ordinary breaker, MCB: protects the cable from overcurrent and short circuits. It trips on large currents (10A, 16A ...).
The RCD / ELCB (earth leakage breaker): protects people. It compares the current going out on the live with the current coming back on the neutral, and if there is a difference of just 30 milliamps (meaning current is escaping to earth, possibly through your body) it trips in less than 0.04 seconds.

Press its T (Test) button once a month to make sure it works.

Try it: the RCD

4The basic tools

Insulated-handle tools must be marked 1000V with the double-triangle symbol (VDE). Properly insulated tools are not the same as tools that just have rubber grips.

Pliers

For gripping, twisting wire and cutting thin wire.

Side cutters

Cut wires cleanly. Never cut a live wire with them!

1000V

Insulated screwdrivers

Flat and Phillips, insulated almost to the tip.

Insulating tape

For insulating joints. Better still, use connectors and wrap tape over them.

Tester screwdriver

Tells you in a second whether a wire is live.

228.4

Multimeter (AVO)

Measures volts, ohms and continuity. Your most important instrument (lesson 8).

9.09

Clamp meter

Measures current without disconnecting a wire (lesson 9).

Wire strippers

Strip the insulation without nicking the copper.

5Do or don’t?

For each sentence, say whether it is the right thing to do or a mistake you shouldn’t make. You need 6 out of 8 right.

?Lesson questions

An RCD for additional protection of people is 30mA according to IEC 60364 and IEC 61008. Insulated tools follow IEC 60900 (1000V). Your progress is saved on this device only.
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