# Section 9 - Safety

Amateur radio is not thought of as a dangerous hobby, but as well as the usual common sense approach we take to everyday life there are a few other dangers we must be aware of.

## 9.1 High Voltage and High Current Power Supplies

Mains powered devices often contain lethal voltages, as do many high power transmitters and amplifiers. Always heed any warning labels printed on the case of the equipment and ensure that it is unplugged before opening it to carry out adjustment or repair.

Some supplies may be low-voltage but capable of supplying extremely high currents. Common amongst these are 12V car and sealed lead-acid batteries, however even the humble Ni-Cad is capable of supplying a substantial current if accidentally short-circuited.

Any short circuit is likely to cause the conductors carrying it to become very hot, maybe even to catch fire. If that conductor is a ring on your finger, you may sustain a nasty burn. The risk of jewellery causing a short circuit is often overlooked when servicing or adjusting equipment, but it is all to easy for a short circuit to be caused, and the wearer be completely unaware of it until they feel the intense pain of a burn, at which point it is normally impossible to quickly remove the vary hot piece of jewellery quickly enough to prevent further injury.

Capacitors, particularly electrolytics, can hold a substantial amount of energy for some time after the power has been switched off, sometimes as long as several days. The types used in power supplies are particularly dangerous from this respect and should be viewed with cautious respect.

## 9.2 - 9.6 Mains Plugs and Wiring

The mains earth is a safety device designed to protect the user from electric shock. If the metalwork of a piece of equipment were to become live, a massive current flows to earth blowing the fuse and cutting the supply of power. For this reason all metal cased equipment must be earthed.

Use of a fused plug for protection relies is reliant upon the correct fuse being fitted. The primary job of the fuse is to protect the mains cable from overheating. Therefore it is dangerous to fit a 13A fuse in the plug of an appliance whose mains cable is only capable of safely passing 4A.

The plug must also be wired correctly. Although all appliances must now come with a fitted plug, we may need to replace the plug on an appliance so we should know how to wire it.

The live wire is coloured brown and connects to the terminal beside the fuse on the right. The neutral conductor is coloured blue and connects to the left hand terminal. The earth is green, or green and yellow, and connects to the terminal at the top. Before wiring a plug we must ensure that the cable insulation is undamaged.

Check the following to ascertain if a plug is safely connected.

1. Cable is securely held by the cord-grip at the base of the plug
2. Insulation has not been damaged by stripping the outer cover of the cable.
3. There are no whiskers of wire poking out of the plug's terminals.
4. The correct fuse is fitted.
5. The insulation continues right up to each terminal
6. The plug is wired correctly.

## 9.7 Electric Shock

In case of an accident there should be a single OFF switch that will cut all power to the shack. Everyone in the household should know the location of the switch. It is best placed as near as possible to the doorway. In the unlikely event of someone sustaining an electric shock, switch off the power first. If you touch the casualty before the power is off, you may receive a shock and become a casualty too!

Adult help should be summoned immediately. All victims of electric shock must receive medical attention

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