Electrical Safety

Poole Radio Society offers the following information ONLY to help candidates obtain their Foundation Licence. It is the responsibility of readers of this site to properly understand and assess the risks and precautions needed when working with electricity, electrical equipment and wiring.

Electrical Risks

· High voltages carry a risk of electrocution (they can kill).

· High currents carry a risk of over heating and fire.

Such things as Watches, Rings, Necklaces, Wires are all able to conduct electricity and potential sources of danger, not only to you if they touch high voltages, but also even on very low voltages if they pass large amounts of current.

Safety Earth

· Mains powered equipment should have a safety earth fitted.

· If a fault develops in the equipment, it is possible that live parts (at mains voltage of 230 Volts) could become connected to the metal case. This poses a risk of electrocution unless the metal case is earthed. If the case is properly earthed and a live part comes into contact with it, then the fuse will blow.

· Double insulated equipment does not have metal cases, and have extra insulation in their construction to prevent faults causing accessible metalwork (e.g. headphone sockets) becoming live.

· Many houses have PME (Protective Multiple Earth) installations. There is a risk that the house earth may rise above earth potential. Special arrangements are therefore needed. You should check the earth arrangements in your home, taking advice from your local electricity supply company if necessary.

Fuses

· A correct fuse must be fitted to all electrical equipment.

· The main purpose of the fuse in the plug is to protect the mains lead and internal wiring in the equipment. Low power devices will have a thin mains lead that can overheat at currents below the protection of a larger value fuse. Do not assume all faults are short circuits. It is possible to have a fault which will not blow a large fuse (e.g. 13A) in adequate time or at all, but which would overheat a 2A flex.

Working on Mains Equipment

· You should only ever work on Mains-Powered equipment when it is fully disconnected from the mains. (The mains plug is removed from the mains socket).

Wiring a Mains Plug

· Mains plugs should only be worked on when they are completely disconnected from the mains.

A 3-Pin Mains Plug is wired up as shown in the diagram below: -

The Wire Colours
Colour	Description
Brown	Live Wire – This is always the wire that is connected to one end of the Fuse.
Blue	Neutral Wire.
Yellow / Green striped	Earth Wire. Not all equipment will have an Earth Wire. If an Earth Wire is part of the equipment’s mains cable, then this MUST be connected as shown

· It is important to make a tidy job of fitting the mains plug.

· Whiskers (odd strands of wire) must be avoided.

· The cable grip must be fitted and the cable grip screws tightened.

Master Off Switch

A clearly marked switch to turn off all station equipment in an emergency is the quickest way to cut the power to all equipment in the event of an accident or suspected accident.

Accidents Involving Electricity

In the event of an accident involving electricity, the first thing to do is to switch off the power. The casualty must not be touched unless the power has been switched off.

Rescuers are at risk of electrocution themselves unless they know that the power is off. They won’t know how the casualty suffered possible electrocution, so they don’t know what is “live”. It is easy to rush up to casualty and risk touching them or moving them. If the casualty is still in contact with a live wire, the rescuer will also become a casualty.