SAS Urban Survival Handbook by John Wiseman

ovens offer just that. There is an electrical gadget for every job, and the demand on domestic supplies is enormous.
    In most houses, particularly older ones, the supply is barely up to the demand. More and more sockets are added—or worse, people start overloading sockets and adding make-do extension leads.
    There are two hazards which must always be remembered when dealing with electricity—FIRE and ELECTROCUTION. Almost half of all domestic fires, some causing loss of life, are caused by electrical faults. Electrocution is less common, but still claims hundreds of lives every year.
    Most common-sense precautions will protect you from both hazards. Because electricity is so dangerous, it is well worth understanding as much about it as possible.

INTRODUCTION
     
    Electricity existed in nature before man ever thought of generating it himself and using it to his advantage. Lightning is probably the most violent and dangerous manifestation—although simple ‘static’ produced when combing your hair or the charge built up in garments during tumbledrying is also electricity. Most of us have walked across a man-made-fibre carpet and then touched something, only to receive a jolt of pain in the fingertips. This is a minor electric shock.
    Even the human body is operated by tiny electrical impulses sent through the brain, nerves and muscles. This is partly why electrocution is so serious.
    Man-made electricity is only useful to us when it is channelled through an appliance. When current flows through a lightbulb, the filament glows. When connected to an electric motor, the motor turns. In all appliances heat is generated—and a magnetic field. The heat may be a problem, although adequate ventilation and careful use of appliances should take care of this. Sometimes the heat generated is the whole point—as in an electric fire.
    The magnetic field is usually too small to matter, unless you live in close proximity to a group of pylons or a generating station, when the powerful magnetic field may have a damaging effect on your health.

The circuit
     
    Think of electricity as energy being pushed under pressure along a wire. The electric current flows because the pressure is greater on the side it enters an appliance—the live wire—than on the side where it leaves the appliance—the neutral wire.
    The electric current moves in a circuit. If that circuit is broken, it cannot flow. By switching off a switch or unplugging an appliance, you are breaking the circuit.
    The supply of electricity you receive flows from the incoming mains, through your meter and fuse box/consumer unit, along the fixed cables which are (usually) hidden in the walls, ceiling and floors. Via socket and plug or lampholder, the current flows through the live wire to the appliance, causes the appliance to do whatever it does, and then returns to the mains supply again down the neutral wire.
    ▶ The live wire—in some countries—is known as the active, positive or hot wire. The earth—especially in the US—is called the ground.
     

Conductors/insulators
     
    The current flows through some substances more easily than through others. Substances which allow electricity to flow are called conductors. Most metals are conductors—copper, brass and aluminium are commonly used for wiring.
    Substances which resist or prohibit the flow of electricity are called insulators. Most non-metals fall into this category—but in practice the most common insulators are plastics, rubber and ceramic.
    For these reasons most domestic wiring is copper, which is a good conductor and flexible enough to work with. It is sheathed in waterproof plastic to restrict the flow of electricity to the copper.

Test of strength
     
    Conductors have to be thick enough to take the amount of current passing through them. Generally, the stronger the current, the thicker the conductor has to be. The longer the run of cable, the thicker too. DON’T expect a thin cable used for wiring a