Read Online SAS Urban Survival Handbook by John Wiseman - Free Book Online
Authors: John Wiseman
Tags: Fiction, General, Reference, Survival, Survival skills, Self-Help, Health & Fitness, safety, Personal & Practical Guides
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wire.
With appliances which have no earth wire, or which claim to be ‘double insulated’, make very sure you use the recommended fuse, both in the plug for the appliance and at the fuse box/consumer unit by the meter.
WARNING
On domestic lighting circuits which do not include on earth wire, be very careful when using metal light fittings. If a fault develops, you are NOT protected. Always turn off the switch when changing the bulb. Put a piece of tape over the switch to avoid someone else turning on the light from habit when entering the room. To be completely safe, turn off the power at the fuse box/consumer unit (or remove the fuse until you have changed the bulb).
NON-EARTHED SYSTEMS
Remote areas may receive mains power on a non-earthing system, whereby current trying to run to earth is fed back into the mains along the neutral wire. These systems are rare and are governed by strict regulations. Do NOT attempt to make changes to the system yourself, unless you are a qualified electrician. This system is sometimes known as a protective multiple earth.
WHAT THE TERMS MEAN
Current is the rate of flow of electricity, and is measured in amperes, known as amps (usually seen as A ).
Voltage is the pressure difference between the live and neutral wires (usually expressed as volts or V ).
The resistance of an appliance to the flow of electricity, or the amount it impedes the flow (impedance), is measured in ohms (usually Ω).
Watts ( W ) are used to measure the power consumption of an appliance. Actually the number of watts indicates the amount of electrical energy the appliance consumes in a set period of time. This sounds complicated, until you remember that a 15 W lamp is pretty much at the lower end of the scale. It doesn’t get very hot or glow very brightly. A 100 W lamp gives out a lot of light and heat, using more electrical energy. An electric fire with one straight radiant element is likely to be 1000 W (1k W). Most of the electrical energy is turned into considerable heat to make the fire effective.
Simple maths
You may be unsure about the power rating of an appliance, but in practice most electrical equipment is well-labelled to tell you the voltage, impedance or power consumption. Often the instruction booklet gives you more information.
If you know two of the values, it is possible to calculate the third:
W = V × A indicates the consumption of power
A = W ÷ V indicates a safe fuse or flex rating
AC/DC
When voltage is expressed on an appliance as, say, 240V, it’s quite usual to see the letters AC immediately following. This refers to the type of supply.
Electricity is produced by a conductor (usually a coil of copper) rotating in a magnetic field. This process produces what appears to be a steady current, but one half of each revolution produces a positive charge, the other results in a negative charge. The current alternates between positive/negative at approximately 50 times a second, in Britain. This is called alternating current—AC.
Direct current (DC) does not alternate positive/negative—and is usually achieved by electronically rectifying the alternating current. In some situations a DC current is necessary—usually in industry. DC current is often used for controlling motors, lifts, trains and underground trains. Many motorized household appliances convert AC to DC—including turntables, some food mixers and some fans.
DOMESTIC SUPPLIES
Electricity for domestic use is not supplied at the same voltage throughout the world. This doesn’t really matter unless you intend to travel with electrical equipment. There may even be regional variations within a country. There are adaptors and transformers available to enable electrical equipment to be used safely. These step up or decrease the voltage accordingly. You should find out in advance if this is likely to be a problem—KNOW YOUR DESTINATION!
WARNING
If an appliance designed for a higher
With appliances which have no earth wire, or which claim to be ‘double insulated’, make very sure you use the recommended fuse, both in the plug for the appliance and at the fuse box/consumer unit by the meter.
WARNING
On domestic lighting circuits which do not include on earth wire, be very careful when using metal light fittings. If a fault develops, you are NOT protected. Always turn off the switch when changing the bulb. Put a piece of tape over the switch to avoid someone else turning on the light from habit when entering the room. To be completely safe, turn off the power at the fuse box/consumer unit (or remove the fuse until you have changed the bulb).
NON-EARTHED SYSTEMS
Remote areas may receive mains power on a non-earthing system, whereby current trying to run to earth is fed back into the mains along the neutral wire. These systems are rare and are governed by strict regulations. Do NOT attempt to make changes to the system yourself, unless you are a qualified electrician. This system is sometimes known as a protective multiple earth.
WHAT THE TERMS MEAN
Current is the rate of flow of electricity, and is measured in amperes, known as amps (usually seen as A ).
Voltage is the pressure difference between the live and neutral wires (usually expressed as volts or V ).
The resistance of an appliance to the flow of electricity, or the amount it impedes the flow (impedance), is measured in ohms (usually Ω).
Watts ( W ) are used to measure the power consumption of an appliance. Actually the number of watts indicates the amount of electrical energy the appliance consumes in a set period of time. This sounds complicated, until you remember that a 15 W lamp is pretty much at the lower end of the scale. It doesn’t get very hot or glow very brightly. A 100 W lamp gives out a lot of light and heat, using more electrical energy. An electric fire with one straight radiant element is likely to be 1000 W (1k W). Most of the electrical energy is turned into considerable heat to make the fire effective.
Simple maths
You may be unsure about the power rating of an appliance, but in practice most electrical equipment is well-labelled to tell you the voltage, impedance or power consumption. Often the instruction booklet gives you more information.
If you know two of the values, it is possible to calculate the third:
W = V × A indicates the consumption of power
A = W ÷ V indicates a safe fuse or flex rating
AC/DC
When voltage is expressed on an appliance as, say, 240V, it’s quite usual to see the letters AC immediately following. This refers to the type of supply.
Electricity is produced by a conductor (usually a coil of copper) rotating in a magnetic field. This process produces what appears to be a steady current, but one half of each revolution produces a positive charge, the other results in a negative charge. The current alternates between positive/negative at approximately 50 times a second, in Britain. This is called alternating current—AC.
Direct current (DC) does not alternate positive/negative—and is usually achieved by electronically rectifying the alternating current. In some situations a DC current is necessary—usually in industry. DC current is often used for controlling motors, lifts, trains and underground trains. Many motorized household appliances convert AC to DC—including turntables, some food mixers and some fans.
DOMESTIC SUPPLIES
Electricity for domestic use is not supplied at the same voltage throughout the world. This doesn’t really matter unless you intend to travel with electrical equipment. There may even be regional variations within a country. There are adaptors and transformers available to enable electrical equipment to be used safely. These step up or decrease the voltage accordingly. You should find out in advance if this is likely to be a problem—KNOW YOUR DESTINATION!
WARNING
If an appliance designed for a higher
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