Read Online SAS Urban Survival Handbook by John Wiseman - Free Book Online Page B
Authors: John Wiseman
Tags: Fiction, General, Reference, Survival, Survival skills, Self-Help, Health & Fitness, safety, Personal & Practical Guides
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with ANY other appliance. The socket would be overloaded.
THREE-PHASE POWER
With apparatus, or even an entire installation, that creates a very heavy demand for electricity, three-phase power is commonly used. Generally speaking, this makes available three times the 240 volt (AC) supply. The three phases are balanced so that they are used equally, and in most cases separately fused and arranged so that the alternations of each supply are ‘out of sync’ with one another.
The commonest uses of three-phase power are kilns, hoists (reversible motors), factories, photographic/film studios, workshops, schools, hospitals and other large buildings with a high number of rooms, sockets and lights.
ADDED DANGER
Three-phase equipment should be regularly checked for safety. In large buildings it should be arranged so that you can never come into contact with more than one phase at a time. To do so could result in a shock of 415 volts. Usually three phases are each assigned different tasks—NOT one phase to sockets, one to lights etc—so the risk of making contact with more than one phase is eliminated. In most cases the three phases each feed an equal number of rooms.
NO NEUTRAL WIRE?
Three-phase motors usually have no neutral wire. The motor is fed by all three phases, and the consumption is balanced so that there is no power to be returned via a neutral wire.
WARNING
Never attempt any work on a three-phase circuit, unless qualified to do so. You would be risking a shock of 415 volts.
FUSES
When a wire carries a current, heat is generated. If the current is high and the wire is too thin to cope with it, the wire will get hot—and probably ‘burn out’ or melt.
A fuse is a deliberate ‘weak link’. If the current rises (usually because a fault has developed) above the intended limit for a fuse, the fuse wire gets very hot, melts and breaks the circuit. This may be caused by:
◑ Electricity leaking to earth, either directly, or through the earth wire. The earthed metal casing of an appliance may have become live and the current is returning to earth. This causes an increase in the current because there’s no resistance.
REPLACING A FUSE
Loosen screws. Remove old wire. Fix new wire at one end (A) with screw. Take wire across, tighten second screw (B). SNIP OFF SPARE WIRE!
With some types of fuse, it is necessary to thread the new piece of fuse wire through (C). Follow path of old wire or compare to another complete fuse.
Cartridge fuses (D) need to be removed and replaced. With minicircuit breakers (E), flip switch or press the reset button.
The live and earth wires may have touched in a faulty plug or socket. Spilled water or another conductor may have formed a new connection.
◑ Similarly, live and neutral wires may have become connected either directly or through a fault in an appliance.
◑ Too heavy a load may have been placed on a circuit—perhaps too many high-powered appliances have been connected to it. The fuse won’t allow the circuit to be endangered by too much current passing through it.
WARNING
When a fault develops and a fuse ‘blows’, a dangerous amount of heat may have been generated in an appliance, a plug or a socket. Check the circuit for signs of overheating.
When a fuse ‘blows’
First check the fuse in the plug or socket. The easiest way to check them is to replace them, since a ‘blown’ fuse may not look any different from a good one.
If these are working, go to the fuse box/consumer unit and check the fuse there or press the reset button (see Replacing a fuse ).
It’s usually more obvious when a fuse has blown at the fuse box (if you know which outlets are on a circuit) because a whole circuit will be rendered inoperative. If a light on one floor’s lighting circuit blows a fuse, then all the other lights on that circuit will go out.
Replacing a fuse
If you know
THREE-PHASE POWER
With apparatus, or even an entire installation, that creates a very heavy demand for electricity, three-phase power is commonly used. Generally speaking, this makes available three times the 240 volt (AC) supply. The three phases are balanced so that they are used equally, and in most cases separately fused and arranged so that the alternations of each supply are ‘out of sync’ with one another.
The commonest uses of three-phase power are kilns, hoists (reversible motors), factories, photographic/film studios, workshops, schools, hospitals and other large buildings with a high number of rooms, sockets and lights.
ADDED DANGER
Three-phase equipment should be regularly checked for safety. In large buildings it should be arranged so that you can never come into contact with more than one phase at a time. To do so could result in a shock of 415 volts. Usually three phases are each assigned different tasks—NOT one phase to sockets, one to lights etc—so the risk of making contact with more than one phase is eliminated. In most cases the three phases each feed an equal number of rooms.
NO NEUTRAL WIRE?
Three-phase motors usually have no neutral wire. The motor is fed by all three phases, and the consumption is balanced so that there is no power to be returned via a neutral wire.
WARNING
Never attempt any work on a three-phase circuit, unless qualified to do so. You would be risking a shock of 415 volts.
FUSES
When a wire carries a current, heat is generated. If the current is high and the wire is too thin to cope with it, the wire will get hot—and probably ‘burn out’ or melt.
A fuse is a deliberate ‘weak link’. If the current rises (usually because a fault has developed) above the intended limit for a fuse, the fuse wire gets very hot, melts and breaks the circuit. This may be caused by:
◑ Electricity leaking to earth, either directly, or through the earth wire. The earthed metal casing of an appliance may have become live and the current is returning to earth. This causes an increase in the current because there’s no resistance.
REPLACING A FUSE
Loosen screws. Remove old wire. Fix new wire at one end (A) with screw. Take wire across, tighten second screw (B). SNIP OFF SPARE WIRE!
With some types of fuse, it is necessary to thread the new piece of fuse wire through (C). Follow path of old wire or compare to another complete fuse.
Cartridge fuses (D) need to be removed and replaced. With minicircuit breakers (E), flip switch or press the reset button.
The live and earth wires may have touched in a faulty plug or socket. Spilled water or another conductor may have formed a new connection.
◑ Similarly, live and neutral wires may have become connected either directly or through a fault in an appliance.
◑ Too heavy a load may have been placed on a circuit—perhaps too many high-powered appliances have been connected to it. The fuse won’t allow the circuit to be endangered by too much current passing through it.
WARNING
When a fault develops and a fuse ‘blows’, a dangerous amount of heat may have been generated in an appliance, a plug or a socket. Check the circuit for signs of overheating.
When a fuse ‘blows’
First check the fuse in the plug or socket. The easiest way to check them is to replace them, since a ‘blown’ fuse may not look any different from a good one.
If these are working, go to the fuse box/consumer unit and check the fuse there or press the reset button (see Replacing a fuse ).
It’s usually more obvious when a fuse has blown at the fuse box (if you know which outlets are on a circuit) because a whole circuit will be rendered inoperative. If a light on one floor’s lighting circuit blows a fuse, then all the other lights on that circuit will go out.
Replacing a fuse
If you know
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