Что влияет на природные условия в городе?? - №13437165

Что влияет на природные условия в городе??
- Предмет:
  Окружающий мир
- Автор:
  carter90
- 6 лет назад

Ответы 1

температура это просто
- Автор:
  jazzkaia
- 6 лет назад
- 0
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Помогите с переводом! Пожалуйста!
Electric shock
In all manual arc welding operations, the principal risk is from electric shock, most likely from contact with bare live parts of the welding circuit. The arc voltage is within the range 10 to 40 V, but, as the voltage required to strike the arc may be substantially higher, power sources have an open circuit voltage (OCV), typically up to 80V. Although these voltages appear low compared with the 230V domestic mains supply, work by the International Electrotechnical Commission shows that only voltages below 50V AC or 120V DC are unlikely to be dangerous to healthy people in a dry working environment. In other conditions such as restricted conducting locations or wet surroundings, potentials of 80V AC have been the cause of fatal electric shocks. Devices are available which reduce the open circuit voltage when welding is not being carried out. These voltage reduction devices (VRD) should meet the requirement of BSEN 60974-1.
Appropriate protective clothing such as gloves, boots and overalls will protect the welder from electric shock.
Stray welding currents
A different kind of electrical hazard can arise from stray welding currents which return to the welding transformer by paths other than the welding return lead. For example, although the return is disconnected, welding is possible when the return current flows through:
• protective earth (PE) conductors of other electrical equipment, or the power source itself
• wire ropes, slings and chains
• metal fittings and pipework
• bearings in motors
Damage to the PE conductor in particular could mean the equipment is no longer being earthed.
Stray currents may be substantial and comparable with the welding current level where there is poor or faulty insulation of the return lead which may be short-circuited by other conductors. When welding on building structures and pipework installations, the welding return lead should be placed as close as possible to the point of welding. The exception is where the metallic grid, support structure or metallic ship hull is used as part of the welding return circuit.
There is an increased risk of stray currents when welding on structures which have an inherent connection to earth such as ships or pipelines. There could be an unacceptable indirect current return path with damage to conductors if, for example, the current return lead is detached and the circuit becomes open. The recommendations for the electrical distribution systems and earth connections in various situations are described in HS(G) 118.
Safe practice and accident avoidance
Welding equipment should conform to the appropriate standards; electrode holders that are insulated overall are recommended so no bare metal can be inadvertently touched.
Welding leads and return leads should be insulated and thick enough to carry the current safely; connectors should also be insulated to avoid inadvertent access to live conductors and adequate for the current being carried.
The welding return lead should be connected as near as practicable to the welding arc; metal rails, pipes and frames should not be used as part of the welding circuit unless they are a part of the workpiece itself.
Check the workpiece earthing requirements. When using a double or reinforced insulation power source, stray currents can be avoided by not earthing the workpiece or the welding output circuit.
The welding leads, connection devices and electrode holder or torch should be checked at regular intervals for 'fitness for use'; repair or replace damaged or worn components.
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- 6 лет назад
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