In explosion hazardous areas, if mechanical ventilation is adopted, it can generally be considered as a well ventilated state（ 2) Release source of production unit area
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Compared with gb50058-2014, gb3638.14-2000 fully considers the impact of ventilation on the division of hazardous areas
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In fact, when selecting cables, we should adjust the ampacity with appropriate coefficients according to specific environmental temperature, laying mode and other factors, so the cable section we selected will be enlarged (appropriately enlarged when selecting cables), which not only meets the explosion-proof electrical design code, but also reduces the gap with the economic section
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If the storage tank is in the embankment, if the distance from the outer wall of the storage tank to the embankment is greater than or equal to 3m, the horizontal distance extending from the outer wall of the storage tank to the embankment is divided into zone 2; Otherwise, it shall be divided into zone 2 within 3M from the outer wall of the storage tank（ 4) Non explosive hazardous area
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Therefore, when selecting the cable section according to the economic current, it is necessary to check with the allowable current carrying capacity, and then select the larger section to ensure the safe operation first
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Based on the consideration of safety and reliability, gb50058-2014 shall prevail
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The current national standards include code for design of electrical installations in explosive and fire hazardous atmospheres (gb50058-2014) and electrical equipment for explosive gas atmospheres, Part 14: classification of hazardous locations (gb3638.14-2010), but the two national standards are very different
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b
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The rated voltage of insulation of working neutral line shall be equal to the phase line voltage and shall be laid in the same sheath or pipe（ 2) In the explosion hazardous environment, two pole switches need to be installed in the single-phase circuit in TN-S system
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The horizontal distance between the overhead line and the explosive gas environment shall not be less than 1.5 times the height of the tower
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Scope division of explosion hazardous area the primary task of electrical design for flammable and explosive environment is to correctly divide the explosion hazardous area of the production site
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Selection of wires and cables according to the national standard gb50058-2014 code for design of electrical installations in explosive and fire hazard environments, the selection of insulated conductor and cable section in zone 1 and zone 2 of explosive gas environment shall meet the following requirements: (1) the allowable current carrying capacity of conductor shall not be less than 1.25 times the rated current of fuse melt, And 1.25 times of the setting current of the automatic switch long time-delay overcurrent release（ 2) The long-term allowable current carrying capacity of the branch line of squirrel cage induction motor with leading voltage below 1000V shall not be less than 1.25 times of the rated current of the motor（ 3) In zone 1, the minimum section of copper core control cable is 2.5mm ²， In zone 2, the minimum section of copper core control cable is 1.5mm ²。 In addition, on the premise of this specification, the cable section shall also be selected according to the economic current
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It shall be comprehensively determined after technical and economic comparison according to the level and location of release source, the nature of flammable substances, ventilation conditions, obstacles and production conditions, operation experience and other factors
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When an embankment is set around the storage tank, the range from the outer wall of the storage tank to the embankment with the height of the embankment top is divided into zone 2
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For a fixed storage tank, the space above the liquid surface in which the tank is not filled with inert gas is divided into zone 0
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In case of poor ventilation in the closed plant, the plant is divided into zone 1
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a
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If the distance between the release source and the external wall of the building is greater than or equal to 12M, the space within 3M of the door and window leading to the open air is also divided into zone 2 under the condition of good natural ventilation
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When the enclosed plant is well ventilated, it is divided into zone 2 bounded by the plant
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When flammable substances are heavier than air, the area with a radius of 15m centered on the release source is divided into zone 2
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General production workshops are closed plants
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If the distance between the release source and the external wall of the building is greater than or equal to 1.5m, the space within 3M of the door and window leading to the open air is also divided into zone 2 under the condition of good natural ventilation
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Generally speaking, the economic current section is 1 ~ 2 levels larger than the allowable current carrying section, but it is also small
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Selection of explosion-proof electrical equipment the explosion-proof type, level and temperature group of explosion-proof electrical equipment shall be defined according to the explosion-proof area level and explosion-proof medium level, which has two forms: (1) the wiring port is threaded
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When flammable substances are heavier than air, if the distance from the release source to the external wall of the building is less than 12M, the area with the release source as the center, radius of 15m and height of 7.5m (outside the plant) is divided into zone 2
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If the distance from the outer wall of the storage tank to the embankment is less than 3m, the explosion hazard area shall be marked out outside the embankment
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If the space in the plant is large and the mass of combustibles released by the release source is small according to the ventilation, the area with explosion risk can be delimited according to part of the space in the plant
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When the storage tank has no dike, the area 3M away from the outer wall and top of the storage tank is divided into zone 2
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Within the building, the scope of explosion hazard area should be delimited by the plant as a unit
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Near the equipment using open fire in the production process, or near the equipment where the surface temperature of hot parts exceeds the ignition temperature of flammable substances in the area, as well as the open or open overhead pipeline area for conveying flammable substances outside the production unit area (but the valve position shall be determined according to the specific situation), can be divided into non explosion hazardous areas（ 5) The scope of hazardous areas is divided according to different standards
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Most foreign explosion-proof motors belong to this form, and many domestic manufacturers have begun to produce them
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When breaking the phase line, the N line must be broken (that is, the phase line and N line must be broken at the same time)
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The scope of other explosion hazardous areas is the same as that in case of poor ventilation
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Other points for attention: (1) the rated voltage of insulated conductors and cables for low-voltage power and lighting lines must not be lower than the working voltage and not lower than 500V
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When flammable substances are lighter than air, the area with a radius of 4.5m centered on the release source is divided into zone 2（ 3) Flammable substance storage tank heavier than air
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The workshop in explosive gas environment can be reduced to non explosive hazardous environment after positive pressure or continuous ventilation dilution measures are adopted
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Gb3638.14-2010 is a mandatory national standard, but not a design code
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This directly affects the following series of design work, such as the selection of main electrical equipment, the selection of wires and cables, installation standards, etc., which is directly related to production and personal safety
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The interior of the building is delimited by room, that is, when class a gas and class A and class B liquid equipment are arranged in the same room, regardless of class C or other liquid equipment, the whole room is divided into zone 2
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The space with the vent as the center and the radius of 1.5m and the pits and ditches under the floor in the explosion hazardous area are divided into zone 1
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When the storage tank has no dike, the area 3M away from the outer wall and top of the storage tank is divided into zone 2
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Therefore, the scope division of gb3638.14-2010 is much smaller than that of gb50058-2014
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Scope division of gas explosion hazardous areas (1) release sources inside buildings
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When the flammable substance is lighter than air, if the distance between the release source and the external wall of the building is less than 1.5m, the area with the release source as the center, radius of 4.5m and height of 7.5m (outside the plant) is divided into zone 2
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For the floating roof storage tank, the space within the moving range of the floating roof is divided into zone 1
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This only means that under the normal operation of the power supply system, it is only one of the measures for safe power use, but can not solve all the problems of safe power use（ 3) Overhead lines of 10kV and below are strictly prohibited from crossing explosive gas environment
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However, generally, enclosed or semi enclosed plants are usually poorly ventilated places
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In addition, this situation is under the condition of single cable laying
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In this form, the steel pipe can be directly connected with the explosion-proof flexible pipe.
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