Do instruments necessarily require explosion-proof wire sleeves?

Flexible tubes merely serve to protect the wires; they have nothing to do with explosion protection. Explosion protection mainly involves installing explosion-proof sealing joints at the instrument inlet ports to prevent combustible gases from entering the instruments. Flexible pipes are subject to explosion-proof verification – do galvanized pipe trays also need to undergo such verification? Personal opinion, for reference only.

Whether an instrument requires an explosion-proof winding tube depends on the specific environment. In flammable and explosive environments, to ensure safety, explosion-proof wire sleeves must be used to prevent explosions caused by electrical sparks. If the environment is safe and there is no risk of flammability or explosiveness, explosion-proof winding tubes are not necessary. It is recommended to refer to specific safety regulations and standards when deciding whether to use explosion-proof wire sleeves. .

GB 50093-2013 \"Code for Construction and Quality Acceptance of Automatic Instrumentation Projects\": Article 7.4.8: Flexible pipes should be used to connect cable conduits to sensing elements or field instruments, and waterproof bends shall be provided. When connecting to field instrument boxes, junction boxes, wiring boxes, etc., it must be sealed and firmly fixed. The specification states that flexible tubes are recommended, but not mandatory, for connecting cable conduits to sensing elements or field instruments. Its main purpose is to prevent dust, water, or other liquids from entering the sensing element or the field instrument. SH/T3521-2013 \"Technical Specifications for the Construction of Petrochemical Instrumentation Projects\": Article 8.4.7: When connecting the protective tube to components such as local control panels, instrument boxes, wiring boxes, and conduit boxes, sealing measures must be taken, and the tube must be fixed securely. The outlet of the protective tube should be about 250 mm lower than the inlet for the instrument equipment. A flexible tube is recommended for connecting it to the sensing elements or local instruments; if a flexible tube is not used, the end of the tube should be shaped like a flared tip or equipped with a cable protection cap. The specification also states that, in the connection between the protection tube and the field instruments, flexible tubes are recommended but not mandatory. SH/T3019-2016 \"Code for Design of Instrumentation Piping in Petrochemical Industries\": Article 7.3.6: When a flexible pipe is used to connect the protective pipe to the sensing element or field instrument, the outlet of the protective pipe should be approximately 250 mm lower than the instrument’s inlet. When the protective pipe is laid from top to bottom toward the instrument, a drain tee should be installed at the end of the pipe. When a flexible tube is not used to connect the protective tube and the instrument, the end of the tube should be fitted with a cable guard or shaped into a flared end. The standard also emphasizes the use of flexible pipes in certain situations, but it does not require their use in all cases.

Flexible pipes are all equipped with explosion-proof markings

The self-control installation manuals are divided into continuous and non-continuous types; for the non-continuous type, flexible pipes are not required. Although flexible pipes are flame-proof, they are not sealed and cannot prevent combustible gases from entering the instruments; sealing is generally provided by gland fittings.

It depends on the sealing location. Generally, it is sufficient to install seals at the instrument box and the inlet points for instruments; gland connections or other sealing methods can be used to isolate the instrument box, electrical boxes, and instruments from flammable and explosive substances. In this case, the flexible hose serves only as a protective and supporting element; it does not need to be explosion-proof. Because ordinary cable trays are usually open, and although the hoses are made to be explosion-proof, they remain exposed once they are in the cable tray. . If it is necessary to make the flexible hose explosion-proof as well, sealing measures such as gland fittings should be used at one end of the flexible hose, allowing direct connection between the flexible hose and the instrument box, electrical box, instruments, etc. Personal understanding~

The need for flexible tubing has nothing to do with explosion protection; it is necessary for cable protection. Cable protection is divided into two methods according to the specifications: one requires an explosion-proof flexible tube for continuity, while the other does not require such a tube for discontinuity. In either case, a sealed joint is needed at the end connected to the measuring instrument in order to achieve explosion protection; theoretically, either method can be chosen. However, during the actual inspection, some experts suggested that continuous systems must be used within the area of major hazard sources. I’m not sure if there are any regulations specifying this, and the experts didn’t provide any relevant standards either. Does anyone among you know anything about this?

Explosion-proof flexible hoses are recommended but not mandatory； Some flameproof instruments require a flameproof flexible tube (this is mandatory in such cases) ； These days, in many situations, explosion-proof flexible hoses are chosen for their protective properties rather than their explosion-proof capabilities. Explosion-proof flexible hoses are a product of the era in which flameproof instruments are widely used. Their working principle is such that when an explosion occurs inside a flameproof instrument, the burning gases that emerge from the inlet burn out before reaching the other end of the flexible hose, and the temperature as well as mechanical stress are reduced to safe levels. Therefore, qualified explosion-proof flexible hoses all have an explosion isolation mark. The structure of the connection between the explosion-proof flexible tube and the instrument follows the same explosion-proof principle as that of flange connectors; both the design and installation must meet the explosion-proof standards for the inlet (no leakage, no air leakage, and the cable must be properly secured). Many instrument technicians these days don’t take this seriously; when water gets into flexible pipes, they look for other causes instead……

Thanks for sharing; it’s all useful information! ! ! ! ! !

This is actually a combination unit, consisting of an explosion-proof sealed joint and a waterproof flexible tube; it is used in situations where cables are laid through tubes, while it is not used in cases where cables are run in small conduit boxes. The common combinations are unarmored cable + conduit + flexible tube, or armored cable + tray + gland.