Selection principles for flameproof equipment and increased safety instruments & G-thread types do not have flameproof certification available

This post was last edited by DLP Meter Liu on 2025-2-12 at 13:36. 1. Yes. It should be noted that in the latest GB standards, explosion protection is also classified into da, db, and dc, corresponding to Zones 0, 1, and 2. 2. Yes, currently, G threads do not have an explosion-proof certification available. 3. Taking the junction box as an example: A safety-enhanced junction box refers to one in which the internal components, including the connection terminals and other parts, have received safety-enhancement certification, so that no large arcs or sparks are generated during use after the connections are made. For explosion-proof types, it doesn’t matter; the housing is made thick so that even if an explosion occurs inside, the outside of the junction box remains unaffected. It can also be seen from the price – the explosion-proof version is almost twice as expensive as the increased safety version.

1. In accordance with the GB50058 standard, electrical equipment in Zones 1 and 2 requires an explosion-proof design with a protection level of Gb. This means that flameproof equipment can be used. 2. If instruments or equipment with G threads are used, only increased safety certification can be obtained. Therefore, if equipment with G threads is used in Zones 1 and 2, it does not meet the requirements for explosion-proof equipment. 3. (1) For Zones 1 and 2, flameproof equipment can be used, but if the equipment features G threads, then consideration should be given to using conversion adapters or opting for other forms of protection, such as intrinsically safe equipment. (2) During design, if flameproof equipment is selected, instruments and devices with G-threaded terminals, as well as the corresponding cable clamping seals and flexible tubes, should be avoided in order to ensure a complete flameproofing effect. (3) The main difference between flameproof equipment and increased safety equipment is that flameproof equipment restricts the spread of explosions through its structural features; even if an explosion occurs inside, it does not affect the external environment ； Enhanced safety equipment prevents the generation of ignition sources inside the equipment by strengthening safety measures such as isolation and insulation. Simply put, explosion isolation means “preventing internal explosions from spreading outward,” while enhanced safety means “preventing explosions from occurring in the first place.” .

(1) Can both intrinsically safe and increased safety types be used for explosion-proof equipment in Zones 1 and 2? According to GB50058 - 2014 \"Code for Design of Electrical Installations in Explosive Atmospheres\", the protection class for electrical equipment in Zone 1 can be Ga or Gb, while in Zone 2 it can be Ga, Gb, or Gc. As can be seen from Table 5.2.2 - 2 provided, the explosion-proof designs for Gb-class electrical equipment can include flameproof type (“d”) and increased safety type (“e”), among others. Therefore, in Zones 1 and 2, it is feasible from a standard perspective to use intrinsically safe and increased safety types of explosion-proof equipment. (2) When designing, intrinsically safe or explosion-proof equipment is generally used. If explosion-proof equipment is chosen, should instrument devices with G-threaded connection ports, cable gland seals, and flexible hoses not be used? Yes. As can be seen from the first image, there are many problems with the use of G threads in flameproof equipment; for example, flameproof equipment certified under the EU ATEX standard and the International Electrotechnical Commission IECEx standard does not use G threads as the flameproof thread interface ； The test for checking whether ignition inside the G-threaded joint surface causes deflagration often results in deflagration occurring ； The large tolerances for pipe thread fits make it difficult to meet the standard parameter requirements, etc. Therefore, if flameproof equipment is chosen, to meet the flameproofing requirements, it is not recommended to use instrument devices with G-threaded connectors, cable clamping seals, or flexible hoses. (3) What are the specific differences between intrinsically safe equipment and enhanced safety equipment? (GB3836 is hard to understand; can someone give a simple explanation?) Explosion-proof equipment (“d”): In simple terms, it means that the equipment’s casing is capable of withstanding the pressure generated by an internal explosion, and it prevents that explosion from spreading to the explosive environment surrounding the casing. Even if an explosion occurs inside the device, the casing will not break, nor will it ignite surrounding explosive gases or dust. For example, a sealed iron box containing flammable gas that explodes – the iron box is strong enough not to be damaged by the explosion, and the flames resulting from the explosion do not escape from the box and ignite any external flammable gases. Increased safety equipment (“e”): Electrical equipment whose safety level is enhanced by taking measures on its design, so that it does not generate arcs, sparks, or high temperatures that could ignite explosive mixtures under normal operating conditions, thereby preventing the occurrence of such phenomena under normal and permitted overload conditions. For example, optimizing the electrical clearance and creepage distance of electrical equipment, as well as ensuring more reliable electrical connections, helps to reduce the likelihood of the equipment generating hazardous energies such as electric sparks, thereby achieving explosion prevention.

First of all, thank you very much for your explanation! From what you’ve said, it seems that the increased-safety type is similar to the intrinsically safe type. But then why are explosion-proof and intrinsically safe devices the ones that are commonly used in practical applications? Are products with the increased safety type of explosion protection not very reliable in practical applications? As far as I know, enhanced safety type explosion-proof junction boxes are more commonly used in the junction boxes for high-voltage electrical equipment, while there aren’t many of them used in the junction boxes for low-voltage equipment? What is the reason for this again? I’m not sure if you are aware of it.

First of all, thank you very much for your explanation! From what you’ve said, it seems that the increased-safety type is similar to the intrinsically safe type. But then why are explosion-proof and intrinsically safe devices the ones that are commonly used in practical applications? Are products with the increased safety type of explosion protection not very reliable in practical applications? As far as I know, enhanced safety type explosion-proof junction boxes are more commonly used in the junction boxes for high-voltage electrical equipment, while there aren’t many of them used in the junction boxes for low-voltage equipment? What is the reason for this again? I’m not sure if you are aware of it.

Firstly, for those working in the field of automatic control instruments, it is necessary to understand the difference between intrinsically safe and increased safety designs. Intrinsically safe systems involve using safety barriers to limit the power supply to the instruments, thereby ensuring intrinsic safety. In other words, with intrinsically safe devices, it is possible to open the enclosure and carry out maintenance while the device is still powered on, without having to worry about sparks caused by short circuits potentially igniting hazardous gases. Increased safety simply means that it operates stably; wires cannot be disconnected or repaired while it is powered on, as the power supply is not limited, and sparks generated by short circuits or failures could cause an explosion. Therefore, for instrumentation equipment, Intrinsic Safety and explosion protection are usually emphasized, which relates to whether maintenance can be carried out while the device is powered on. As for the junction boxes, domestic chemical plants generally use intrinsically safe and flameproof types. On one hand, GB50093-2013 stipulates that intrinsically safe circuits should use intrinsically safe-rated junction boxes; on the other hand, since intrinsically safe junction boxes have lower requirements regarding materials and quality compared to intrinsically safe-rated ones, the common approach is to use an intrinsically safe-rated junction box, together with intrinsically safe-certified terminal blocks and flameproof connectors. Finally, as for why explosion-proof devices are used less often, the reason is simply cost savings. It can also be said that, in accordance with regulatory requirements, enhanced safety enclosures are sufficient for explosive environments in Zones 1 and 2; since there is no mandatory requirement, no one is willing to spend this money, except those with substantial financial resources. . . .