Is it okay to connect the wires on site in this way? Intrinsic safety instrument + explosion-proof box
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A newbie in the instrumentation field is asking questions. I’ve been searching through various posts on forums, and now there are a few issues I’m not sure how to resolve. I hope everyone can give me some advice. Now we need to install the intrinsically safe instruments on site, equipped with safety barriers. The safety barrier and instruments require 24V DC power supply; therefore, a switching power supply module (220V~24V) is also needed. The current plan is to place the safety barrier in the vicinity as well (in the hazardous area), so an explosion-proof box has been purchased with the intention of putting both the safety barrier and the switching power supply inside it. There are currently the following questions: 1. Is this configuration reasonable? 2. The explosion-proof box has one inlet and one outlet hole; is it necessary to purchase a sealing joint separately? The cables currently used are intrinsically safe cables. 3. Can a high-power power supply module together with N safety barriers be placed in an explosion-proof enclosure to connect to multiple intrinsically safe instruments on site? (This is mainly because intrinsically safe instruments have low power consumption; if one power supply module is used for each instrument, it would be somewhat wasteful.) The plug on the 220V side isn’t long enough to fit either, I guess. . . ）
Intrinsic safety explosion protection requires the creation of an intrinsic safety circuit, meaning that in addition to the intrinsic safety instruments, the connections within the circuit as well must be of an intrinsic safety type. To achieve intrinsically safe explosion protection, a safety barrier is required to isolate the hazardous area from the safe area; in other words, the safety barrier limits the electrical power supplied to the hazardous area, so that even if sparks occur in that area, their energy is not sufficient to ignite the explosive mixture. Since the owner has placed the power supply in a hazardous area, the function of the safety barrier to limit energy flow becomes meaningless. Even if the power supply is placed inside an explosion-proof box, such a box is typically only capable of providing explosion isolation or positive pressure protection; as a result, the entire setup does not constitute true explosion protection.
The safety barrier is installed inside the cabinet, and it is powered by the power supply of the cabinet. The field instruments are connected to the safety barrier using intrinsically safe cables.
First of all, thank you for answering my questions. I would like to ask: I saw a cabinet on site that contained various power supplies and things of that kind. Is it a power distribution cabinet? Can a safety barrier be placed inside it?
Thank you for the answer. I have another question: if I want to place N safety barriers and a few switching power supplies in a cabinet, are there any recommended containers for this? It’s because it shares a cabinet with other devices; I was wondering if there are any good solutions?
Since there are high-power electrical equipment (electrical cabinets) in the site (hazardous area), using safety barriers is no longer meaningful. If possible, it is recommended to adopt an explosion-proof approach, that is, by using explosion-proof instruments, explosion-proof cabinets, or positive-pressure ventilation cabinets.
In a flameproof box, if a positive pressure can always be maintained, then the environment inside the box is equivalent to a safe zone. . . That’s what I think. . . But achieving this is not easy. . . Moreover, positive pressure purging must be performed before powering on, and operations must be carried out with the power off during maintenance. In this way, with the wires from the explosion-proof box leading to the instrument side, it should meet the intrinsically safe requirements. As for the flameproof box section, it should be considered positive-pressure flameproofing. . . . As a complete system, it is non-intrinsic-safe; it is an explosion-proof system ..........
@Hao Liang Zhi Le @1111111 If it’s the image above, and the product description for the white DTU states that it’s safe, then in that diagram where 220V power is supplied from outside into the hazardous area, is it still considered dangerous? Seeking advice
“\"Hazard\" refers to the occurrence of explosions or fires. There are various measures to prevent such explosions or fires, including intrinsically safe measures and explosion-proof measures, all of which serve to eliminate the \"hazard\". As for whether there is any danger in the above situation, it depends on whether the pouring and explosion-proofing measures have been properly implemented; if so, it is safe. Regarding explosion protection, sometimes a single measure is used, while at other times multiple measures are applied together; the DTU shown in the diagram represents explosion protection through multiple measures.
Whether such a configuration is reasonable or not depends on your specific situation. I don’t understand where the signals from these instruments end up going The control room? If so, why not install the safety barrier directly in the control room? If you’re not going to send it anywhere and just want a few displays on site, then your approach is feasible. However, what needs to be considered is how to deal with the heat generated by the power supply inside the explosion-proof box?