What are the specifications for the field wiring boxes used with common instruments?
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I would like to ask everyone: are there any relevant standards specifying the specifications for the wiring boxes used with common instruments, such as those with 24 or 36 terminals, or those with even more terminals? For intrinsically safe instruments, an intrinsically safe junction box is required; is it possible to use one for increased safety type instruments?
For explosion protection, an explosion-proof wiring box must be used; one with enhanced safety features can only be called an enhanced-safety wiring box.
There are no specific regulations; there is one principle: the number of terminals should match that of the main cable. For a simple junction box, the intrinsically safe box (the main unit) can be used in all areas; additionally, if the instruments are located in Zone 0, an intrinsically safe circuit must be used, in which case the box is equipped with intrinsically safe light blue terminals. If the instrument is in Zone 1/2 and you use a \"non-intrinsic safety circuit\", then the enclosure should be equipped with intrinsically safe gray terminals. The explosion-proof type of the junction box must be suitable for the area where it is installed; it does not need to match the explosion-proof type of the instrument.
Strictly speaking, there is a limit to the number of terminals that can be inside a box of a certain size; it’s not possible to have just any number of them! It is necessary to meet the explosion-proof requirements after calculations based on current capacity, temperature rise, and other factors!
“The explosion-proof type of the junction box must be suitable for the area where it is installed; it does not need to match the explosion-proof type of the instrument. ”Understood, thank you for your guidance, senior