Do analog signals and digital signals need separate junction boxes?
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My current understanding is that it is not necessary; the specifications do not provide any such indication. I would appreciate guidance from those with more experience. Previously, I connected them to the junction box nearby, without making any special distinction between analog and digital signal cables.
This post was last edited by qugd on 2020-7-20 at 17:19. In principle, separate junction boxes are required; however, if the number of circuits is very small, one junction box should also work. Cables for different signals must be separated and have reliable shielding.
I’m not sure if it exists; this is just my own understanding, and it’s also a personal suggestion given to clients during discussions – it’s not meant to serve as a guiding principle.
The method you suggested makes a lot of sense. Thank you
HG/T 20512 8.1.7 Signals of different levels shall not share the same multi-core cable and junction box. SH/T 3019, Clause Explanation 7.1.7: Instrument signal voltage levels can be classified as low-level voltage levels: such as those from thermocouples and pulse signals ； Medium-level voltage ranges: such as 4mA~20mA DC signals, thermistor signals, 24V DC switch signals, etc ； High-level voltage ranges: such as DC switch signals greater than 28V, DC control signals less than 250V, AC signals less than 28A, etc.
I’ve seen all of that, but it’s not enough to show that analog and digital signals need to be separated; analog and digital signals are at the same voltage level, ignoring special cases such as compensation wires for thermoresistors and thermocouples
The classification is based on the voltage level of the signal. Switch signals, divided into DI and DO. A DO is generally a power load with a source output; considering its relatively thick wire gauge, it is usually housed in a separate enclosure. For AI and DI, the specifications do not require binning, but from a maintenance perspective, it is recommended that you perform binning. For some packaged devices, their signals can be combined in the same box to reduce the use of main cables. My experience: This is how the large ethylene main unit was introduced (AI and DI can be mixed in the same container)
Four-wire power supply cables, flame-retardant cables, and intrinsically safe cables can be separated
Professional terms: power supply, intrinsically safe circuit, non-intrinsically safe circuit, sub-cabinets and main cables.