In a junction box which is having 3 nos of analog signals from instrument (4-20 ma ouput), and main cable (6 core shielded cable) is going to control room in marshalling rack cabinet. In this JB, i want to put 2 NOS of digital signal (24 V. digital input).

Is it acceptable to put didgital signal in analog junction junction box as per international standards. i am not getting spare in othe JB's and this is the only choice.

 

that's no problem. In my factory,field boxes collect several signal types. Is in the connections room, where the signals are cross-connected to the propper FTA. You should avoid mix intrinsically safe signals with "standard" signals at the same J.B., multicable, rack assembly or FTA.

 

I agree with Enric_Tgn, it's quite OK. I wouldn't run 120 AC in the same cable though or mix IS with Non IS

Roy

 

Dear Friend,

Thank you for your reply. Please find attached ISA guidelines about signal mix up in Junction box. Kindly suggest further.

ISA GUIDELINES:
Signal segregation in instrumentation cabling, it is a good practice to segregate various signals from each other. For optimum segregation, each type of signal (within each NSL) shall transmit on dedicated cables and rout to dedicated junction boxes.

For example, 4-20 mA signals shall route on separate cables from all other signals under NSL-1. The same applies on all other signal types. From the junction boxes to the control room, the cables for each NSL level can share the same cable tray or trench.

They can also share the same marshaling cabinet provided the cables get enough air and adequate terminal strip identifications are in place.
In addition, all emergency shutdown signals should have their own cables, junction boxes, and marshaling cabinets. They also have to be segregated based on signal type as discussed above.

Separation between different NSL: The recommended separation distances are from IEEE-518 and PIP standard PCCEL001. It is important to note the zero separation distances between signals of the same NSL do not mean different signals within the same NSL can use the same cable. Separate cables must carry and serve different signals even if they are of the same NSL.