instruments cabling engineering

How about the Client's cable specifications?

what do you mean?

If I have to select cable to wire instrument to junction box and select the cable out of the junction box to the control system how can I do this?

is there is any chart or guid says that if ......then chose.....

BS 5308 part 1/2 & API 552 may give you prelimanary Idea ,but as mentioned in the previous post its the clients contract doc , which may be used for RFQ & datasheet

As a general case,

for conduit system use unarmoured else armoured

4-20 ma 1 pair shielded

4-20 ma multi pait I &O Shielded

110 vac 1/MULIT PAIR unshielded

24 VDC mulitpair overall Shielded

Regards

Jose John

thank you very much

a m shiha,

This is a design and specification question. The instrument maker will typically tell you the type of signal that the instrument is producing. Experience and cable manufacturers' data will help you get there. A number of general guidelines can be given:

1) Separate cables having different voltages, such as 24V, 120V, 480V.

2) Keep cables which contain low-current analog signals, such as 0-5V or 4-20mA physically away from AC and higher voltage cables, and preferably shielded (screened).

3) If cables of different systems are in the same tray or enclosure, all need to be insulated for the highest voltage present.

4) Control or Signal cables can only run in the same conduit as power cables for that specific device; not with unrelated power cables.

5) Communications cables need to run separately from others; where they run parallel keep them at least 15cm away from power cables; where they cross, do so at right angles.

6) Special insulation properties will be needed if cables are run in air-handling plenums, or are in an area where smoke or other factors become requirements.

7) Select cable gauges suitable for the signal's amplitude and the maximum allowed error, keeping in mind the probable length the cable needs to run and characteristics of the source and receiving device(s).

8) Allow room for errors and growth of the system. Specify spare conductors or spare pairs/triads, etc.

9) Many signaling and communications cables have been designed for very specific purposes or signal types. Pay careful attention to manufacturers' recommendations or specifications.

10) You can encounter other environmental problems, such as corrosive gases (example is H₂S), or high temperatures, or acid fumes (battery plants). These will require certain cable characteristics (nickle-plated for H₂S exposure, no nylon for acid fumes). Equally important will be flexibility in cold, or resistance to sunlight.

11) Armor, conduit, and/or other protection will be needed if run in areas subject to damage or abuse.

12) Electrical codes specify protection and other rules depending on the voltage levels, amount of energy the cables can carry, any hazardous environments, etc.

I haven't given you any specific answers, but I hope the above can keep you from too many errors. Your question is a general one, so I can't do much more

--JMM

jmueller

thank you very much this is great help

regards

There are so many things need to check before going for Inst. Cabling, 1st of all we need to check area clasifications which is delevered by elecrical people based on that we can say IS, Non IS etc.

One more thing we can assume that from any instrument to Junction box the branch cable distance shall be taken 25 to 30 metergenerally in design engineering.