Underground cable for Flow meter?

[iamcaring]

Can somoene suggest me which cable can be used for feeding flow meter from PLC (24VDC). This cable will be burried from PLC to flow meter and the distance is 600 meters.
I was thinking to use 4pair #16 AWG with PVC jacket? Is PVC jacket is good for underground and do you think i have to worry about voltage drop? Please advise.

 

[SteveWag]

600 meters is not far, but WHAT kind is signal is being sent? Is the flowmeter powered and a signal generated or is it loop powered (powered by the same two wires that carry the signal). Does it generate pulses? Is the meter exposed to lightening? Is/are there any other wires in the vicinity, like motor power, perhaps a VFD in the area?
Steve

 

[iamcaring]

Thanks steve for the quick reply.

Well FQIT(0-24mA) will be looped power and yes it is exposed to lightening, there are no other wires in the vicinity and this is the only cable that would feed from PLC to the production well flow meter which is 600 meter away from PLC.
I am still convencing myself to use #16-4 pairs (2 spares) to power this flow meter but I need full confidence before giving an answer to client. Please advise if I am on right lines?

Cheers

 

[SteveWag]

I am still a little confused, but here goes. If it is loop powered, then only one pair (two conductors) would be required. 600 meters is close to 2000 feet so 4000 feet total loop distance. #16 wire has a resistance of about 4 ohms/thousand feet so say 16 ohms total. I am not sure of 24 ma., but if that is correct, then voltage drop would be 0.024 amp x 16 ohms or about 0.5 volt, certainly nothing to worry about in a current loop. Are you proposing direct burial? PVC is OK, unless there are code restrictions in your case. I would recommend TVSS devices at each end, with the manufacturers grounding instruction closely followed. Unless you can get 600 meters plus in an unbroken length you are going to need a (some) splicing. I suggest a surface accessible pull/splice box(s). Use waterproof splicing devices and splice all conductors in each box.
Steve

 

[djs]

I would also advise using shielded cable. Ground the shield at the PLC end. Do not connect the shield at the instrument end.
If possible a second cable, possibly #8 AWG should be run to ground the instrument.

 

[iamcaring]

Steve your response is much apprecited. So mist use TVSS on both ends. If you are confused why I wana use 4 pairs? 2 pairs will be spare(future).

djs is saying that i have to run #8 as well parallel to this #16 for grounding purpose as the flow meter needs to be grounded? is that what you suggest? If so, then I can add #8 along with #16 and again thanks for such knowledable discussion. I am way confident to justify my choice.

Its all coz of you guys!! Live long

 

[SteveWag]

iamcaring, a loop powered device only requires two wires or ONE pair. You are proposing FOUR pairs or eight wires. That is why I am confused. Not that two OR three spares is not good, the cost of the spares is insignificant compared with the labor, but yousay install four and have two spares, implying that you are USING TWO PAIR.

The TVSS device is entirely optional. In my experience it is prudent.

A number 8 ground is good for a safety ground but will not help prevent damage from lightning (distance induced voltage). Since your using 24 volts (maybe) a safety ground is not required. If a TVSS is installed, it should be “grounded” to the meter body.

Steve

 

[iamcaring]

Steve
Thanks for the clarification. I really appreciate your help. Because of you people its way easy to do my job. May be one day i will return this knowlede(i'm gaining) to newocmers(just like me today).

 

[danw2]

You're sure the flow meter is loop powered? Not all devices with 4-20mA output are loop powered . . .

Magnetic flow meters are typically AC powered.

 

[iamcaring]

100% this loop powered and getting signal from PLC 24VDC.
Thanks for the concerns.