4-20m signal in a multiconductor cable

[Wagner]

hello guys,

I wonder if I can connect a 4-20ma signal in a multiconductor cable when the other conductors is primary used for control signal (125Vdc) in it?

Is-it douabe? Does the measurement of the 4-20ma will biais because of the impedance of the other signals in the same cable?

The thing is I wanted to avoid pull a new cable between my equipement in the yard and the building.

Thanks for your help guys,

 

[mylespetro]

It's doable, probably not advisable. Although if the other signals are DC then the noise may be manageable, but that's not really based on anything concrete. I would always want a shield on the pair that the analog signal is coming in on.

 

[arpus4KM]

It's not worth trying if you are trying to save money.

Which I assume is the reason you would want to run them together is to avoid having another run made.

Over a short distance it wouldn't be much of a problem, but, over a long distance you're asking for problems and may spend more time trying to make it work instead of just running another cable. The other option depending on your setup, may be to try to send the signal over another medium that doesn't involve putting a wire in a conduit, such as wifi/radio

 

[Ken Moore]

IF all the conductors are twisted/shielded pairs, you should be okay.

 

[mylespetro]

IF all the conductors are twisted/shielded pairs, you should be okay.

This is the real answer, but when I hear "multi-conductor" I think 12 (or however many) individual non-shielded/twisted conductors, especially for what sounds like higher voltage discrete control signals on the other wires. If it is indeed multi-pair cable with twisted/shielded pairs, I wouldn't hesitate to use it.

 

[Tom Jenkins]

Good practice is to NOT run AC and analog signal wiring in the same conduit, much less the same cable. My expectation is that any money (or space) you save will be quickly eaten up by troubleshooting spurious analog values and noise. Shielding is a good idea, but it isn't a miracle.

 

[TheWaterboy]

primary used for control signal (125Vdc) in it?

The signal voltages are 125v DC ?

I have found 4-20mA signals to be be pretty resilient. The exception being I have seen the need to install and isolator between endpoints because a current path is formed from different ground potentials.

Try it and see. Then you will know if it will work in your situation.

 

[widelto]

I would never do it. Stay away from a P.I.T.A. .

 

[danw]

Remember the Ironclad Rule: You touch it, you own it.

 

[dummy_bit]

remember the ironclad rule: You touch it, you own it.

ditto!

 

[Tom Jenkins]

Good practice is to NOT run AC and analog signal wiring in the same conduit, much less the same cable. My expectation is that any money (or space) you save will be quickly eaten up by troubleshooting spurious analog values and noise. Shielding is a good idea, but it isn't a miracle.

In my response I failed to note that the original post did indicate 125 V DC. That does make a difference, as DC current doesn't generate the EMI (ElectroMagnetic Interference) that AC current creates. If the control wiring is indeed DC you can probably get away with common cabling. You still should use shielded twisted pair for the 4-20 mA signal as that will minimize EMI effects from other sources.

 

[TheWaterboy]

That DC was what made me think it would be OK as well.
It's sad that area economics sometimes dictate doing the best you can with what little you have, but it's a real concern that we shouldn't look down on out of hand.

We have a nearby city that is a bedroom community with no tax base to draw from though they are surrounded by very affluent and high tax base communities literally yards away. What those folks have to deal with is just bad for everyone.

Having said that, if you have the funds, run a new cable. If you don't, try it first.

 

[lfe]

If these 125VDC control an on-off motor, for example a servo, or a solenoid it may not be recommended that the 4-20 mA pass in the same cable