Selecting Cables to Transmit 4-20mA Signals

Mechanical strength of the conductors is the primary consideration.

0.75mm² is typical.

I join PWSlack and add a few. You can calculate the resistance, and most likely will find not to be a problem. the twisted pair will need to be shielded, If you do not want large noise contamination. And keep it away from power cables.

Quite. Useful additional points.

Hi Asitha,

usually you have a configuration like that:

Example:

Given UB = 24V DC
Usource = 2V (thats for UCE, e.g.)
Usignal = 10V (depends on your following input like ADC etc.,
is the maximum voltage at maximum current of 20mA)
Then RL = 10V / 20mA = 500 Ohm
UB = Imax * (Rlead1 + Rlead2) + Usignal + Usource
Rlead = (UB - Usignal - Usource) / (2 * 20mA)
(with Rlead = Rlead1 = Rlead2)

So each of the two leads may have a voltage drop of max. 6Volts and you can
evaluate your required mm².
Having a distance of several hundred meters a twisted shielded wire is recommended.

Regards Uwe

In the telecom world we guarrenty the customer 23ma to his phone set. To do this we suply -50Vdc at the Centeral Office so this means we can have a maximum of 1500 ohms in the cable pair if we allow for 400 ohms in the CO wiring, 200 ohms in the phone set and 35 ohms for the house wiring.

Why not do it without wires, check out www.remotecontroltech.com.