Induced Voltage in Control cable

[cherry2000]

We are planning to use LV motor starter of a certain make which has an electronic unit utilising 24VDC as the control voltage. Now we have long lengths of control cable from MCC to Local Control station with control cable running parallel to the 600V power cable. Is there any calculation to show the limiting length of control cable before induced voltage cause spuriuos operation of starter? Also if VFD driven motors also have power cables running in the same tray, will this aggravate the problem? I believe using twisted shielded pair control cable may mitigate the problem. Is spatial seperation also required? I believe a certain IEEE code on induced voltages in cables has been archived!

 

[controlsdude]

24vdc running long lengths will cause a problem with voltage drops out to the control station. Look up the 24vdc voltage drop on the web to make sure that your device will work. I beleive most devices will work in the 18-30vdc range.
VFD leads always need to be run in seperate conduit, even if you have two vfd for two motors, run the wiring for each motor seperate. Or you can use shielded multiconductor cable and put these in the tray and this should work.

If your using tray, you can get the trays that have a metal seperation for low voltage and high voltage. I have used these before for separating 24vdc and 480vac and have been successful with the results (no noise problems).

 

[OperaHouse]

Last time we used a 24VDC motor starter the power supply had to be redesigned to handle the current. This took a shocking amount of amps. These contactors have two coils in them, the second being an additional pull in coil that disconnects when it finally pulls in. Look at the specs closely to be sure you can drive that much initial current and voltage losses from wire length.

 

[cherry2000]

Thanks for the replies. Shielded cables with spatial seperation should do the trick. Normally we route 24VDC cables in a totally different tray seperated from power cables. However, in the present Project, we are routing both power & control cables together in the same tray. Hence the best option would be to use barriers along with shielded cables. However, I have still not come across any calculations to give evidence of EMI. IEEE papers do give guidance to develop a Transfer function to derive induced voltages.