control voltages in same conduit

[hunt4679]

I guess I will post this here. Im working on some automation controls and was wondering if running 4-20ma shielded cable for tank level sensors and such in the same conduit as 24v dc control wires (thhn) would interfere with the 4-20ma? Most work done in this plant is wired like this. Has anyone had any issues with this?

 

[Volta]

I guess I will post this here. Im working on some automation controls and was wondering if running 4-20ma shielded cable for tank level sensors and such in the same conduit as 24v dc control wires (thhn) would interfere with the 4-20ma? Most work done in this plant is wired like this. Has anyone had any issues with this?

I doubt you would have any trouble with the data loop unless the dc is switched at a high frequency rate.

The 24vdc is a Class 2 circuit, right?

 

[charlie k.]

I doubt you would have any trouble with the data loop unless the dc is switched at a high frequency rate.

The 24vdc is a Class 2 circuit, right?

You should have no problems. Just remember to groung the shield an one end only.

Charlie

 

[rcwilson]

Godo advice, Charlie. Msot of the time when we have noise problems on signal wires, it is blamed on interference from power cables. Checking the shield grounding and isolation on the signal wires usually resolves the issue.

 

[lakee911]

Should be fine. rcwilson is right ... first time you have troubles, it will be blamed on the power wiring.

 

[weressl]

I guess I will post this here. Im working on some automation controls and was wondering if running 4-20ma shielded cable for tank level sensors and such in the same conduit as 24v dc control wires (thhn) would interfere with the 4-20ma? Most work done in this plant is wired like this. Has anyone had any issues with this?

Yes, you may. If the control wires happen to switch an inductive load, like a solenoid you can get a kickback that will give a fals H/L signal that can trigger unwanted things.

 

[Haldor]

Puttin a reverse biased diode across DC relays or solenoids (or a Quencharc across AC relays or solenoids) should go a long way to preventing issues with noise coupling between the control and power wiring. 4-20 mA current loop is pretty good at resisting electrical noise anyway. Also be sure to use twisted pair wiring to minimize EMI coupling.

Anybody doing industrial controls should have a box of these in their install kit. http://www.paktron.com/pdf/Quencharc_QRL.pdf

 

[weressl]

Puttin a reverse biased diode across DC relays or solenoids (or a Quencharc across AC relays or solenoids) should go a long way to preventing issues with noise coupling between the control and power wiring. 4-20 mA current loop is pretty good at resisting electrical noise anyway. Also be sure to use twisted pair wiring to minimize EMI coupling.

Anybody doing industrial controls should have a box of these in their install kit. http://www.paktron.com/pdf/Quencharc_QRL.pdf

The proper order of design is first to PREVENT the event from happening, and only mitigate when it is not practical to prevent the problem from occuring.