Running 24VDC signal wire and 90VDC Power Wires

Quick question: Can I run 24VDC signal wire (shielded) in the same 1 inch conduit with 2 cables (+ & -) with 90VDC to power a permanent magnet DC motor? I am a bit concern with noise issues. The run should be about 30Ft. Thank you!

Probably.
But first:
What is carried on the 24vdc signal wire?

Is the 90vdc pwm modulated (like from a DC drive)?

If the 90VDC is not modulated (no carrier frequency or PWM frequency) then it won't make much noise except when it switches off and on.

If the 24vdc wiring is a discrete signal or 4 to 20mA analog current signal you should be fine. Even a 0-10vdc voltage signal and the higher voltage changes infrequently and is not from a rapidly switching source it will probably be fine.

The signal wire carries 24VDC coming from a proximity switch (sensor) (NO/NC). Yes, the 90VDC is modulated from a DC Drive. Voltage will vary from 0-90VDC. Thank you!

I would at least shield the 24vdc wires. The switching of the voltage to the DC motor, whether PWM or SCR-Pahse-Controlled, could kill an input, the prox, or the power supply. Not to mention possible false readings.

Just good practice.

checkout drives-in001 from Rockwell, chapter "Wire Routing", currently on page 71.

You have wiring level 3 (AC power, eg AC motor) and level 6 (24VAC/DC logic) which should be 75mm apart in steel conduits, or 150mm apart in cable trays.

My recommendation is that you should not mix wires that go to PLC inputs with 230/400/480V cables and even less with frequency converter output wires.

PWM waves are the worst in terms of noise generation.

caleno said:

Quick question: Can I run 24VDC signal wire (shielded) in the same 1 inch conduit with 2 cables (+ & -) with 90VDC to power a permanent magnet DC motor? I am a bit concern with noise issues. The run should be about 30Ft. Thank you!

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You can't run them in the same conduit if the insulation ratings don't match.

As a matter of good engineering practice, I never design a system which calls for low voltage control wiring to be pulled into conduits with power circuits.

I thought all that mattered was the insulation rating of both wires... is that wrong?

If the communication wires have shielded insulation rated over 90v, they still can't be run together with the power?

LoganB said:

I thought all that mattered was the insulation rating of both wires... is that wrong?

If the communication wires have shielded insulation rated over 90v, they still can't be run together with the power?

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Not if the power wiring insulation is rated for 600 Volts.

Bit_Bucket_07, I think you are referring to NFPA 70 300.3(C)(1). That states that the limitations are based on the maximum voltage in any of the circuits, not the maximum insulation rating of the conductors in the mixed circuits. In fact, the Handbook makes a point of saying that it is the applied voltage not the conductor insulation rating that matters.

Having said that, I would separate circuits of different types if I could. But, if you have to mix functional types in a pinch, be very careful about shielding the low level conductors. I would go as far as shielding the power conductors also, making sure to ground the shield of the power cable on both ends.

Look at it this way. If it was completely impossible to run mixed conductors in close proximity, single cable servomotors like the Rockwell VPL series wouldn't exist.

Keith

kamenges said:

Bit_Bucket_07, I think you are referring to NFPA 70 300.3(C)(1). That states that the limitations are based on the maximum voltage in any of the circuits, not the maximum insulation rating of the conductors in the mixed circuits. In fact, the Handbook makes a point of saying that it is the applied voltage not the conductor insulation rating that matters.

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It's both, really:

Conductors of different systems can occupy the same raceway, cable, or enclosure if the insulation voltage rating is not less than the maximum circuit voltage.

LoganB said:

I thought all that mattered was the insulation rating of both wires... is that wrong?

If the communication wires have shielded insulation rated over 90v, they still can't be run together with the power?

Click to expand...

Theoretically, since the "power circuit" in this case is 90 Volts, but I've personally never seen insulation rated for 90 Volts.

The insulation voltage rating doesn't need to exactly match the voltages in the circuits being combined. The only stipulation is that the insulation rating of ALL conductors in the conduit must be as high or higher than the HIGHEST voltage being applied to ANY of the conductors.

For example, I can run conductors with insulation ratings of 30V, 300V and 600V through the same conduit as long as all of the conductors are carrying a voltage of 30V or less. The fact that the insulation rating of some of the conductors is 600V doesn't matter as long as I only run 30V through those conductors.

If I decide to run 120V through one of the 600V conductors I will need to replace the 30V conductors in the conduit with conductors that can handle 120V or more, since at least one of the conductors in the conduit is carrying a voltage higher than the 30V rating of those conductors.

So, as I said, the insulation voltage rating of the conductors is only incidental to the voltage applied to the conductors. It is the applied voltage that matters.

Keith

kamenges said:

The insulation voltage rating doesn't need to exactly match the voltages in the circuits being combined. The only stipulation is that the insulation rating of ALL conductors in the conduit must be as high or higher than the HIGHEST voltage being applied to ANY of the conductors.

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Yes. I agree.