Separation distance between high power cables and low power Instrumentation signals

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HSB_007

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I do have a quick question regarding the proper separation distances between low power instrumentation signals (24 VDC, 4-20 mA) and high power cables, say 4.16KV AC to reduce/eliminate electromagnetic noise. We currently require them to be at least 1 meter.
If we are to enclose the power cables inside conduits, or say concrete ducts, how much would we be able to reduce this limit? Is there a formula I could use?

Thank you :)
 
IDK, but shielding does help, and a metal raceway is an effective shield.

Also you have less interference if they are close but cross perpendicularly as opposed to running parallel to one another.

Sometimes the two do need to come close together at the equipment they supplement.
 
300 mm seems the safest

300 mm seems the safest

kwired said:
IDK, but shielding does help, and a metal raceway is an effective shield.

Also you have less interference if they are close but cross perpendicularly as opposed to running parallel to one another.

Sometimes the two do need to come close together at the equipment they supplement.
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Kwired, Thank you for your quick reply. I know the conduit should help, but after reading online, it seems that a conservative figure of 300 mm is required. Any comment on that? I really do not know where they got that from. Thank you again.
 
HSB_007 said:
...it seems that a conservative figure of 300 mm is required. Any comment on that?...
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Code has the minimum separation at 2 inches. However, Code's concern is safety*, not EMI rejection.

*At least that's supposed to be its mandate. :blink:
 
Smart $ said:
Code has the minimum separation at 2 inches. However, Code's concern is safety*, not EMI rejection.

*At least that's supposed to be its mandate. :blink:
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And that 2 inches is from the higher voltage conductors within equipment. If the higher voltage conductors are within a raceway or cable they can be routed right next to one another or even touching. If associated with same equipment even can support the low voltage cable from the higher voltage wiring method in some instances.
 
kwired said:
And that 2 inches is from the higher voltage conductors within equipment. If the higher voltage conductors are within a raceway or cable they can be routed right next to one another or even touching. If associated with same equipment even can support the low voltage cable from the higher voltage wiring method in some instances.
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No, it is not.

Within "equipment", it can be as little as 0 where Class 2 or 3 conductors are installed as Class 1 and the EL&P etc circuits are 150 volts or less. Otherwise, 1/4" without a barrier is all that is required for associated systems. With a barrier, as close as the barrier permits.

The above is for Class 2 and 3 per 725.136. A 24V 4-20mA circuit can also be a Class 1 circuit, so see Article 725 for specifics.
 
Smart $ said:
No, it is not.

Within "equipment", it can be as little as 0 where Class 2 or 3 conductors are installed as Class 1 and the EL&P etc circuits are 150 volts or less. Otherwise, 1/4" without a barrier is all that is required for associated systems. With a barrier, as close as the barrier permits.

The above is for Class 2 and 3 per 725.136. A 24V 4-20mA circuit can also be a Class 1 circuit, so see Article 725 for specifics.
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725.136(A): "Cables and conductors of Class 2 and Class 3 circuits shall not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power, Class 1, non–power-limited fire alarm circuits, and medium-power network-powered broadband communications circuits unless permitted by 725.136(B) through (I)"

Maybe I threw thing off a little when saying within equipment. When I said that I was thinking outside equipment you don't typically have individual conductors without a raceway or cable covering. What it says is not to place the CL 1 or 2 control circuit cable or conductors with the lighting/power conductors. Placing said control cables/conductors can be placed with power/lighting raceways or cables though. Once you get inside a piece of equipment there may be more complex details of what you can or can't do.

If a particular application wants say two feet of separation, that is a design specification that exceeds the minimum code requirements
 
Could you let me know where you got the 2 inch requirement?

Could you let me know where you got the 2 inch requirement?

kwired said:
What is the issue with 2" from 4160 if it is in an approved cable or raceway?
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I really do not know where the 2 inch requirement came from. Could you or someone else let me know where to find it?

I do believe we still use the IEEE 518 (which I know it has been withdrawn, but it is a basis).

We feel 2 inches (51 mm) may not be enough as the EMI may interfere with the signal quality and cause us some operational disruption. Any comments? Thank you all.
 
HSB_007 said:
I really do not know where the 2 inch requirement came from. Could you or someone else let me know where to find it?

I do believe we still use the IEEE 518 (which I know it has been withdrawn, but it is a basis).

We feel 2 inches (51 mm) may not be enough as the EMI may interfere with the signal quality and cause us some operational disruption. Any comments? Thank you all.
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2 inches may not be enough for your application. Other applications may not matter. It all depends on how your control/signaling components handle any interference that may be imposed on them.
 
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