noise induced on non-shielded wires in cable

[BrkfldEE]

I have a 125VDC control circuit that uses a non-shielded cable in a tray with AC power cables. There is 60 Volts AC being induced on a 125VDC wire. I know that the solution is to pull in a new shielded cable, but, does anyone know of a way to "drain off" this induced AC instead of pulling a new shielded cable?

 

[IRstuff]

Well, depending on the situation, one could possibly put an input filter to notch out the 60-Hz signal; that's assuming that your "DC" signal is tolerant of that.

TTFN
faq731-376

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[SceneryDriver]

Can you place a ballast resistor at one end of your 125vdc run to "swamp" the induced voltage? Will your source tolerate the increased load that would create?


SceneryDriver

 

[ScottyUK]

Or perhaps a capacitor significantly larger than the inter-core capacitance which is the source of the problem AC signal?

 

[Comcokid]

If the 125VDC signal consist of both the positive and negative wires (that is the negative doesn't return by some other route like the frame of a machine) then you can put a common mode choke. Take a large ferrite toroid core (high u), and wind the pos and neg pair together several times through the core.

 

[BrkfldEE]

Thank you for sharing the common mode choke idea, I definetely learned something new with that. It will not work in this application because the negative wire is not run in the same place as the positive wire. However I will keep that in my back pocket for the future.

I tried googling more info on the ballast resistor and capacitor idea with no luck. Do you guys have any more information on those ideas?

Thank you for your responses!

 

[VEBill]

...the negative wire is not run in the same place as the positive wire...

OMG. Look up the concept of "loop area" in respect to EMI/EMC/EEE.

Hint: That's not a transmission line, it's a transformer winding.

 

[DanEE]

Hint: That's not a transmission line, it's a transformer winding.

ditto... on interconnecting wiring, I always lace the applicable cabling together to minimize the cross sectional area that any stray magnetic fields may cut through...

also learned to appreciate what proper cable and balanced driver/receivers designed with good longitudinal balance were capable of achieving. I didn't appreciate or understand this electrical characteristic until I worked on the design of a telephone PBX system years ago. Same design characteristic applied to ethernet twisted pair wiring allowed the original ethernet coax transmission system to be replaced with greatly improved the distance, speed capability, using inexpensive twisted pair wiring.

 

[VEBill]

Lesson on EMI/EMC compatible wiring:

You know antennas? Do the opposite.

Here endeth the lesson.