How close is too close

[captstent]

We have a situation that has developed with our new construction. The electricians are wanting to run 2 ? 2 inch emt conduit with electrical feeders in them. I believe the voltage is 120/208. They want to install them near a cable tray that will have Cat 6 installed in it. From what I remember if they cross each other at 90 degrees it?s ok but if in parallel they need to be a certain distance away to prevent interference. If this is true, what is the difference and does the wires being in conduit make any difference?
Thanks for any information
bob

 

[infinity]

IMO it wouldn't matter if they're right next to each other.

 

[rbalex]

I happen to agree with Rob especially since the "power" conductors are enclosed in EMT.

I can't answer what is too close, but Section 725.136(I) suggests what is far enough apart. Also, especially see Subsection 725.136(I)(a).

 

[ghostbuster]

If it is standard emt not rigid the unbalanced residual mag field will go straight through with very little attenuation.Normally the circuits should be balanced if it is correctly wired and the mag field radiated from the conductors will be quite small (current dependent)

 

[kwired]

To add to what others have said - it also depends on how much interference is tolerable - if there is any interference.

NEC has no objection to placing the cables right next to the raceway.

The communication cable, or devices it is used with could have some recommendations though.

 

[rlundsrud]

Given that the emt surrounds the power cable, that would make an effective Faraday cage that should prevent nearly all emf from being transmitted to the adjacent cables. Georgia Tech actually did a study on this phenomena and concluded that steel raceways like GRC and EMT block about 95% of the emf from a 60 hz signal.

 

[GoldDigger]

Given that the emt surrounds the power cable, that would make an effective Faraday cage that should prevent nearly all emf from being transmitted to the adjacent cables. Georgia Tech actually did a study on this phenomena and concluded that steel raceways like GRC and EMT block about 95% of the emf from a 60 hz signal.

Did they distinguish between electric field and magnetic field EMI?

Electric field effects should be blocked almost 100%, while magnetic fields are more of a problem.
Was there any difference between the blocking percentage of EMT and RC?

One point about a Faraday cage:
It will effectively block electrostatic and dynamic electric fields and therefore also radio waves, but it cannot block or even reduce "static" magnetic fields like that of the earth or even of 60Hz sources.