Sheilding Cable in a Steel Duct? 1

[marko333]

Hello,

A cable that requires sheilding for EMC has, if it is a multi-core cable, an earthed sheild around it, and several earth conductors it in, but if your using single core cables, with several in parallel, can you install the single active cores in an earthed steel duct? Assuming the duct is manufactured to be continuous.

Should the earth wires also run inside the duct?

Will this duct make a good sheild, or is it better to wrap each single active core in a copper tape?

Thanks,

Marko.

 

[GOTWW]

I am assuming we are talking power cables.

I would not advise wraping individual cables with copper. This would form coaxial transmission lines that would promote the propogation of the EMI.
For high currents the shields would heat up simular to running a single phase conductor in it's own conduit, bad bad idea.

multi core cables should be tightly bundeled as to cancel the net magnet field. The shield helps isolate this further from imbalanced currents and from getting external signals induced common mode on the phase conductors. Three phase conductors, neutral, and ground is a standard practice in power distribution, and by itself should be adequate for most applications. For EMC isssues, the inputs to the sensitive area should have filters to mitigate EMC, hamonics, common modes, etc.

 

[jbartos]

Suggestion to marko333 (Mechanical) Mar 3, 2004 marked ///\\A cable that requires sheilding for EMC has, if it is a multi-core cable, an earthed sheild around it, and several earth conductors it in, but if your using single core cables, with several in parallel,
///Please, elaborate on this. Are you using the single core cables in parallel as subconductors?\\ can you install the single active cores in an earthed steel duct?
///It depends on the circuit(s). Since the steel is ferromagnetic material, the induced currents would elevate temperature of the steel duct. Try aluminum ducts.\\ Assuming the duct is manufactured to be continuous.
Should the earth wires also run inside the duct?
///The earth wires do not have to run inside the duct; however, it is practical to run them there.\\Will this duct make a good sheild,
///Yes, it may; however, it depends on the circuitry design.\\ or is it better to wrap each single active core in a copper tape?
///The wrap would create a screen shield that is often used on medium and high voltages to force the electrical field be symmetrical within the cable or conductor insulation to avoid any asymmetric electrical field stresses.
Visit

http://www.ewh.ieee.org/soc/pes/icc/subcommittees/subcom_e/education/2002/fall02dudas.ppt

etc. for more info on the cable design or construction.\\