# Cable derating at higher frequencies



## slarocque (Oct 5, 2012)

Some VFD applications are running at higher frequencies such as 800Hz.
Also, some of these applications have a high current requirement.

I have a question regarding cable derating: does anybody know how to calculate the effect that the 800Hz will have on the cable size?

I know that a derating needs to be applied but not sure how much.
Any information would be greatly appreciated.


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## JRaef (Mar 23, 2009)

It's only based on the fact that you have effectively more resistance and reactance in the conductors, but is also affected by things like proximity to other conductors etc. The bottom line though is that any de-rate is based on the added voltage drop that you might incur as a result. So it isn't automatic that you de-rate, you just have to take the possibility of more VD into account.

This article actually does a pretty good job of explaining it.
http://ecmweb.com/basics/basics-conductor-resistance-high-frequencies


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## John Valdes (May 17, 2007)

Whats the application. 800Hz is screaming. Who's VFD? Motor? Just curious.


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## slarocque (Oct 5, 2012)

Aeronautical application.


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## slarocque (Oct 5, 2012)

By the way, thanks JRaef for the article link.
Very informative!


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## Peewee0413 (Oct 18, 2012)

I am not an expert on high frequencies, but I believe if your wire isn't rated for it, you will have interference with surrounding wires and increased resistance due to eddy current.( interference I am unsure about but resistance increases with frequency, in a curve I believe.)


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