Ask Professor Watson: mPPE insulation and capacitance

Posted on Wednesday, August 27, 2014 by Dave Watson

Dave Watson, Director of Engineering, also known as Alpha Wire's resident wire and cable expert was prompted with the question below regarding mPPE insulation.  Check out Professor Watson's explanation!



Q. How does the conductor to conductor and conductor to shield capacitance change with MPPE insulation?

 

A. Well, the conductor to conductor capacitance (also known as mutual capacitance) is a function of the dielectric constant and the ratio of the insulation diameter to the conductor diameter. I'll spare you from the exact formula. Having a thinner insulation would tend to increase capacitance values, but relative to PVC, the lower dielectric constant would lower capacitance.

If you take PVC's, the dielectric constant ranges from about 3.5 to 5, depending on the formulation. Data cables often use Polyethylene or Polypropylene insulation and the dielectric constant of these materials ranges from about 2.2 to 2.6.

The mPPE's we are using tend to have dielectric constants in the 2.4 to 2.6 range. So what this all means is if you compare a PE/PP insulated cable with an mPPE cable having the same insulation thickness, the capacitance values should be the same.

The electrical principles are the same in conductor to shield (also known as ground capacitance), so the discussion on conductor to conductor capacitance would be the same for conductor to shield, it's just a bit of a different formula. If you look at our online data sheets, you will find that we do list these capacitance values.

If you would like to try out mPPE insulation, you can check out our EcoGen line of products!

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