## EMC Question of the Week: August 31, 2020

In a multiwire transmission line, parallel signal conductors carry currents I_{1} and I_{2}, respectively, where I_{1} and I_{2} point in the same direction. The common-mode current on the wire pair is

- I
_{1}- I_{2} - I
_{1}+ I_{2} - (I
_{1}- I_{2})/2 - (I
_{1}+ I_{2})/2

## Answer

The correct answer is "b". This question is similar to last week's question, but it asks for the common-mode current instead of the differential-mode current. The differential-mode current was (I_{1} - I_{2})/2 if and only if the wire pair is balanced. The common-mode current is the sum of the currents on the wires. It is not divided by 2, and there is no requirement that the wire pair be balanced.

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