PowerSum compliance is a requirement of any cabling system that is going to run protocols that utilise more than one pair at any time. In bi-directional simultaneous transmission systems more energy is flowing in the cable. To ensure that the signals can flow freely a measure of the effects of multiple transmission needs to be made. This is called a PowerSum measurement. Although PowerSum can be measured it is more often than not calculated from the pair to pair values of crosstalk. For example to calculate the PowerSum NEXT or PSNEXT on a cable for the blue pair, three pair to pair NEXT measurements would need to be taken, Blue-Orange, blue-green and blue-brown. These three pair to pair measurements are then combined using the following formula and the PowerSum value is calculated. PowerSum tests are required for NEXT, ACR and ELFEXT. The limits for PowerSum tests are about 3dB less stringent than for Pair to Pair (Pr-Pr)
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