A large number of Overhead Switchgear and Fault Passage Indicators (FPIs), such as Fusesavers, Tripsavers and Smart Navigators, use the current flow on individual phases of power cables, to power communications and keep batteries charged. 

Whilst desktop studies can identify suitable sites for switchgear and FPIs to be installed based on customer numbers or rated capacity, real world installations have shown that these two factors do not always correspond to guaranteed load.