A power distribution monitoring system is provided that can include a number of features. The system can include a plurality of power line sensing devices configured to attach to individual conductors on a power grid distribution network. In some embodiments, the power line sensors can include a split-core transformer. In some embodiments, a power line sensing device is disposed on each conductor of a three-phase network. The sensing devices can be configured to measure and monitor, among other things, current and electric-field on the conductors. Methods of installing, sealing, and protecting the split-core transformers of the power line sensors are also discussed.