There are a number of reasons. Existing protection, particularly if quite old, typically has very limited sensitivity (2-300 Ω to maybe 3 k Ω). The S700 delivers up to 10 kΩ so that hazardous high resistance faults can be detected. Secondly, the S700 has a large number of detection algorithms all working in parallel to increase reliability. When coupled with an L700 System or M700 system, hih resistance earth faults can be readily located on the network.