A gas-insulated substation (GIS) uses a superior dielectric gas, sulfur hexafluoride (SF6), at a moderate pressure for phase-to-phase and phase-to-ground insulation. SF6 is an inert, nontoxic, colorless, odorless, tasteless, and nonflammable gas consisting of a sulfur atom surrounded by and tightly bonded to six fluorine atoms. GIS is assembled from standard equipment modules to match the electrical one-line diagram of the substation. The use of rupture disks as a safety measure is common although the pressure rise due to internal fault arcs in a GIS compartment of the usual size is predictable and slow enough that the protective system will interrupt the fault before a dangerous pressure is reached. Current Transformers are inductive ring type installed either inside the GIS enclosure or outside the GIS enclosure. Voltage and current testing of the internal parts of the GIS can then be done without removing SF6 gas or opening the enclosure.