Reactors may be installed at any industrial, distribution, or transmission voltage level and may be rated for any current duty from few amperes to tens of thousands of amperes and fault current levels of up to hundreds of thousands of amperes. Modern dry-type air-core reactors feature fully encapsulated windings with the turns insulation provided by film, fiber, or enamel dielectric. Oil-immersed reactors may be of gapped iron-core or magnetically shielded construction. Bus tie reactors are used when two or more feeders or power sources are connected to a single bus and it is desirable to sectionalize the bus due to high fault levels, without losing operational flexibility. The short circuit current rating of the grounding reactor is equal to the three-phase generator short circuit current, when the machine is an isolated generator or operating in a unit system. Duplex reactors are usually installed at the point where large source of power is split into two simultaneously and equally loaded buses.