For delta-connected 3-wire electrical systems with no star point, one solution to the absence of a neutral for connection to the earth or ground connection is to create an artificial neutral by using a zigzag or star open delta earthing transformer with a low voltage secondary winding. The zig-zag neutral or the transformer secondary can be connected to a suitably rated resistor to limit the fault current.

The Neutral earthing transformer (NET) will be a dry type, rated for the on time of the earthing package. This may be a short term rating of 10 or 30 seconds, or in some cases continuous – for example for offshore installations where safety considerations may require that faults are not cleared immediately.

Cressall Resistors manufactures complete earthing transformer systems of this type, with the transformer and resistor mounted in a single enclosure.

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