New design based on the original public domain image that was created and uploaded by Markus Kuhn. This adds a neutral connection, which may be provided in an IT system and was missing for no good reason in the original.

This diagram represents one of the earthing system arrangements defined by the IEC 60364-1 standard.

Only the three-phase four-wire conductor arrangement is shown. It should be understood that not all installations will have a connection to every distribution conductor, and not all distribution systems will include all conductors depicted (three-phase three-wire cases for example will not include a neutral).

To give a broad overview of the diagram: The box at the top-left, as labelled, represents a generator or transformer, with the curved lines depicting transformer coils. The horizontal lines at the top represent the distribution system. The vertical lines coming down from them represent the supply connection to an individual property/installation. The dashed box with the label 'Consumer installation' beneath it represents an individual property/building and its electrical installation as a whole. The set of 'dots' (connection points) just within the dashed box represent where the external supply has entered the property and is connected to the installation. (The dot on the far right in the TT and TN systems is the 'main earthing terminal'). The solid box labelled 'Equipment' represents an example item of equipment within the installation. This equipment includes items such as sockets and light fittings, along with appliances ('loads') of either 'fixed' nature (e.g. shower; cooker; boiler; machinery), or more portable and pluggable nature (e.g. hair dryer; kettle; television). (Note that in the TN-C system case the link between neutral and earth would likely take place at a socket rather than in each appliance).

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