by David Wren
New in MEPworx 2021 is the ability to specify different Supply Earthing Types in a single Wiring project. As in previous versions of Wiring, when setting up a Wiring project, the Supply’s Earth Type is selected in the Edit General details.
Additionally, this can now be selected at a Final Board in the board’s General Details dialog. As can be seen below.
This function applies to Single Section or Spilt Section Final boards, which are at the end of a distribution leg. i.e. the Final Board for which the Earthing System is being changed must not be feeding other downstream boards/loads. When the Earthing system for a Final Board is changed to be different from the rest of the supply network, the allowed Maximum Disconnection times for final circuits are automatically adjusted accordingly.
For example, this new function can be used to model a supply to an older remote outbuilding which is using a TT earthing system, where the main incoming supply is TN-C-S.
To recap the details of the different Earthing System types:
TN-C-S
Neutral and protective functions combined in a single conductor in a part of the system. (PEN)
TN-C
Neutral and protective functions combined in a single conductor throughout the system. (PEN)
TN-S
Separate neutral and protective conductors throughout the system.
TT
All exposed conductive parts of an installation are connected to an earth electrode which is electrically independent of the source earth.
IT
All exposed conductive parts of an installation are connected to an earth electrode. The source is either connected to an earth through a deliberately introduced earthing impedance, or it is isolated from earth.