MEPworx Wiring – CPD sizing for Sub Sections of Final Boards

By David Wren

New to MEPworx 2026 is the functionality in a Final Board, for the program to size board-level protective devices (CPDs) at the source of Single Section Final Boards.
Also for Split section Final Boards, at both at both the board’s Sub Sections and Parent Section.

These added system checks will assist to provide sizing and protection for:

• Board Rating
• Board Loading
• Discrimination checks with upstream devices
   

Please see below for an overview of the revised design checks, where the program will select an appropriately sized Unfixed CPD:

In a Single Section Final Board.
When the Fxd box is unchecked, i.e. the CPD is left as Unfixed, the board's incoming CPD will be automatically sized to be:

• Greater than the board's diversified load.
• Greater than the largest Way CPD, by at least one size.

For a Split Section Final Board.
When the incoming CPD at a Sub Section is set as Unfixed, the same sizing criteria will apply as for a Single Section Board. e.g.:

• The CPD will be sized to be greater than that Sub Section's diversified load.
• The CPD will be sized to be greater than the largest Way CPD, in that Sub Section, by at least one size.
   

When the incoming CPD at the Parent Section is is set as Unfixed, the board's incoming CPD will be automatically sized to be:

• Greater than the board's diversified load
• Greater than the largest Sub Section CPD, by at least one size.

If the size/ratings of the board level CPDs have been Fixed at a level that is too low to achieve the correct protection, error messages will highlight any relevant design issues.  

 

If there are any identified Discrimination issues between:

• The Way CPD and the Sub Section CPD
• The Sub Section CPD and the Parent Section CPD

The design errors will be highlighted at the appropriate location within the board.

For more information and details with illustrated examples, please refer to the

Wiring Program's Help (F1) for, ‘Final Boards - General Details’. 
Then scroll down to the link for, ‘Fxd - Auto CPD Sizing for Board Isolation/Protection’.