MEPworx Wiring – SC and Backup protection for Board Level CPDs

By David Wren

For MEPworx 2026, in addition to the new functionality where the program will auto-size Unfixed board-level protective devices (CPDs) at the source of Single Section and Split section Final Boards, design checks are also in place for Board level CPDs to provide Backup Protection to the outgoing Ways.

For example, looking at the image below we can note the following observations relating to; SC levels and the SC rating of the various CPDs inside a Final Board.

1. The Type C MCBs on the outgoing Ways of Sub Section 1, have an SC Rating of 10kA.
2. The incoming CPD protection at the board's Sub Section is a Type A RCD, which is also rated at 10kA.
3. The supply characteristics for the Sub Section show an SC value of 19.47kA, which is inherited from the Parent Board.
4. The CPD Protection at the incomer of the Parent Board is a BS-88 fuse, which has an SC rating of 80kA

With the combination of these CPD SC ratings and the magnitude of the prospective SC for the supply characteristics, the BS-88 at the Parent Board is providing Backup Protection for the Sub Section and it's outgoing Ways.

The board level Backup and SC checks are applied automatically by the program to ensure the SC rating of the selected protective device(s) is/are greater than the board's supply characteristics.

If these checks are not satisfied, there will be an appropriate error message in the board’s/section’s General Details dialog. e.g.

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’.