If its the type of board I'm thinking of its very similar to contemporary GE and Steeple (Denmans) branded ones but just a lovely chocolatey brown colour! The later GE branded RCBOs will fit on the rail and line up with the busbar but the enclosure is physically not tall enough to terminate them , so in practice can't really be done. Interestingly Wylex NSB RCBOs are physically very similar too...anyway its all academic, doesn't comply with the 18th...!
The metalclad version is a bit taller and they will fit, did 1 myself a few months ago, obvs designed before Jan...!
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