Shower circuit design.

OK.

But you do not know the “rationale” for the design. The regs are not prescriptive. Sometimes a balance is made between one need and another. The rationale can simply be a judgment on what is the most safe choice given a particular set of circumstances and requirements of the Client.  It is the original installers judgement; someone later will not likely have all the information, unless you fully dismantle everything.

If someone has selected and erected a cable and an OPD and have a particular rationale at install for doing so, any person coming along later and increasing that OPD would surely have to have 100% confidence in exactly how and where that cable has been installed. Do you excavate the lot and have a look?  If you you do not have such assurance, then it is no more than a punt to up the ante “to fully comply with the regs”

You can see this from both extremes if you unbox it. Your “solution” could also “not fully comply with the regs”, but is that really the point?

OK.

But you do not know the “rationale” for the design. The regs are not prescriptive. Sometimes a balance is made between one need and another. The rationale can simply be a judgment on what is the most safe choice given a particular set of circumstances and requirements of the Client.  It is the original installers judgement; someone later will not likely have all the information, unless you fully dismantle everything.

If someone has selected and erected a cable and an OPD and have a particular rationale at install for doing so, any person coming along later and increasing that OPD would surely have to have 100% confidence in exactly how and where that cable has been installed. Do you excavate the lot and have a look?  If you you do not have such assurance, then it is no more than a punt to up the ante “to fully comply with the regs”

You can see this from both extremes if you unbox it. Your “solution” could also “not fully comply with the regs”, but is that really the point?