It can be done in a way that is safe and regs compliant, but it needs a bit of thought. It also falls into the category of things that might worry folk whose idea of design is to see if there is an example in the On Site Guide - the same folk who think a centre fed radial is two circuits and wonder how to test it...

Practical issues not all fittings and back boxes work well with 4mm cables so if you need 2 lots of 4mm and some 2.5mm  in the same back box/ terminals it may get a bit tight.

As you note , well centred on the ring it is not an issue, as the current split down the two 2.5mm legs is fair. However, if it was a heavily loaded branch near one end it might be worth thinking harder, though of course spurred from the MCB direct it would  be fine.

When things are non-standard It is worth leaving a plan in an envelope near the consumer unit for future use, so that whoever has to do some inspect and test in the future is not confused by it. I know nobody does leave notes, but it is a good idea.

Mike.

It can be done in a way that is safe and regs compliant, but it needs a bit of thought. It also falls into the category of things that might worry folk whose idea of design is to see if there is an example in the On Site Guide - the same folk who think a centre fed radial is two circuits and wonder how to test it...

Practical issues not all fittings and back boxes work well with 4mm cables so if you need 2 lots of 4mm and some 2.5mm  in the same back box/ terminals it may get a bit tight.

As you note , well centred on the ring it is not an issue, as the current split down the two 2.5mm legs is fair. However, if it was a heavily loaded branch near one end it might be worth thinking harder, though of course spurred from the MCB direct it would  be fine.

When things are non-standard It is worth leaving a plan in an envelope near the consumer unit for future use, so that whoever has to do some inspect and test in the future is not confused by it. I know nobody does leave notes, but it is a good idea.

Mike.

Thanks Mike, a full wiring schematic will be left but let's hope others keep it updated :-)