30amp to 45amp

[securespark]

The idea being that a board with a sub-100A main switch is not designed to carry loads above 30/32A.

 

[Spark123]

And a board with a 100A main switch can only carry one fuse greater than 30A/32A

 

[securespark]

Well, certainly the older Standard Wylex range.

That is my rule of thumb, not to put more than one >32A circuit on any one 1P board, but having spoken to manufacturers of modern din-rail-based units, they don't seem to object to more than one large circuit on one board.

Even Hager, whose split-load RCD's are still rated at 63A, didn't bat an eyelid when I asked whether two 40A circuits could be connected through the same RCD.

Imagine 2 x 9+kW showers on one RCD and whatever else was on at the time....

Personally, I think split boards should have an RCD rated the same as the main switch.

 

[ban-all-sheds]

the cable is approx 14mm wide so it must be a 10mm

Nope - that's 6mm² - guarantee it.

I understand I will have to get a pro in to certify the work.

No - you need to get a pro in to do the work..

 

[Softus]

you will need to seek the services of a professional because the likely work is illegal as a DIY

This is untrue - no DIY domestic electrical work is illegal; it's the failure to notify that's against the law.

 

[bongos]

the cable is approx 14mm wide...

As this cable sounds like it is actually 6mm then your 30A fuse blowing is doing exactly as it is supposed to - protecting the supply cable to the shower.