2 phases into standard CU?

[hagmeister]

I want to introduce an IR heating system into an existing split load CU. It is supplied at the moment by 1 phase of a 3 phase input, controlled by a 60A main fuse and a 40A meter. The 5 existing circuits are 2 x 32A ring mains, 2 x 6A lighting and 1 x 16A water heater.
The total wattage for the heaters would be 9KW, giving a potential draw of 39.13 amps.
Is it ok if I move the 5 existing circuits to the dipole (mains) side of the split, (with rcbo protection) and route the new heating circuits thru 32A and 16A MCB's (2 heaters and 1 heater) using another rcbo as a dipole on the other side of the split, using a second phase and another 60A mains fuse + a new meter? I know I would have to clearly label the new RCBO as MAINS or should I add another mains dipole and rcbo from the second phase and meter?
Or would this be totally out of the question as there would now be 2 x 230v supplies entering 1 x 230v CU, even though it is split load? All tails - 25mm2, meters 60/80 amps, earths 10mm2, FUSES 60A and mains feed 40/50mm2 SWA.
Diversity is not easy to calculate for upgrading to 100A with 25mm2 tails and the premesis would be perceived to be commercial.
Thanks for your help - had a few confilcting bits of advice on this...as you can imagine

 

[Darkwood]

Can you draw and post your idea, i got confused with the amount of info your trying to fit in and your explanation, but what i can make out its not a problem having 3phase within a board but the way your trying to achieve don't sound right, i would just buy a 3phase D.B. change existing meter to polyphase meter and then balance all loads over the phase, a electrical inspection of existing electrics will need to be carried out to make sure you dont create any problems if putting existing across different phasing (borrowed neutrals, proximity 400v labels etc ).

Regarding the main switch and fuse are you refering to the DNO service meter and cutout or is this a consumer property 40amp fuse and meter.... if DNO then you have no authority to interfere with said equipment, can you clarify your experience etc so we can tailor our answers to suit.

 

[swparksey]

Off the top of my head I would say no, you would need a 3ph CU. or 2 CU's
Equipment not suitable / designed for the job, their is a reg for this, someone will know the number i am sure.

Hope this helps

 

[Knobhead]

Just on a safety point, use two CU’s. Clearly mark them as 400V potential between them. I’ve fallen foul of three phase in what looked like a single phase board. Going back many years to 230V three phase under M&Q regs they were confusing to say the least. It would be quite normal the find a single phase board with the bus-bar chopped in to three sections.

Play it safe, don’t be sorry at a later date.