Help with Reg 551.7.2 Ina >= In + Ig(s) on 3 Phase Supply Electrical Advice

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Help with Reg 551.7.2 Ina >= In + Ig(s) on 3 Phase Supply Discussion ThreadHelp with Reg 551.7.2 Ina >= In + Ig(s) on 3 Phase Supply Electrical Advice

Hello, I'm struggling to understand how to apply Reg 551.7.2 [in particular the formula Ina >= In + Ig(s) ] to the following situation.

I hope the attached image is clear enough, it shows an existing 3 Phase Domestic supply with:
A) CU1 is a single phase consumer unit serving the main house with circuits as shown (uses Line 3 from the 3 Phase supply)
B) CU2 is a 3 Phase consumer unit with circuits as shown which are: (i) a 3 Phase Electric Vehicle charger, (ii) the circuit labelled "spare" takes an SWA feed from Line 3 to a second new property in the back garden. I don't have a photo of the CU (lets call it CU3) in the second smaller property yet, I imagine its another 100A Mains CU.
Note that the 2 Lucy Blocks have a "100 Amp" annotation on them in red text.
I also do not know the spec of the existing 3 Phase EV Charger.


This is the existing setup to which the following will be added: installation of a single phase Solar PV system with battery storage which will be installed in the garage in close proximity to the image shown. A new single phase 63A RCD (bidirectional) Consumer Unit will be added which will serve a a 5kW Hybrid Inverter which will manage both the solar generation and the battery storage.

I think the issue in this case is that in theory according to this Reg, there could be a risk of >100Amps passing through the Lucy blocks.

In order to mitigate this risk I think a solution would be to:

1) Replace the 100A blocks with a higher rating. I have not managed to find a 150 Amp connector block but there are single pole 200A blocks available such as this: https://www.cef.co.uk/catalogue/products/1149265-200a-single-pole-connector-block

2) Install a 63A Switch Fuse and redirect the tails for CU1 to come from this to derate the CU1 Mains from 100A down to 63A using for example one of these: https://www.cef.co.uk/catalogue/products/1538601-100a-fused-switch-metal-ip40

Does anyone have any views or alternative suggestions?

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