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With only 1 spare circuit on my existing internal consumer unit, I am thinking about adding a 2nd consumer unit outside, right next to the external meter box, which is the best location wise for connecting 2 PV system inverters (along with their metering requirements) and an EV charge-point.

The 18th edition regs dictate a new consumer unit needs to be constructed of a non-combustible material which is usually steel. These however are not outdoor rated at IP65 or better, and I can only find IP65 units made of ABS. The Famatel UK Acqua range appears to be suitable, with built-in neutral and earth rails, and meeting EN 62208 (Empty enclosures for low-voltage switchgear and controlgear assemblies - General requirements).

My thinking was to have Henley blocks to split the 25mm2 meter tails inside the existing meter box, with one branch to the existing CU, and a new branch to a new external CU.

Then work out how many ways are required to meet the 18th edition, with surge protection (SPD) taking 2, a 100A switch taking another 2, 4 MCBs for EV, solar1, solar 2 and metering supply, along with 4 metering devices (each using 1 DIN way). So at least 12 ways required.

Could the new CU be close coupled to the bottom edge of the existing meter cabinet (660 mm above the outside ground level), with top entry in with LNE and metering cables, and bottom entry for the 3 power cables for EV, solar 1 and solar 2?

Any thoughts or guidance would be much appreciated.

I would only be supplying a suitable enclosure (to ensure availability on the day), and get the electrical installer to provide all the switch-gear, testing and certification.

Why not fit another meter box/cabinet next to the exiting one and fit the new consumer unit inside that. That way you can use what ever compliant consumer unit you want. Also has the advantage of "hiding" the consumer unit behind a, all be it simple, locked door.

Plastic consumer can be used if in a fire proof enclosure.

Seems to be a few metal IP65 consumer units around, like this one: https://www.toolstation.com/bg-metal-ga ... p65/p42830

Yes I think that’s the one I have for my car..
Been in for 2 years no issues, I have a mcb size meter to record usage for the car charger

All good ideas thanks.

The BG IP65 units are only 5 way though, and I am looking for at least 10 way in total.

I have found some smaller meter boxes that may suit say a Wylex 10 way with 2 pole 100 A switch and SPD built-in that just use up 3 ways, leaving 7 ways free for my planned MCBs and metering devices.
There is not enough room for a full size meter box to be surface mount, and with a recessed box I do not want any more draughts passing through my cavity wall and appearing in the bathroom via the plumbing routes under the floor-boards.

Just waiting for some feedback on the 18th edition requirements from a local electrician.

Join two together with IP rated kopex?

I have found a supplier of metering boxes that does a reduced size one at 360H x 252W x 140D, so that is now on order.

After trawling through data sheets from multiple manufactures I have found a couple of small CU (8 or 9 ways in total) that should fit inside.
I am waiting for delivery of the meter box first though so I can get accurate internal measurements.

Still pondering where best to locate the surge protection device(s) to meet the latest 18th edition regs.

The small metering box has arrived and seems solidly built.

https://www.meterboxesdirect.co.uk/elec ... 40-mm.html

Having checked the internal measurements, I can fit a Lewden 9 way CU inside (only just in the case of the depth).

So the plan is to use 8 ways in the CU for 2p 100A switch, 2 ways for SPD, then 4 ways for the MCBs, with 1 way spare.

A separate 5 way IP65 DIN enclosure for the 4 x meters is now on order. This will just have a 6A mains feed to it from 1 of the MCBs, the 4 x CTs to be wired out to clamp around the relevant live cables, along with the modbus data cable(s) back to the inverter(s).

Just need to arrange with the electrician to wire it up and test it.

Sounds like a plan
Love to see photos when complete