How to add ~25kw to garden?

[anthony_0]

Hi all, we're renovating our property and looking to install a sauna (7kw), electric shower (9kw), outdoor heater (4kw), small lights (200w) and an electric point for things like a lawn mower. In total, I was estimating around 22kw if we had all devices on with no diversity. The current fuse box in the basement is getting quite full and in the future we're planning to put a car charger in that one which I imagine would be 7kw-9kw. Would it make sense to put another fuse box in the garden and run a 10mm cable from the one in the basement to the one in the garden? I think the cable running from the main road into the house is only 16mm? The overall distance between the two fuse boxes would be 22 meters. The cable would be running through a 32mm conduit buried under the concrete. The main thing I'm thinking is that if I switched on everything in our house such as lights, induction hob, ovens, sockets, and everything in the garden mentioned above, etc, it would come to a total of 76k for the overall house. Many thanks in advance.

 

[pc1966]

You really should get a professional electrician involved for this.

Not only as it falls within Part P of the England and Wales building regulations so is notifiable work, but the sort of loads you are talking about potentially exceed the typically 80A domestic supply capability by a large amount and you might need to look at other demand control means or even an upgrade to a 3-phase supply with significant related changes to your CU (consumer unit / fuse box / distribution board).

76kVA is 330A at 230V after all!

 

[anthony_0]

You really should get a professional electrician involved for this.

Not only as it falls within Part P of the England and Wales building regulations so is notifiable work, but the sort of loads you are talking about potentially exceed the typically 80A domestic supply capability by a large amount and you might need to look at other demand control means or even an upgrade to a 3-phase supply with significant related changes to your CU (consumer unit / fuse box / distribution board).

76kVA is 330A at 230V after all!

Thanks, I understand that I'll need a professional for the installation and this isn't something I would attempt myself. I'm looking to hear a couple of views on the actual installation though so I can at least understand what would be required.

 

[Avo Mk8]

Thanks, I understand that I'll need a professional for the installation and this isn't something I would attempt myself. I'm looking to hear a couple of views on the actual installation though so I can at least understand what would be required.

I think before you worry about the 'actual installation' you need to check out the practicality and cost of upgrading your supply. If you can upgrade it to 70kW there will be a very different design approach to trying to manage with a 100A single phase supply.

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[pc1966]

Thanks, I understand that I'll need a professional for the installation and this isn't something I would attempt myself. I'm looking to hear a couple of views on the actual installation though so I can at least understand what would be required.

The biggest factor, as mentioned above, is the decision on upgrading the supply capability versus trying to manage your overall demand by other means (manual or automatic).

If you can afford to get more power available, then it becomes reasonably easy to look at the design of the outside supply sub-main once you know the supply characteristics (Zs, any need for TN-C-S sized extraneous bond) and the max load. You have several factors on that alone:

• Current carrying capacity
• Voltage drop
• End of cable Zs for fault disconnection

Generally speaking it is better to put in a larger cable if you can afford it as it allows any future additions and also marginally reduces wasted power (though pay-back time can be quite long), but you have to start with what is the minimum requirement to meet all of the above.

 

[pc1966]

However, if it is too expensive to upgrade then you are looking at means to limit the worst-case load. That could be various "shower priority" style units, or it could be something significantly more complicated.

EV chargers often allow for max supply management, it would be essential here to have that aspect, and desirable in any other case as well.