Hey @corey , hope this helps.
So 1st off, fuses have been getting phased out over here for about the last 10-15 years, no new builds have them and any upgrades have them removed.
Our home is about 20 years old, so it did have a 63amp fuse, the fuse was removed and replaced with a 63amp rcb (= residential circuit breaker.
We don’t call them fuse boxes anymore, just electrical boxes.
I added a 40amp mcb (= mini circuit breaker) into the electrical/fuse box and ran a feed from there out to the grow space. I used what we call 10 square swa cable. Its capable of taking 65amps and is armoured as its buried outdoors.
Using the 10square swa cable, I was able to set up a new electrical/fuse box in the grow space. I connected the 10 square swa cable to the new box using another 40amp mcb (1st switch on the left in the pic below). That essential meant the new electrical box was now live.
Once the box was live it was just a case of adding in more mcbs to run sockets/outlets and lights from. I used 20amp mcb (seen in the pics above) just daisey chained power from 1 to the other as needed. A lot easier and modern method is to use buzz bar, just saves on time and dont have to worry about lose connections.
In order to spread the electrical load, I allocated 2 walls of outlets/sockets to a 20amp mcb. So every room of 4 walls is split between 2 x 20amp mcbs.
The cable I used for running from the breakers to the outlets is 2.5mm twin and earth (pic above). It can take 25amps. Took about 350’ of the cable to do the whole place.
Apologise if I’ve rambled on, hope its some help.
To anyone reading this please be careful with electricity.