Fuse box in my garage keeps tripping out

most of the time it is things like freezers, heaters microwaves and kettles etc to cause the trip because they have faulty components and cause earth leakage which causes the main RCD to trip. If you want to prove what is the cause, unplug all plugs in the sockets and check the RCD still stays on and if so plug each plug back in and you will find what is the faulty appliance and call out the manufacturer to rectify it or replace it. Hope this helps.

Well if that's the case then you had better contact a registered full scope electrician to diagnose the problem by way of the appropriate testing and get him/her to rectify the said problem. (It may even be your freezer that's at fault.)