I do take it seriously. That's why I cam on here really. I totally respect your advice, all of you. You're the pros. I'll take your advice.
The load is mainly the pond pump at 60A and the lights. I'll only plug stuff into the sockets occasionally.
The cable depth: hmmm, well, it leaves the house and is clipped to the wall for maybe 10m, across the patio and raised decking. Then it goes below the decking, through open space, for maybe 4m, until it goes underground.
Our garden is on a steep slope, house at the top. Once it goes underground it runs underneath a water feature made of concrete, probably 60cm deep, then under a series of very big stone slabs around the edge of a pond. At this section it's not 18" deep, but has huge boulders on top of it. I was going to trench it into the garden but thought it was safer under these big rocks (they weigh maybe 1-2cwt each).
After that, it dips underneath the stream which drains the pond. Runs through the ground beneath the liner and the rocks, gravel etc, all the way down the garden. Not sure exactly how deep it is here, but well buried and completely inaccessible. It emerges close to the shed and is currently above ground for the last 12 ft or so. This part is intended to run behind a stone wall bordering the steps leading down to the shed, the last 2ft from the stair foot being buried in the soil under concrete slabs.
So, it doesn't follow a straight path. It follows the stream line. It's not marked with tape, but to a limited extent, I could retro that. The cable runs in the same trench as the water pipe from the pond pump which supplies the upper pond.
