They aren't actually buried in the ground - they are on top of a layer of gravel and sand, and below a layer of pebbles, i.e. it's all well drained.Besa boxes are not supposed to be buried in the ground.
"Protects electrical connections from moisture and corrosive vapours and is widely used in a variety of electrical applications including work on junction and conduit boxes." Were the boxes to be truly buried or immersed I wouldn't have used it, but it seemed a useful insurance policy for boxes which may be in a shallow puddle now and then. This coming winter will be the first one they've been through, and I plan to look during or just after periods of heavy rain to see if any standing water collects there.Filling them with a putty type filler will not make the connections waterproof.
OK - I'll check them too if the self-amalgamating tape covering looks dodgy.Fitting fibre washers that will rot means the gland connection will become loose.
I don't at the moment foresee any need for truly underground joints, but OOI do Pratley boxes not do what it says on the tin (IP68)?The only way to make an underground joint is to use a resin cast joint.
OK - take your point about fibre washers, but is lead OK? Lead and Zinc are a fair way apart on the Galvanic Table - is corrosion not a worry? Are there any non-metallic materials that could be used, e.g. nylon or neoprene?If the joint is not underground you could use a besa box with grommet and heavy duty lid - nothing else required. There is no need to add washers to the gland but if you think they are required you should use lead washers.
I can't help noting that the enclosures come with holes in the back...It is bad practise and to drill holes in the sides or tops of weatherproof enclosures, all holes should be on the underside. For the same reason your photo cell should be fixed to the brickwork
There are often cases where the "ideal" is not what is wanted, and I believe that I have done what was necessary to maintain an adequate IP rating for the enclosure. I may turn out to be wrong, but only in that case would it be right to accuse me of poor workmanship - if my work does what I expect then it's not poor.
Without it being interpreted as a challenge, I'm curious to know why, given that the enclosure is not hermetically sealed, and everything is at the same temperature and humidity.The socket should have been external to the enclosure, if you leave the bottom plate off to plug something in you will get condensation problems.
But I will watch out for that if ever I do remove the plate.
Thanks for all the answers.