Trying to get to the bottom of an issue with patio lights tripping both RCBO and and intermediate breaker. Something like 15 IP rated boxes to work through and I am finding the supplied and installed choc blocks have all rusted! Brass does not rust, it gets a little surface corrosion but never rusts. Further investigation shows that the screws and blocks themselves have been made from steel and flashed with brass, so one minor scratch and moisture penetrates starting off the rust. Causing the screws to rust in ... The boxes are dry inside, so this is just seepage and moisture in the air. So, somewhere there will be tracking across, but which one and where? A slow process and I will need to find some brass choc blocks as the enclosures are too small for Wago connectors and cable sizes too different for crimping. A penny or two saved in production results in a costly exercise to fault find!