Too much weight?

[grenfell]

In thirty plus years of fitting kitchens I've only ever seen wall cabinets come away from the wall once and that was due the installers (Not us ) using the wrong sized wall plugs and screws. It would have to be a pretty flimsy chipboard cupboard to fail from the weight of what was placed on them. (First time for everything though now that Ive said that..... )

I've seen a couple with noticeable distortion , sagging shelves and such like although only on the metre wide ones and the cheap ones at that. I've seen fixings fail and more often the wall structure , soft lime and the like , fail but I have to agree that it's unlikely to fail just because of the load.
I've fitted a few and haven't times had to resort to fixing ply on the wall first. I asked a question about longevity on another forum recently as we were looking at a new kitchen and while even a happy shopper kitchen will look as good as a top off the range one when it's first fitted it's rare asa fitter to go back in a couple of years time to see how it has fared .

[hedgerowpete]

i would say on a modern kitchen cupboard, made from melanine or chipboard faced materials that 25kg per 500mm width is enough thats for all shelves inside a small cupboard.

Yes they are strong but not that strong and as they get older they will become weaker.