Struggling with insulated consumer units and information on power dissipation

The rest of the world continued to use plastic CU enclosures after we switched to metal - and we did have things like all RCBO units even before the switch, so all in all I doubt there is a huge problem in reality.

   - Andy.

I suspect you are right, I am probably over thinking it.

If the garage is so damp that a steel-enclosed DB would rust away, it will not do much for the cars.

Chris Pearson said:

If the garage is so damp that a steel-enclosed DB would rust away, it will not do much for the cars.

Yes ... and no ... it depends on how long you want to keep the cars, but also on whether there's anything else going on (such as salt spray in the atmosphere) that might affect the corrosion of the CU vs the vehicle (latter may be better protected against salt corrosion than damp).

a car gets driven about and maybe replaced after a few years, a CU less so - what about a CU in a car port for example ?

Hello Alan.

Fit a metal one. The metal 8-way Wylex all RCBO CU  in my unheated detached garage has been there since 2008 and has no corrosion at all.

If the garage is so damp that a steel-enclosed DB would rust away, it will not do much for the cars.

At lot depends on individual circumstances - how much rain seeks under the up-and-over door when it rains with the wind in the wrong direction, how much overhanging trees reduce warming/drying when they sun's out. Even within the garage a metallic box screwed directly to a single brick outside wall is likely to get cooler quicker (and so suffer more from condensation) than a metal box stood off the floor on rubber tyres and with a foot or so of still air around it. Of course in the old days we'd mount CUs on a slab of chipboard with a 3/4" air gap behind it which would act as a thermal break, but that's probably not fashionable now. It's not just the steel enclosure rusting either - a bit of damp can wreck havoc to the terminals and internals of delicate modern devices like RCBOs.

   - Andy.

gkenyon said:

CU vs the vehicle (latter may be better protected against salt corrosion than damp)

I find it extraordinary that cars made in the past 15 years or so do not rust.

mapj1 said:

a car gets driven about and maybe replaced after a few years, a CU less so

Strange that people seem to want something as cheap as a CU to last longer than a car!

How long do people expect a washing machine, for example, to last?

it is fixed infrastructure. I'd like the wiring and accessories to last the life of the building, much like the bricks and roof tiles which are also cheap, a brick is cheaper than a CU (!)  if it's that sort of garage and not some temporary wooden thing.
I see no reason why PVC or PE wires going in now that are lightly loaded and out of the sunshine, should not be still in service in a century or two. A washing machine is not infrastructure, and has parts that perish or fatigue over time and so has finite life, looking at our own washing machine history, typically ten to twenty years perhaps.  Cars seem to fail due to something being beyond economic repair, suspension, dual mass flywheels etc. or collision damage.  Corrosion in a big way was more of a 20th century thing  - I presume modern paints are better, and maybe modern steels too.

Mike.

Well, I do a few site temporaries for construction sites outdoor compounds.

I usually source my DBs from a company called Blakley

These things sit out in the cold & rain and snow for years. They're pretty tough. Perhaps see if they do a DB you'd be happy with?