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Is it safe to connect a 3mm electrical wire (running 240 V) in a complete closed no air environment (Completely sealed "Hazard proof" cabinet) ?

I will use similar to the below

Marcus Müller
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Short answer: Your question doesn't even remotely indicate that you know what you need to know about electrical safety.

When I went to school, I did a 14 day internship at a small company that builds control/switch cabinets. If I had delivered a work of craftmanship of the quality of that picture, my boss would have said very ugly things to me. From the third day on. So, this isn't even acceptable in any other installation. Hope you didn't take that photo yourself, but got it from somewhere else¹.

So, no, under no circumstances is it OK to, with your level of knowledge, install electrical stuff in an explosion-safe environment. Only certified electricians should do that.

¹ things that are wrong:
  • stranded wire must have a crimped-on strand sleeve when screwed fast
  • wires on the left change diameter – that isn't per se impossible, but I'd very much expect a fuse there.
  • is that freaking unisolated copper wire freedangling between contacts? What if any friction breaks loose a few strands, which then end up in contacts!?!??
  • screw terminals aren't properly secured to the rail, and although these cables look far from mechanically rigid, are rotated by the cable forces.
  • my boss would have felt his aesthetic feelings hurt by the non-alignment of the wires. But that's just personal taste.
Marcus Müller
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  • Using bare copper wire for GND seems to be common (and up to code) in several countries though – PlasmaHH Jul 20 '17 at 08:47
  • I've seen that done with single-wire copper cable, yes, but a) single wire, and b) wire somehow secured/ducted along a side of a cabinet. Then again, I might totally be missing "real-world implementation" vs "Oh, isn't that a nice cabinet done by someone who was preparing to demo it" – Marcus Müller Jul 20 '17 at 08:50
  • have a look at a google image search of maybe "ground wire breaker box" and prepare to have a good seat ;) – PlasmaHH Jul 20 '17 at 08:53
  • I. Uh. Um. Yeah. Great. Good that I have still more than half a day to go until this will haunt me in my sleep :D – Marcus Müller Jul 20 '17 at 08:56
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    @PlasmaHH yes, there are apparently countries where to get certification all you need to do is make sure the inspector has a good meal with the correct wine :) ... Codes?? – Solar Mike Jul 20 '17 at 11:20
  • @SolarMike: Inspector? What inspector? – PlasmaHH Jul 20 '17 at 11:26
  • @PlasmaHH perhaps we should start a rogue's gallery of pictures showing bad practice that we find - I did shout at my employer once when I found the welder had a bolt in place of the fuse that should have been there... He told me "well, the fuse keeps blowing" .... – Solar Mike Jul 20 '17 at 11:27
  • @SolarMike: side note: the "home inspector" business seems to be mostly a north american thing, in most other countries nobody cares about it, and in some other countries there is enough trust in the industry and home owners that this seems to be unnecessary. – PlasmaHH Jul 20 '17 at 11:29
  • I know that the inspector who came to see my Dad's house is capable of identifying who did which cabinet by the layout etc "oh, that's so and so, works for xxxx" - mind you his face dropped when my Dad said "my son wired this". It was ok though - he was actually impressed : "better than some I've seen"... – Solar Mike Jul 20 '17 at 11:30
  • Uk has inspections - see comment above, but they are not regular and can be because significant changes have been made. In Switzerland, there are inspections of the electrical installation for all buildings once every 10 years. For the UK, I know because I have the certification... – Solar Mike Jul 20 '17 at 11:33