The "and is and is" is a typo. There should be just one "and is." A "practice" is something that somebody does on a regular basis. "Unacceptable" means cannot be agreed to or cannot be allowed to continue. "This is not acceptable practice" means that the thing that they are doing on a regular basis cannot be allowed to continue -- in this case, because it creates a high risk of fire.

Lexically - it is (this) is not (acceptable practice) and is (....) 'acceptable practice' means a practice that is 'generally accepted' or 'accepted by some body' - depending on context. 'practice' is 'a way of doing something'. So - in a general sense, you could say that various socially unacceptable habits are not 'acceptable practice'. Here - I think that it is referring to an engineering practice. So 'blocking fire exits is not an acceptable practice', 'using rewireable fuses is no longer acceptable practice'. In other words (whatever it was) is not an appropriate way to do it, and is also dangerous.