Why short circuit occur when the hot line touches the neutral wire (aka ground)?
Why short circuit occur when the hot line touches the neutral wire (aka ground)?


The neutral wire is not and should not be "also known as ground". They serve different purposes.


  The charges move from negative (hot wire) to positive/negative (neutral) to make the device work right? 


No. You are asking about an AC circuit (live, neutral and protective earth) so the current and voltage alternate. Polarity changes at the mains frequency, 50 Hz or 60 Hz, depending on your location.


  So why would the Short occur only when they are directly connected? 


"Short" in electrical jargon is an abbreviation of "short-circuit". This is analogous to a short-cut on a journey. The current flows through the short-circuit instead of through the intended load.


  Wouldn't they just flow freely to Earth? 


This question is unclear.


  Or it's different when DC passes the neutral line? 


We're mixing up DC and AC terminology here.


  Or Because it was weaken by the transformer after passing the device?


This question is unclear.



A short-circuit can occur on a system with no earth connection. Short circuits can occur in a torch (flashlight) that is floating in space if a fault causes one power supply wire to touch the other.

In most AC electrical systems one wire is bonded to Earth at the local transformer and is, therefore, "neutralised". You should never read a high voltage on it. This means that there are two means of current returning from the live wire to the source: either through the neutral (normal way) or through the earth (during a fault).