Electrical Engineering/electrics

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Question
Hi, hope you dont mind some very basic questions.
I am converting a van into a motorhome(RV).
This has led me to think more about electrics.
Could you give me a quick overview of difference in 12v to 240v systems. I have noticed 12v systems have a higher current to give same power output. Why is 240v more dangerous? What have I misunderstood about current as opposed to voltage?
What does earthing to a van body actually achieve?
What happens if a fault triggers the use of the earth (current passes through it) and someone happens to be touching the earth (van body). I have never really understood why earths are connected to (easily touched)copper pipe in the home. Clearly I do not understand earths! I always thought an earth was an easier route for electric to get to earth but what if someone is touching that earth? Also, how does the earth work in a vehicle? with no route to the ground. The van conversion has just made me think why we connect wire (even an earth) to readily touched areas.
Appreciate any help you can give.
Thanks

Answer
Let me help you understand some basics of electricity.  

Do you know about ohms law?  Voltage = current * resistance.  It always works.

Do you know about electric power?  Power (in watts) = current * voltage.

If your 12v system is consuming 10amps of current the power to supply that amount is: 12v * 10amps = 120w.  And if a 240v system were supplying 1/2amp the power would be 240 * 1/2 = 120w.

Voltage is measured between two points.  It is a measure of the potential difference.  In an automobile the chassis of the car becomes the ground point for current flow.  

Let me suggest you study these easy, simple lessons about basic electrics and simple circuits.  It will help you immensely and these courses are the best I know of.

http://utwired.engr.utexas.edu/rgd1/lesson01.cfm

I suggest you study lessons 1 through 5;  it will make you an expert!  

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