An electrical cable contains three wires: live, neutral and earth. The cable is correctly wired to a plug which contains a 3 A fuse. The insulation becomes damaged and bare metal wires show.

 

Five possible events can occur.

• A person touches the earth wire.
  
• A person touches the neutral wire.
  
• A person touches the live wire.
  
• The live wire touches the neutral wire.
  
• The live wire touches the earth wire.
  

 

How many of these five events cause the fuse in the plug to blow?

 

A. 1 B. 2 C. 3 D. 4

What do you think, and why?

I think the 3rd, 4th and 5th events will lead to a surge in current which will cause the fuse to blow. So, I think the answer is C (3). Am I right?

If a person touches the live wire, what causes the fuse to blow?

The electricity will bypass the appliance. Presumably the human body is of lower resistance thance the appliance. Hence there is a surge in current exceeding 3 A, and this will cause the fuse to blow. Events 4 and 5 will cause short circuit and the fuse will blow too.

Presumably the human body is of lower resistance thance the appliance.

 

That can be investigated (it's somewhere around 1 to several [math]k\Omega[/math]), but there must also be a path to ground. If I'm standing on a plastic crate, is there any way to complete the circuit?

 

The question doesn't clearly indicate if it means "might cause" or "must cause." A person touching the wire might cause the fuse to blow, but it might not.