Which is better conductor of electricity aluminium or copper and why?

Copper! It's like the Usain Bolt of electrical conductivity among common metals. Copper is a much better conductor than aluminum, with a conductivity of around 5.96×10^7 S/m compared to aluminum's 3.5×10^7 S/m. 

Why is copper such a great conductor? It's all about those free electrons! Copper has one valence electron that's just itching to move around, creating a strong repelling reaction in other electrons. This means it takes very little resistance for an electric current to flow through copper.

Aluminum, on the other hand, is like the tortoise in this race. It's a decent conductor, but it just can't keep up with copper. Aluminum has three valence electrons, which makes it harder for an electric current to flow smoothly.

So, if you're looking for a metal that's a whiz at conducting electricity, copper is your go-to metal. Just remember, with great conductivity comes great cost - copper is more expensive than aluminum. But hey, you get what you pay for, right?

Why neutral cable size is half of phase cable?

The neutral wire, often seen as the unsung hero of the electrical world, is indeed half the size of the phase cable. Why, you ask? It's all about balance.

In a perfectly balanced system (which, let's face it, is as rare as a unicorn sighting), the neutral wire carries no current. But in the real world, where unicorns are as mythical as a perfectly balanced electrical system, the neutral wire does carry some current due to the imbalance between the phases. This imbalance is the reason the neutral wire is allowed to be smaller.

Think of it like a seesaw. If you have two perfectly equal weights on either side, the seesaw stays level, and the fulcrum (the neutral wire in our electrical analogy) doesn't move. But if one side is heavier, the fulcrum has to work a bit harder. The neutral wire is like that fulcrum, only working harder when the phases are out of balance.

So, there you have it, the neutral cable size is half of the phase cable size because it's designed to handle the imbalance current between phase A and phase B. It's not that it's less important, it's just that it's designed for a different role in the electrical symphony.