reg 431.2.1 of 17th edition explained.

[paulthemagpie]

hi guys,

just wonderign if you could help me understand reg 431.2.1

basically it says the netural shall be protected by short circuirt

but were cross-sectional area of netural is at least equiv of line conducter then its not nessarry to provide over current over current protection

and were cross sectional are of netural is less than line conductor then it is neccessary to provide over current protection.


so i cant get my head round that the small cross sectiona area requires protection and the bigger one doesnt. If anything i thought it would of been the other way around or both need protection.

can anyone help me understnd this?

 

[JUD]

Basically it is saying that if the neutral conductor is of smaller csa than the line conductor(s) then there should be overcurrent detection for the neutral conductor which should disconnect the line conductor(s), thus there will no longer be current in the neutral conductor.

 

[GaryM]

If you have a line conductor rated to carry 35A and a neutral rated to carry 23A then it's saying you should use an MCB in the line conductor rated to protect the neutral - 20A for example. It goes on to say the neutral itself doesn't need to be disconnected so a double pole MCB isn't required, only a single pole.