4 Core vs 3.5 Core Cables

The neutral wire is a current carrying conductor. In order to handle the same current it needs to be the same size. AC current flow changes sources from the hot wire to the neutral.

You have to look at the harmonics of the neutral conductor.

With modern equipment it is getting to be a major problem especially with IT gear.

Some cable manufacturers can now supply cable with a neutral 1.5 X phase conductor.

I would only add to this that the standards or regulations in your area may also be the determining factor.

e.g. In Australia the standard (AS\NZ 3008) dictates that the neutral shall never be less that the smallest active conductor, so a 3.5C cable would not be permissible under any circumstances, but allows for 4C or greater (>4.5C).

Regards,
Sapper

Two main factors decide the 4core cable in three phase panel boards

1. All the loads connected on the panel board are single phase loads. They are balanced that is each phase carries same value current. In such case, due to any reason, two phases single phase loads are off and third phase full single phase loads are on, then same amount of current passes from phase to neutral. It must be 4-core cable which is used in the panel board.

2. If a panel board is supplying all fluorescent lighting loads and they equally connected on the each phase of a 3-phase panel board. Third harmonics current generated by the fluorescent lights will be additive in the neutral. Hence additive third harmonics current in the neutral will be nearly same amount of current as that of each phase. It is mandatory to use 4-core cable as per NEC.

thnks every one for ur valuable answer....

Dear All,

Very useful posting

It depends upon where and who the <...we...> are. Does the <...we...> have qualifications to trade as a competent Electrician locally?

It is permitted in some countries' national codes. For example:

• In the UK, a reduced cross-section of earth conductor is employed in twin-and-earth cable. It might be called a 2.5-core cable.
• In the Republic of Ireland, the same cable would not be permitted for the same job, and a same-size earth conductor is needed as the line and neutral conductors. It might be called a 3-core cable.

Until that matter is addressed, the inevitable game of "20 questions" must ensue, which some readers find offensive. Do help the forum to provide the help needed.