Difference Between 3.5 C and 4C Cable

Anywhere they are deemed suitable within the provisions of British Standard 7671.

Well thanks man for the reply but i want specific location or case which gives clear picture where these cables can be used.

There are training courses for electrical design and installation. An internet search will reveal the opportunities.

<...man...> How abstruse.

Quote "Well thanks man for the reply but i want specific location or case which gives clear picture where these cables can be used."

We can not answer that question. There are hundreds of places these cables can be used. Is your question in regards to the reduced neutral?

Yes my dear friend i mean why neutral core size has been increased from 0.5C to 1C

During the design stage Neutral current should be assessed properly and if necessary over-sized neutral should be recommended.

Quote sanketgoswami1986 "Yes my dear friend i mean why neutral core size has been increased from 0.5C to 1C"

It seems to me that the Fox in post #4 gave a good answered your question. In addition

1.the amount of single phase load connected phase to neutral will influence the neutral current. If you can balance this load, the current in the neutral will be small. No need for the full size neutral.

2. Triplen harmonics add to the current flow in the neutral. The designer must give this type load consideration when making this decision.

3. Fault current at times will require the neutral to be increased.

Excellent article on sizing the neutral

http://www.electrical-installation.org/enwiki/Sizing_the_neutral_conductor

You are welcome.

our man still doesn't have an answer.

On a system where there are only 3 phase loads there would be no requirement for a neutral.

On an old Motor control centre with many 3 phase loads it was usual to use a 3 1/2 core cable - the neutral was reduced. This type of cable was used simply to save costs - less copper.

The danger comes when you try to feed a distribution board / a building etc where there are many single phase loads. The worse case would be a single phase load where the phase conductor would be of sized ok but the neutral is undersized.

The issues with triplen harmonics must not be ignored.

If you have one of these cables, as I assume you must have, assume that the phase conductors are the same size as the neutral i.e. if its a 50mm² cable and the neutral is on 25mm² then assume all cores are 25mm².

Look to the single cables that come from the secondary of a large 11kV/433V transformer on an industrial site. Its usual to have 3 conductors per phase but only 2 for the neutral. This is your situation.

I agree for 3 phase it will not matter much but for single phase neutral core size has to be same as phase core.

It depends neutral

depends on the neutral ???

No it doesn't.

Phase and neutral conductor must be the same size on a single phase circuit. The lowest size conductor determines the value of current that can be safely passed.