Premium Membership ♕

Save 50% on all EEP Academy courses with Enterprise Membership Plan and study specialized LV/MV/HV technical articles & guides.

Home / Technical Articles / Selection Of Number Of Cable Cores With Emphasis On Sizing Parameters

Dependance On Installation Site

The selection of number of cable cores basically depends on the type of system where it is going to be installed.

Selection Of Number Of Cable Cores With Emphasis On Sizing Parameters
Selection Of Number Of Cable Cores With Emphasis On Sizing Parameters (photo by

Generally we have two types of systems:

  1. A perfectly balanced system and
  2. A system with some degree of unbalance (or Unbalanced System).

Generally cable sizing includes below parameters:

  1. Cable installation conditions and the load it will carry
  2. Continuous current rating of the cable
  3. Voltage drop and short circuit considerations
  4. Earth fault loop impedance

Here, I am going to describe that how the number of cores can be selected.

3-Core Cables

These cables are used generally for a perfect balanced 3-phase system. When the currents on the 3-live wires of a 3-phase system are equal and at an exact 120° phase angle, then the system is said to be balanced. The 3-phase loads are identical in all respects with no need of a neutral conductor.

An important example of 3-phase load is electric motor and that is why, they are fed through 3-Core cables in most cases.

3.5-Core Cables

A 3-phase system may have a neutral wire. This wire allows the 3-phase system to be used at higher voltages while it will still support lower voltage single phase loads.

It is not likely in such cases that the loads will be identical, so the neutral will carry the out-of-balance current of the system. The greater the degree of imbalance, the larger the neutral current.

3-5-core cable construction
3-5-core cable construction (figure by

When there is some degree of unbalance and the amount of fault current is very small, then 3.5 core cables are used. In these types of cables, a neutral of reduced cross section as compared to the 3-main conductors is used, which is used to carry the small amount of unbalanced currents.

4-Core Cables

When there is severe out-of-balance conditions, the amount of fault current will raise to a very high level. Generally in the case of linear loads, the neutral only carries the current due to imbalance between the phases.

4-core PVC insulated and sheathed copper conductor power cable
4-core PVC insulated and sheathed copper conductor power cable

The non-linear loads such as switch-mode power supplies, computers, office equipment, lamp ballasts and transformers on low loads produce third order harmonic currents (Definition of Harmonics and Their Origin) which are in the phase of all the supply phases.

These currents do not cancel at the star point of a three-phase system as do normal frequency currents, but add up, so that the neutral carries very heavy third harmonic currents.

That is why the neutral of the cable feeding the equipment are not reduced and made with cross sectional area same as that of the main conductor to carry this high amount of current.

5 and 6-Core Cables

Some conditions may arrive when the amount of fault (neutral) current becomes very large than the phase currents. When the load concerned to this type of situation is fed through a multi-core cable, it is necessary to use a 5-Core or 6-Core Cable.

4-core PVC insulated and sheathed copper conductor power cable
5-core PVC insulated and sheathed copper conductor power cable

In this condition, two (or three) conductors can be used in parallel formation to carry the high amount of generated unbalanced currents.

Premium Membership

Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It helps you to shape up your technical skills in your everyday life as an electrical engineer.
More Information

Chirag Singhal

Completed my B.Tech in Electrical & Electronics Engineering from UPTU (Lucknow). A competent engineer with 2 Years of experience in designing electrical systems’ components to required specifications focusing on economy, safety, reliability, quality and sustainability. Strong ability to work and communicate effectively with multidisciplinary team comprised of engineering, technical, field and business support units.


    Jun 05, 2020

    Please , i want answers to these 3 questions :-
    1) Why must MV & HV cable insulation done as a co extrusion and not one after the other ?
    2) Why is co extrusion always done at a height ?
    3) why are MV cables in 1 or 3 cores and never in 4 cores ??

  2. Kamran
    Sep 15, 2019

    1C X 1.5mm Sq. Cable , 1P X 1.5 Mm Sq. Cable , 1T X 1.5mm Sq. Cable (Please Tell Me Meaning Of 1C, 1P & 1T) THANKS

Leave a Comment

Tell us what you're thinking. We care about your opinion! Please keep in mind that comments are moderated and rel="nofollow" is in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Let's have a professional and meaningful conversation instead. Thanks for dropping by!

three  +  5  =  

Learn How to Design Power Systems

Learn to design LV/MV/HV power systems through professional video courses. Lifetime access. Enjoy learning!

Subscribe to Weekly Newsletter

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and guides (PDF).
EEP Academy Courses - A hand crafted cutting-edge electrical engineering knowledge