Selection of 3P-TPN-4P MCB & Distribution Board

Type of breakers based on number of pole:

  • Based on the number of poles, the breakers are classified as
  1. SP – Single Pole
  2. SPN – Single Pole and Neutral
  3. DP – Double pole
  4. TP – Triple Pole
  5. TPN – Triple Pole and Neutral
  6. 4P – Four Pole

1.     SP ( Single Pole ) MCB:

  • In Single Pole MCCB, switching & protection is affected in only one phase.
  • Application: Single Phase Supply to break the Phase only.

2.     DP ( Double Pole ) MCB:

  • In Two Pole MCCB, switching & protection is affected in phases and the neutral.
  • Application: Single Phase Supply to break the Phase and Neutral.

3.     TP ( Triple Pole) MCB:

  • In Three Pole MCB, switching & protection is affected in only three phases and the neutral is not part of the MCB.
  • 3pole MCCB signifies for the connection of three wires for three phase system (R-Y-B Phase).
  • Application: Three Phase Supply only (Without Neutral).

4.     TPN (3P+N) MCB:

  • In TPN MCB, Neutral is part of the MCB as a separate pole but without any protective given in the neutral pole (i.e.) neutral is only switched but has no protective element incorporated.
  • TPN for Y (or star) the connection between ground and neutral is in many countries not allowed. Therefore the N is also switches.
  • Application: Three Phase Supply with Neutral

5.     4 Pole MCB:

  • 4pole MCCB for 4 wires connections, the one additional 4th pole for neutral wire connection so that between neutral and any of the other three will supply.
  • In 4-Pole MCCBs the neutral pole is also having protective release as in the phase poles.
  • Application: Three Phase Supply with Neutral

Difference between TPN and 4P (or SPN and DP):

  • TPN means a 4 Pole device with 4th Pole as Neutral. In TPN opening & closing will open & close the Neutral.
  • For TPN, protection applies to the current flows through only 3 poles (Three Phase) only; there is no protection for the current flow through the neutral pole. Neutral is just an isolating pole.
  • TP MCB is used in 3phase 4wire system. It is denoted as TP+N which will mean a three pole device with external neutral link which can be isolated if required. 
  • For the 4 pole breakers, protection applies to current flow through all poles. However when breaker trips or manually opened, all poles are disconnected.
  • Same type of difference also applies for SPN and DP.

Where to Use TP, TPN and 4P in Distribution panel:

  • For any Distribution board, the protection system (MCB) must be used in the incomer. For a three phase distribution panel either TP or TPN or 4P can be used as the incoming protection.
  • TP MCB: It is most commonly used type in all ordinary three phase supply.
  • TPN MCB: It is generally used where there are dual sources of incomer to the panel (utility source and emergency generator source).
  • 4P MCB: It is used where is the possibility of high neutral current (due to unbalance loads and /or 3rd and multiple of 3rd harmonics current etc) and Neutral / Earth Protection is provided on Neutral.

Where to use 4 Pole or TPN MCB instead of 3 Pole (TP) MCB.

  • Multiple Incoming Power System:
  • When we have a transformer or a stand-by generator feeding to a bus, it is mandatory that at least either of the Incomers or the bus coupler must be TPN or 4-Pole Breaker please refers IS 3043.
  • In multi incomer power feeding systems, we cannot mix up the neutrals of incoming powers to other Power Source so we can use TPN or 4P breakers or MCB instead of TP MCB to isolate the Neutral of other power sources from the Neutral of incomer power in use.
  • We can use 4 Pole ACB instead of TP for safety reasons .If there is power failure and DG sets are in running condition to feed the loads, if there is some unbalance in loads(which is practically unavoidable in L.V. distribution system ), depending of quantum of unbalance, there will be flow of current through Neutral. During this time, if Power Supply Utility Technicians are working, and if they touch the neutral conductors(which is earthed at their point ) they will likely to get electric shock depending on the potential rise in common neutral due flow of current through Neutral conductor as stated above. Even fatal accident may occur due the above reason. As such, it is a mandatory practice to isolate the two Neutrals.
  • We can use 4-pole breakers or TPN Breakers when the system has two alternative sources and, in the event of power failure from the mains, change-over to the standby generator is done. In such a case, it is a good practice to isolate the neutral also.
  • 4 pole circuit breakers have advantages in the case when one of the poles of the device will get damage, and it also provides isolation from neutral voltage.
  • Normally, Neutral is not allowed to break in any conditions, (except special applications) for human & equipment safety. So for single incomer power fed systems, 3P breaker is used, where only phases are isolated during breaking operations.
  • Where We have dual Power like in DG & other electricity supply sources ,it is required to isolate neutral, where neutral needs to be isolated  in internal network TPN MCB or 4P MCB can be used.

Where to use 4 Pole MCB instead of TPN MCB

  • Any Protection Relay used on Neutral (Ground Fault Protection of Double ended System):
  • The use of four poles or three poles CB will depend on system protection and system configuration.
  • Normally in 3phase with neutral we just use 3pole CB and Neutral is connected on common Neutral Link but if application of 3pole will affect the operation of protective relay then we must use 4pole CB.
  • System evaluation has to be required to decide whether three-pole circuit breakers plus neutral link can be used or four-pole breakers are required.
  • If unrestricted ground fault protection is fitted to the transformer neutral, then the bus section circuit breaker should have 4-poles and preferably incomer circuit breakers should also have 4-poles because un cleared ground fault located at the load side of a feeder have two return paths. As shown in fig a ground fault on a feeder at the bus section “A” will have a current return path in both the incomers, thus tripping both Bus. The sensitivity of the unrestricted ground fault relay is reduced due to the split current paths.


  • For System Stability :
  • In an unbalanced 3phase system or a system with non-linear loads, the neutral gives the safety to the unbalanced loads in the system and therefore It must not be neglected. In perfectly balanced conditions the neutral functions as a safety conductor in the unforeseen short-circuit and fault conditions. Therefore by using 4-pole MCB will enhance the system stability.
  • 4 Poles will be decided after knowing the Earthing Systems (TT, TN-S, TN-C, IT).

(1) IT (with distributed neutral) System:

  • The Neutral should be switched on & off with phases.
  • Required MCB: TPN or 4P MCB.

(2) IT (without distributed neutral) System:

  • There is no neutral.
  • Required MCB: TP MCB.

(3) TN-S System:

  • Required MCB: TP MCB because even when neutral is cut off system remains connected with Ground.

(4) TN-C System:

  • Required MCB: TPN or 4P only, because we cannot afford to cut neutral doing so will result in system loosing contact with Ground.

(5) TN-C-S System:

  • Neutral and Ground cable are separate
  • Required MCB:  TP MCB Because Neutral and Ground cable are separate.

(6) TT System

  • Ground is provided locally
  • Required MCB:  TP MCB because ground is provided locally.
  • Conclusion: Its compulsory to use TPN in TN-C system rest everywhere you can use MCB.

Nomenclature of Distribution Board:

  • Distribution Box can be decided by “way” means how many how many single phase (single pole) distribution. Circuit and Neutral are used.

1)     SPN Distribution Board (Incoming+ Outgoing)

  • 4way (Row) SPN = 4 X 1SP= 4Nos (Module) of single pole MCB as outgoing feeders.
  • 6way (Row) SPN = 6 X 1SP= 6Nos (Module) of single pole MCB as outgoing feeders.
  • 8way (Row) SPN = 8 X 1SP= 8Nos (Module) of single pole MCB as outgoing feeders.
  • 10way (Row) SPN = 10 X 1SP= 10Nos (Module) of single pole MCB as outgoing feeders.
  • 12way (Row) SPN = 12 X 1SP= 12Nos (Module) of single pole MCB as outgoing feeders.
  • Normally single phase distribution is mainly used for small single phase loads at house wiring or industrial lighting wiring.

2)     TPN Distribution Board (Incoming, Outgoing)

  • 4way (Row) TPN = 4 X TP= 4nos of 3pole MCB as outgoing feeders =12 No of single pole MCB.
  • 6way (Row) TPN = 6 X TP= 6nos of 3pole MCB as outgoing feeders =18 No of single pole MCB.
  • 8way (Row) TPN = 8 X TP= 8nos of 3pole MCB as outgoing feeders =24 No of single pole MCB.
  • 10way (Row) TPN = 10 X TP= 10nos of 3pole MCB as outgoing feeders =30 No of single pole MCB.
  • 12way (Row) TPN =12 X TP= 12nos of 3pole MCB as outgoing feeders =36 No of single pole MCB



About Jignesh.Parmar
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 13 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

61 Responses to Selection of 3P-TPN-4P MCB & Distribution Board

  1. Dan says:

    i am happy for you dear, please keep on updating technical enthusiast on electrical works and devices.I need more of your electrical note.Thanks and remain blessed

  2. Hemrajsinh Chudasama says:

    Very usefull guidLine for Electrical Persons working in industril/comm. field.Thanks Jignesh Sir.

  3. DK Sharma says:

    Very useful information.
    when a changeover arrangement between Three Phase mains supply and Generating set is required, 4 pole MCCB is a must for the safety of the persons working on dead lines.
    In such cases separation of Mains Neutral and Generator Neutral is a must.

  4. DK Sharma says:

    Please differentiate between MCB and MCCB.

  5. vimal kumar says:

    these notes are useful fo me, thanks

  6. Rajesh Kumar says:

    yes its very useful
    Please differentiate between MCB and MCCB.usage

  7. sheikh says:

    Useful information regarding electrical installation
    please also inform about SF6,OCB ,& VCB

  8. mohd shamse alam says:

    Thanks Very useful to us , Please be continued

  9. mukesh kumar chaurasia says:

    your information is really valuable

  10. abdul khadeer says:

    thankx so much to increase my electrical knwoledge

  11. vilas k says:

    Thnax a lot dear sirji !! the info is of great help. It is well said that common things are uncommon.Thanx & regards pl once again request pl throw some highlight on OC+EF IDMT relays setting in EHV s/s with exercise.

  12. hasan says:


  13. rahul baishya says:

    Dear Jignesh.Parmar Sir, Those articles are very helpful for all electrical professionals specialyy for beginners.Thank you for your great dedication…..

  14. saurabh patel says:


  15. Amit Kishore says:

    interesting getting some ideas about it thankz alot!!!

  16. WinComp says:

    Respected Sir, i need to know about the working of Automatic Voltage Regulators/ Servo Voltage Regulators and series transformers but its contents are less available on internet. Please Help

  17. Mohamed Al Najjar says:

    Thanka a lot, you have put great effort on putting these valuable informations on the hands of every electrical engineer specially for the beginners.

  18. Tarun Hirpara says:

    Sir, I have one LV panel with 1 I/C feeder and 2 nos. O/G transformer feeder (I.e A and B).
    A Tr. has 3P ACB & also B Tr. has 3P ACB and there is 1 bus coupler with 4P ACB type.

    Now i want to shift the load of Tr. A to Tr. B with the use of Bus couple.
    How can I do this? what is the procedure which i followed? Bcoz there is different type of coupler.

  19. a.narayana says:

    Thanks a lot. Your information is very valuable.

  20. George says:

    Great work here. Quite enlightening. Would you please get me more materials on electrical distribution and installation via the above email address. Thank you.

  21. David says:

    if I have 2 upstream power, genset and normal power supply to main switchboard. Then connected to UPS. Should use 4 pole or 3 pole MCCB?

  22. Sonny says:

    Thanks for your info. For residential distribution board, only main switch needs to cut both phase and neutral. The mcb feeding outgoing circuit needs only cut the phase. But I find the regulations requiring to cut all live conductors. I could not find where the outgoing circuits need not to so. Could you help. Thanks

  23. Karthik says:

    Dear sir,

    Thanking you for giving valuable information, I’ve quires
    1). What is the meaning of loose wire box in D.B,
    2). What is the abbreviation of EB in Change over Switch connection

    Thanking you

  24. Abhra Pachal says:

    what is the calculation of reactive power injection to the Bus bar?

  25. mohamed rafi says:

    hi sir,

    i have a doubt,

    where to use RCCb and where to use ELCB?

    Thanks & regards

    AH Mohamed Rafi

  26. J. Mohan says:

    my house load capacity is 5000 watts ,which capacity of 3 phase MCB i may installed in my house .

  27. Hemant Arora says:

    Dear Jagnesh

    We are executing a multi-billion industrial project where it is insisted to use 4 pole breaker through out the installation. (Incomers & Outgoings)

    Local regulation call for the use TT & TN-S combined system. TN-S Utility Supply Neutral through cable armour, while incoming power feed is 33KV-Primary substation. We think TT & TN-S shall not apply since utility supply is 33KV not 380/400/415 or 433V 3 Ph.

    We understand the use of 4 Pole Breaker in the following situations.

    1. Electrical Power input of TXR & Generator OR TXR & TXR to common LV MDB with auto- changeover through 4 ACBs to isolate the neutral of two power sources.
    2. Parallel Supply Systems with Restricted earth fault protection, as summarized by you.
    3. Where 3rd Harmonic presence is established resulting in current in the neutral.
    What if we use Harmonic Filters to neutralize Harmonics?
    4.Hazardous (inflammable/explosive) material areas where spark on Neutral is dangerous.

    Do you have any document BS or NEC or NFPA or IEE which categorically state/ guide usage of 4 Pole Breakers in the electrical power disruption system.

    Earliest response shall be appreciated.

    Hemant Arora.

  28. Muruga says:

    Dear sir,

    Whether 3Pole MCCB can be converted in to single pole + Neutral . if so
    What about the protection

  29. pushkar says:

    what is cheng over in which capacity changeover are available were to use
    what is nesacari to check?

  30. adedayo alo says:

    Going through the notes, I now have better understanding of the mccb/mcb protection systems. Thank you so much for the notes. How I wish you could send notes to me on earthing systems.

  31. Dipesh says:

    What is the meaning of 6way ( 8+18)TPN MCB DB

  32. gaurav says:

    Sir, I had a query; we have a 4 pole ACB for DG. Now we are planning to get 2nd Dg & intend to synchronize both DGs. For this we’ve to install separate neutral contactors. So can we use our existing 4 pole ACB on DG having only 3 phases going through it( N protection set to off) & neutral through contactor. Kindly reply

  33. Krishna says:

    Jignesh.Parmar:) Sir how to design the MSB, DB, Sizes if i know the Total Connected Load.
    Please tell me the whole process step by step.
    Thank you

  34. sumit says:

    thanks your note is useful

  35. Alex says:

    Why in TN-C system required TPN or 4P only if we cannot afford to cut neutral? I think PEN should be directly and all ways connected. Sorry for my English

  36. ANOOP R L says:

    SIR PLZ CLARIFY…max power load that can mix up with normal light loads under a single phase db or three phase db in 30mA protected RCBO.

  37. L n Singhal says:

    Kindlylet me know what type of contractor AC1 AC3. Should be used in neutral circuit

  38. nisar says:

    hello sir i am thank ful to u for your guideline i want to know that in spn 4way db contain how many mcbs with neutral and in tpn 4 way contain how many mcb with neutral
    sir plz do needfully

  39. anand jain says:

    Hello Jigneshbhai! i refer your notes on a regular basis and i must appreciate that you provide very accesible and valuable insights for people like me. Keep up the good work that you are doing by sharing very valuable knowledge.

  40. GOVIND muni says:

    I want the quotation of mccb TPN 4 pole
    Pls send me quotation urgently

  41. olakunle says:

    Good work, thanks alot

  42. ATTIQ says:


  43. akmal says:

    Dear sir in my project lighting panel board is 3 phase 230v and all the light fitting are 220v and to get 220 volt they have installed all branch lighting breaker with 20A 2 ploe mcb . they used two hot wires and one earthing wire I have the doubt with unbalance current where it will go since we dont have connection with neutral ? can u tell this installation acceptable according tO NEC OR other standard

  44. Atiku Muiz says:

    Good day I have problem with my loading, from generator to my house. The reading on my generator screen is 30, 0 and 5amps. Generator stops at every 5mins. Pls how can I balance the loading? Thanks bunch I really enjoy your explanations.

  45. atiku muiz says:

    Pls, I need pictures showing the SPN and TPN incoming and Outgoing. Pls

  46. an phan says:

    what a useful info ! thank Sir a lots !

  47. salil prasad says:

    sir could you please help me with some calculation for selection of incomer in MCC, PCC, 11 KV SWGR

  48. salil prasad says:

    Sir could you please help with some calculation for selection of I/C for PCC, MCC and 11KV swgr.

  49. Atiku Muiz. says:

    Thanks a bunch it’s fantastic. This will really go in along way for me. Pls keep on.

  50. Ritesh Amarnath Jaiswar says:

    Electricalnotes provides very clear and brief explanations on concerned topics, helping both students and those who are practising in industries THANKS ! to WordPress……..

  51. nelson says:

    Please i appreciate this publishing but illustrate for me how to connect ups dfb to main dfb

  52. Manikandan says:

    hai i am a civil engineeer, even i can understand electrical basics, you have written so simple and easy understanding way, keep rock, thanks

  53. BVSN RAJU says:

    thanks for valuable information provided to the public in a systematic way

  54. Kandasamy says:

    63amps ELCB how to output trip in three phase ?

  55. rakesh says:


  56. Mulani Jishan Jakirhusen says:

    it was a valuable information

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