Selection of 3P-TPN-4P MCB & Distribution Board
November 1, 2013 89 Comments
Type of breakers based on number of pole:
- Based on the number of poles, the breakers are classified as
- SP – Single Pole
- SPN – Single Pole and Neutral
- DP – Double pole
- TP – Triple Pole
- TPN – Triple Pole and Neutral
- 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
JIGNESH PARMAR
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
Very usefull guidLine for Electrical Persons working in industril/comm. field.Thanks Jignesh Sir.
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.
Please differentiate between MCB and MCCB.
these notes are useful fo me, thanks
yes its very useful
Please differentiate between MCB and MCCB.usage
It is already given in the Blog..
Really a good information,
thank you
I WNT
Useful information regarding electrical installation
please also inform about SF6,OCB ,& VCB
Thanks Very useful to us , Please be continued
your information is really valuable
thankx so much to increase my electrical knwoledge
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.
thanks
Dear Jignesh.Parmar Sir, Those articles are very helpful for all electrical professionals specialyy for beginners.Thank you for your great dedication…..
good
interesting getting some ideas about it thankz alot!!!
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
Thanka a lot, you have put great effort on putting these valuable informations on the hands of every electrical engineer specially for the beginners.
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.
Thanks a lot. Your information is very valuable.
Great work here. Quite enlightening. Would you please get me more materials on electrical distribution and installation via the above email address. Thank you.
Sir kindly give a clarification abt what is 7 segment tpn double door db box
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?
It is depend upon your distribution system i,e TT,TS..
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
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
what is the calculation of reactive power injection to the Bus bar?
hi sir,
i have a doubt,
where to use RCCb and where to use ELCB?
Thanks & regards
AH Mohamed Rafi
my house load capacity is 5000 watts ,which capacity of 3 phase MCB i may installed in my house .
4 way TPNDB with 63Amps MCCB incomer and 20Amps MCB- Geyser, A.c, Fridge, rest of Mcb for circuits-switch boards,
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.
Dear sir,
Whether 3Pole MCCB can be converted in to single pole + Neutral . if so
What about the protection
what is cheng over in which capacity changeover are available were to use
what is nesacari to check?
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.
What is the meaning of 6way ( 8+18)TPN MCB DB
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
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
thanks your note is useful
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
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.
Kindlylet me know what type of contractor AC1 AC3. Should be used in neutral circuit
Thanks
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
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.
Thanks
I want the quotation of mccb TPN 4 pole
250amp
200amp
150amp
100amp
660amp
Pls send me quotation urgently
Good work, thanks alot
I HAVE 80A TPN ISOLATOR HOW I KNOW THE CABLE SIZE WHICH ONE IS USE
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
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.
Thanks.
Pls, I need pictures showing the SPN and TPN incoming and Outgoing. Pls
Thanks.
what a useful info ! thank Sir a lots !
sir could you please help me with some calculation for selection of incomer in MCC, PCC, 11 KV SWGR
Sir could you please help with some calculation for selection of I/C for PCC, MCC and 11KV swgr.
Thanks a bunch it’s fantastic. This will really go in along way for me. Pls keep on.
Electricalnotes provides very clear and brief explanations on concerned topics, helping both students and those who are practising in industries THANKS ! to WordPress……..
Please i appreciate this publishing but illustrate for me how to connect ups dfb to main dfb
hai i am a civil engineeer, even i can understand electrical basics, you have written so simple and easy understanding way, keep rock, thanks
thanks for valuable information provided to the public in a systematic way
63amps ELCB how to output trip in three phase ?
thnks
it was a valuable information
how to select db enclosure size for 4way,6way,8way,12way,16way db?
kindly share details. i need it very urgent.
Dear sir;
Kindly brief me the meaning of ‘2’ and ’12’ in (2+12) way distribution board
what is different between sp and spn ..
sp mcb used to 3 phase DB with common neutral its good or not
in this case one phase shorted means main breaker also trip
Thank you sir for the simple elaboative description
sir what is the orange ball put in the transmission line..
draw the control circuit diagram of capacitor bank 200kvar showing the details of capacitors,contactors,regulator,exhaust fan,thermostat fuses etc
Thanks.It is good information for a designer.
sir my factory load 200 kw but per day at the time of 4 to 5 mnt load goes to 200 above. so how can control my load…. plz suggest me how to break my main circuit at the time of goes load.
USEFUL INFORMATIONS
I have applied 63A TPN MCB for machine & 5 Hp pressure pump. Machine is rated 32A & pressure pump is 16A. Total: 48 Amps & my TPN MCB is 63A. Is it ok or should I get it changed. ?
Hello Jignesh,
Is there a typo in your above notes. I think item 3: (TN-S) should have TPN or 4pole and item 4 (TN-C) should have TP as we cannot breaker neutral in TN-C.
Seriously Your Data is very Helpful.
Thanks A Lot
wow, very useful information on electrical engine
ering field, thank you and God bless you Sir
At what current will 25A B type MCB will trip? ,voltage is 230v
1) How many Wiring connection In Neutral link of 6 way SPN DB ?
would do you please explain about Types of distribution box such as VTPN ,i heard there is 7 types like this ,please expllain
Hi, Good explanation. However in case of a Switch what is the difference between 3P+N and 4 POLE?
Suepr
Great information
Thanks
Dear Mr. Jignesh Parmar
Thanks for your valuable inputs and contributions to electrical Field.One question i request if you can help to answer as i tried in IEE regulations could not get clear answer so far;
1). Is it COMPULSORY to provide separate DB for Power (feeding industrial Outlets say upto 125A , 3phase in final sub circuit) & Lighting (indoor/outdoor) or its allowed to have one common DB provided requirements of separate wiring is complied ,provided RCD/RCBO requirements are complied in final sub-circuit.
2), The question above is specifically for TN-C-S system
Appreciate answer with respect/reference to IEE (BS) or IEEE or IEC any equivalent code references.
thanks & regards
rajesh
if i have to use mcb for two phase supply (R and B), which mcb type would be most suitable?
Dear Mr. Jignesh Parmar,
You have mentioned that
– – – – –
“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.”
– – – – – –
My question is when the Bus Section CB is open or any one of the Incomers is open, then how the return current flows through the open (phase conductor)circuit? There is no electrical path for the fault current to flow.
Please clarify on this.
Thank you.
Dear Mr Jignesh Parmar,
Thank you for sharing, i learn a lot in this blog.
if you don’t mind, i have a question. For TNC system, why using TPN or 4P? Because the neutral line, which is combine with ground, might be cut off
Worthy Information , thanks for the sharing .
Is there any IEC guidelines for the same TPN or 4P applications
This is very useful..
can 3p MCCB will work if we use 2P of it as single phase suply
UPS DB Having 25Amp TP MCB & Out going 32Amp DP RCCB is correct. Whay Consider higher rating