How to select MCB / MCCB (Part:1)
October 4, 2016 47 Comments
Introduction:
MCB or MCCB are widely used in electrical distribution system for ON/OFF Electrical supply and it also gives over current and short circuit protection. Selection of MCB or MCCB involved technical, Mechanical parameters. Some parameters are important but some parameters are confusing and mislead to wrong selection of MCCB. Some parameters are directly affected on cost of MCCB.
Specification / Name Plate Details of MCB/MCCB:
Following specifications are required to select appropriate MCB or MCCB.
(A) Current Related:
- Frame Size (Inm): Amp
- Rated current (In/ Ie): Amp
- Ultimate short circuit breaking capacity (Icu): KA
- Rated short-circuit breaking capacity (Ics): % of Icu
(B) Voltage Related:
- Rated voltage (Ue): Volt
- Rated Insulation voltage (Ui): Volt
- Rated impulse withstand voltage(Uimp): KV
- No’s of Pole : SP,DP,TP,TPN,FP
(C) Application Type:
- Utilization Category/ Characteristic : B,C or D curve
(D) Accessories:
- Rotary Handle: Extended/ Direct
- Alarm Contact:
- Shunt Trip:
- Under voltage Trip:
- Mechanical interlocking:
- Manual /Auto operation
- Motorized Operation:
(E) Protection Type:
- Protection : Over current / Short circuit
- Trip Mechanism: Thermal / Magnetic / Solid / Microprocessor
- Trip Mechanism adjustment : Fixed / Adjustable
(F) Others:
- Frequency;
- Reference temperature: (if different from 30°C)
- Pollution degree:
- Suitability for isolation:
- Type of Mounting arrangement
- Electrical Life Cycles:
- Mechanical Life Cycles:
- Dimension: mm
- Weight: Kg
- Reference Standard: IEC: 60947-1/2, IS: 13947-1/2
(A) Current Related:
(1) Frame Size (Inm):
- Breaker Frame Size indicates the basic framework of the Plastic shell of MCCB that can hold the biggest rated current.
- It is the maximum current value for which the MCCB is designed (upper limit of the adjustable trip current range) and it also determines the physical dimensions of the device.
- There are varieties current ratings MCCB for the same series frame Size.
- For example, DX100 Frame Size MCCB for rated current of 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A.
- Same DX225 Frame Size MCCB for rated current of 100A, 125A, 160A, 180A, 200A, 225A.
- In above DX100 and DX225 has two Type of frame Size for rated current of 100A, but the shape and size of breaking capacity of circuit breakers is not the same.
(2) Rated Current (In /Ie):
- It is the current value above which overload protection is tripped.
- For MCB it is fixed while in MCCB the rated current is an adjustable range instead of a fixed value.
- Standard rating of MCB is 1A, 2A, 3A, 4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 100A for MCB.
(B) Voltage Related:
(3) Ultimate short-circuit breaking capacity (Icu):
- Breaking capacity can be defined as the maximum level of fault current which can be safely cleared.
- It is the highest fault current that the MCCB can trip without being damaged permanently.
- The MCCB will be reusable after interrupting a fault, as long as it doesn’t exceed this value.
- It is indicate operation reliability of MCCB
- This parameter may increase or decrease the cost, so it should be properly decided. Breaking capacity should be higher than the possible fault level. For domestic application fault level may be 10kA.
(4) Operating short-circuit breaking capacity (Ics):
- It is expressed as a percentage ratio of Icu and tells you the maximum short-circuit current if a circuit breaker can break three times and still resume normal service.
- The higher the lcs, the more reliable the circuit breaker
- It is the maximum possible fault current that the MCCB can clear. If the fault current exceeds this value, the MCCB will be unable to trip and another protection mechanism must operate.
- If a fault above the Ics but below the Icu occurs, the MCCB can interrupt it successfully but will need a replacement due to the damage suffered.
- The Main difference between Ultimate Short Circuit (Icu) and Service Breaking Capacity (Ics) that Icu (Ultimate Braking Capacity) means Circuit breaker can remove the fault and remain usable but Ics (Service Braking Capacity) means Circuit breaker can remove the fault, but it may not be usable afterwards.
- For example, if a circuit breaker has an Ics of 25,000 Amperes and an Icu of 40,000 Amperes:
- Any fault below 25kA will be cleared with no problem.
- A fault between 25kA and 40kA will cause permanent damage when cleared.
- Any current exceeding 40 kA can’t be cleared by this breaker.
(5) Rated working voltage (Ue):
- It is the continuous operation voltage for which the MCCB is designed.
- This value is typically equivalent or close to a standard system voltage.
- In three phase it is usually 400V or 415 V. For single phase it is 230V or 240V.
(6) Rated Insulation voltage (Ui):
- It is the maximum voltage that the MCCB can resist according to laboratory tests.
- It is higher than the rated working voltage, in order to provide a margin of safety during field operation.
(7) Rated impulse withstands voltage (Uimp):
- It is the value of transient peak voltage the circuit-breaker can withstand from switching surges or lighting strikes imposed on the supply.
- This value characterizes the ability of the device to withstand transient over voltages such as lightning (standard impulse 1.2/50 μs).
- Uimp = 8kV means Tested at 8 kV peak with 1.2/50μs impulse wave.
(8) Number of Poles:
- No of Pole for MCCB depends on Single Phase & Three Phase Power Controlling /Protection
- Single Pole (SP) MCB:
- A single pole MCB provides switching and protection for one single phase of a circuit.
- Used: for Single Phase circuit
- Double Pole (DP) MCB:
- A two Pole MCB provides switching and protection both for a phase and the neutral.
- Used: for Single Phase circuit
- Triple Pole (TP) MCB:
- A triple/three phase MCB provides switching and protection only to three phases of the circuit and not to the neutral.
- Used: for Three Phase circuit
- 3 Pole with Neutral (TPN (3P+N) MCB):
- A TPN MCB, has switching and protection to all three phases of circuit and additionally Neutral is also part of the MCB as a separate pole. However, Neutral pole is without any protection and can only be switched.
- Used: for Three Phase circuit with Neutral
- 4 Pole (4P) MCB:
- A 4 pole MCB is similar to TPN but additionally it also has protective release for the neutral pole. This MCB should be used in cases where there is possibility of high neutral current flow through the circuit as in cases of an unbalanced circuit.
- Used: for Three Phase circuit with Neutral
JIGNESH PARMAR
Thank you, a very good clarification.
One Comment: The title of ((B)Voltage Rated), I think it was put by mistake in wrong line.
Thanks dear for the informations
Eng.Saad Swaireh 1
Very super translation
Hi sir, Hope your doing good. Sir I have ordered your electrical notes and I have a question which is not cleared yet. Can you please let me know that “If my Transformer is 1250KVA then what should be the size of the Primary Cable.On what basis the cable is selected? Please let me know with its Calculation and not by thumb rule.
what is primary voltage?
Many thanks for the information Sir. Kindly send me such updates please.
Regards
Nitin
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>
blockquote, div.yahoo_quoted { margin-left: 0 !important; border-left:1px #715FFA solid !important; padding-left:1ex !important; background-color:white !important; } Greeting,Can you send 22/132kv transmission line parameters in PDF formate. Thanks in advance.
Sent from Yahoo Mail for iPhone
thank you
On 4 October 2016 at 17:32, Electrical Notes & Articles wrote:
> Jignesh.Parmar posted: “Introduction: MCB or MCCB are widely used in > electrical distribution system for ON/OFF Electrical supply and it also > gives over current and short circuit protection. Selection of MCB or MCCB > involved technical, Mechanical parameters. Some parameters are i” >
Dear Sir, This article is so helpful and many thanks for sharing to enrich our knowledge. With best regards R S Babji Hyderabad
Thank you much sir.
Nice and useful article..
this article is useful and filled with information about selecting the correct type of breaker.
Thank you so much sir. Ur article is very useful to me.
thanks my friend , good work
Hi Jignesh ,it was very useful and helpful note.Thanks a lot to share the such kind of information.
sir send me basic electrical article of my id..
great efforts jigneshbhai, keep it u
1.It is the maximum possible fault current that the MCCB can clear. If the fault current exceeds Ics value, the MCCB will be unable to trip and another protection mechanism must operate.
2.If a fault above the Ics but below the Icu occurs, the MCCB can interrupt it successfully but will need a replacement due to the damage suffered.
Sir i confused with the above points in your article.Kindly clarify the main difference between Ics and Icu. In olden days MCCB manufactures provide the Ics value is 25, 50, 75 & 100% of Icu.In present day every manufacturer provided with Ics = Icu.My doubt is what will be the benfits if we choose Ics =Icu and what will be the dis-advantage if Ics is IN % of Icu.Please clarify.
Icu (Ultimate Braking Capacity) means Circuit breaker can remove the fault and remain usable but
Ics (Service Braking Capacity) means Circuit breaker can remove the fault, but it may not be usable afterward
i am confused hear.
Thanks for detailled information
Point # 3 and 4 under Voltage related heading are having contradictory statements. Please rectify if this is still a live thread and post.
how to select right MCB for motor . (using KW)
please how to calculate.. Ex 25hp 3p motor- what do i select current. ( csgurusingha@gmail.com
Thanks for info.This article is very clear for understanding of selection of MCCB.
REQUIRED DETAILS FOR HOME PURPOSE MCB AMP SHOULD BE USED AS ALL LOAD.
HI, thank you very much can you send How to select MCB / MCCB (Part:1) mohsin.ansari78@yahoo.com
Very good article. Sad to note that people have copy pasted into their website.
One error: “ Main difference between Ultimate short circuit capacity and service short circuit capacity….”
It is written Icus circuit breaker can remove the fault and remain usable..
May be reviewed. Pls keep up the good work .
Thank you!
Sir,
Please write a blog about 765kv line construction.
Dear its good information. Can you clear me on the Lightning protection system for industrial
& building structures. How to calculate or determine the distance between two arrestors, size of the copper conductors & earthing system (number of earthings) for this system as per size of the structure etc.
Very Good Information for Practcal Guys
Awsome always usefull for me as i am MCCB engineer….Provide more on switchgear
Many Thanks…….Madawa (Sri Lanka)
Thanks you so much it’s best best knowledge
I think definitions of Ultimate Short Circuit (Icu) and Service Breaking Capacity (Ics) are mixed by mistake. Please check and inform me if i wrong .
Thanks you very much
Thanks sir very good information about MCB & MCCB
I like this explanation, Thank you sir. keep telling us more!
When the application is:
– rated voltage AC240V
– rated current 10A
– DIN rail mounting
there will be a good selection of MCCB, MCB and CBE
But when the additional requirement is:
– no trip at 130 x rated current at a 165µsec pulse
I strongly assume that magnetic or thermal-magnetic devices with standard trip curves will trip. Only thermal devices left, therefore in this application, MCB or MCCB is more suitable?
In my opinion, Icu is the ultimate breaking capacity of MCCB and can be defined as below:
If a circuit breaker trips on short circuit fault and an operator by mistake switch it again and the persisted fault again trips the breaker than this fault current comes under the category of Icu , it means if Icu is 40KA , the breaker can make following sequences against fault – OPEN-CLOSE-OPEN and after these operations the breaker is usable but it can not make one more CLOSE-OPEN operation.
In Ics – this is similar to Icu , but the difference is that it can make one more CLOSE-OPEN operation in fault condition and can be used further, means if a breaker is rated for 40KA Ics , it can make following operation successfully OPEN-CLOSE-OPEN-CLOSE-OPEN on 40KA fault condition and can be used further.
Very good information on mccb
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Very simple and concise
Thank you for explaining it clearly.
Can I use single pole mccb for DC voltage (450vdc) /breakdown
Hello Sir..
Thanks in advance.
will 4pole / 3pole MCCB (TMD type trip unit) will act for earth fault current ? , if possible, please guide me with some technical literature.
Hiiiiiiiii
Hello sir! Can you pls explain the symbol of MCCB. The symbol appears near the nameplate of every MCCB
Thank you very much. The explanations are simple, clear and concise.