MCB/MCCB/ELCB/RCCB

MCB/MCCB/ ELCB /RCBO/ RCCB:

MCB (Miniature Circuit Breaker)

  • Rated current not more than 100 A.
  • Trip characteristics normally not adjustable.
  • Thermal or thermal-magnetic operation.

MCCB (Moulded Case Circuit Breaker):

  • Rated current up to 1000 A.
  • Trip current may be adjustable.
  • Thermal or thermal-magnetic operation.

Air Circuit Breaker:

  • Rated current up to 10,000 A.
  • Trip characteristics often fully adjustable including configurable trip thresholds and delays.
  • Usually electronically controlled—some models are microprocessor controlled.
  • Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance.

Vacuum Circuit Breaker:

  • With rated current up to 3000 A,
  • These breakers interrupt the arc in a vacuum bottle.
  • These can also be applied at up to 35,000 V. Vacuum breakers tend to have longer life expectancies between overhaul than do air circuit breakers.

RCD (Residual Current Device) / RCCB( Residual Current Circuit Breaker) :

  • Phase (line) and Neutral both wires connected through RCD.
  • It trips the circuit when there is earth fault current.
  • The amount of current flows through the phase (line) should return through neutral .
  • It detects by RCD. any mismatch between two currents flowing through phase and neutral detect by RCD and trip the circuit within 30Miliseconed.
  • If a house has an earth system connected to an earth rod and not the main incoming cable, then it must have all circuits protected by an RCD (because u mite not be able to get enough fault current to trip a MCB)
  • The most widely used are 30 mA (milliamp) and 100 mA devices. A current flow of 30 mA (or 0.03 amps) is sufficiently small that it makes it very difficult to receive a dangerous shock. Even 100 mA is a relatively small figure when compared to the current that may flow in an earth fault without such protection (hundred of amps)
  • A 300/500 mA RCCB may be used where only fire protection is required. eg., on lighting circuits, where the risk of electric shock is small
  • RCDs are an extremely effective form of shock protection

Limitation of RCCB:

  • Standard electromechanical RCCBs are designed to operate on normal supply waveforms and cannot be guaranteed to operate where none standard waveforms are generated by loads. The most common is the half wave rectified waveform sometimes called pulsating dc generated by speed control devices, semi conductors, computers and even dimmers.
  • Specially modified RCCBs are available which will operate on normal ac and pulsating dc.
  • RCDs don’t offer protection against current overloads: RCDs detect an imbalance in the live and neutral currents. A current overload, however large, cannot be detected. It is a frequent cause of problems with novices to replace an MCB in a fuse box with an RCD. This may be done in an attempt to increase shock protection. If a live-neutral fault occurs (a short circuit, or an overload), the RCD won’t trip, and may be damaged. In practice, the main MCB for the premises will probably trip, or the service fuse, so the situation is unlikely to lead to catastrophe; but it may be inconvenient.
  • It is now possible to get an MCB and and RCD in a single unit, called an RCBO (see below). Replacing an MCB with an RCBO of the same rating is generally safe.
  • Nuisance tripping of RCCB: Sudden changes in electrical load can cause a small, brief current flow to earth, especially in old appliances. RCDs are very sensitive and operate very quickly; they may well trip when the motor of an old freezer switches off. Some equipment is notoriously `leaky’, that is, generate a small, constant current flow to earth. Some types of computer equipment, and large television sets, are widely reported to cause problems.
  • RCD will not protect against a socket outlet being wired with its live and neutral terminals the wrong way round.
  • RCD will not protect against the overheating that results when conductors are not properly screwed into their terminals.
  • RCD will not protect against live-neutral shocks, because the current in the live and neutral is balanced. So if you touch live and neutral conductors at the same time (e.g., both terminals of a light fitting), you may still get a nasty shock.

ELCB (Earth Leakage Circuit Breaker):

  • Phase (line), Neutral and Earth wire connected through ELCB.
  • ELCB is working based on Earth leakage current.
  • Operating Time of ELCB:
  • The safest limit of Current which Human Body can withstand is 30ma sec.
  • Suppose Human Body Resistance is 500Ω and Voltage to ground is 230 Volt.
  • The Body current will be 500/230=460mA.
  • Hence ELCB must be operated in  30maSec/460mA = 0.65msec

RCBO (Residual Circuit Breaker with OverLoad):

  • It is possible to get a combined MCB and RCCB in one device (Residual Current Breaker with Overload RCBO), the principals are the same, but more styles of disconnection are fitted into one package

Difference between ELCB and RCCB.

  • ELCB is the old name and often refers to voltage operated devices that are no longer available and it is advised you replace them if you find one.
  • RCCB or RCD is the new name that specifies current operated (hence the new name to distinguish from voltage operated).
  • The new RCCB is best because it will detect any earth fault. The voltage type only detects earth faults that flow back through the main earth wire so this is why they stopped being used.
  • The easy way to tell an old voltage operated trip is to look for the main earth wire connected through it.
  • RCCB will only have the line and neutral connections.
  • ELCB is working based on Earth leakage current. But RCCB is not having sensing or connectivity of Earth, because fundamentally Phase current is equal to the neutral current in single phase. That’s why RCCB can trip when the both currents are deferent and it withstand up to both the currents are same. Both the neutral and phase currents are different that means current is flowing through the Earth.
  • Finally both are working for same, but the thing is connectivity is difference.
  • RCD does not necessarily require an earth connection itself (it monitors only the live and neutral).In addition it detects current flows to earth even in equipment without an earth of its own.
  • This means that an RCD will continue to give shock protection in equipment that has a faulty earth. It is these properties that have made the RCD more popular than its rivals. For example, earth-leakage circuit breakers (ELCBs) were widely used about ten years ago. These devices measured the voltage on the earth conductor; if this voltage was not zero this indicated a current leakage to earth. The problem is that ELCBs need a sound earth connection, as does the equipment it protects. As a result, the use of ELCBs is no longer recommended.

MCB Selection:

  • The first characteristic is the overload which is intended to prevent the accidental overloading of the cable in a no fault situation. The speed of the MCB tripping will vary with the degree of the overload. This is usually achieved by the use of a thermal device in the MCB.
  • The second characteristic is the magnetic fault protection, which is intended to operate when the fault reaches a predetermined level and to trip the MCB within one tenth of a second. The level of this magnetic trip gives the MCB its type characteristic as follows: – ·
  • Type               Tripping Current                                      Operating Time
  • Type B            3 To 5 time full load current                    0.04 To 13 Sec
  • Type C             5 To 10 times full load current               0.04 To 5 Sec
  • Type D            10 To 20 times full load current              0.04 To 3 Sec
  • The third characteristic is the short circuit protection, which is intended to protect against heavy faults maybe in thousands of amps caused by short circuit faults.
  • The capability of the MCB to operate under these conditions gives its short circuit rating in Kilo amps (KA). In general for consumer units a 6KA fault level is adequate whereas for industrial boards 10KA fault capabilities or above may be required.

Fuse and MCB characteristics

  • Fuses and MCBs are rated in amps. The amp rating given on the fuse or MCB body is the amount of current it will pass continuously. This is normally called the rated current or nominal current.
  • Many people think that if the current exceeds the nominal current, the device will trip, instantly. So if the rating is 30 amps, a current of 30.00001 amps will trip it, right? This is not true.
  • The fuse and the MCB, even though their nominal currents are similar, have very different  properties.
  • For example, For 32Amp MCB and 30 Amp Fuse, to be sure of tripping in 0.1 seconds, the MCB requires a current of 128 amps, while the fuse requires 300 amps.
  • The fuse clearly requires more current to blow it in that time, but notice how much bigger both these currents are than the `30 amps’ marked current rating.
  • There is a small likelihood that in the course of, say, a month, a 30-amp fuse will trip when carrying 30 amps. If the fuse has had a couple of overloads before (which may not even have been noticed) this is much more likely. This explains why fuses can sometimes `blow’ for no obvious reason
  • If the fuse is marked `30 amps’, but it will actually stand 40 amps for over an hour, how can we justify calling it a `30 amp’ fuse? The answer is that the overload characteristics of fuses are designed to match the properties of modern cables. For example, a modern PVC-insulated cable will stand a 50% overload for an hour, so it seems reasonable that the fuse should as well.

Typical methods of provision of the main earthing terminal:

Supply type code : TN-S

  • Supplier provides a separate earth connection, usually direct from the distribution station and via the metal sheath of the supply cable.

Supply type code : TN-C-S

  • Supplier provides a combined earth/neutral connection; your main earth terminal is connected to their neutral

Supply type code : TT

  • Supplier provides no earth; you have an earth spike near your premises.
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About Jignesh.Parmar
Jignesh Parmar has completed his B.E(Electrical) from Gujarat University. He has more than 11 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 Assistant 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.

60 Responses to MCB/MCCB/ELCB/RCCB

  1. Sathiyaraj says:

    All the details super, excelant. But i need one clearance. Fuse is fast of action compare to MCB.its true also, but u mention here fuse need more current to trip the circuit compare to MCB

  2. Dosh Sonam says:

    Thanks You Sir, For ur help/information.
    i m Mr.sonam Wangdi, Engineer (Electrical ) in Bhutan(Known as land of thunder dragon) ,Asia.
    here , i would like to know about more in power system i.e power distribution system…

    thank you.

  3. DEBRAj says:

    Thanks for all above notes.
    Sir i need the formula or procedure of how to selection of a mcb/mccb in any load.
    Thanking you
    Regards
    Dev

  4. jogie paraiso- Power Engineer says:

    The topics on your site are very much interesting & important for us. It give a big help and give additional technical knowledge that we can used in our job.

    Sir can you publish also about Power Distribution system & Protection system in both transmission & distribution? Thanks and more power.

  5. Surajit Dey says:

    Thank u very mch Sir !!!!!!!!

  6. shashidhar says:

    Is it possible to check earth connection integrity when ELCB is connected on incomer side?

  7. Bharat Solanki says:

    Dear Sir,
    First of all thanx,
    I have one question that which is better for house hold ?

  8. Sundharv says:

    Hai i wand electrical work safety

  9. Nitesh says:

    hi,
    I want to ask some basic thing that do we consider fault current for LV cable sizing ?
    Fault current on LV bus remains approx. 50 kA for 1 sec., so if we are using outgoing MCB/MCCB and the fault current remains in the circuit for 100 ms.
    then fault current will apprx. 16 kA so we have to go for min. 185 sq. mm. cable.
    But we even use 2.5/4/6 sq.mm. cable in LT circuit for lesser load demand.

    MCB is available for 10 kA so it is also difficult to use MCB’s in this circuit, even MCB can’t be use in LDB’s for substation lighting as the fault current will not drop to 10 kA up to these LDB’s.

  10. Anish says:

    Dear Sir,

    Greetings!

    Thank you for the informative article… Some of the equipment terms are relatively new to me, though am aware of the MCB… I have a couple of queries if you could kindly help me out with them that would be of great help…

    1. Where can I find these devices – ELCB and RCBO since some of the electric device dealers and electricians included were unaware of the same other than MCBs – Am from Bangalore any info of the Brand and dealer would be much appreciated…

    2. I have 3 Large MCBs installed at the Meters location for each of the Lines (3Phase) and indoors smaller MCBs that control the internal layout in terms of sections…. I had a 6ft Pit dug out and installed a GI Pipe with Copper plate at the bottom and screw and the required Copper wire and had them filled with Salt and Charcoal…. yet some time back had the MCB at borewell starter burn out without any of the MCBs tripping we identified the burnout by smell… the electrician did change the MCB to a smaller capacity and the problem was resolved… a few days back we had an issue with the TV and again the Technician blamed the fluctuation as the culprit…. another incident was while installing lights during diwali… we did get an electric shock,but the MCBs remained in their on Position… My question is we have installed quite a few MCBs Brand Legrand hoping they would adequately keep the residents and equipment protected… but they seem inadequate, these were installed as per the Electricians & Engineers specification in terms of electric ratings… Would you suggest we install the ELCB and the RCBO to achieve a complete cover if yes do they need to be installed at the meters end where the inputs are or internally where the Circuit Breakers are installed (Must add internally at the MCBs location there arent any free slots to accommodate)

    3. I remember while vacationing at one of the hotels each time there was a powerful lightning strike the power used to trip and be back on and yet none of the bulbs would blow out… used to wonder what kind of equipment was installed…. Just a thought sharing…

    Any help in this regard would be highly appreciated…

    Regards
    Anish

  11. SM NAIK says:

    Jignesh parmarji,

    We are constructing housing quarters . The conducting is of concealed type. ALl our power ,Telephone wiring ,Inetnet wiring & Cable TV Wiring goes on the roof and comes down through the walls and ends at specified heights. Now our client wants that the Telephone,TV,Internet wiring to be below the floor (Below the tiles.).In this matter I want to know wheather it is permissible according to IndianTelegraphic Rules.Kindly guide me. If you give me your mobile number it will be more helpful.

  12. farid ahmed khan says:

    good

  13. afiq says:

    sir..1 qstion..wht hppen to the electricity in final circuit when one mcb trip..explain

  14. sureshkumar.A says:

    i need ELCB&RCCB circut diagram

  15. Yusuf says:

    Thank u sir 4 helping me out

  16. amarjeet says:

    i have one question elcb some time triping (mean after 10 day or 2o day why

  17. Rahman says:

    your all updates are very useful to me

    can you explain how to select switch gear on H.T side with step by step, and what are the factors need

    Thanks in advance for all repliers

    my mail id is h_rahman21@yahoo.com

    realy ur doing great job

    Regards,
    Rahman

  18. Vipu p k says:

    SIR YOUR ARTICLE VERY USEFUL FOR ME.I HAVE ONE QUSTION THAT I HAVE ONLY ONE RCCB AND ONE DP MCB .CAN I MAKE RCBO USIN THESE ITEMS

  19. Similar to tripping characteristics of MCB(tyes B,C,D etc) please give same for MCCB for various types of OC/SC/EF protection ranges. Also give for other types of MCBs. Give tripping curves of MCBs and MCCBs.

  20. Prakash says:

    Thanks for your blog explaining the circuit breakers. It helps non technical people like me.

  21. Karthik says:

    Thanks for your blog explaining the circuit breakers. It helps non electrical trade people also

  22. hardik khalas says:

    we r working of project on kirloskar diesel generating set.
    the problem is that the dg set works at lower efficiency.
    we need the solution of this problem.
    it must be electrical view solution not mechanical.
    we also need some written material on it.please elp us.

    f:-hardik khalas
    hardikkhalas@yahoo.com

  23. Thnks. This info is very much usefull to me.

  24. Ainak Basu says:

    Another important issue is the designed SC withstand capacity of the ELCB. Normally , it is around 10kA which is suitable for household application, but it will not be suitable for industries where fault level can be in the tune of 50 kA.

  25. suresh says:

    Thanks this very usefull for us the we need load calculation method single and three phase load and total load amps.kw,kva per phase as well as total

  26. Joseph says:

    Dear sir, thank u very much for these informations..

  27. Arun Kumar says:

    Sir i was sooooo thankful for your notes

  28. tmwin says:

    Thanks , sir

  29. Md Shafi says:

    Well

  30. robin kumar says:

    mcb.mccb.rccb.

  31. adam says:

    good day.
    how do we select the elcb whether to use 30mA or 100mA etc?

  32. I am really inspired along with your writing abilities
    and also with the layout for your blog. Is this a paid topic or did you modify it your
    self? Anyway keep up the nice quality writing, it’s rare to look a great weblog like this one nowadays..

  33. balakrishnan says:

    A superb Electrical engineer

  34. Somjit Mohanty says:

    Hi, i have a doubt regarding the hold and trip setting for one of the Square-D MCCB. The concerned MCCB is of type FHP36020 and it has an hold current setting of 275 A and trip setting of 600 A. I would like to know what is the significance of hold current setting and what is the criteria to set it? Actually i have worked with MCCB’s where magnetic trip has two setting options i.e. low and high. Is hold setting similar to low setting option.

  35. Subin idicula says:

    Please tell me how to find out the mccb mpcb and overload relay rating from kw of the motor.

  36. dushyant kumar says:

    good metrial

  37. ASHRUMOCHAN NATH SHARMA says:

    thanks sir..
    for ur post i can able to know what the mcb is?

  38. ASHRUMOCHAN NATH SHARMA says:

    thanks sir..
    for ur post i can able to know what the mcb is?thank u vry mch.

  39. Manish says:

    Thanks A Lot Sir. You are Great

  40. shareef ka says:

    Thank u very mch Sir :)

  41. dharmveer.kheriya says:

    thank you very much sir.you are very grate

  42. umeshchandra says:

    Electricity

  43. Azadvishwakarma says:

    Very helpful topic given by U, But working of MCB and fuse likely doubtful please clarify it..,,,,Thanks

  44. VINOD KUMAR NAIR says:

    thank u very much for the information.
    could u plz tell how to choose mcb at respective voltages. and how to calculate cables for respective voltages,

  45. Md Zaid Ali says:

    Thanks You Sir, For ur help/information.
    i m Mr.Parwez Wangdi, Engineer (Electrical ) in Bhutan(Known as land of thunder dragon) ,Asia.
    here , i would like to know about more in power system i.e power distribution system…thank you

  46. sandeep kumar says:

    Thankyou sir very much

  47. ramphal says:

    Please tell me lag and lead current. How the capacitor send the reverse current to control the main current. Tell me it practical. Thankyou

  48. Mayank says:

    sir,
    what does mean by 300/500 mA RCCB

  49. Ashoke Ghosh says:

    Thanx for best opinion.

  50. SUNIL says:

    SIr,
    I have recently replaced 1.5 TON new Window AC & while demo. it was observed that, the reletaed MCB got tripping frequently. What will be reason behind it? or I have to replace MCB?
    OR MCB Can be resetted for higher current draw?
    Regards,
    SUNIL

  51. Pulakesh MAity says:

    It’s really helpful for Engineers. But I am interested to know out of MCB and RCD which one offers better safety against shock prevention? If u please answer me this question.

  52. Manojkumar says:

    Dear sir,

    I need clarification for below points
    1. How to select ELCB size for 230V/415V Welding Machine

    Kindly clarify my question sir.

    Regards
    Manojkumar

  53. Salomon Schuhe Gtx says:

    I constantly spent my half an hour to read this blog’s posts every day along with a mug
    of coffee.

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