What is an MCB

What is the difference between MCB, MCCB, ELCB and RCCB?

MCB (circuit breaker)

  • Nominal current not more than 100 A.
  • The driving characteristics are usually not adjustable.
  • Thermal or thermal-magnetic operation.

MCCB (molded case circuit breaker)

  • Nominal current up to 1000 A.
  • The tripping current can be adjustable.
  • Thermal or thermal-magnetic operation.

Air circuit breaker

  • Nominal current up to 10,000 A.
  • The trip characteristics are often fully adjustable, including configurable trip levels and delays.
  • Usually electronically controlled - some models are microprocessor controlled.
  • Often used for main distribution in large industrial plants where the breakers are placed in pulled-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 used at up to 35,000 V. Have vacuum circuit breakers tends to have a longer lifespan than reconditioning switches.

Residual current circuit breaker (residual current circuit breaker / residual current circuit breaker)

  • Phase (line) and neutral are both wires connected via RCD.
  • It trips the circuit when a ground fault current is present.
  • The amount of current flowing through the phase (line) should return through the neutral wire.
  • It recognizes by RCD. Any asymmetry between two currents flowing through the phase and neutral conductor is detected by -RCD and the circuit is triggered within 30 miliseconed.
  • If a house has a grounding system that is connected to a ground rod and not the main power cord, then all circuits must be protected by an RCD (because it is not possible to get enough residual current to trip an MCB)
  • RCDs are an extremely effective form of shock protection

The most common are 30 mA (milliamps) and 100 mA devices. A current flow of 30 mA (or 0.03 amps) is small enough that it is very difficult to receive a dangerous shock. Even 100 mA is a relatively small number compared to the current that can flow in an earth fault without such protection (one hundred amps).

A 300/500 mA FI circuit breaker may only be used if only fire protection is required. eg in lighting circuits where the risk of electric shock is low.

Limitation of the RCCB

  • Standard electromechanical RCCBs are designed to operate on normal supply waveforms and are not guaranteed to operate unless standard waveforms are generated by loads. Most common is the half-wave rectified waveform, sometimes referred to as pulsating DC voltage, which is generated by speed controllers, semiconductors, computers, and even dimmers.
  • Specially modified RCCBs are available that work with normal alternating current and pulsating direct current.
  • Residual current circuit breakers do not provide protection against current overloads : Residual current circuit breakers detect an imbalance in the live and neutral currents. A current overload, no matter how large, cannot be detected. Replacing an MCB in a fuse box with an RCD is a common cause of problems with newbies. This can be done in an attempt to increase shock protection. If a fault occurs in the de-energized state (short circuit or overload), the RCD does not trip and can be damaged. In practice, the main MCB for the building or the electrical ignition is likely to trip so the situation is unlikely to lead to disaster; but it can be inconvenient.
  • It is now possible to have an MCB and an RCD in a single unit called an RCBO (see below). Replacing an MCB with an RCBO with the same rating is generally safe.
  • Fault shutdown of the residual current circuit breaker: Sudden changes in the electrical load can cause a brief current flow to earth, especially in old devices. RCDs are very sensitive and work very quickly; they can be triggered if the engine of an old freezer cuts out. Some devices are notoriously "leaky", ie they generate a small, constant flow of electricity to earth. Some types of computer equipment and large televisions are widely reported to cause problems.
  • RCD does not protect against one not correct wired socket with its active and neutral terminals .
  • RCD does not protect against overheatingthat occurs when conductors are not properly screwed into their terminals.
  • RCD does not protect against live neutral shocksbecause the current is balanced in the live and neutral range. So if you touch active and neutral conductors at the same time (e.g. both terminals of a lamp), you can still get an unpleasant shock.

ELCB (earth fault circuit breaker)

  • Phase (line), neutral and earth cables connected by ELCB.
  • ELCB works based on earth leakage current.
  • Operating time of ELCB:
    • The safest current limit that the human body can withstand is 30 msec.
    • Suppose the human body resistance is 500 Ω and the voltage to earth is 230 volts.
    • The body current is 500/230 = 460mA.
    • Therefore the ELCB must be operated in 30 ms / 460 mA = 0.65 ms

RCBO (residual circuit breaker with overload)

  • It is possible to have a combined MCB and RCCB in one device (Residual Current Breaker with Overload RCBO), the principles are the same but more types of separation are put in one package

Difference between ELCB and RCCB

  • ELCB is the old name and often refers to voltage operated equipment that is no longer available and it is recommended that you replace it if you find one.
  • RCCB or RCD is the new name that indicates the current operation (hence the new name that differentiates from the voltage).
  • The new FI circuit breaker is best suited because it detects every earth fault. The voltage type only detects earth faults that flow back through the main conductor, which is why they are no longer used.
  • The easy way to spot an old voltage controlled trip is to look for the ground wire connected to it.
  • RCCB only has the line and neutral connections.
  • ELCB works based on earth leakage current. But the FI circuit breaker has no detection or connection to earth because the phase current is basically the same as the neutral current in a phase. Therefore, RCCB can trip if both currents are different and both currents are the same. Both the neutral and phase currents are different, that is, current flows through the earth.
  • After all, they both work for the same thing, but the thing is connectivity is the difference.
  • RCD does not necessarily require an earth connection itself (it only monitors the phase and neutral conductors). It also detects RCD currents in devices that do not have their own earth.
  • This means that a residual current circuit breaker will continue to provide protection against shock in devices with a faulty ground. It is these characteristics that have made the RCD more popular than its rivals. For example, about ten years ago, electronic leakage circuit breakers (ELCBs) were widely used. These devices measured the voltage on the earth conductor; If this voltage was not zero, it indicated a loss of current to earth. The problem is that ELCBs require a solid earth connection, as does the equipment that protects them. The use of ELCBs is therefore no longer recommended.

MCB selection

  • The first property is overload, which is designed to prevent accidental overloading of the cable in a healthy situation. The speed of the MCB trip varies with the degree of overload. This is usually achieved through the use of a thermal device in the MCB.
  • The second property is the magnetic fault protection, which is supposed to work when the fault reaches a predetermined level and triggers the MCB within a tenth of a second. The level of this magnetic tripping gives the MCB its type characteristics as follows:
    ArtTrip currentOperating time
    Type B3 to 5 times full load current0.04 to 13 sec
    Enter C.5 to 10 times full load current0.04 to 5 seconds
    Enter D.10 to 20 times full load current0.04 to 3 seconds
  • The third property is short circuit protection, which is designed to protect against serious faults that can occur in thousands of amps due to short circuit faults.
  • The MCB's ability to operate under these conditions gives its short circuit rating in kiloamps (KA). In general, a 6KA fault level is sufficient for consumers, while 10KA fault capabilities or above may be required for industrial boards.

Fuses and MCB properties

  • Fuses and MCBs are rated in amps. The amperage indicated on the fuse or MCB case is the amount of current that flows continuously. This is usually referred to as the rated current or rated current.
  • Many people think that if the current exceeds the rated current, the device trips immediately. So if the rating is 30 amps, a current of 30.00001 amps will trip it up, right? That is not true.
  • The fuse and the MCB, although their current ratings are similar, have very different properties.
  • For example, for 32Amp MCB and 30Amp Fuse, to be sure to trip in 0.1 seconds, the MCB needs a current of 128A while the fuse needs 300A.
  • The fuse clearly needs more current to blow during this time, but note how much larger these two currents are than the rated current marked "30 amps".
  • There is a small chance that a 30 amp fuse will blow in about a month if 30 amps are carried. If the backup has already been overloaded (which may not even have been noticed), it is much more likely. This explains why backups can sometimes "blow" for no apparent reason
  • If the fuse is labeled "30 amps" but can hold 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 characteristics of modern cables. For example, a modern PVC insulated cable will withstand 50% overload for an hour, so it seems reasonable that the fuse should too.

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