This document explains the key differences between various types of circuit protection devices: - MCB (Miniature Circuit Breaker) is rated up to 100A and has non-adjustable thermal or magnetothermal operation. - MCCB (Molded Case Circuit Breaker) is rated up to 1000A and has adjustable trigger characteristics and thermal or magnetothermal operation. - Air and vacuum circuit breakers are for larger industrial systems, rated up to 10,000A and 3000A respectively, with fully adjustable settings. - RCD/RCCB (Residual Current Device/Circuit Breaker) detects imbalance between phase and neutral currents to quickly trip if current flows to ground. It provides

1. Difference Between MCB, MCCB, ELCB and RCCB
What is the Difference Between MCB,
MCCB, ELCB and RCCB
Explain the Difference Between MCB, MCCB, ELCB and RCCB and also explain in
details with Characteristics.
Difference
Between MCB, MCCB, ELCB and RCCB
MCB (Miniature Circuit Breaker)
Characteristics
• Rated current not exceeding 100 A.
• Travel characteristics normally not adjustable.
• Thermal or magnetothermal operation.
MCCB (molded case circuit breaker)
Characteristics
• Nominal current up to 1000 A.
• The trigger current can be adjustable.
• Thermal or magnetothermal operation.

2. Difference Between MCB and MCCB
Air circuit breaker
Characteristics
• Nominal current up to 10,000 A.
• Trigger characteristics are often fully adjustable, including configurable trigger points and
delays.
• Usually electronically controlled – some models are microprocessor controlled.
• Often used for main power distribution in large industrial installations, where circuit
breakers are placed in removable enclosures for ease of maintenance.
Vacuum circuit breaker
Characteristics
• With nominal current up to 3000 A,
• These circuit breakers interrupt the arc in a vacuum bottle.
• These can also be applied up to 35,000 V. Vacuum circuit breakers the service life
between overhauls is generally longer than that of air circuit breakers.
RCD (residual current device / RCCB (residual current circuit breaker))
Characteristics
• Phase (line) and neutral the two wires are connected via a differential.

3. • It trips the circuit when there is an earth fault current.
• The amount of current flowing through the phase (line) should return through the neutral.
• It detects by RCD. Any discrepancy between two currents flowing through phase and
neutral is detected by -RCD and trips the circuit within 30 minutes.
• If a house has a ground system connected to a ground rod and not the incoming main
cable, then all circuits must be GFCI protected (as they cannot have enough fault current
to trigger an MCB)
• RCDs are an extremely effective form of shock protection
The most widely used are 30mA (milliamps) and 100mA devices. A current of 30 mA (or
0.03 amps) is low enough to make it very difficult to receive a dangerous shock. Even
100 mA is a relatively small number compared to the current that can flow in a ground
fault without such protection (one hundred amps)
A 300/500 mA RCCB can be used when only fire protection is required. for example, on
lighting circuits, where the risk of electric shock is low.
RCCB limit
• The standard electromechanical RCCBs are designed to work with
normal waveform power and cannot be guaranteed to work if any standard waveforms
are generated by loads. The most common is the rectified half-wave waveform,
sometimes referred to as pulsed direct current, generated by speed control devices,
semiconductors, computers, and even dimmers.
• Specially modified RCDs are available for normal AC and pulsed DC operation.
• RCDs do not offer overcurrent protection: RCDs detect an imbalance in real life and
neutral currents. A current overload, however large, cannot be detected. Replacing an
MCB in a fuse box with a differential is often a cause of trouble with novices. This can be
done for the purpose of increasing impact protection. In the event of a fault in the neutral
under voltage (short circuit or overload), the RCD does not trip and may be damaged. In
practice, the main MCB of the premises is likely to trip or the service fuse, so the
situation is unlikely to result in a disaster; but it can be annoying.
• It is now possible to get an MCB and an RCD in one unit, called RCBO (see
below). Replacing an MCB with an RCBO of the same value is generally safe.
• Harmful RCCB Trip: Sudden changes in electrical load can cause a short, short current
to ground, especially in older devices. DDRs are very sensitive and operate very
quickly. They may be triggered when the motor of an old freezer goes out. It is well
known that some equipment has “leaks”, that is, it generates a small constant current to
the earth. Certain types of computer equipment and large televisions are generally
reported to be problematic.
• The RCD does not protect against plugging into an outlet with its live and neutral
terminals. Wrong trick.
• The RCD will not protect against overheating this occurs when the conductors are
not properly screwed into their terminals.
• The RCD will not protect against neutral shocks, because the current in the direct
and neutral is balanced. So, if you touch live conductors and neutral conductors at the
same time (for example, both terminals of a light fixture), you may still be in danger of
being shocked.

4. ELCB (Earth leakage circuit breaker)
Characteristics
• Phase, neutral and earth (line) wires connected via ELCB.
• ELCB operates on the basis of earth leakage current.
• ELCB operating time:
• The safest safety limit that the human body can withstand is 30 ma.
• Suppose the resistance of the human body is 500Ω, and the voltage to earth is 230
volts.
• The body current will be 500/230 = 460mA.
• Therefore, ELCB must be used in 30 maSec / 460mA = 0.65 ms
RCBO (residual circuit breaker with overload)
• It is possible to combine an MCB and an RCCB in a single device (residual current
circuit breaker with RCBO overload), the principles being the same, but several styles of
disconnection are integrated in the same box
Difference between ELCB and RCCB
• ELCB is the old name and often refers to powered devices that are no longer
available. It is advisable to replace them if you find one.
• RCCB or RCD is the new name that specifies current (hence, the new name to
distinguish it from voltage).
• The new RCCB is preferable because it will detect any earth fault. The voltage type only
detects earth faults that go up through the main earth wire, which is why they have
ceased to be used.
• The easiest way to detect an old energized trigger is to look for the main ground wire
connected across it.
• RCCB will only have line and neutral connections.
• ELCB operates on the basis of earth leakage current. But RCCB has no earth sensing
and connectivity, because basically phase current is equal to neutral current in single
phase. This is why RCCB can trigger when the two currents are deferent and they resist
until the two currents are identical. The neutral and phase currents are different, which
means that the current flows through the Earth.
• Finally, both work for the same thing, but connectivity is the difference.
• The RCD does not necessarily require a ground connection (it only monitors phases and
neutrals). In addition, it detects current currents to earth, even in ungrounded equipment.
• This means that an RCD will continue to give protection against shock in equipment with
defective ground. It is these properties that have made RCD more popular than its
competitors. For example, earth leakage circuit breakers (ELCBs) were widely used a
decade ago. These devices measured the voltage on the earth conductor; if this voltage
was not zero, it indicated a current leakage to earth. The problem is that ELCBs need a
good ground connection, just like the equipment they protect. Consequently, the use of
ELCBs is no longer recommended.
MCB selection
• The first feature is overload which is intended to prevent accidental overloading of the
cable in a fault-free situation. The MCB’s tripping speed will vary depending on the

5. degree of overload. This is usually achieved through the use of a thermal device in the
MCB.
• The second characteristic is the magnetic fault.This protection is intended to operate
when the fault reaches a predetermined level and to trigger the MCB in less than a tenth
of a second. The level of this magnetic trigger gives the MCB its type characteristics as
follows:
• The third feature is short circuit protection, which is designed to protect against large
faults, possibly thousands of amps, caused by short circuit faults.
• The ability of the MCB to operate under these conditions gives its short circuit rating in
kilo amps (KA). In general, for consumer units a fault level of 6KA is sufficient, while for
industrial boards a fault capacity of 10KA or more may be required.
Difference between ELCB and RCCB
Type Tripping current Operating time
Type B 3 to 5 times full load current
0.04 to 13 sec
Type c 5 to 10 times the current at full load 0.04 to 5 seconds
Type D 10 to 20 times full load current 0.04 to 3 seconds

6. Characteristics of the fuse and circuit breaker
• Fuses and circuit breakers are rated in amperes. The wattage in amperes indicated on
the fuse or circuit breaker body is the amount of current it will continuously pass
through. This is normally referred to as rated current or rated current.
• Many people think that if the current exceeds the rated current, the device will trip
instantly. So if the rating is 30 amps, a current of 30.00001 amps will trigger it,
right? This is not true.
• The fuse and the circuit breaker, although their rated currents are similar, have very
different properties.
• For example, for a 32 AMP fuse and a 30 A fuse, the MCB requires a current of 128
amps to be able to trip in 0.1 second, while the fuse requires 300 A.
• The fuse clearly needs more current to blow it in this time, but notice how both of those
currents are above the current rating marked “30 Amps”.
• There is a small probability that in the courseFor example, after a month a 30 amp fuse
will trip when it carries 30 amps. If the fuse has already been overloaded several times
(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 makes 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 withstand a 50% overload for one hour; so it seems reasonable that
the fuse is too.
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