Download What is the Difference Between MCB MCCB ELCB and RCCB PDF

TitleWhat is the Difference Between MCB MCCB ELCB and RCCB
TagsElectrical Wiring Building Engineering Electric Power Distribution Wire
File Size108.3 KB
Total Pages6
Table of Contents
                            What is the difference between MCB, MCCB, ELCB, and RCCB
	MCB (Miniature Circuit Breaker)
		Characteristics
	MCCB (Moulded Case Circuit Breaker)
		Characteristics
	Air Circuit Breaker
		Characteristics
	Vacuum Circuit Breaker
		Characteristics
	RCD (Residual Current Device / RCCB(Residual Current Circuit Breaker)
		Characteristics
		Limitation of RCCB
		ELCB (Earth Leakage Circuit Breaker)
			Characteristics
	RCBO (Residual Circuit Breaker with OverLoad)
		Difference between ELCB and RCCB
		MCB Selection
		Fuse and MCB characteristics
                        
Document Text Contents
Page 1

http://electrical-engineering-portal.com/what- is- the-difference-between-mcb-mccb-elcb-and- rccb February 7, 2013

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

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MCB (Miniature Circuit Breaker)

Characteristics

Rated current not more than 100 A.

Trip characterist ics normally not adjustable.

Thermal or thermal-magnet ic operat ion.

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MCCB (Moulded Case Circuit Breaker)

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Characteristics

Rated current up to 1000 A.

Trip current may be adjustable.

Thermal or thermal-magnet ic operat ion.

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Air Circuit Breaker

Characteristics

Rated current up to 10,000 A.

Trip characterist ics of ten fully adjustable including conf igurable t rip thresholds and delays.

Usually electronically controlled—some models are microprocessor controlled.

Often used for main power distribut ion in large industrial plant, where the breakers are
arranged in draw-out enclosures for ease of maintenance.

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Vacuum Circuit Breaker

Characteristics

With rated current up to 3000 A,

These breakers interrupt the arc in a vacuum bott le.

These can also be applied at up to 35,000 V. Vacuum circuit breakers tend to have
longer life expectancies between overhaul than do air circuit breakers.

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

Characteristics

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Phase (line) and Neutral

Limitation of RCCB

Standard electromechanical RCCBs are designed to operate on normal supply
waveforms

RCDs don’t offer protect ion against current overloads

Nuisance tripping of RCCB:

RCD will not protect against a socket out let being wired with its live and neutral
terminals

RCD will not protect against the overheat ing

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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 t ime (e.g.,
both terminals of a light f it t ing), you may st ill get a nasty shock.

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ELCB (Earth Leakage Circuit Breaker)

Characteristics

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

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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 disconnect ion are
f it ted into one package

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Dif ference between ELCB and RCCB

ELCB is the old name and of ten refers to voltage operated devices that are no longer
available and it is advised you replace them if you f ind one.

RCCB or RCD is the new name that specif ies current operated (hence the new name to

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dist inguish from voltage operated).

The new RCCB is best because it will detect any earth fault . The voltage type only
detects earth faults that f low 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 connect ions.

ELCB is working based on Earth leakage current. But RCCB is not having sensing or
connect ivity 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
dif ferent that means current is f lowing through the Earth.

Finally both are working for same, but the thing is connect ivity is dif ference.

RCD does not necessarily require an earth connect ion itself (it monitors only the live and
neutral).In addit ion it detects current f lows to earth even in equipment without an earth of
its own.

This means that an RCD will cont inue to give shock protect ion in equipment that has a
faulty earth. It is these propert ies 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 connect ion, as does the equipment it protects. As a result , the use of ELCBs is no
longer recommended.

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The f irst characterist ic is the overload which is intended to prevent the accidental
overloading of the cable in a no fault situat ion. 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 characterist ic is the magnet ic fault protect ion, which is intended to operate
when the fault reaches a predetermined level and to t rip the MCB within one tenth of a
second. The level of this magnet ic t rip gives the MCB its type characterist ic as follows:

Type Tripping Current Operat ing Time

3 To 5 t ime full load current 0.04 To 13 Sec

5 To 10 t imes full load current 0.04 To 5 Sec

10 To 20 t imes full load current 0.04 To 3 Sec

The third characterist ic is the short circuit protect ion, 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 condit ions gives its short circuit rat ing
in Kilo amps (KA). In general for consumer units a 6KA fault level is adequate whereas for

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