MCB, MCCB, ELCB, RCBO, RCCB: Explaining the different types of circuit breakers
RCBO (Residual Circuit Breaker with OverLoad):
● RCBO (Residual Current Circuit Breaker with Overcurrent protection) is a kind of comprehensive circuit breaker which can provide overcurrent protection and residual current protection. It is an important safety device in the field of household and industrial electricity, which can automatically cut off the circuit in case of current overload or ground fault to protect personal safety and electrical equipment.
● It is possible to combine MCB and RCCB in one device (Residual Circuit Breaker with Overload RCBO), the principle is the same, but more disconnection methods are installed in one package.
Learn more about the Principle of operation of RCBO
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 aranged 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
● lt 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 trp the circuit within 30Mliseconed
● 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 (mlliamp) and 100 mA devices. A current flow of 30 mA (or 0.03 amps) is suficienty small that it makes it very
dificut to receive a danoerous shock ven 100 mA s a relafivel sma foure when compared to the current that may fow in an earth taut witrout 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 rectfed 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 curent overloads: RCDs detect an imbalance in the live and neutral currents. A curent overload, however arge, 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 attemot to increase shock protection. fa live-neutral faul occurs a short circuit. or an overoad the CD won't trip. and may be damaoed. In practice, the main MCB for the premises wll 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 sinole 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 smal, brief current flow to earth, especialy in old appliances. RCDs are very sensitve and operate very quicky, they may wel trp when the motor of an old freezer switches of. Some equipmentis notorously "eaky , that is generate a smal. constant curent fow to earth. Some ivpes of comouter eouioment. and aroe television sets. are widelv 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 wi not protect adainst ive-neutra shocks because the current in the lve and neutral is balanced So if vou touch ive and neutra 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 5000 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
