Electrical Designing. However, it looks like you listened to. SYLLABUS BACHELOR OF ELECTRICAL ENGINEERING. Examination Scheme Subject Title Theory. 01 Mathematics - I 3 - - 4 1. 02 Communication Skills 0 2 - - - 2 2. 03 Mechanics of solids 2 1 - 3 1. What is difference between the mcb. 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). Feb 16, 2017  The difference between MCB and RCCB. Miniature circuit breaker and Residual current circuit breaker. Miniature circuit breaker - Short Circuit and overload protection Device. Residual Current.

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. A residual-current device ( RCD), or residual-current circuit breaker ( RCCB), is a device that instantly breaks an electric circuit to prevent serious harm from an ongoing electric shock. Injury may still occur in some cases, for example if a human falls after receiving a shock. In the and, the device is more commonly known as a ground fault circuit interrupter ( GFCI), ground fault interrupter ( GFI) or an appliance leakage current interrupter ( ALCI). In the, these are better known by their initials RCD, and a combined RCD+MCB is known as a RCBO ( residual-current circuit breaker with overcurrent protection).

In, they are sometimes known as safety switches or an RCD. An (ELCB) may be a residual-current device, although an older type of voltage-operated earth leakage circuit breaker also exists.

These devices are designed to quickly and automatically disconnect a circuit when it detects that the is not balanced between the energized (line) conductor(s) and the return conductor. Under normal circumstances, these two wires are expected to carry matching currents, and any difference can indicate a or other electrical anomaly is present, such as leakage. Leakage can indicate a shock hazard (or shock in progress) which is a potential danger to a person. Current leakage can result in harm or death due to electric shock, especially if the leaking electric current passes through the torso of a human. A current of around 30 (0.030 amperes) is potentially sufficient to cause or serious harm if it persists for more than a small fraction of a second.

RCDs are designed to disconnect the conducting wires quickly enough to prevent serious injury from such shocks, commonly described as the RCD being 'tripped'. An RCD does not provide protection against unexpected or dangerously high current (called spikes or surges) when current is in the usual wires in the circuit, therefore it cannot replace a or protect against overheating or fire risk due to (overload) or if the fault does not lead to current leakage. Therefore, RCDs are often used or integrated as a single product along with some kind of, such as a fuse or miniature circuit breaker (MCB), which adds protection in the event of excessive current in the circuit (the resulting RCD with overcurrent protection called an RCBO). RCDs also cannot detect the situation where a human accidentally touches both conductors at the same time, since the current through an expected device, an unexpected route, or a human, are indistinguishable if the current returns through the expected conductor. RCDs are usually testable and resettable devices. Commonly they include a button that when pressed, safely creates a small leakage condition, and a switch that reconnects the conductors when a fault condition has been cleared. Depending upon their design, some RCDs disconnect both the energized and return conductors upon a fault, while others only disconnect the energized conductor and rely upon the return conductor being.

The former are commonly known as ' designs; the latter as ' designs. If the fault has left the return wire ' or not at its expected ground potential for any reason, then a single-pole RCD will leave this conductor still connected to the circuit when it detects the fault. Contents.

Purpose and operation RCDs are designed to disconnect the circuit if there is a leakage current. By detecting small leakage currents (typically 5–30 mA) and disconnecting quickly enough (.

Opened 3-phase residual-current device The diagram depicts the internal mechanism of a residual-current device (RCD). The device is designed to be wired in-line in an appliance power cord. It is rated to carry a maximal current of 13 A and is designed to trip on a leakage current of 30 mA. This is an active RCD; that is, it latches electrically and therefore trips on power failure, a useful feature for equipment that could be dangerous on unexpected re-energisation. Some early RCDs were entirely electromechanical and relied on finely balanced sprung over-centre mechanisms driven directly from the current transformer.

As these are hard to manufacture to the required accuracy and prone to drift in sensitivity both from pivot wear and lubricant dry-out, the electronically amplified type with a more robust solenoid part as illustrated are now dominant. The incoming supply and the neutral conductors are connected to the terminals at (1), and the outgoing load conductors are connected to the terminals at (2). The earth conductor (not shown) is connected through from supply to load uninterrupted. When the reset button (3) is pressed, the ((4) and another, hidden behind (5)) close, allowing current to pass. The (5) keeps the contacts closed when the reset button is released. The sense coil (6) is a which surrounds (but is not electrically connected to) the live and neutral conductors. In normal operation, all the current down the live conductor returns up the neutral conductor.

The currents in the two conductors are therefore equal and opposite and cancel each other out. Any fault to earth (for example caused by a person touching a live component in the attached appliance) causes some of the current to take a different return path, which means that there is an imbalance (difference) in the current in the two conductors (single-phase case), or, more generally, a nonzero sum of currents from among various conductors (for example, three phase conductors and one neutral conductor). This difference causes a current in the sense coil (6), which is picked up by the sense circuitry (7). The sense circuitry then removes power from the solenoid (5), and the contacts (4) are forced apart by a, cutting off the electricity supply to the appliance. The device is designed so that the current is interrupted in milliseconds, greatly reducing the chances of a dangerous being received. The test button (8) allows the correct operation of the device to be verified by passing a small current through the orange test wire (9).

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This simulates a fault by creating an imbalance in the sense coil. If the RCD does not trip when this button is pressed, then the device must be replaced.

RCD with additional overcurrent protection circuitry (RCBO or GFCI breaker) Residual-current and overcurrent protection may be combined in one device for installation into the service panel; this device is known as a GFCI (ground fault circuit interrupter) breaker in the USA and Canada, and as an RCBO (residual-current circuit breaker with overload protection) in Europe. In the US, GFCI breakers are more expensive than GFCI outlets. As well as requiring both line and neutral inputs and outputs (or, full 3-phase), many GFCI/RCBO devices require a functional earth (FE) connection. This serves to provide both EMC immunity and to reliably operate the device if the input-side neutral connection is lost but live and earth remain. For reasons of space, many devices, especially in DIN rail format, use flying leads rather than screw terminals, especially for the neutral input and FE connections. Additionally, because of the small form factor, the output cables of some models (Eaton/MEM) are used to form the primary winding of the RCD part, and the outgoing circuit cables must be led through a specially dimensioned terminal tunnel with the current transformer part around it.

This can lead to incorrect failed trip results when testing with meter probes from the screw heads of the terminals, rather than from the final circuit wiring. Having one RCD feeding another is generally unnecessary, provided they have been wired properly.

One exception is the case of a, where the may be high, meaning that a ground fault might not cause sufficient current to trip an ordinary circuit breaker or fuse. In this case a special 100 mA (or greater) trip current time-delayed RCD is installed, covering the whole installation, and then more sensitive RCDs should be installed downstream of it for sockets and other circuits that are considered high-risk. Typical US AFCI/GFCI RCD with additional arc fault protection circuitry In addition to Ground Fault Circuit Interrupters (GFCIs), devices (AFCI) are equally important as they offer added protection from potentially hazardous arc-faults resulting from damage in branch circuit wiring as well as extensions to branches such as appliances and cord sets. By detecting hazardous arc-faults and responding by interrupting power, AFCIs helps reduce the likelihood of the home's electrical system being an ignition source of a fire. Dual Function AFCI/GFCI devices offer both electrical fire prevention and shock prevention in one device making them a solution for many rooms in the home, especially when replacing an existing standard receptacle or existing ungrounded receptacle.

Common features and variations Differences in disconnection actions Major differences exist regarding the manner in which an RCD will act to disconnect the power to a circuit or appliance. Two differing nomenclatures are in use to identify what is essentially the main feature viz. Either 'Active' or 'Passive', and 'Latched' or 'non-Latching'.

All RCDs have a latching feature. The latch becomes set when the device is armed - typically by moving a switch to the on position, or depressing a reset button. Once armed, the device permits power to flow until some electrical event occurs that causes the latch to become un-set. That trigger is normally intended to be the detection of a serious electrical irregularity, but un-latching can also occur by the disconnection of the power; such power-disconnection is not regarded as an irregular event, and includes such events as a user disconnecting the power intentionally or unintentionally, or a temporary power failure attributed to the electricity service provider. 'Active' RCDs operate to un-latch themselves when any irregular power event occurs, and that includes any simple power-disconnection caused by any means whatsoever; no automatic re-connection operation follows the cessation of whatever caused the RCD to be triggered; the power to the circuit or appliance will remain disconnected until the RCD has been manually reset by the user.

'Passive' RCDs operate to un-latch themselves solely when the power irregularity appears to be a serious electrical fault. However, except where the power has been disconnected by the RCD un-latching itself (or by the user manually triggering the device), the RCD will remain latched throughout any period when the power is not connected, and remain latched and ready to continue usage in its armed mode as soon as the power supply is restored. RCDs installed as fixed devices within a consumer power distribution unit are almost always of the passive variety, so that household appliances such as refrigerators and freezers will return to their regular mode of operation as soon as the power supply resumes normal operation. RCDs of a portable type are mostly of the active variety, and all trigger events will cause them to un-latch the settings - specifically to avoid power resumption when the power supply previously disconnected by the RCD itself is restored.

This type of action is particularly desirable with appliances such as power tools and garden machinery that could become dangerous if they were re-activated without personal supervision. Such portable RCD types are generally active types of either a plug-top design intended to be hard-wired to an individual appliance, or as plug-in units to fit between an appliance plug and a wall-socket, or built into extension cables.

However, it is possible to obtain a few types of passive latched devices for permanent attachment directly to an appliance power cord, or for incorporation into the power line of selected appliances - sometimes embodied within a manually-wired plug top form such as the British rectangular blade variety. There is a presumption that a passive RCD will have been fitted both solely and directly to appropriate equipment. A further variety of fitting for an RCD is by incorporation within a wall-socket, where a choice of either active or passive fittings are available - on the presumption that the user will be aware of the nature of the appliances to be so connected and will restrict the usage of such wall sockets accordingly. Passive RCDs tend to be made in the 30 milliamp + 40 millisecond rating (and higher within a CPDU for special purposes). The active varieties are often available in lower trip ratings (as low as 10 ma), and more choice of those lower ratings may be available; their trip timing is often 30 milliseconds. (All currents expressed here are at 250 volts).

Lower ratings in RCDs are more prone to cause nuisance tripping for no necessarily obvious reason. Number of poles and pole terminology The number of poles represents the number of conductors that are interrupted when a fault condition occurs.

RCDs used on single-phase AC supplies (two current paths), such as domestic power, are usually one- or two-pole designs, also known as and. A single-pole RCD interrupts only the energized conductor, while a double-pole RCD interrupts both the energized and return conductors. (In a single-pole RCD, the return conductor is usually anticipated to be at at all times and therefore safe on its own, however see below). RCDs with three or more poles can be used on AC supplies (three current paths) or to disconnect an earth conductor as well, with four-pole RCDs used to interrupt three-phase + neutral supplies. Specially designed RCDs can also be used with both AC and DC power distribution systems. The following terms are sometimes used to describe the manner in which conductors are connected and disconnected by an RCD:.

Single-pole / SP / one-pole - the RCD will disconnect the energized wire only. Double-pole / DP / two-pole - the RCD will disconnect both the energized and return wires. 1+N and 1P+N – non-standard terms used in the context of RCBOs, at times used differently by different manufacturers. Typically these terms may signify that the return (neutral) conductor is an isolating pole only, without a protective element (an unprotected but switched neutral), or that the RCBO provides a conducting path and connectors for the return (neutral) conductor but this path remains uninterrupted when a fault occurs (sometimes known as 'solid neutral'), or that both conductors are disconnected for some faults (such as RCD detected leakage) but only one conductor is disconnected for other faults (such as overload). Sensitivity RCD sensitivity is expressed as the rated residual operating current, noted I Δn.

Preferred values have been defined by the IEC, thus making it possible to divide RCDs into three groups according to their I Δn value:. high sensitivity ( HS): 5. – 10 – 30 mA (for direct-contact / life injury protection),. medium sensitivity ( MS): 100 – 300 – 500 – 1000 mA (for fire protection),.

low sensitivity ( LS): 3 – 10 – 30 A (typically for protection of machine). The 5mA sensitivity is typical for GFCI outlets. Break time (response speed) There are two groups of devices.

G (general use) instantaneous RCDs have no intentional time delay. They must never trip at one-half of the nominal current rating, but must trip within 200 milliseconds for rated current, and within 40 milliseconds at five times rated current. S (selective) or T (time-delayed) RCDs have a short time delay. They are typically used at the origin of an installation for fire protection to discriminate with Gdevices at the loads, and in circuits containing surge suppressors. They must not trip at one-half of rated current.

They provide at least 130 milliseconds delay of tripping at rated current, 60 milliseconds at twice rated, and 50 milliseconds at five times rated. The maximum break time is 500 ms at rated current, 200 ms at twice rated, and 150 ms at five times rated. Programmable earth fault relays are available to allow co-ordinated installations to minimise outage. For example a power distribution system might have a 300mA, 300msec device at the service entry of a building, feeding several 100mA S type at each sub-board, and 30mA G type for each final circuit. In this way, a failure of a device to detect the fault will eventually be cleared by a higher-level device, at the cost of interrupting more circuits. Type, or mode (types of current leakage issue detected) IEC Standard 60755 ( General requirements for residual current operated protective devices) defines three types of RCD depending on the waveforms and frequency of the fault current.

Type AC RCDs trip on sinusoidal residual current. Type A RCDs also respond to pulsating or continuous direct current of either polarity. Type BRCDs also respond to higher frequency current, or for combinations of alternating and direct current as may be found from single-phase or multi-phase rectifying circuits. Surge current resistance The surge current refers to the peak current an RCD is designed to withstand using a test impulse of specified characteristics. The IEC 61008 and IEC 61009 standards require that RCDs withstand a 200 ampere 'ring wave' impulse. The standards also require RCDs classified as 'selective' to withstand a 3000 amp impulse surge current of specified waveform.

Testing of correct operation RCDs can be tested with built-in test button to confirm functionality on a regular basis. RCDs may not operate correctly if wired improperly, so they are generally tested by the installer to verify correct operation. Use of a from live to earth provides an external path and can test the wiring to the RCD. Such a test may be performed on installation of the device and at any 'downstream' outlet. Limitations A residual-current circuit breaker cannot remove all risk of electric shock or fire. In particular, an RCD alone will not detect overload conditions, phase-to-neutral short circuits or phase-to-phase short circuits (see ).

Over-current protection ( or ) must be provided. Circuit breakers that combine the functions of an RCD with overcurrent protection respond to both types of fault. These are known as RCBOs and are available in 2-, 3- and 4-pole configurations.

RCBOs will typically have separate circuits for detecting current imbalance and for overload current but use a common interrupting mechanism. An RCD helps to protect against electric shock when current flows through a person from a phase (live / line / hot) to earth. It cannot protect against electric shock when current flows through a person from phase to neutral or from phase to phase, for example where a finger touches both live and neutral contacts in a light fitting; a device cannot differentiate between current flow through an intended load from flow through a person, though the RCD may still trip if the person is in contact with the ground (earth), as some current may still pass through the persons finger and body to earth. Whole installations on a single RCD, common in older installations in the UK, are prone to 'nuisance' trips that can cause secondary safety problems with loss of lighting and defrosting of food. Frequently the trips are caused by deteriorating insulation on heater elements, such as water heaters and cooker elements or rings. Although regarded as a nuisance, the fault is with the deteriorated element and not the RCD: replacement of the offending element will resolve the problem, but replacing the RCD will not. In the case of RCDs that need a power supply, a dangerous condition can arise if the neutral wire is broken or switched off on the supply side of the RCD, while the corresponding live wire remains uninterrupted.

The tripping circuit needs power to work and does not trip when the power supply fails. Connected equipment will not work without a neutral, but the RCD cannot protect people from contact with the energized wire. For this reason circuit breakers must be installed in a way that ensures that the neutral wire cannot be switched off unless the live wire is also switched off at the same time. Where there is a requirement for switching off the neutral wire, two-pole breakers (or four-pole for 3-phase) must be used. To provide some protection with an interrupted neutral, some RCDs and RCBOs are equipped with an auxiliary connection wire that must be connected to the earth busbar of the distribution board. This either enables the device to detect the missing neutral of the supply, causing the device to trip, or provides an alternative supply path for the tripping circuitry, enabling it to continue to function normally in the absence of the supply neutral. Related to this, a single-pole RCD/RCBO interrupts the energized conductor only, while a double-pole device interrupts both the energized and return conductors.

Usually this is a standard and safe practice, since the return conductor is held at ground potential anyway. However, because of its design, a single-pole RCD will not isolate or disconnect all relevant wires in certain uncommon situations, for example where the return conductor is not being held, as expected, at ground potential, or where current leakage occurs between the return and earth conductors. In these cases, a double-pole RCD will offer protection, since the return conductor would also be disconnected.

History and nomenclature The world’s first high-sensitivity earth leakage protection system (i.e. A system capable of protecting people from the hazards of direct contact between a live conductor and earth), was a second-harmonic magnetic amplifier core-balance system, known as the magamp, developed in. Electrical hazards were of great concern in South African, and Rubin, an engineer at the company C.J.

Fuchs Electrical Industries of Alberton Johannesburg, initially developed a cold-cathode system in 1955 which operated at 525 V and had a tripping sensitivity of 250 mA. Prior to this, core balance earth leakage protection systems operated at sensitivities of about 10 A.

The cold cathode system was installed in a number of gold mines and worked reliably. However, Rubin began working on a completely novel system with greatly improved sensitivity, and by early 1956, he had produced a prototype second-harmonic magnetic amplifier-type core balance system (South African Patent No. 2268/56 and Australian Patent No.

The prototype magamp was rated at 220 V, 60 A and had an internally adjustable tripping sensitivity of 12.5–17.5 mA. Very rapid tripping times were achieved through a novel design, and this combined with the high sensitivity was well within the safe current-time envelope for ventricular fibrillation determined by of the, USA, who had estimated electrical shock hazards in humans. This system, with its associated circuit breaker, included overcurrent and short-circuit protection. In addition, the original prototype was able to trip at a lower sensitivity in the presence of an interrupted neutral, thus protecting against an important cause of electrical fire. Following the accidental electrocution of a woman in a domestic accident at the Stilfontein gold mining village near, a few hundred F.W.J.

20 mA magamp earth leakage protection units were installed in the homes of the mining village during 1957 and 1958. Electrical Industries, which later changed its name to FW Electrical Industries, continued to manufacture 20 mA single phase and three phase magamp units. At the time that he worked on the magamp, Rubin also considered using in this application, but concluded that the early transistors then available were too unreliable. However, with the advent of improved transistors, the company that he worked for and other companies later produced transistorized versions of earth leakage protection. In 1961, Dalziel, working with Rucker Manufacturing Co., developed a transistorized device for earth leakage protection which became known as a Ground Fault Circuit Interrupter (GFCI), sometimes colloquially shortened to Ground Fault Interrupter (GFI). This name for high-sensitivity earth leakage protection is still in common use in the U.S.A.

In the early 1970s most North American GFCI devices were of the circuit breaker type. GFCIs built into the outlet receptacle became commonplace beginning in the 1980s.

The circuit breaker type, installed into a, suffered from accidental trips mainly caused by poor or inconsistent insulation on the wiring. False trips were frequent when insulation problems were compounded by long circuit lengths. So much current leaked along the length of the conductors' insulation that the breaker might trip with the slightest increase of current imbalance. The migration to outlet receptacle based protection in North American installations reduced the accidental trips and provided obvious verification that wet areas were under -required protection. European installations continue to use primarily RCDs installed at the distribution board, which provides protection in case of damage to fixed wiring; In Europe socket-based RCDs are primarily used for retro-fitting. Regulation and adoption.

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What is an ELCB? An Earth Leakage Circuit Breaker was the first name given to what is now called a Ground Fault Circuit Interrupter (GFCI). The original type of ELCB or GFCI was designed only to detect a current flowing in the safety 'ground' or 'earth' wire. If there is no fault anywhere in a circuit supplying single-phase alternating power to a unit such as an electrical appliance, machine or other equipment, the current flowing to the unit at any instant in the 'hot' or 'live' wire should exactly match the current flowing away from the unit in the neutral wire. Similarly, there should be no current flowing in the unit's safety 'ground' or 'earth' wire. It is a basic fact of electrical engineering design that all current flowing to an electrical appliance, machine or other equipment from the power generation station via its supply circuit's 'hot' or 'live' wire should only return to the power station via that same circuit's 'neutral' wire. So, as a result of that basic fact, if any current is flowing in the ground wire, it must be caused by a fault condition and the supply of current to the circuit needs to be stopped urgently.

Many years ago, before today's electronic RCDs or GFCIs were designed, much simpler electro-mechanical relays called Earth Leakage Circuit Breakers (ELCBs) were invented so that, if any such ground current exceeding just a few milliamps was detected, they would 'trip' - meaning 'operate' - to break the current supply to the circuits for which they were installed to protect. The original type of ELCB or GFCI did not check for any difference in current flowing in the live and neutral wires, which is another indication of a very serious fault condition - even if no current can be detected flowing in the ground wire - because the 'missing current' may actually be flowing to ground via someone's body! When RCDs were invented, most manufacturers of GFCIs adopted the same technology because it offers so much more protection to users than the original GFCI could ever give.

In the US and Canada such devices are still commonly known as 'GFCIs' or 'GFIs' even though they have the additional 'residual current detector' functionality, whilst in Europe and elsewhere the more accurate name of 'Residual Current Detector' or RCD has been widely adopted for general use instead of using the name of the much simpler GFCI device. What is an MCB?

A Miniature Circuit Breaker. An MCB is a device designed to protect a circuit's wiring from the serious damage which would be caused if it has to carry a current which is too high for the diameter of its wires. Such a current could easily heat up the wires so much that their insulation melts.

If that situation were allowed to develop further it would soon cause the wires in a cable to short out and to burn so hot that they could easily cause a house fire. Before circuit breakers were invented, simple wire fuses were used: the wire in the fuses was deliberately made much thinner than the wires in the circuits they were intended to protect. Thus, if a fault condition occured, as the current in the circuit grew higher and higher, a point would be reached at which the thin wire of the fuse would get so hot that it would melt - all safely contained within the body of the fuse - and thus break the flow of current in the circuit it was protecting. The problem with fuses is that - depending on their design, as some are faster-acting than others - it can take a significantly longer amount of time for them to operate compared with today's very-fast-acting circuit breakers. That fact means that, if a circuit overload current fault condition occurs, considerable damage can still occur both to the circuit wiring and/or to the unit it is supplying with power. Then, after the fault condition has been fixed, the melted or 'blown' fuse wire in a rewireable type of fuse has to be replaced or - if it is a 'disposable cartridge' fuse - the blown fuse cartridge has to be thrown away and replaced by a new one. A circuit breaker, if it is still in good condition, only needs to be reset.

It is no joke to say if it is still in good condition.! One more fact needs to be mentioned: a significant design feature built into today's circuit breakers is their ability to 'self-destruct on a crowbar fault '. A 'crowbar fault' is a very serious overload condition, so bad that it would cause many thousands of amps to flow, just as if someone had thrown down a heavy metal crowbar tool onto power lines to connect both hot and neutral wires.

Such a fault condition can only be stopped by what is the ultimate fail-safe function of all modern circuit breakers: by using electro-magnetic technology similar to that of a simple relay, they are designed to self-destruct at least as fast as - if not faster than - the fastest acting fuses! In brief, wherever electrical equipment - and the wiring which supplies it - need to be protected from overload current fault conditions then: a) if the physical space available allows circuit breakers to be installed, and b) if the higher initial costs of deploying circuit breakers can be afforded then it is significantly better to deploy circuit breakers instead of fuses. For more information on all these topics see the answers to the Related Questions shown below. What is an ELCB?

An Earth Leakage Circuit Breaker was the first name given to what is now called a Ground Fault Circuit Interrupter (GFCI). The original type of ELCB or GFCI was designed only to detect a current flowing in the safety 'ground' or 'earth' wire. If there is no fault anywhere in a circuit supplying single-phase alternating power to a unit such as an electrical appliance, machine or other equipment, the current flowing to the unit at any instant in the 'hot' or 'live' wire should exactly match the current flowing away from the unit in the neutral wire. Similarly, there should be no current flowing in the unit's safety 'ground' or 'earth' wire. It is a basic fact of electrical engineering design that all current flowing to an electrical appliance, machine or other equipment from the power generation station via its supply circuit's 'hot' or 'live' wire should only return to the power station via that same circuit's 'neutral' wire.

So, as a result of that basic fact, if any current is flowing in the ground wire, it must be caused by a fault condition and the supply of current to the circuit needs to be stopped urgently. Many years ago, before today's electronic RCDs or GFCIs were designed, much simpler electro-mechanical relays called Earth Leakage Circuit Breakers (ELCBs) were invented so that, if any such ground current exceeding just a few milliamps was detected, they would 'trip' - meaning 'operate' - to break the current supply to the circuits for which they were installed to protect. The original type of ELCB or GFCI did not check for any difference in current flowing in the live and neutral wires, which is another indication of a very serious fault condition - even if no current can be detected flowing in the ground wire - because the 'missing current' may actually be flowing to ground via someone's body!

When RCDs were invented, most manufacturers of GFCIs adopted the same technology because it offers so much more protection to users than the original GFCI could ever give. In the US and Canada such devices are still commonly known as 'GFCIs' or 'GFIs' even though they have the additional 'residual current detector' functionality, whilst in Europe and elsewhere the more accurate name of 'Residual Current Detector' or RCD has been widely adopted for general use instead of using the name of the much simpler GFCI device.

What is an MCB? A Miniature Circuit Breaker. An MCB is a device designed to protect a circuit's wiring from the serious damage which would be caused if it has to carry a current which is too high for the diameter of its wires.

Such a current could easily heat up the wires so much that their insulation melts. If that situation were allowed to develop further it would soon cause the wires in a cable to short out and to burn so hot that they could easily cause a house fire. Before circuit breakers were invented, simple wire fuses were used: the wire in the fuses was deliberately made much thinner than the wires in the circuits they were intended to protect.

Thus, if a fault condition occured, as the current in the circuit grew higher and higher, a point would be reached at which the thin wire of the fuse would get so hot that it would melt - all safely contained within the body of the fuse - and thus break the flow of current in the circuit it was protecting. The problem with fuses is that - depending on their design, as some are faster-acting than others - it can take a significantly longer amount of time for them to operate compared with today's very-fast-acting circuit breakers. That fact means that, if a circuit overload current fault condition occurs, considerable damage can still occur both to the circuit wiring and/or to the unit it is supplying with power. Then, after the fault condition has been fixed, the melted or 'blown' fuse wire in a rewireable type of fuse has to be replaced or - if it is a 'disposable cartridge' fuse - the blown fuse cartridge has to be thrown away and replaced by a new one. A circuit breaker, if it is still in good condition, only needs to be reset. It is no joke to say if it is still in good condition.! One more fact needs to be mentioned: a significant design feature built into today's circuit breakers is their ability to 'self-destruct on a crowbar fault '.

A 'crowbar fault' is a very serious overload condition, so bad that it would cause many thousands of amps to flow, just as if someone had thrown down a heavy metal crowbar tool onto power lines to connect both hot and neutral wires. Such a fault condition can only be stopped by what is the ultimate fail-safe function of all modern circuit breakers: by using electro-magnetic technology similar to that of a simple relay, they are designed to self-destruct at least as fast as - if not faster than - the fastest acting fuses!

In brief, wherever electrical equipment - and the wiring which supplies it - need to be protected from overload current fault conditions then: a) if the physical space available allows circuit breakers to be installed, and b) if the higher initial costs of deploying circuit breakers can be afforded then it is significantly better to deploy circuit breakers instead of fuses. For more information on all these topics see the answers to the Related Questions shown below. MCB (Miniature Circuit Breaker)-rated current not more than 100 A.

Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation. Breakers illustrated ab ove are in this category.MCCB (Molded Case Circuit Breaker)-rated current up to 2500 A. Thermal or thermal-magnetic operation.

Trip current may be adjustable in larger ratings. MCB (Miniature Circuit Breaker)-rated current not more than 100 A.

Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation. Breakers illustrated above are in this category.MCCB (Molded Case Circuit Breaker)-rated current up to 2500 A. Thermal or thermal-magnetic operation. Trip current may be adjustable in larger ratings. From Manu anand.

Fuses and minature circuit breakers (MCBs) are both overcurrent protection devices, designed to disconnect a circuit in the event of an overload current or a short-circuit cur rent. Fuses use the heating effect of current in order to operate.

When an overcurrent occurs, the temperature of the fuse element causes it to melt, disconnecting the circuit. Its speed of operation is based on the inverse-time characteristic of the melting process -i.e. The higher the overcurrent, the faster it melts.

Miniature circuit breakers use the heating effect, together with the magnetic effect, of current to operate. Overload currents cause a bimetallic strip to bend, releasing the trip mechanism. Short-circuit currents cause an electromagnet to release the trip mechanism. The inverse-time characteristics of these two processes overlap. MCBs have the advantage that they do not have to be replaced, once the fault has been removed from the circuit, and can be reset to their closed position.

Fuses must be replaced. Fuses are also subject to abuse, as people sometimes replace 'blown' fuses with fuses of the wrong rating, or even replace them with strips of tinfoil or nails which completely removes any circuit protection. RCCB - Residual Current Circuit Breaker. Works by sensing the  current exiting the live and returning via the neutral wire.

If the  difference passes a threshold (marked on the device) the RCCB will  register a fault and trip.   ELCB - Earth Leakage Circuit Breaker. Works by sensing the current  in the earth wire. If the difference passes a threshold, the ELCB  will register a fault and trip.

   Although both just about do the same thing, all modern circuit  breakers are RCCB types. The ELCB will only trip if the current  leaks to Earth, meaning the electrical item must be earthed. That  also means the electrical item must be wired with a 3 prong plug.    An RCCB, current out must equal current back in, or that current is  leaking somewhere else (maybe through you.) and it is a fault.