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Cj24

Can someone please explain to me the difference between an mcb, rcd and an rcbo and in wat circumstances is each used, I knw an mcb is your circuit breaker and rcd is a circuit breaker but wat u wud use in say a wet area but y is it better then an mcb is it a better disconnection time and iv been told an rcbo is an mcb n rcd all in one but to me I thought an rcd was a mcb with better disconnection time sorry if confused u I just not had it explained properly to me n told y u wud use 1 over an other thanx
 
MCB: A miniature circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.

RDC: A residual-current device (RCD), similar to a Residual Current Circuit Breaker (RCCB), is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Such an imbalance is sometimes caused by current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit. A lethal shock can result from these conditions. RCDs are designed to disconnect quickly enough to mitigate the harm caused by such shocks

RCBO:
An RCBO (residual current breaker with overload protection) is a device that is a combination of both of the above.

Cheers!
 
RCD is residual current device A mechanical switching device intended to operate when the residual current attains a given value (this will be in mA milliamps)

MCB Mechanical operated circuit breaker this operates when current drawn is greater than the deigned level this will be in amps

RCBO residual operated circuit breaker with integral overcurrent protection A residual current operated device designed to perform the function of both overload and short circuit
 
An MCB is used to protect the cable from damage due to overload and short-circuit currents by disconnecting the supply within a certain time.

The time in which it disconnects the supply is dependent on the amount of current that is flowing.

This is why we have maximum Zs values, so that in the event of a fault to earth, enough current will flow to operate the MCB within the specified time. (0.4 seconds for circuits ≤ 32A and 5 seconds for circuits > 32A)

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An RCD is used as additional protection against electric shock by detecting earth leakage (imbalance between line & neutral) but it will not detect a short-circuit between line & neutral.

17th Edition currently requires the use of RCDs for
  1. socket outlets not exceeding 20A for use by ordinary persons except where the socket outlet is labelled for a particular item of equipment
  2. mobile equipment with a current rating not exceeding 32A for use outdoors
  3. all circuits installed in a Special Location
  4. cables concealed in walls < 50mm and not mechanically protected

An RCD will operate much faster and at much lower fault currents than an MCB and usually protects multiple circuits

1 x IΔn = 300mS
5 x IΔn = 40mS (≤ 30mA only)


IΔn = RCD operating current (e.g. 30mA)


RCDs are also used in TT installations where the Zs of circuits is too high for the MCBs to operate in the specified times.

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An RCBO combines the 2 above. If RCBOs are used there is no need for them to be protected by RCDs
 
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RDC: A residual-current device (RCD), similar to a Residual Current Circuit Breaker (RCCB)

Not quite. An RCCB is a TYPE of RCD, as is an RCBO, SRCD etc.

RCD is simply a generic term for a number of types of residual current device. It is not synonymous with an RCCB.
 
Thank u they are excellent, sorry if I sound stupid but u say mcb obv Protects the cable n overload n short circuit and u say an rcd does that aswell as earth leakage, wat exactly do u mean by earth leakage and earth leakage is that not something u pick up via testing so previously it wud have been an mcb
 
Thank u they are excellent, sorry if I sound stupid but u say mcb obv Protects the cable n overload n short circuit and u say an rcd does that aswell as earth leakage, wat exactly do u mean by earth leakage and earth leakage is that not something u pick up via testing so previously it wud have been an mcb

The only type of RCD with overcurrent protection are RCBOs. So an RCCB will not provide overload or short circuit protection - only protects against earth faults.
 
Thank u they are excellent, sorry if I sound stupid but u say mcb obv Protects the cable n overload n short circuit and u say an rcd does that aswell as earth leakage, wat exactly do u mean by earth leakage and earth leakage is that not something u pick up via testing so previously it wud have been an mcb

An RCD DOESN'T protect against overload or a line/neutral short-circuit.

It monitors the current flowing through the line & neutral conductors. If one of the conductors was "leaking" some current to earth, let's say through you touching something live then the line and neutral would be out of balance and the RCD would trip.
 
An RCD DOESN'T protect against overload or a line/neutral short-circuit.


Have I missed something???

*EDIT* Just seen your question in Jurasic Spark's quote.
Mcb's, rcd's and rcbo's {filename} | ElectriciansForums.net
Mcb's, rcd's and rcbo's {filename} | ElectriciansForums.net
Mcb's, rcd's and rcbo's {filename} | ElectriciansForums.net
 
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