Rcd / rccb - mcb

[Lee Gold]

However many tripping devices and breakers. I cannot, how ever many times I read what they are and how they work and what there differences are, I still don't get it. Can someone explain in short terms what is the difference between rcd/ RCCB, MCB and whatever else please, I seriously don't see why you can't just have RCD as a tripping switch, MCB as a minature circuit breaker? Why have so many different things? What is there purpose in short terms can someone please explain. Thanks

 

[Richard Burns]

RCD: general term for a device which trips on a current difference between live conductors: Residual Current Device
RCCB : Specific term for one of the devices described as an RCD: Residual Current Circuit Breaker.
RCBO : a device incorporating an RCD and an MCB: Residual Current circuit Breaker with Overcurrent protection.
MCB: a small circuit breaker designed to operate on overcurrent and short circuit current : Miniature Circuit Breaker
MCCB : a device, often adjustable, designed to operate on overcurrent and short circuit current can have larger current ratings than an MCB: Moulded Case Circuit Breaker

 

[Darkwood]

MCB - gives overload protection and short circuit
RCD - gives earth leakage protection
RCBO is a combination of the above two devices

Regulations will stipulate whether a circuit requires RCD protection and is not always required, An RCD can be found to cover multiple circuits so in the event of it tripping you may find you lose several circuit, if this is an issue you can have a circuit with its own independant rcd protection and this is usually achieved by using a device that is a combination of both mcb and rcd thus we have a RCBO.

Nearly all circuits will require overload and short circuit protection to ensure the cables are not damaged, don't overheat and/or create a fire or shock hazard - this is achieved with a correctly rated mcb.

Their are many more types and rating of overload protective devices with each been suitable to certain situations whether its is to achieve discrimination or to allow for the inrush of a high inertia load, some can be controlled with additional aux controls like some MCCB's which can be directly connected to say a E-stop circuit that will force a trip if any E-Stops are triggered.

For now its best to just concentrate on what you have been introduced to as part of your course work to keep things simpler.

 

[Lee Gold]

Cheers mate put in a simple way thanks

 

[Pete999]

However many tripping devices and breakers. I cannot, how ever many times I read what they are and how they work and what there differences are, I still don't get it. Can someone explain in short terms what is the difference between rcd/ RCCB, MCB and whatever else please, I seriously don't see why you can't just have RCD as a tripping switch, MCB as a minature circuit breaker? Why have so many different things? What is there purpose in short terms can someone please explain. Thanks

https://www.youtube.com/results?search_query=how+a+RCD+works
https://www.youtube.com/results?search_query=how+a+mcb+works

 

[Lee Gold]

Thanks Pete

 

[Pete999]

Thanks Pete

You are welcome, hope it helps.

 

[D00DY_T00DY]

There are 3 types of circuit faults;
Short circuit - A direct connection between any of the live conductors(L1,L2,L3 and Neutral)
Earth leakage - abnormal current on the earth conductor(Not sure if this is the best way to describe it)
Overload - too much current on an otherwise electrically sound circuit
Different Protective devices protect the circuit(And you) from one or more of these types of faults.

RCD(Residual Current Device) detects differences between the conductors and if for any reason the neutral comes back with less current then it should(Through the CPC) at a maximum of 30mA but a good RCD usually trips around 20mA a magnetic field within the device collapses operating(Tripping) the device. disconnecting the supply. This only protects against Earth leakage faults.

MCB(Miniature Circuit breaker) although now should be just called a Circuit Breaker(CB) technically. Works by either Thermally using two dissimilar metals(Called a bimetallic strip) where one expands at a different temperature from one another causing it to bend therefore tripping the device or magnetically protects against overload AND short circuits

On the left is the thermal and the right being magnetic
MCCB(Moulded Case Circuit Breaker) like an CB but can be adjusted and fine tuned. these protect against all three faults
RCBO(Residual Current Circuit Breaker) a combination of an RCD and a CB. Protecting against all three faults and are quite costly

Reiterated what's already been posted but I hope but a different perceptive on it and helped you to understand more
I'm not expert on this so if someone could correct me where ever i may have been wrong that'd be great :lol:

 

[Richard Burns]

I might say that earth leakage might be alternatively expressed as two classes of fault.
1) direct contact of a line conductor with earth, this is a full fault current fault and will be disconnected by an RCD and an MCB.
2) A person or object of reasonable resistance touching a line conductor whilst they are partially or fully connected to earth, this will be a low current fault and normally only disconnected by an RCD.

Note: that a person fully insulated from earth can touch a line conductor and a neutral conductor and nothing will disconnect but the current will still flow through the person.

RCDs measure the balance between line and neutral currents, that in a healthy circuit should be the same. If current is diverted elsewhere, say to another circuit or to earth (possibly via a person) then the two currents will not be the same, once the difference reaches 30mA the RCD will trip.
An RCD must not trip at half its rated current but must trip at its rated current.

MCBs or MCCBs can trip magnetically when there is a high current flow, this current flows to operate a solenoid effect and pull in the trip mechanism.