difference between a RCD and a MCB
RCD/MCB
- Thread starter plumber (new blood)
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rcd senses non equal current flow of the twp live conductors, any residual current from one live conductor must be passing to ground, possibly through a person, so to prevent death the supply is cut off before that current reaches 40mA. Hence the rcd's are set at 30mA and usually trip at 20mA in about 15ms or thereabouts. This will save your life.
mcb is just like a fuse. It is an overcurrent device. It detects too much current passing through both live conductors, even though it is equal. This would happen when the circuit is overloaded or there is a leakage to earth across both conductors. It will not cut off the supply until .4 seconds (usually but can also be 5 seconds) at it's rated current, but is more likely not to trip at all. It will not be as likely to save your life.
The benefit of a mcb is that it can be reset. cartridge fuses are as safe, rewireable fuses should have been banned by now.
mcb is just like a fuse. It is an overcurrent device. It detects too much current passing through both live conductors, even though it is equal. This would happen when the circuit is overloaded or there is a leakage to earth across both conductors. It will not cut off the supply until .4 seconds (usually but can also be 5 seconds) at it's rated current, but is more likely not to trip at all. It will not be as likely to save your life.
The benefit of a mcb is that it can be reset. cartridge fuses are as safe, rewireable fuses should have been banned by now.
RCD detects an imbalance between live and neutral and if it is greater than the set amount, eg 30milliamp or 100 milliamp it trips shutting off power to all circuits it controls. It assumes that the imbalance is caused by a leakage to earth. They are sometimes refered to as RCCD or earth leakage detectors.
The MCB trips if too much current is drawn in that circuit. A 6 amp one will trip if 7 amps is drawn to protect the cable from overheating and the appliance itsself.
They are much more sensitive than the older 'fuse wire' fuses as they could take up to 4 times their rating to blow.
To summarise RCD protects life and property, MCB protects cables and appliances.
The MCB trips if too much current is drawn in that circuit. A 6 amp one will trip if 7 amps is drawn to protect the cable from overheating and the appliance itsself.
They are much more sensitive than the older 'fuse wire' fuses as they could take up to 4 times their rating to blow.
To summarise RCD protects life and property, MCB protects cables and appliances.
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thanks for that lads, very informative! so in what situation would you fit a RCD not a MCB
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fit RCD's to any socket outlet(ring final or radial) where equipment that can be used out doors is to be connected.
Shower manufacturers now recommend fittindg RCD's
A S type RCD must be fitted to all TT installations.
RCD is almost like the main switch MCB is the seperate fuse, combine both and you get JohnD favourite items RCBO.
Shower manufacturers now recommend fittindg RCD's
A S type RCD must be fitted to all TT installations.
RCD is almost like the main switch MCB is the seperate fuse, combine both and you get JohnD favourite items RCBO.
come june next year you won't have to bathroom supplenmentary bond, but you must rcd protect all bathroom equipment. I am not sure yet if this includes equipment outside the zones. Zone 3 is probably going, and socket outlets 3m from zone 1 are probably inevitable (though stupid as someone might then think it is ok to sit in the bath and dry their hair).
There is no live and neutral, they are both live conductors one named phase the other named neutral.
There is no live and neutral, they are both live conductors one named phase the other named neutral.
You can't fit an rcd and not an mcb or fuse because you must have overcurrent protection. As already said an rcbo does both jobs, but costs £50. However there is about to become a huge increase in demand, due to new regs iminent, and that will raise production levels, hopefully to promote economies of scale passed on to us. I have found a local supplier of 5 and 5 split rail DB's that take a £10 rcbo. It looks like a fairly average din rail device that will probably fit Haeger and Square D. I don't know the make as I use square D at the moment, but local to us the firm who handles it is called Danby's.
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