rcd protection on CU

[jimbobz]

so there is a single large rcd swirch on my cobnsumer unit. does this protect all the circuits from the consumer unit to the house?
so it would be pointless to use extra RCD protection say in the form of a circuit breaker on a socket?

 

[EFLImpudence]

so there is a single large rcd swirch on my cobnsumer unit. does this protect all the circuits from the consumer unit to the house?

If there is not a MAIN SWITCH as well, then yes.
If there is a main switch as well, then the RCD may only protect some of the circuits.
Switch off the RCD and see if anything still works.

so it would be pointless to use extra RCD protection

Yes, pointless.

say in the form of a circuit breaker on a socket?

It would be a Residual Current Circuit Breaker - not Miniature Circuit Breaker.

 

[AndyPRK]

so it would be pointless to use extra RCD protection say in the form of a circuit breaker on a socket?

Only pointless if the CU RCD states 30mA on it.

 

[EFLImpudence]

Good point.

 

[PrenticeBoyofDerry]

so there is a single large rcd swirch on my cobnsumer unit. does this protect all the circuits from the consumer unit to the house?

It could but it may not.
In some cases the board is split, where a number of circuits will be protected by the RCD and MCB and a number by MCB only.
If as mentioned by EFLImpudence, if you press the test button of the RCD whilst all circuits are on, this will give you a could guide of what circuits are protected if they power down.

so it would be pointless to use extra RCD protection say in the form of a circuit breaker on a socket?

Depending on rating and type, but more often than not yes.
If you unload photo of the unit with both cover on and off would be helpful, if your still not sure. When removing cover take circuits off load and isolate unit first.

 

[AndyPRK]

Is it really worth the risk and hassle of a DIYer removing the cover, when most people on here will be able to give an answer when shown a photo with the cover on ?

 

[ericmark]

There are two points.
1) What does RCD cover. This is easy to find out turn it off and see what does not work.
2) Type of RCD. There are basically two types of RCD.
a) One is used where the earth is not good enough without one or to disconnect in the case of fire and often have a delay and trip at around 100ma to 300ma and are not designed to protect personal.
b) The other type is 30ma or less and designed to protect personal.

It is common with a large system to gradually go down the size of RCD and normally we work on 1/3 rating for each stage. So for example garden supply at 10ma, then other sockets at 30ma, whole house at 100ma, and with factories next would be 300ma then 500ma then 1A and so on.

With two exceptions we don't feed a 30ma with a 30ma. The exception is caravans and boats where both park/marina output 30ma and caravan/boat is 30ma but other than that we always go down by approx 1/3 for each unit.

In the main we would not use a single 30ma RCD for a house. It's too likely to trip without real cause. At least 2 would be used if using 30ma. But with 100ma it was common to have one protecting whole house.

So likely answer is it's no it's not pointless using a RCD socket when one is also in the consumer unit if the one in the consumer unit is bigger than the one in the socket be that 10ma socket and 30ma consumer unit or a 30ma socket and a 100ma consumer unit. But it is pointless if both same size.