consumer unit rcb

29 Jan 2008
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United Kingdom
I have recently moved into a new house and the electrics were periodic checked beforehand and everything was ok. Just wondered if someone could explain a bit about the switches on the consumer unit. I am aware of the circuits on MCB which are labelled.

My questions are:

1.) Judging by the pic are all circuits protected by RCB? am I right in thinking that the MCB on left are protected by the left RCB and those on the right have another?

2.) If an fault was to trip a circuit, would the RCD trip, or would the MCB trip or both?

3.) On the very far right of the unit there is a double switch. Is this the main electricity isolator?

4.) the MCB next to the double switch - is this the main electricity fuse?

Just curious thats all

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1) Yes - it's poor practice to have all lights / all sockets on the same RCD. You have lights on one, sockets on the other. A better arrangement would be lights up / sockets down + lights down / sockets up split between the two RCD's so when you loose one RCD, you still have means of lighting (table lamps etc)
2) It depends on the fault. An MCB protects against overcurrent (i.e. a short circuit) and an RCD protects against earth leakage (i.e. a faulty piece of equipment, water ingress etc)
3) This isolates the power to all of your circuits, there will still be live cables inside though
4) No, this is one of your circuits, I can't see from the picture what size MCB it is, it might be the one that should belong in that gap (you really should get a spare blank to cover that hole)
You have two RCCB, one protects
Lights up, down and door bell. Ideally lights should have been shared between RCCBs.
Then the second cooker, sockets and immersion
The spare should be blanked!
The you have one remaining circuit only protected by the MCB.

If you have an earth leakage fault on any circuit covered by these RCCBs that RCCB will trip, it's likely the MCB for the circuit will not.
If you have an overload or faulty current on a circuit, the MCB should trip, but the RCCB could also trip at the same time.
I'm not 100% sure but does the sticker under the righthand breaker say Circuits not protected by RCCB?
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Theres a missing blank cover on the right hand side this needs sorting ASAP as there are live parts accessable if little fingers go poking around.
Looks like there is a non RCD protected circuit on the MCB right next to the main isolator switch im guessing it could be a supply to a garage, outbuilding or smoke detector circuit.
The circuits are split between two RCDs to minimise danger in the event of a "trip"
An MCB will trip when an overcurrent or short circuit occurs prime example is when a bulb blows on switch on the MCB for the lighting circuit will trip off.
An RCD is an essential potenialy life saving device it looks and whats going out in the live and returning in the neutral in a healthy circuit the current will be the same but when a fault to earth occurs an imbalance occurs which trips the device in milliseconds.
The RCD must be tested every 3 months by pressing the T test button the device should switch off.
im not at home at the moment but i think the one at the end says not protected.

where can i get blank plates from B&Q?
Having said that, MCG seems to be a CEF brand (don't use them but the MCG website says they are)

If you have a cef close to you, just pop in and ask them for an MCB blank for an MCG consumer unit. Will be a better fit
I am not sure what the non RCD protected circuit is, but am interested to know what! As someone suggested it could well be the mcb that is removed which is labelled sockets.

Im guessing the only way is to turn it off and see what stops working?

I have no mains powered smoke alarms or house alarm. A new boiler was wired into the loft a couple of years ago with new earth etc which I guess could possibly be it.

Is a boiler acceptable not to be on RCD - what is the point of not being on the RCD when there is one there already?

thanks for all the replies!
Boiler can be non RCD protected. But the cable would need to be mechanically protected, a depth of 50mm (or more) within walls or surface mounted and the the connection would ideally be by fused connection unit and not a 13A socket outlet!
But I guess the old immersion neating circuit would be used for boiler.
Do you have a garage, what size rating is this MCB
You would normally non-RCD something critical, such as a fridge/freezer / smokes / alarms so that if the RCD trips in the night you do not loose the functionality of this critical system (because an RCD protects more than one circuit the possibility of it tripping and taking all of it's circuits is increased)

It could be the boiler, not sure why this would be installed as non-rcd protected though, you would cope without the boiler until you noticed you had no socket outlets (freezer not so much)

It is acceptable to be on a non RCD socket, with a few provisos (the cable is buried deeper than 50mm or protected by an earthed steel conduit (or is armoured cable)

Best thing to do is turn it off and see what stops working, if it is the boiler, be prepared to reset your CH controls

**dang too slow**
the boiler is connected to a permanent fused switch which situated next to it in the loft. the only wiring I see that goes up there is the earth but that's bonding as its attached to copper.

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