CU as isolator box

[Brightonguy]

Hi, I am to renovate a house and I am at the "design" stage. No builders have been contacted yet, until I lay down what I want.

The kitchen will have a cupboard with a full length door off it. It will contain the combi and electric consumer unit which will be at a convenient face level height and easy to see and use. I prefer a Wylex as they have a plastic cover you can see through. The kitchen is to have a fridge, integrated m/wave, oven. I intend to have separate mcb's for these appliances at the CU. These mcb's will also be isolators, precluding having ugly isolators next to the appliances. The appliance will be in large units and it will be difficult to get any in a decent location anyhow. The idea is to have nice and clean kitchen lines with only sockets on show. To isolate each appliance, all is needed is to flip the mcb in an adjacent cupboard which will be clearly labelled. I wondered if this it to full regs.

ta.

 

[Taylortwocities]

The big issue with your plan is that the MCB will only isolate the live conductor.
In these days of "all RCD protected circuits" you need to be able to isolate live and neutral in the event of a faulty appliance.

Better to provide proper isolation (eg DP grid switches) in a panel next to the consumer unit.


PS why are you concerned with having a see-through panel. A consumer unit is not something that you need to be looking at every day. Or are you expecting problems?

 

[PrenticeBoyofDerry]

I don't think your proposal is in breach of any regulations, although isolation of the standard single pole MCB, would only isolate the line conductor.
So if you have an earth leakage fault at the appliances or the circuit connected to them, and a number of breakers/circuits protected by the same RCD/RCBO, then with neutral still connected, you could have power loss to several circuits. Which is not a convenient situation.

 

[Taylortwocities]

Slow, too slow

 

[Brightonguy]

Two replies came in at exactly the same time. Thanks. The clear cover was to show where the isolation is.

I see your points. As there is no double pole isolation, if a neutral is to earth at the appliance the RCD will trip and a whole bank of circuits will be out. I suppose this is the problem when banking circuit on one RCD. The solution I suppose is have an RCBO for each circuit: oven, m/wave, fridge.

I don't see the point of having a bank of DP switches next to bank of CU switch, when an RCBO is neater and does the trick?

 

[bernardgreen]

Three points

A consumer unit in the same cupboard as a boiler may be subjected to higher than normal air temperature and this could affect the thermal trips makng them act faster than normal.

Using a RCBO as switch will put abnormal wear on the mechanism and contacts which may reduce it's reliability to act as an RCBO when needed.

Do you want leaks or a plumber / service technician spraying water from the boiler pipe work onto the CU ?

 

[Brightonguy]

Thanks. Firstly the combi and CU will be well enough apart. It is no different to the water maincock and CU in the cupboards under the stairs as most were at one time and there were few problems with that setup.

Isolation switches are rarely used and only for maintenance purposes in the vast majority of cases. These RCBOs will not be switched on and off regularly. Don't the makers recommend you test them every month or so anyhow?

The RCBOs will save expense as well as making matters neat in the kitchen.

 

[bernardgreen]

There is a difference between a cold water stop cock and a complex of pipe work to a complex boiler that gets hot and can need to be serviced or repaired.

 

[JohnW2]

I agree with most of what has been said, particularly in relation to the issue of a standard MCB only providing SP isolation.

What no-one has yet said is that, if one really wanted to do this, and had enough money and a big enough CU, one can get DP MCBs and RCBOs, even if they're not necessarily all that easy to find.

Kind Regards, John

 

[Brightonguy]

Thanks JohnW2. Yes the ultimate is DP RCBOs all through. I did see these in France and Germany in vertical CUs. Do they have superior regs than us? I have not seen them here at all, but I am sure they are available if you look. And probably not cheap either.

So you agree with having RCBOs for each appliance?

Bernard I agree that complex combi is different but there is enough room here and the modern boiler with lagged pipes do not give off that much heat. It is using common sense really.

 

[JohnW2]

Thanks JohnW2. Yes the ultimate is DP RCBOs all through. I did see these in France and Germany in vertical CUs. Do they have superior regs than us? I have not seen them here at all, but I am sure they are available if you look. And probably not cheap either. So you agree with having RCBOs for each appliance?

They are certainly avialable here, but neither all that easily found nor all that cheap. As you say, DP RCBOs for each appliance would be the ultimate, but using DP MCBs (with severalof them protected by one RCD)would not be any different from, or worse than, what most people have.

Kind Regards, John

 

[Iggifer]

I have an all RCBO board with SP+N RCBOs and, whilst the improvement over a split load MCB and RCD board is vast, I really can't see that it's worth going for DP RCBOs throughout.

Although I can see more of a benefit of having individual appliances on a 10mA RCBO vs a 30mA one

 

[JohnW2]

I have an all RCBO board with SP+N RCBOs and, whilst the improvement over a split load MCB and RCD board is vast, I really can't see that it's worth going for DP RCBOs throughout.

I'm sure that's right for most people. Unless one has a TT installation with an ('unavoidable') up-front RCD to protect long tails, having DP RCBOs is really of very limited value. However, if (per the OP) one wants to use RCBOs (or MCBs) to isolate individual appliances, then it's obviously desirable that they should be DP.

Although I can see more of a benefit of having individual appliances on a 10mA RCBO vs a 30mA one

On the face of it, I suppose that, in terms of protection against the consequences of electric shock, one can argue that the lower the trip threshold, the better. However, in practice, the majority of potentially lethal electric shocks are probably well over 30mA, and a 10mA RCBO/RCD is not going to limit the duration of that current any more than a 30mA one would. The actual benefit of using a 10mA one is therefore probably very small, and the price to be paid is presumably an increased risk of 'nuisance trips'. ... so, as with so manyvthings, it's a 'judgement call'.

Kind Regards, John

 

[JohnD]

A DP switch on the wall above or beside the appliance is perfectly suitable unless you have a dislike of switches.

IMO the idea of concealing switches is akin to putting bloomers on piano legs.

 

[DetlefSchmitz]

IMO the idea of concealing switches is akin to putting bloomers on piano legs.

+1