My house is about 30 years old and has a six way + cooker consumer unit with wired fuses. What would be an approximate cost to have this replaced with a modern MCB unit. I realise that this is not a DIY job.
The lighting circuit is split - upstairs & downstairs, but the power circuit is single, with a 30A fuse. I am worried in case I overload the power circuit as I have added many extra sockets into the ring main. If I have a new consumer unit installed, would it be possible to split the power circuit into separate upstairs/downstairs circuits?
What reasons do you have for wanting to change it?
This is a question that comes up from time to time, and often there is a assumption that a modern CU with MCBs is automatically "better". The reality is often a bit more complex, as there are pros and cons to changing.
At 30 years old there is a reasonable chance that there is not much drastically wrong with your installation apart from a lack of outlets to deal with modern usage patterns, and it sounds as if you have addressed that already. You are unlikely to have rubber insulated cables in place etc.
The ones to check would be the size of the earth wire in your power circuit cables, since at one time only 1mm^2 wire was used for this, and this does not really perform well enough with rewireable fuses. Also look to see what RCD protection you have, since having this for most power circuits can offer significant safety enhancements, and protection of sockets that you use to power appliances outside is vital. Having said that, see the mitigating nuisance trips and system design sections here:
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I realise that this is not a DIY job.
What makes you say that?
You will find plenty of folks here who have DIYed this job.
It would... although you may find that a split of kitchen and rest of house makes more sense, or even three circuits. Kitchens typically have the largest concentrations of high current loads in a modern house. Unless you routinely use fan heaters and the like the chances are the rest of your loads are relatively small.
Agree here. I would carefully check a CU of that age for signs of overheating due to deteriorating contacts, and retighten the connections. Beware that unless you isolate the supply elsewhere, there will be exposed live conductors inside a unit of that age, and besides the obvious electric shock risk, there's a risk of high energy arc flash burns if you end up shorting out the supply.
Yes, we were in exactly the same position so I did as John described. I left the ring main completely alone but added extra circuits for the kitchen appliances and utility room (where our washing machine and dryer are located). More often than not, the load on the main ring main will be a fraction of what it was designed for once you have done this. I think the only thing plugged into our ring main now is about four hundred chargers!
On Sun, 02 Dec 2007 02:53:39 GMT someone who may be "Terry D" wrote this:-
Personally I would consider replacing the wire fuses with HBC fuses or MCBs. Before doing so I would make the appropriate calculations and see what is available for the model of consumer unit before deciding on the replacement. Replacing the wire fuses is a DIY job, though some DIYers would be unable to make the appropriate measurements and calculations.
I would only consider replacing a consumer unit of that age if it was deteriorating or more ways were wanted.
Unless you are plugging high current appliances into those sockets this is unlikely. However, as others have suggested, a separate circuit for the kitchen and any utility area would be worth considering, to separate washing machines, dishwashers and so on.
A new consumer unit would not help that much, apart from perhaps making available extra circuits and the extra convenience of MCB's - your big problem then is how to make use of them.
If the ring was wired as a single ring to cover the entire house, then it will likely prove to be almost impossible to split up into two or more ring circuits. The best/cheapest/quickest solution will probably be to start again and install new circuits.
You can't overload a ring by adding extra outlets, you only overload by using them.
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