Under what circumstances is a new consumer unit needed

As a part of our kitchen renovation we are having four additional double sockets installed - not because we anticipate increasing the number of appliances or load in any significant way, just to ensure that there will always be a spare outlet where it could be needed.
The first electrician to quote has said that we need an additional ring main because of the new sockets (he did not check to see how many existing sockets were on the existing ring main) and a new consumer unit.
As far as I am aware the limit on sockets is based on floor area (100sq m for the building?) and there is no other limit on the number of sockets although clearly common sense should prevail.
What concerns me more is the apparent need for a new consumer unit (and equipotential bonding?) - the existing is an elderly but visually sound metal 6 way Wylex fitted with mcb's with an added RCD for the ring main.
Grateful for any advice.
--
Robert

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The main equipotential bonding will need doing before the electrician can install any new sockets in the kitchen. You are allowed to DIY the bonding yourself, you do not need an electrician to do that.
If the electricain is suggesting that you need a new CU but not extra circuits then he is most probably after extra money. A CU swap is easy money. If he is concerned that the new sockets need their own MCB (with RCD protection of course) due to the loading of the circuits loading and there are no spare ways on your existing CU he may be telling some truth. A seperate CU alongside your existing one could also be added for a new circuit at considerably less cost than a CU swap.
How old is your wiring?
There comes a time when having a kitchen refurb may me a good excuse to rewire the kitchen instead of just adding extra sockets.
When my parents had a new kitchen last year and I did exactly that. Their house was built c1970 and I supplied the kitchen with its own circuit. You can make as much mess as you want as the tiles are already off the walls.
Adam
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Many thanks for the quick response.
Are we talking about the theoretical maximum loading of a circuit? Having done some searching I cannot find a regulatory maximum loading for a ring main with a 32A mcb.
The wiring is late 1970's or later but all appears to have been well installed in the first place and visually in good condition.
--
Robert

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robert wrote:

32A :-)
Owain
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... providing it's not concentrated near the ends of the ring.
--
Andrew Gabriel
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Indeed :) but there is nothing to indicate a maximum number of sockets so I cannot see how he could state that another circuit was necessary, particularly without checking to see what else was on the existing wiring, unless he was just trying it on.
--
Robert

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Likewise. My parents wiring is late 1950's, but PVC, and in perfect condition, although the Wilex CU was past its best, and no RCD protection. Replaced CU with a Memshield2 one with RCBO's on all the socket outlet circuits (except one, below).
When it came to wiring the kitchen, I stripped the kitchen, and put in two dedicated ring circuits; an RCD one for accessible sockets, and a non-RCD one for stationary/fixed items such as the fridge, freezer, oven, boiler (that would be more difficult with 17th Ed regs nowadays). Joined up the existing ring to bypass the kitchen. Then discovered their extension must have been spurred off the now disconnected bit of the old ring in the kitchen, so brought that back as a separate radial to the CU.
They went from having one ring, to having 3 rings and one radial for their sockets!
--
Andrew Gabriel
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I have got around the 17th Ed RCD rules a few times when installing new cooker circuits by using armoured cable on a few occassions.
It worked out cheaper for the customer to do it that way.
The other options were (probably others not listed)
Fitting a new CU with an RCD (and all the tests that are needed when you change a CU). Fitting an RCD unit along side the existing CU (cost of Henley Blocks and RCD unit) Fitting an RCBO.(The RCBO cost more than the armoured cable and glands)
Adam
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ARWadsworth wrote:

Have you tried one of these earthshield type cables yet?
--
Cheers,

John.

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If you mean the BS8436 stuff then no, I have not tried it.
Adam
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ARWadsworth coughed up some electrons that declared:

I looked into those (Earthshield, flexishield, XL-Shield etc). IIRC, they have some constraints, such as Prospective fault current being <6kA (or might have been 5kA) and use of Type B breakers and limits on the maximum circuit rating (I don't think they can manage a 40A circuit). I think it was to do with ensuring that a fault to the foil screen would knock out the breaker before blowing a hold in itself. They're not cheap either.
Although FP200 has a similar construction and is ubiquitous, it doesn't hold a BS8436 rating (pity).
OTOH, seemed a neat solution for lighting in particular where there may be many drops.
Cheers
Tim
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The prices are vertical not steep.
You do know that the low smoke and fumes are just there to help pikeys burn cable
Adam
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robert wrote:

Its a ring circuit, not a ring main. You're not increasing loading significantly, you've got an rcd, so there's no need for a new CU, unless its physically broken.
There are 2 things known as equipotential bonding. Main services bonding should ideally be done if its missing, but the risk of it being missing is more or less zero, people arent dying that way, and it doesnt start fires.
So now you know what your sparky is trying, and no doubt will try again. Why not fit the sockets yourself, by the time you've find someone whos not out to con you you could have done it long ago, and for all of 10. One reason we like diy!
NT
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In message
snipped-for-privacy@care2.com writes

The RCD is fine - it has activated a couple of times since fitted and tests OK.
The sparky in question is now out of the running - we have 2 more due to quote for the job (I would have done it myself but for Part P).
--
Robert

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robert wrote:

Some local authorities have yet to have even their first application from a diyer to comply with part pee.
NT
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snipped-for-privacy@care2.com coughed up some electrons that declared:

Mine got confused. We settled on I'll do a 4 day course and they'll accept my EIC without whining.
Then the subject of gas came up - poor bloke...
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robert wrote:

What appliances do you currently have?

Which tells you either he was running on autopilot, or perhaps it was obvious from the kitchen appliances that it was already close or over design load.

That is correct.

Indeed. Kitchens are often wired with their own socket circuit these days since they tend to have a number of high current, long duration loads concentrated in them (washer, drier, dishwasher, oven etc)

If the main EQ bonding is not to current standards, then fixing that will usually be a prerequisite before an electrician can tackle most jobs.
As to why he suggested a CU change, it would wither be a case of making extra money, or there was a valid reason. These include:
http://wiki.diyfaq.org.uk/index.php?title=Changing_a_consumer_unit#Reasons_for_a_change
(the most likely being the need for an extra circuit, and there being no free ways in the present one)
--
Cheers,

John.

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A dishwasher and fridge freezer (+kettle, toaster and radio) on the ring circuit plus a 13A maximum load oven on a cooker circuit.
The same ring serves the rest of the bungalow which has the usual range of low load items.

What does this involve - I imagine that it is a link to the copper water piping and perhaps the gas piping? The gas piping is adjacent to the CU but the nearest copper water pipe is a few metres away.

Many thanks for the link to the wiki - of the indicated reasons for change 2 - 7 do not apply in this case, leaving the possible question of 1.
--
Robert

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In the kitchen a dishwasher, fridge freezer and microwave (+kettle, toaster and radio) [1] and on a separate 'cooker' circuit a 13A maximum load oven.
[1] The same ring circuit serves the rest of the bungalow which has the usual range of low load items except for the washing machine that is on a separate circuit

What does this entail - I imagine that it is a link to the water and gas piping? The gas piping is adjacent to the CU but the nearest copper water pipe is 6 metres away.

Many thanks for the link to the wiki - reasons 2 - 6 do not appear to apply in this case which leaves the possible need for the additional circuit?
--
Robert

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robert wrote:

It may be the chap assumed the washing machine was on the same circuit. Combined with the dishwasher that is a reasonable lump of the circuit capacity gone.

Yup, a link in the correct wire to the correct style of pipe clamp:
http://wiki.diyfaq.org.uk/index.php?title rthing_and_Bonding#Main_Bonding

Perhaps...
Given the way the place is currently wired, separating out the kitchen would probably be an easy way of partitioning the circuits.
--
Cheers,

John.

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