If you are not replacing the T and E submain, then it is not part of the rewire - actually it may be in part of the common part of the flats and not even the leasholder or tenant 's to maintain, so not even in your gift to change, at least without permission of the building owner / free holder. If so your paper work will need to reflect that.

You may be able to make some assumptions if the flat is small, that there will not be multiple users so the total load will not be as high as you think ;-)  There are things called 'priority switches' that can be used for example to cut the power to the Immersion or heaters  when the shower is on. Not that common but certainly possible, if the alternative is no shower.

Let us know what you find. and see what others on here say.

Mike

I would expect it to be OK if the customer does not demand the most powerful shower and induction hob.  Diversity is wonderful in most domestic situations.. Unless they are cooking three course lunches while someone takes long showers it is unlikely there will be an overload.I would recommend an off peak immersion with a boost function from the normal supply. I would also question if they have hot water from the immersion why they need an electric shower as well. If the storage heaters are properly sized there should be little additional heating load, they have improved considerably compared with the old ones that usually ran out of steam in the late afternoon just when most people wanted heating. But at the end of the day you are the one who knows the customer, their lifestyle and the size/condition/insulation/ventilation  of the flat. 

As Mike has said there are also load shedding/priority relays available and there was a recent thread about diversity regarding a situation similar to your's.

Hi guys thanks for the input

It's a 1 bedroom flat, bathroom, kitchen, lounge, a young couple living there.

The shower will be 8.5kw so around 35amps, induction hob 27amp cooker 13amp...(I know we can apply diversity here but still high)

Then there is water heater 3kw which is peak supply only atm, the off peak supply is just a 30amp 6mm supply and has 3 heaters on it, again we can't upgrade this supply.

My thoughts were new storage heaters on off peak only so keeping the load low on the main supply, and then maybe install the priority board between shower and cooker circuit (the cooker and hob on one circuit)

There are other appliances as in, dishwasher, washing machine, kettle etc

Thanks again guys 

For all the ban on coal, and the encouragement to have electric heat pumps instead of gas calorifiers, we have to be realistic. That includes not placing excessive demands upon the electrical installation. A 60 A long load would be rather expensive. Any chance of PV panels?

It has been a glorious day here in Hampshire and my neighbour's PV panels must have generated 60 kWh or so. Ground floor flat = not much chance, but top floor could be a goer.

It makes little difference which supply the immersion is on. Just fit a timer and they can set it to the off peak times anyway and boost it in the day if they want. 

Gary

It makes little difference which supply the immersion is on. Just fit a timer and they can set it to the off peak times anyway and boost it in the day if they want. 

Depends on the metering system - on "modern" systems (including E7) that have a single dual-rate meter yes that's true, but some older systems (e.g. E10 in my area) often had two separate meters and a timeswitch on the off-peak supply - so anything on the peak supply was charged at full rate whatever time it was used.  So might be worth double checking what's in the basement.

induction hob 27amp cooker 13amp...(I know we can apply diversity here but still high)

Is the "cooker" just a single oven (on a 13A plug) - if so check that rating, oven elements are often only 2kW - together with a 6.2kW hob that's less than 18A after diversity.

   - Andy.

Thanks Andy

Do you combine the hob and cooker before applying diversity then, or treat them individually. Obviously makes a big difference as individually we have first 10 Amps of each and the 30% of the remainder?

Thanks

Presuming that that hob and oven are separate appliances, it would in my view be reasonable to consider them as a single appliance when calculating diversity, the pattern of use, and likely demand should be similar.

Despite this, I still consider that the proposed loads are excessive on a 60 amp supply. I would connect the space heaters and water heater to a small dedicated consumer unit, supply this from a "shower priority control" Wired such that use of the shower disables the heaters, until after the shower.

There is still some risk of the shower and the cooker plus lighting and small appliances overloading the supply, but this is probably more theoretical than actual.

I think with maybe a 7.5kw shower, diversity on the cooker/hob as one, immersion on a overnight timer and storage heaters on off peak board then should be no need for a priority board.

Do you combine the hob and cooker before applying diversity then, or treat them individually.

I combined them. For the purpose of cooking it makes no difference overall if the hobs/grills/ovens etc are within a single box or separate boxes - if you had a separate circuit for each then certainly treat them individually for sizing each circuit, but for overall loading (or if they both shared the same circuit) then it makes sense to me to treat them together.

   - Andy.