Hi There

In direct reponse to your questions the answer is no, no, and no.

With regards power consumption, unless you have all the equipment on at the same time, and had it on full-heat, it is unlikely you will ever get up too the full rated capacity that you state.

I don't know that much about the loading/power requirements for under-floor-heating as I've never installed any. But 44-Amps sounds rather a lot, it must be a huge area to require that much power. Are you sure it takes that much power??

If you have two seperate cables entering the meter then you obviously have two seperate consumer units/fuse boards/or switch fuses. It is always best if you can have all your circuits supplied from one up-to-date consumer unit encorporating RCD-protection. But for reasons of cost and liability, people often take the easy route of adding seperate boards, which creates mess and more confusion for householders.

Also three cables is pushing it for the meter, it would be best to have these connected into a suitable 100Amp connector block, unless they already are (you might be confusing the incomming and outgoing live & neutral cables)

With regards the electricity supply cable, most are fused at 60-80Amps, some are fused at 100Amp. You can ask to have your fuse upgraded to 100Amp if it's 60 or 80 but it's unlikely you will ever actualy surpass this. In addition the electricity supplier cannot supply you with more than 100Amp for normal domestic supplies as this is the maximum power the cable can take.

To summerise, 80-100Amps should be more than enough for any normal sized house or flat. Don't worry too much about maximum ratings as it is unusual to draw this much power in practice.

Thanks so much for the advice! It's great to know that the NDO wouldn't increase the supply current.  I'd love to be able to give Mum some suggestions on how she can get around her shower problem.

Just to clarify the details of the system, the consumer unit in the flat is fed by two submains (each made up of twin and earth 10mm) which originate in the communal meter cabinet. One of these 10mm submains runs from the meter to a 60amp switchfuse located in the communal cabinet before running into the flat. The second 10mm submain goes directly to the flat without first passing through a switchfuse located in the communal cabinet. (Incidentally, because the length of this second submain is more than 3 m, I suspect that the absence of a switchfuse near the meter is a violation of code.) The first 10mm submain runs to a 12-way consumer unit in the flat that powers most of the household. The second submain runs to a smaller consumer unit that powers only the underfloor heating.

It also seems like you think that a third 10mm submain dedicated to the electric shower might not be the right/necessary solution.

The electric shower is definitely going to be installed: the flat is fairly big and the (already large) immersion heater can't cope with the demand for hot water. Mum is willing to have the whole set-up reworked so that she can have everything (electric shower, underfloor heating, and main supply) running off a single consumer unit. I hope you won't mind that I have a couple of follow-on questions:

(a) At the moment, each of the 10mm submains (sheathed twin and earth p.v.c.-insulated cables) is rated for a maximum of 63 amps each. Both of these two submains wouldn't fit into the main switch of a single consumer unit. Should these submains be replaced with a single 16mm cable which is rated for a maximum of 85 amps? Or isn't this necessary?

(b) If she keeps both submains, should she have her electrician install another 60 amp switchfuse at the meter cabinet for the submain that is currently unprotected by one? Also, is there any way to fit both 10mm submain feeds into a single consumer unit in the flat?

(c) Alternatively, if you advise to upgrade to a single 16mm submain, should she also upgrade to an 80 amp switchfuse in the meter cabinet?

Huge thanks for your patience and your very, very helpful advice!

Cam

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Im just gonna go for it and hope that I am not wrong in saying this piece of advise,

You can get dual tariff consumer units which have two separate isolators, here are links to some

http://www.moeller.co.uk/documents/xboard_consumer_units.pdf
http://www.memonline.com/mem2.html#4

You can take one sub-main to one isolator and the other sub-main to the other isolator. As long as each isolator is clearly marked where each one is being fed from, and each sub-main is clearly marked as to which isolator its feeding at the cu. I would also use RCBO's for the individual circuits too.

Having said this, you could install a new split load cu that complies with the 17th edition and have everything fed from there. Diversity plays an important role within an installation and so not everything will be used at the same time and neither will anything be used to its full operating current. There would then only be a need for one sub-main, where i would install an 80 fuse if your main fuse is 100a. I would then use a 16mm supply cable to the cu.

haha ok, for what part?

probs for the bits u added that i never did in the 1st place

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Usually, the flow of water is regulated through the shower and not the power consumed by the element, hence why the water pressure from the head usually drops when the shower is at its highest temperature.

Some units do, I believe incorporate two elements which may be 'stepped' but this isn't the case in most models.

Refer to the on-site guide for the diversity factors that must be applied.

Personally, I think your gonna be too close to the mark if the UFH is rated as you have described. I'd be looking at swapping out the existing dhw cylinder and installing a megaflow with additional immersion if required.

Paul

They do.

Amtech flow boilers have an add on module which breaks the low current trigger connection by means of a relay attached to the shower circuit.  I have done this once before, but connected it to a flow switch in the supply pipe to the shower (which is what I also use for shower fans fairly often too).

Amtech flow boilers are basically electric boilers to replace a gas or oil boiler in a normal wet system.  They are ideal for underfloor heating as the flow temperature is lower and the boilers are more able to 'keep up'.

It's "only" 10KW peak or so. That would be small for a gas boiler. Could be a big flat?

Yes electric heating in general is very expensive. Last time I looked daytime electricity was three times the cost of gas per KWH and even Economy 7 night time rates were similar to gas.