Suppplies to local hot water stores.

It's the small undersink storage type I have in mind. I think they're all 2.4 - 3 kW, as a type. But there would be 8 of them which is around 100 Amps. Building is to be rewired but would this alone be an expensive problem (extra)? 3 phase likely requirement?
Alternative is lots of plumbing, which I charge a lot for!

are they all in the same "room?"

the reason i ask is if they are, it may be cheaper to have one "big one" (i know you mentioned 8 but it depends on if all 8 are in the same room)

or if in different " rooms" let the electrcian worry about it.

If it is a big building it may already be having a 3 phase supply.

each heater should be on its own mcb.

NO it's a big Victorian place which has 8 bedsits in it. Each currently has CW only. I'm the plumber. I have to organise HW to each bedsit (sink only) somehow - there are many options. Am looking for insight from pro sparky on what issues there may be for the suggested solution of locally heated water.

The place does not currently have 3 - phase supply..

Hiya,

There are several issues here (I am a pro by the way). Can't be too detailed in my response because there is more to it than the info we currently have. I know this goes beyond the scope of your question, but it opens up other issues.

If my memory is correct (don't have access to my regs book at the mo), any water storage heater with less than 15 litre capacity could be fed from a ring circuit within the regulations, any higher capacity must have independant circuits. A 2.4 or 3Kw instantaneous undersink heater could be fed from a ring. However, you could not really have more than one on each ring circuit, and to be honest it's by far the best practice for them to be on dedicated circuits. I can clarify this if needs be once I get my regs book back.

If there are shared bathrooms, why not have two immersion tanks - one to feed the shared bathroom, one to feed the bedsit sinks.

I'd have to recommend that the issue of electrical capacity is looked at in more depth - a sparks needs to do a site survey. Eight bedsits from a 100A single phase supply seems a bit optimistic to me. Let's think of the numbers - eight undersink heaters, at least one communal immersion heater (?), eight kettles, maybe eight toasters, washing mashine(s), maybe electric showers etc etc. Are tenants going to have electric cookers or hotplates? Much more load.

If the tenants are sharing one communal kitchen and a couple of bathrooms, it may just cope on a 100A supply, I certainly wouldn't commit to it without a site survey, nor based on the info we currently have.

Another issue is whether there are going to be independant electrics for each bedsit - Ie will each one have it's own consumer unit/wiring and it's own private (or supply authority) meter? Also does each bedsit have a kitchinette?

I suggest you get the landlord to get a full survey done, I would think that you'd need at least a two phase, or probably a three phase supply into the building.

This is my first thoughts based on the info given. Pass the buck and ask the landlord to clarify the electrical arrangements. Sorry to be vague but there are a lot of variables that could affect this.

Cheers

paul

Thanks Paul
Thanks for that
Flagging issues is all I'm after - I'm not trying to design the electrics! The owner of this little lot is wonderfully dotty but does have the resources. (When it's all finished (refurbed) the building is going to be given away to a trust.) Issues like washing machines and cookery haven't been thought through at all

The reason for considering local hw storage is that to pipe new supplies from a central store (which wouldn't otherwise be necessary) they'd have to be on a "circular" loop of pipe (called a secondary return) covering the 3 floors which would need a timed pump, and insulation a plenty. Or trace heating on each long radial pipe to avoid time lags and water wastage.

The heating will be a tad unusual - something like 9 zones all separately time/temperature controlled. (Probably provided by 2 combis)

Good point about other "kitchinette" usage - there's bound to be some of what you mention.

I gather from what you say that 100A is the max per phase? There are several old meters at the mo (didn't count!) I'm sure each occupancy will have to have its own rcd or there will be hystrionics. (All musicians). From what I have read on diversity , 2 cooking things + 2 kettles would be about the limit for a ring so its probably 1 CU per bedsit anyway ... er um so HW stores would "merely" add another phase..

OK so the question then - is it a big deal to install an extra phase? London Electricity job in this case. Will look into it just to get an idea of whether it's prohibitively expensive (any idea for your area?). Otherwise it's major plummin - £5-6k+ at a guess. The heaters themselves (ie electric route) look like costing £2.5k or so with vented taps.

I also need to find out how many washing machines/dryers would be needed for 8 bedsits say 12 people. Owner thought there would be a launderette somewhere...

Chris,

I'm not sure what it would cost to upgrade the supply - used to come accross it now and again, but can't remember what the local supplier charged.

It's usually cheaper in a town where there is often a 3 -phase supply wire in the street - just a case of digging a shart trench into the house. I think I can remember one that cost just under a grand, but that was a long time ago (pre-privatisation!!)

My uncle had a barn in the country fed by overhead wires and was quoted about 3Kto upgrade the supply - the engineer will quote based on the amount of work, I doubt they have a fixed price structure.

You can have more than 100A per phase in a 3-phase install (though you probably wouldn't need more than 3 x 100A, but never seen more than a 100A single-phase supply. The middle ground is a two-phase supply, which would give 200A.

Before they quote for a supply upgrade, they will want to understand the usage and layout of the building, and have the answers to the sort of issues above (or they may just quote you for a 3-phase supply anyway - they are probably on commision!!).

If you come accross any more info on the issues I raised, I'll be pleased to offer any more advice that I can.

Take care

Paul

100A single phase is not likely to be enough for 8 bedsits period
there are 2 ways of handling electricity in a setup like this afaict

1: seperate supplies ie all flats have thier own meter installed by the borad (and you have one for comunal areas)
2: 1 big syste you have one big meter from the electricity board and split it yourself possiblly with meters

Save money by digging the trench yourself, if this is an option. The EB's charge through the snozz for this.

The easiest and the cheapest solution would be to have a second 100A supply installed by the EB.

You do not need a 3 phase supply.

This second 100A supply could be used to power all the water heaters and the communal lighting.

I would suggest that this board be of good quality and that all water heaters are protected by RCBO's. Do not be tempted to have an RCD main switch if the board contains the communal lighting as you will lose this if the main RCD trips. Before someone says it, yes I am aware that there will be and must be emergency lighting in the property.

Not all the water heaters will be on at any one time so the loading is not an issue.

The existing 100A supply would then be free to supply all power and lighting to the 8 bedsits in the building. That will be more than enough.


This is quite a common situation in London, many of our Landlord Maintenance contracts are in such properties, and they work fine if quality kit is used and kept locked away from nosy fingers.