Diversity opinions?

[cjard]

Hi all

Asking on behalf of my (well, actually my father in law's) spark because he's not big into forums but has a slight concern about the father in law's house. Background is were converting a barn, and in his side of the resulting semis he's got a lot of electrical stuff, 2 ovens, 2 hobs, electric showers, a garage, a granny annexe with its own shower n kitchen, air source heat pump etc. If everything were on at once, sparky reckons things would be knocking on for 70 to 75 kw, having looked at all the appliance specs etc

The supply recommended by the DNO way back when was to deliver 3 phases to the lobby, and then split it at the meter board, one phase per house and one phase for common areas lighting, power for cleaning etc. Now with the blackpool illuminations next door spark's thinking it would be better to use 2 of the 3 phases (100amp) for the other house and leave me with 1 (and then we have to come to some agreement about supplying/paying for the common areas) because my power needs are much more modest - normal kitchen, no heat pump, no electric showers, annexe in the future possibly etc

What opinions can I get from you good folks on this approach? Is it the right one to take? (essentially to have one phase for downstairs, other phase for upstairs plus annexe, and he pays 2 power bills)

 

[JohnW2]

The supply recommended by the DNO way back when was to deliver 3 phases to the lobby, and then split it at the meter board, one phase per house and one phase for common areas lighting, power for cleaning etc. Now with the blackpool illuminations next door spark's thinking it would be better to use 2 of the 3 phases (100amp) for the other house and leave me with 1 (and then we have to come to some agreement about supplying/paying for the common areas) because my power needs are much more modest - normal kitchen, no heat pump, no electric showers, annexe in the future possibly etc.

Only the electrician can really tell but it is unlikley that any 'ordinary' house would need more than one (80A or 100A) single phase supply - so the DNOs original plan was probably fairly reasonable.

What opinions can I get from you good folks on this approach? Is it the right one to take? (essentially to have one phase for downstairs, other phase for upstairs plus annexe, and he pays 2 power bills)

I'm not totally clear as to what the DNO were proposing. If they provided a 3-phase supply, they would normally regard that as 'one supply/account', with one (3-phase) meter and one bill, with any subsequent metering (and use) of the separate phases being the responsibility of the consumer. However, if the DNO themselves separated the three phases for different uses/users, that would be three supplies/accounts, three meters and 3 bills - in other words, apart from the physical fact that the supply entered the building as 3-phase, it would be wired and metered/billed as three separate single-phase supplies (just as if it had been three separate buildings, in the normal way).

Kind Regards, John.

 

[cjard]

I believe the latter is how the dno arranged things, as the service head has 6 holes in the top, 2 per fuse. I don't know if it thus means it has 3 MPANs as I've pu the paperwork somewhere..

In terms of a normal house, I suspect that the goalposts for one of the houses have moved quite a bit since the form was filled out describing the planned development :/

 

[JohnW2]

I believe the latter is how the dno arranged things, as the service head has 6 holes in the top, 2 per fuse. I don't know if it thus means it has 3 MPANs as I've pu the paperwork somewhere..

I doubt that you can safely draw that conclusion, so, as you say, you need to check the paperwork. My house has a 3-phase supply, with potentially two 'holes' for each of the fuses, but it is very much a single supply, with a single account, a single MPAN, a single 3-phase meter and a single bill.

In terms of a normal house, I suspect that the goalposts for one of the houses have moved quite a bit since the form was filled out describing the planned development :/

From what you've said, unless either of the 'houses' has more than one electric shower, I doubt that it qualifies as more than a 'normal house', in terms of electricity requirements.

Kind Regards, John

 

[cjard]

the ovens and hobs are all in the same region of a shower, or more.. and one of them is 17kw! The showers are 9 or so..

Will check the paperwork..

 

[JohnW2]

the ovens and hobs are all over 10kw, and one of them is 17kw! The showers are a paltry 9 or so..

Are you sure about that? 17 kW for a single domestic cooking appliance would be extremely unusual! Whatever, even a domestic cooking appliance of 17kW (probably quoted at 240V, so probably around 68A total at 230V), is only regarded as a load of about 27.4A at 230V (aka ~6.3 kW ) after application of diversity. In contrast, one is not allowed any diversity with a shower (since "when it's on, it's all on") so a 9kW shower always counts as 9kW (i.e. nearly 50% more than a "17 kW" cooking appliance). Most domestic cookers (or oven+hob) are appreciably less that 17 kW total (before diversity), hence well under 6 kW after application of diversity.

Will check the paperwork..

Fair enough.

Kind Regards, John

 

[JohnD]

I was very startled to read "If everything were on at once, sparky reckons...."

Doesn't this sparky know anything about diversity?

 

[JohnW2]

I was very startled to read "If everything were on at once, sparky reckons...." .... Doesn't this sparky know anything about diversity?

Indeed and, in contrast, judging by the title of this thread, the OP clearly is at least aware of the concept of diversity!

I'm still far from convinced that we are talking about anything more (electricity-demand-wise) than a 'average normal house'.

Kind Regards, John

 

[cjard]

I'll dig up the specs of everything.. Father in law was kind enough to email everything over to the spark (product manuals and specs etc) though I haven't had sight of them myself; all figures are anecdotal. One of the hobs is some massive induction thing that probably makes the house a bit like the hatch in Lost, magnetising the entire district if a button isn't pressed every 27 minutes..

I'd dearly love for the load to not be in excess of the 100amp supply because it means that the 3 phases that were delivered to the lobby could be purposed as intended originally which removes one admin headache in paying for common lighting for the residents long after the contractors have gone.. Also better for me, having forked out 50% of the cost for the supply and acquired only 33% of the utility..

 

[JohnW2]

I'll dig up the specs of everything.. Father in law was kind enough to email everything over to the spark (product manuals and specs etc) though I haven't had sight of them myself; all figures are anecdotal. One of the hobs is some massive induction thing that probably makes the house a bit like the hatch in Lost, magnetising the entire district if a button isn't pressed every 27 minutes....

Fair enough.

I'd dearly love for the load to not be in excess of the 100amp supply ...

It won't be! I'm not, but if I were a betting man ..... (unless there are welders, kilns, electrically heated swimming pools or suchlike that you haven't told us about!).

....because it means that the 3 phases that were delivered to the lobby could be purposed as intended originally which removes one admin headache in paying for common lighting for the residents long after the contractors have gone.. Also better for me, having forked out 50% of the cost for the supply and acquired only 33% of the utility..

Indeed so. I would be very very surprised if the DNO's 'Plan A' is not still appropriate. Mind you, someone will have to pay for (at least usage) of that 3rd phase! As I said before, you need to ascertain whether the DNO is planning to provide a single 3-phase supply (for you to sub-meter - with one standing charge and one bill) or three single-phase supplies (three bills, each with a standing charge).

Kind Regards, John

 

[cjard]

Spark sent me the power ratings of various bits through, said he's calced things, with diversity, at 180 amps

Using the tables/worked example from guidance on TLC direct's site https://www.tlc-direct.co.uk/Book/6.2.3.htm, I came up with 188 - workings attached (do you agree with them? did I do it right?). Note, this is just for the house, no annexe :/

 

[cjard]

ps; think there's a mistake on the heat pump; 14kw is its output, 6.5kw is the consumption.. reduces my workings to 157 amps

 

[JohnW2]

Spark sent me the power ratings of various bits through, said he's calced things, with diversity, at 180 amps. Using the tables/worked example from guidance on TLC direct's site https://www.tlc-direct.co.uk/Book/6.2.3.htm, I came up with 188 - workings attached (do you agree with them? did I do it right?). Note, this is just for the house, no annexe :/

ps; think there's a mistake on the heat pump; 14kw is its output, 6.5kw is the consumption.. reduces my workings to 157 amps

Although I can't see anything fundamentally wrong with your calculations, per se, that's an extraordinarily high figure for what, conceptually, differs from a bog standard house (which will have a 60A or 80A supply) only by virtue of the heat pump. It's largely the cooking appliances which are doing it - can you tell us a bit more about these "13kW, 10kW and 10kW" appliances? The total (pre-diversity) cooking appliance load is not usually much over 10 kW (even with induction hobs), nowhere near 33 kW.

Don't forget that, per recent discussion in another thread, if it were not for the heat pump (I'm not too sure how they would treat that), in terms of network power requirements and voltage drop in their network, a DNO would regard the "After Diversity Maximum Demand" of that house as 2 kW (at most 3kW)!

I realise that you have done nothing more than follow the guidance of the OSG, but if one did that for almost any house one would end up with a 'ridiculously large' answer - primarily because, unlike the DNO approach, it does not consider diversity across the various types of load - and the OSG is far from clear in what it suggests about estimating the after-diversity demand of a whole installation. Almost no equipment is 'on' 24/7 - in many cases nothing remotely like that. Just a shower plus the after-diversity load of a cooker would add up to around the 'supply current' of the average house - but, of course, the shower is hardly ever going to be in use, and never used for appreciable periods of time. I think that common sense has to prevail in these situations.

Kind Regards, John

 

[cjard]

the common sense thing may be a significant factor. My spark usually works on industrial install rather than domestic, and will hence probably have a preference for following a design that is OTT/big numbers and doesn't have "common sense" applied as much as calculations, margins for error, health and safety and someone's insurance on the chopping block.. I'll see if I can convince him to put it all on one phase and just leave. Spare supply cable lying around so a second cu could be installed later if one phase pops..

Here's a list of the appliances-

Neff teppanyaki 1.9kw
Neff induction 7.2kw
2x warming drawers 0.8kw each
2x neff ovens 5.7kw each

Dishwashers, waste disposal, blah.. Part of the kitchen ring

Er.. Think I need to go back to him and ask him where he got his power consumptions from!

 

[JohnW2]

the common sense thing may be a significant factor. My spark usually works on industrial install rather than domestic, and will hence probably have a preference for following a design that is OTT/big numbers and doesn't have "common sense" applied as much as calculations, margins for error, health and safety and someone's insurance on the chopping block.. I'll see if I can convince him to put it all on one phase and just leave. Spare supply cable lying around so a second cu could be installed later if one phase pops..

It won't pop ... but, yes, as you realise, that would be my approach.

Here's a list of the appliances-
Neff teppanyaki 1.9kw
Neff induction 7.2kw
2x warming drawers 0.8kw each
2x neff ovens 5.7kw each

Thanks. For a start, by my reckoning, that all adds up to only 22.1 kW (much less than the 33 kW you suggested) - and (doing all calcs at 230V, for convenience) that lot would only amount to about 35.8A (aka 8.2 kW) after diversity ... and even that's assuming that you had absolutely everything 'on' at once.

Kind Regards, John