Interesting, I've only given it a quick once-over, but if initial reactions are of any use to you...

1. "Traditional methods, such as those outlined by the IET, often result in inaccuracies" - couldn't agree more. The forum has had loads of questions over the years where someone has diligently applied the OSG final-circuit based approach and come out with ridiculously high numbers (>>150A for a simple domestic). Often the suggested remedy is to point out that it's appliances that are loads, not circuits, so the OSG method works best if you ignore what circuits are actually installed and instead imagine the minimal circuit arrangement that could supply the actual loads (e.g. one ring final circuit per 100m² of floor space, rather than one per (maybe 40m²) storey plus another for the kitchen), probably a single lighting circuit, small loads on FCUs off the socket circuit, not on their own circuits from the CU, etc. Oh and LED lighting at a sensible wattage (e.g. closer to 10W instead of the traditional 100W per lampholder).

2. "focusing instead on the actual number of occupants" - that looks like it'll pose difficulties to me, since the actual number of occupants can vary significantly during the lifetime of an installation. In the last 10 years we've gone from 3, to 2 to 4 and back to 2 (plus a dog). I wouldn't want to be in the position of having to re-wire (or even re-check/modify) the installation or re-negotiate a DNO supply every time we added someone to the household.

3. Per final circuit.. as above (1.) - that seems to be introducing an unnecessary degree of randomness. Many people prefer extra circuits for all sort of reasons that don't imply extra loads (often minimising inconvenience in the case of a fault, following the natural layout of the building (e.g. per floor circuits), or just personal preference (e.g. radials rather than rings - so maybe 2off 20A circuits rather than 1off 32A)). I've seen houses go from a 4- or 6-way fusebox to a 10 or 15 way CU during a re-wire - with no actual change of load at all. Often a more abstract metric (e.g. floor area) can provide a simpler general use load approximation, although maybe non-linear (larger homes may tend to use less per m² than smaller ones).

4. circuit demand factors ... Security Alarm 1 - combi boiler 1 - door bell 0.2 - those feel incredibly inaccurate - a security alarm probably takes <10W - a combi <200W, and a door bell really is pretty negligible, if they're fed from 6A MCBs to reckon them at over a kW (or 276W for the door bell) and still get the right overall answer at the end suggests to me that they might be hiding a mis-calculation somewhere else.

5. "This overestimation is a significant concern when engaging with DNO networks and applying for grid connections ...  Outdated calculations tie up valuable grid capacity, causing consumers and electrical distributors to pay for unnecessary upgrades." I'm not entirely following the logic here. AFAIK the DNOs have their own methods of calculating loads and diversity (ADMD) based on their own experience, which traditionally come out with figures getting towards order of magnitude less than OSG calculations, e.g. somewhere in the region of 8-10A per household (for non-electric space heating), but it does depends on a quite a number of factors, including number of customers on each supply.  I thought they only take the numbers declared on the application form as a signal to look out for anything unusual (e.g. large disturbing loads), they certainly don't size their mains and transformers by just adding up all the declared MDs.

  - Andy.

Interesting ideas indeed - I too agree that the OSG methods of sizing for MD are way off reality for any normal domestic.  Personally I find building size more useful -100A fuses feeding half a dozen 1 bed flats each with 63A fuses seem to work OK for ever.

Can I suggest a 'maximum likely occupancy' - using the no of bedrooms or something (allowing for multiple occupation of double beds I suppose.) to sidestep the uncertainty about the no of folk in the house and their loads over the life of the building.

One needs to be careful with how the results of such a calculation may be used - the maximum demand, as used to size a transformer feeding a street of 50 houses per phase and a row of small shops with 3 phases, can be a lot lower that the no. of houses times the ADMD of each house, as the peaks in load never coincide, and if they ever did the thermal time constant of the transformer to reach a dangerous temperature is a few hours.

However, the meter tails in each house should really at least use the ADMD or maybe the MD for that building, as they heat up in a few tens of minutes.

Mike.

PS it's a detail but the spelling of 'revision' in the footnotes, needs, shall we say, revision - such things stick out and make you wonder what other detail has perhaps been missed.

Interesting ideas indeed - I too agree that the OSG methods of sizing for MD are way off reality for any normal domestic.  Personally I find building size more useful -100A fuses feeding half a dozen 1 bed flats each with 63A fuses seem to work OK for ever.

Can I suggest a 'maximum likely occupancy' - using the no of bedrooms or something (allowing for multiple occupation of double beds I suppose.) to sidestep the uncertainty about the no of folk in the house and their loads over the life of the building.

One needs to be careful with how the results of such a calculation may be used - the maximum demand, as used to size a transformer feeding a street of 50 houses per phase and a row of small shops with 3 phases, can be a lot lower that the no. of houses times the ADMD of each house, as the peaks in load never coincide, and if they ever did the thermal time constant of the transformer to reach a dangerous temperature is a few hours.

However, the meter tails in each house should really at least use the ADMD or maybe the MD for that building, as they heat up in a few tens of minutes.

Mike.

PS it's a detail but the spelling of 'revision' in the footnotes, needs, shall we say, revision - such things stick out and make you wonder what other detail has perhaps been missed.

Hi Mike,

Yes, good catch with the spelling, unfortunately one of my weak points in life, the document is still in its infancy, and good feed back like that only helps it become stronger. Yes I do check items etc thing get through, I'm not posing to be perfect part of the process in making the document enhanced is sharing like this and review good productive feed back like yours.

The new calculations are trying to address more is the  installation MD when were looking at network planning (so when we put a application in to the DNO for a new EV charger, ASHP, etc we want to reduce the number of limitations on load or upgrade charges to the customer when they are not required). Were not looking at promoting these to be used as final circuit MD calculations which will have an impact on conductor CSA and OCPD. 

I tried the building size in an earlier version of the formula, but that variant didn't prove to be useful in it accuracy to take forward.

For the meter tails, going from my comment above, the CSA of the tails is already standard normally for domestic installs, but the CSA of the tails would also be subject to the up stream OCPD rating.

Don't get hung up on the spelling, other folk can fix that. (me perhaps ;-)

My main point was that 'network planning' does mean different things, transformers for the street see an averaged load, but the branches that feed just one or two properties are likely to see a more peaky load.
Keep up the thinking..

Mike.