Maximum demand and diversity

[Helix737]

Hey guys I really need urgent help understanding this

Basically I'm trying to calculate what the diversity factor/percentages would be for the following circuits which are inside a hotel:

3x 32A socket outlet circuit
2x Vending machine circuit
Fridge circuit
Dishwasher
Servery food holding unit
Pool lighting (6A)

I don't see any mention of these in the OSG appendix A - table 2, other than the sockets for a hotel where it says "100% current demand of largest point of utilisation +75% of current demand of every other point in main rooms +40% of current demand of every other point of utilisation.". I'm not sure how to apply that to what I have (which is two same size socket radials and 1 other separate socket radial

 

[timhoward]

I don't think there's a "perfect science" answer to the question.
I think the main point is that BS7671 says that maximum demand must be assessed (in section 3 somewhere) and that when doing this diversity can be taken into account. But BS7671 does not provide guidance on diversity itself - the guidance comes in the OSG.
Using the OSG is more suitable for some installations than others. When not looking at a house, the guidance rapidly becomes less useful.

I'd first divide into constant loads and loads that cycle on and off.
The Fridge, Dishwasher, Vending machines and servery will all be thermostat controlled so current draw will fluctuate.
The lighting will be constant when on, and can be measured with a clamp meter - is any of it it LED?

The hardest bit is definitely the 3 x 32A sockets, and questions around their location, propensity to be used, amount of equipment lurking nearby that could use them, whether more than one is likely to be used at once etc. etc. all come into it.
But also, is this a 3 phase supply and how are the phases balanced?

Sometimes the best you can do is experiment with a clamp meter and apply as much logic as you can muster, e.g. power on the dishwasher from cold and see what it's drawing when the main tank and rinse tank are both heating.
I hope that helps a bit even if it doesn't answer the question!

 

[GM at CA UK]

If it is of any interest I just wrote an article about maximum demand measurement as an alternative to diversity calculations following a case study on a multi-occupancy building in Richmond, London (5 flats in a converted house of 50 years). It has a single phase 100A supply split into 6 and in a 2 week log the maximum current drawn was 48.83A, and that was only for 2 minutes during an evening. The article is in Energy Manager Magazine and can be read here Energy Manager Magazine May 2023 - https://issuu.com/abbeypublishing/docs/em_may_2023/22