The on-site guide use to (not bought one in years) tell one what diversity is allowed, but it seemed to be aimed at industrial installations, as my supply like many other homes is 60 amps, some homes do have 80 or 100 amps, but the standard fuse box was limited to 60, and modern consumer unit (CU) limited to 100 amps, so in real terms that is our limit, and it does not matter if the CU has 30 RCBO/MCB's will still only have 100 amp total.
So the appendix to BS 7671 warns about the problems with ring finals, note we don't have the same problem with radials.
The load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable (Regulation 433.1.5 refers). This can generally be achieved by:
(i) locating socket-outlets to provide reasonable sharing of the load around the ring
(ii) not supplying immersion heaters, comprehensive electric space heating or loads of a similar profile from the ring circuit
(iii) connecting cookers, ovens and hobs with a rated power exceeding 2 kW on their own dedicated radial circuit
(iv) taking account of the total floor area being served. (Historically, limit of 100 m² has been adopted.)
If we were to follow this, that would mean most non-portable (over 18 kg and no wheels) electrical equipment would need a dedicated supply, in most homes this would be silly, where the CU is in the kitchen, then we could over load one leg of a ring final, but in the main this will not happen, and note it says "long periods" it takes time for a cable to heat up.
So we do need a dedicated supply if over 3 kW, but at or near the limit, ovens, washing machines (not washer driers), dishwashers, and the like have large heaters, but do not use those heaters for long, a thermostat will start to work and the high load is only for a short time.
So the only, 3 kW or less, items which need a dedicated supply are the immersion heater, and maybe the tumble drier. The latter does not include heat pump types. A tumble drier may run for an hour or more at over 2 kW, the same with washer/drier, the immersion heater could take 4½ hours, so no debate there, it needs a dedicated supply, but an hour is up for debate, is that too long?
There is also a debate to if a washing machine belongs in a kitchen? In days gone by, we dragged the twin tub into the centre of the floor, and on washing day, no cooking could be done, so there was no mix of food and dirty clothes, but with the Bendix washing machine,
bolted to the floor, we got the mix of washing and cooking, there were problems, as soap/detergent of the time, caused foam, and it was not unknown for bubbles to shoot out of that lid on the top, and all over the floor, so cooking was limited when doing the washing. But load wise, it was hot and cold fill so very little load on the electrics.
Also cooking was at that time likely solid fuel, so that was also no load on the electrics.
So new homes around 1980/90 started to have untility rooms, so washing clothes and cooking did not mix. And we started to have two ring finals, best split side to side of the house, so more even loaded. Around the 90's to turn of the centrary we started to get RCD protection, and as time went one the RCD dropped from 100 mA to 30 mA and we started to get problems with them tripping, and the regulations in 2008 talked about taking account of danger that may arise from the failure of a single circuit such as a lighting circuit and reducing the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced
by equipment in normal operation. And being cheap skates, we wanted to try and get away with using just two RCD's, today we realise that did not really comply, but at the time, we thought we could get away with it, so to ensure a problem with a socket supply did not plunge one into darkness, we had to split the sockets to match the lights, so we started to split up-stairs and down-stairs to match the lights.
This increased the load down-stairs, so we started to use a third ring final for just the kitchen, and the debate started in earnest about using radials instead of ring finals, but then we moved to the RCBO which combines the RCD and MCB, so the split could return to side to side of the house, and having 20 odd circuits increased the cost of the installation, so the ring final came back into favour.
All this means we have many ways that the home, in particular the kitchen, is wired, there is no one system suits all. In 2004 the kitchen became a special location, as kitchen fitters were being blamed for some horrors in wiring, in Wales it still is, but England dropped the kitchen and garden as special locations, but still more care needs taking with both locations.
The problem is, we tend to look at our own house when answering questions, and I have three power supplies to my kitchen, cooker, ring final, and freezers, my freezers are supplied for an UPS supply so do not fail with a power cut, and my washing machine and tumble drier (heat pump) are in an utility room, not really checked if the utility room is the same RCBO, but the back-kitchen still has a washer/drier in the kitchen.
So two cookers, two showers (electric) washing machine, tumble drier, 2 dishwashers, and a washer drier, on a 60 amp supply, and the fuse has never ruptured since I have lived here for 5 years. There are only 2 of us, and there is a limit to how much power we can use, around 12 kWh per day. We have 5 bedrooms, so I suppose we could have many more living here.
But the whole reason for 6, 16, 32 amp RCBO's is so if we do overload a circuit, worse case scenario is it trips. If I look at total power used for the home (House and Flat)
the highest load is when we take a shower, and rare do we draw over 3 kW at any one time, except 00:30 to 05:30 when we have off-peak and run dishwasher etc. I think you are worrying about something unlikely to happen.
