Diversity settings for apartment blocks and ADMD standard norms

For information, I was involved in the installation (NOT design!) of 4 blocks of 70 new build flats. A mixed of 1 & 2 bed, 3kW of heaters in the 1 bed, 5kW in the 2 bed, all had a 3kW immersion, a 2kW oven and 3kW hob. So potentially around 9kW load for each flat when everything is on, obviously for a shortish period until the stats kicked in.

The trouble was, the incoming fuses were 3x 100amp to each block. And the immersions were on a timer. As is typical, the immersion timers were commissioned, and left exactly as they left the factory, so at 6am each morning, all 280 immersions would come on, giving a 300amp surge on each phase in each block. We'd arrive at 7.30, to find no power to each of the blocks. After the third time this happened, (it took out a transformer fuse one time) it dawned on the site Management that 3x 100 amps fuses were not going to be enough. So they were changed to 200 amps (the cable from the cutouts to the panel board in each block was, luckily, big enough). We had 3 weeks of non-tripping, however, I brought up that we hadn't turned on the heating, or ran the cookers simultaneously yet, so should we do that?  They said no, as "It'll be fine now".

I was off site the following week, so didn't find out how it fared when people were living there.

I'd be going for 25amps per flat if electric water/heating, 16-20A for gas heating. 

alanblaby said:

And the immersions were on a timer.

What poor design! So somebody who gets up at 05:50 might have had a cool shower. Had the immersions been on constantly, I feel sure that diversity would have worked.

Even if you had fan heaters, the 'stats would have opened and closed independently. And yes, the cookers might all go on at around 18:30, but not every hotplate all at once.

Dylan Wilding said:

Say for example the total diversified load per apartment is 50A and there is 8 apartments.

alanblaby said:

I'd be going for 25amps per flat if electric water/heating, 16-20A for gas heating. 

70 flats at 3 x 100 A is a little over 4 A per flat, and (obviously) 8 A on 200 A fuses.

alanblaby said:

3kW of heaters in the 1 bed, 5kW in the 2 bed

An extra 2 kW is a lot for a bedroom - just put more blankets on the bed. Seriously, the heat loss from a modern small apartment should be well under 3 - 5 kW.

If you know the heat loss at an indoor temperature of 20°C, does that not give a reasonable estimate of after diversity heating load? Granted some people may leave the heating off during the working day, but they do not turn it back on at exactly the same time.

alanblaby said:

And the immersions were on a timer.

What poor design! So somebody who gets up at 05:50 might have had a cool shower. Had the immersions been on constantly, I feel sure that diversity would have worked.

Even if you had fan heaters, the 'stats would have opened and closed independently. And yes, the cookers might all go on at around 18:30, but not every hotplate all at once.

Dylan Wilding said:

Say for example the total diversified load per apartment is 50A and there is 8 apartments.

alanblaby said:

I'd be going for 25amps per flat if electric water/heating, 16-20A for gas heating. 

70 flats at 3 x 100 A is a little over 4 A per flat, and (obviously) 8 A on 200 A fuses.

alanblaby said:

3kW of heaters in the 1 bed, 5kW in the 2 bed

An extra 2 kW is a lot for a bedroom - just put more blankets on the bed. Seriously, the heat loss from a modern small apartment should be well under 3 - 5 kW.

If you know the heat loss at an indoor temperature of 20°C, does that not give a reasonable estimate of after diversity heating load? Granted some people may leave the heating off during the working day, but they do not turn it back on at exactly the same time.

Chris Pearson said:

An extra 2 kW is a lot for a bedroom - just put more blankets on the bed. Seriously, the heat loss from a modern small apartment should be well under 3 - 5 kW.

 The 3 or 5kW was for the whole flat. The 2 bed ones were bigger overall, plus had the extra bedroom.

Chris Pearson said:

What poor design! So somebody who gets up at 05:50 might have had a cool shower. Had the immersions been on constantly, I feel sure that diversity would have worked.

Well yes, but no instructions were given to whoever commissioned them, so they were all set for the same time, then left for the (eventual) Renter to adjust the timing.

Chris Pearson said:

70 flats at 3 x 100 A is a little over 4 A per flat, and (obviously) 8 A on 200 A fuses.

Yes, that's why the fuses popped! I don't think it is enough, that's why I said 16A+ per flat. This was before anyone moved in, when they did move in, the heaters and appliances would be on, 8A per flat is looking a little small to me.