Block of flats. Max Demand

[bartkusal]

Hi Richard, thanks a lot, all that detailed sharing of experience I was waiting for, invaluable, you are my top spark now.

Sorry to be a pain, just a little clarification again. When you say I was close in option 2. I did have 53A per flat, but taking all flats in consideration I applied diversity again and had 80A per Ph. So it seems that you are not applying diversity anymore between the flats, just added them up.Is this correct?

If that’s the case, its seems a lot, but then it is what it is, I suppose.

Thanks again, its most appreciated.

Al

 

[Richard Burns]

My approach here is not applying diversity as such. It is more looking at the reality of the situation and considering likely loads from normal loading of houses in general. Taking into account the high load appliances that affect maximum demand.

Because I am looking at average values for a flat I do not apply diversity again because the reductions are fully incorporated already.

As a basic rule over a large number of dwellings the demand is likely to be about 15A per house, however as you get closer to a single dwelling variations in demand mean that you cannot apply these individually to dwellings and it is likely that peak demands could cause an overload, so the protection increases.

I got 40kW you got 55kW, overall I would not really like to supply 4 flats with electric showers through a 100A fuse but it would probably be OK in most cases.

 

[bartkusal]

My approach here is not applying diversity as such. It is more looking at the reality of the situation and considering likely loads from normal loading of houses in general. Taking into account the high load appliances that affect maximum demand.

Because I am looking at average values for a flat I do not apply diversity again because the reductions are fully incorporated already.

As a basic rule over a large number of dwellings the demand is likely to be about 15A per house, however as you get closer to a single dwelling variations in demand mean that you cannot apply these individually to dwellings and it is likely that peak demands could cause an overload, so the protection increases.

I got 40kW you got 55kW, overall I would not really like to supply 4 flats with electric showers through a 100A fuse but it would probably be OK in most cases.

Sorry Richard, where this 100A fuse came from? In previous post you came to 170A per phase. Is it because there is no BS 1361 and BS 88-3 fuses higher then 100A? What other options DNO have, perhaps BS 88-2 160A? Or is this only for motors and inductive loads? Thanks.

 

[Richard Burns]

Look this is really something that you need to be sure about yourself.
I have said 100A fuse because a basic 100A three phase supply is going to be easy and (relatively) cheap to install, going above this will have the DNO charging more and taking longer.
Looking at my breakdown for the flats if each one is able to run at the limit on a 40A fuse then for four flats you would have 160A giving a bit more leeway takes you to 170A, however from the above posts from others giving you some useful realistic information it is probable that four flats would never take out a 100A fuse as you would need a consistent 200A for more than 20 minutes to blow the fuse.

Again you need to be confident that what you say will be suitable.

The DNO could probably supply whatever you want but may charge you £50,000 for a new transformer!

 

[Silly Sausage]

We all agree that the fuses will handle being overloaded for short periods of time.
What is the general consensus of opinion about cables being overloaded occasionally, but regularly, eg shower usage?
re Shower, design the cct to take the current, I mean the supply calbles.

 

[driverman]

Re flats: Generally now all meters to each flat have to be on the ground floor altogether in a community room whereby each tenant/ owner has 24 hour access. The DNO would have to install a suitable sized mains cable (possibly 95cne) into a Ryefield box to cater for 11 flats plus "Landlords supply" for corridor lighting and fire alarm. From the Ryfield box a separate cable to a 60/80amp cut out (header) fuse is supplied for each flat. The supplier will the connect a separate meter to each and every flat. A suitable sized switch fuse is then fitted by the electrician, running a separate sub main to each flat consumer unit. To accommodate all the DNO's equipment , meters, switch fuses etc a large area is required. Basically all the cut -out fuses and meters are next to each other along with the switch fuses.