DNO maximum demand message.

[Cadgey123]

Just started doing my first block of flats as a Qualified supervisor.

I have 5 flats and a landlords supply to wire up.

Done my calculations a while back and told the DNO I would need require ADMD of 12.5 kva for each flat which I thought was reasonable, Considering I have 3 rings, 2 lighting , 1 UFH supply and a small oven circuit.

Just to check I phoned the NICEIC technical to reassure I done the right calcs in the Onsite guide table etc. They basically said you can make it up it's more or less common sense to the load you would achieve??

But my dilemma is the DNO wrote this back to me but I would have thought this was a rather small supply?


UK Power Networks would in general expect the (ADMD - after diversity
maximum demand) for a gas heated flat/house to be between 1.5kVA and
3.0kVA and an electric heated flat/house to be between 5kVA & 10kVA
unless abnormal high usage appliances are being installed.

 

[davesparks]

Yes that's in line with their network design guide,

What's your question??

 

[Cadgey123]

Yes that's in line with their network design guide,

What's your question??

Well suppose it may be why is there such a high diversity on their side of things for a supply to each flat?

 

[davesparks]

Well suppose it may be why is there such a high diversity on their side of things for a supply to each flat?

It's not all that high a diversity factor.

Personally I've never measured an average demand above 20A for a domestic installation.

 

[Richard Burns]

Generally the DNO will want to supply as little as possible and for multiple properties (streets) they can apply massive diversity as people use things at different times and so it all evens out.
For your situation you have less flexibility but even so you can expect much lower than the design current. For your list you could assess the sockets as taking no more than 10A in general (assuming they are not running electric heaters) even though there are three rings (good division of circuits) and I do not know the size of the flats mostly there will only be kettles taking significant power and then only for a very short time.
lighting will take minimal current, especially as it should be energy efficient.
UFH unless huge will take maybe a couple of amps.
Oven (perhaps cooker?) circuit taking 15A for short periods.
So maybe a total of 30A (7kVA) at maximum use and this would be for short periods so say halving this to balance across for five flats over time in general on average is close to their 3kVA.

This is just an off the cuff example of how you might want to assess actual loading, obviously you know a lot more about the flats size and expected use which may make significant changes to the demand.

 

[Wilko]

Can I ask please - what fuse size is planned for each installation?

 

[Cadgey123]

Can I ask please - what fuse size is planned for each installation?

I have ran 25mm2 cables to each flat and the are relatively short runs so probably a 80amp switched fuse will fit the bill.

 

[Cadgey123]

Generally the DNO will want to supply as little as possible and for multiple properties (streets) they can apply massive diversity as people use things at different times and so it all evens out.
For your situation you have less flexibility but even so you can expect much lower than the design current. For your list you could assess the sockets as taking no more than 10A in general (assuming they are not running electric heaters) even though there are three rings (good division of circuits) and I do not know the size of the flats mostly there will only be kettles taking significant power and then only for a very short time.
lighting will take minimal current, especially as it should be energy efficient.
UFH unless huge will take maybe a couple of amps.
Oven (perhaps cooker?) circuit taking 15A for short periods.
So maybe a total of 30A (7kVA) at maximum use and this would be for short periods so say halving this to balance across for five flats over time in general on average is close to their 3kVA.

This is just an off the cuff example of how you might want to assess actual loading, obviously you know a lot more about the flats size and expected use which may make significant changes to the demand.

Cheers Richard, that makes a lot of sense.
Thanks for taking the time to explain it for another angle.