Supply and demand. Is a 300A head enough?

[sparkysey]

Hi guys,

I have been asked to price up a job thats a little outside of what I generally do and im hoping to get some advice from you sparks who are more experienced in the design of an installation.

Iv got a block that an investor is converting to 24 studio flats, all electric, no gas.

3 floors, 8 flats per floor, and a 3 phase supply comprising of 3 x 300 amp main heads.

each flat will have

2 x 2 kw heaters
1 x 8.5kw shower
1 x 8.5kw water heater

And then the obvious general of course.

now im working out each flat with a maximum demand load of approx 20kw

approx 160kw per floor or 696amps. I know I have to take into consideration diversity, But even so this does seem way to high for the head to handle.

Thanks in advance for your opinions.

 

[Rockingit]

Look at it another way..... 900A / 24 flats = 37.5A per flat. I think you'll be fine!

 

[Moses]

Hi guys,

I have been asked to price up a job thats a little outside of what I generally do and im hoping to get some advice from you sparks who are more experienced in the design of an installation.

Iv got a block that an investor is converting to 24 studio flats, all electric, no gas.

3 floors, 8 flats per floor, and a 3 phase supply comprising of 3 x 300 amp main heads.

each flat will have

2 x 2 kw heaters
1 x 8.5kw shower
1 x 8.5kw water heater

And then the obvious general of course.

now im working out each flat with a maximum demand load of approx 20kw

approx 160kw per floor or 696amps. I know I have to take into consideration diversity, But even so this does seem way to high for the head to handle.

Thanks in advance for your opinions.

You have taken a load of 20Kw per flat.

You have not included the common loads (Landlord loads), e.g. communal kitchen, Communal heating in corridors, stairs common rooms entrances etc., Lift load, loads for ancillary services such as security/cctv/fire/integrated TV system etc.

You need to add-up all the loads and then apply diversity to the total load, ensure loads are balanced across the phases.

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[TD="colspan: 4"]The figure of 33% Diversity for the Main infeed for group of 24 dwellings, on the Curve "a" on Figure 3.1 page 24 of the "Commentary on IEE Wiring Regulations 16th Edition" by Paul Cook.[/TD]
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[johnboy6083]

a glance at the electricians deign guide will help massivley with this.

 

[Guest55]

a glance at the electricians deign guide will help massivley with this.

Which i have , and its massively generous in its diversity allowance for multi occupied dwellings.
It suggests a guide factor of about 0.3 of total load for a block of 20 odd flats with electric heating.

 

[Moses]

Which i have , and its massively generous in its diversity allowance for multi occupied dwellings.
It suggests a guide factor of about 0.3 of total load for a block of 20 odd flats with electric heating.

So the 300A supply should be well sufficient.

 

[Guest55]

So the 300A supply should be well sufficient.

I agree but theres alot of info missing from sparksey's list to get an accurate figure.
If theres no gas , then every flat will have an electric hob & oven which isnt in his list.
Number of ring mains per flat would help as well but i'd imagine 2 , one for kitchen , one for rest of flat.
Lots to consider thoroughly on a job this size.

 

[Moses]

I agree but theres alot of info missing from sparksey's list to get an accurate figure.
If theres no gas , then every flat will have an electric hob & oven which isnt in his list.
Number of ring mains per flat would help as well but i'd imagine 2 , one for kitchen , one for rest of flat.
Lots to consider thoroughly on a job this size.

good call Biff

 

[johnboy6083]

i think thast the main head will be sufficient. As trhey are studio flats, i would be suprised if there was more than one ring. There are likely to be a maximum of 2 people per flat. i

 

[Moses]

i think thast the main head will be sufficient. As trhey are studio flats, i would be suprised if there was more than one ring. There are likely to be a maximum of 2 people per flat. i

come back a year after the flats have been occupied and tell us whether the max demand calculation was correct?