applying diversity

[ianphilip007]

hi guys

ive got myself a little confused here when trying to calculate a max demand figure for the installation below.

60amp TNCS supply to a bungalow.

1x 30A Ring Main
1x 30A cooker unit(with socket)
1x 40A Shower (8.5kw)
2x 20A Radials
1x 5A Lights (7x100w)

using table 1B app 1 OSG

ring main (30a) no diversity = 30A
cooker unit(30a) 10A+30%(fl)+5A =24A
shower(40a) no diversity = 36.9A
radial(20a) 40% = 8A
radial(20a) 40% = 8A
lights 66% =3.04A

using these figures it comes out at a diversified current of 109.9Amps what am i forgeting as this cant be right can it? do i have to apply diversity to the diversified currents

when i use my usual method of adding up the MCB's and then multiplying by 0.4

40+30+30+20+20+5 x 0.4 = 58 Amps

which is what id expect. any help would be appreciated.

 

[Engineer54]

I use the IET design guide.

And always come up with a totally unrealistic end figure!! lol!!!

 

[Engineer54]

hi guys

ive got myself a little confused here when trying to calculate a max demand figure for the installation below.

60amp TNCS supply to a bungalow.

1x 30A Ring Main
1x 30A cooker unit(with socket)
1x 40A Shower (8.5kw)
2x 20A Radials
1x 5A Lights (7x100w)

using table 1B app 1 OSG

ring main (30a) no diversity = 30A
cooker unit(30a) 10A+30%(fl)+5A =24A
shower(40a) no diversity = 36.9A
radial(20a) 40% = 8A
radial(20a) 40% = 8A
lights 66% =3.04A

using these figures it comes out at a diversified current of 109.9Amps what am i forgeting as this cant be right can it? do i have to apply diversity to the diversified currents

when i use my usual method of adding up the MCB's and then multiplying by 0.4

40+30+30+20+20+5 x 0.4 = 58 Amps

which is what id expect. any help would be appreciated.

In reality, you would be hard pushed to see even that 58Amps flowing in your bungalow!! Even if you did, it would only be for a few minutes at most. ...lol!!

 

[drew35]

I think the max demand calculation needs a rethink. It works fine if its a small house with six circuits, but goes to poo when its a large barn conversion with six socket circuits, six lighting circuits, in a twenty way board!

 

[thekingiam]

just a thought i have.
32x4 rings
16x1 radial combi boiler
40x1 cooker
6 x4 lights

total 208x0.4=83.2 amps
at the moment it has a 60 amp main fuse and working fine,will get dno to put larger one in though.
the chances of them using half the load would be something though

 

[bartkusal]

hi guys

ive got myself a little confused here when trying to calculate a max demand figure for the installation below.

60amp TNCS supply to a bungalow.

1x 30A Ring Main
1x 30A cooker unit(with socket)
1x 40A Shower (8.5kw)
2x 20A Radials
1x 5A Lights (7x100w)

using table 1B app 1 OSG

ring main (30a) no diversity = 30A
cooker unit(30a) 10A+30%(fl)+5A =24A
shower(40a) no diversity = 36.9A
radial(20a) 40% = 8A
radial(20a) 40% = 8A
lights 66% =3.04A

using these figures it comes out at a diversified current of 109.9Amps what am i forgeting as this cant be right can it? do i have to apply diversity to the diversified currents

when i use my usual method of adding up the MCB's and then multiplying by 0.4

40+30+30+20+20+5 x 0.4 = 58 Amps

which is what id expect. any help would be appreciated.

I think we missed something in the OP.
When you do by OSG, you not going by the fuse size, you going by the load size, so for cooker you apply all that 30% and everything to the load not fuse, unless it really draws 30A as you say, but that means your cooker is 6.9kW, is that correct.
And shower only draws 37A if to go by load, 8500/230=37A
But anyway, to do by OSG would be a big sum, I like everyone else, go by 40% rule.

Best regards: Al

 

[Sparky Ninja]

And always come up with a totally unrealistic end figure!! lol!!!

Overcompensation it may be.

But I would rather go with the guidance and instruction of the nationally recognised productions in the court of law than guess work.

 

[Engineer54]

Overcompensation it may be.

But I would rather go with the guidance and instruction of the nationally recognised productions in the court of law than guess work.

Overcompensation, ....that has to be the understatement of the year!!

Come on Widdler, we both know that the criteria within BS 7671 and it's guide doesn't work and come to that has never worked!! I have never seen or known of a single Electrical Design Engineer/Consultant etc, ever use them either!!!

You may need to support and use them as a collage lecturer, ...but they are going to be of little use to anyone outside that collage classroom...

 

[Sparky Ninja]

- - - Updated - - -

Overcompensation, ....that has to be the understatement of the year!!

Come on Widdler, we both know that the criteria within BS 7671 and it's guide doesn't work and come to that has never worked!! I have never seen or known of a single Electrical Design Engineer/Consultant etc, ever use them either!!!

You may need to support and use them as a collage lecturer, ...but they are going to be of little use to anyone outside that collage classroom...

I'M DONE WITH THIS.

 

[Engineer54]

i give up, i'm done with this!

Did i say something wrong?? Also sorry if the Facts stand out for themselves....

 

[Farmelectrics]

0.4 value has allways worked out ok for me

 

[Guest55]

the OSG and bs7671 only give very basic guidlines on diversity , mainly for domestic installs with very conservative figures.
move onto big commercials etc , then diversity takes on a much more important and complex role , otherwise we'd be using 25mm for lighting on the top floor of 6 storey office block ;-)

so at this point the designer has to go beyond suggested " one size fits all" tables and look more closely at assessing demand.

 

[malcolmsanford]

I would imagine it comes from 100 yrs of experience of supplying electrical supplies. Diversity is one area where there is no hard and fast formula, every, literally every, installation will have an amount of diversity applied and every one will and could be different.

 

[dagrat]

Totally agree with Malcolm, the X0.4 is a good starting point when assessing diversity, but this must be applied in light of experience.