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.

 

[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.