main tail calculations

[markysparky]

My question is on calculating the total load allowed on different main tail sizes. I have asked my colleagues and fellow students the same question, and got different answers. What is your opinon, do you follow the regs to the book by calculating the total current demand and apply diversity? Or just put the new circuits in?

I cant get my head round it as we are only starting to cover design in l3 2330.

The question is say you have a 60a cut out, 16 mm tails. Current board has 2 x 32a shower, ring, 1x16 Boiler,2x6 amp. If you wanted to add 3 x 32a , ring,Hob, double cooker and 1x6amp lighting.

Some one at college said just install it all on a big board the hrc fuse could take it applying diversity for a long time if it ever was all on at the same time?

Some one at work disagreed and said upgrade the supply?

What is your opinon from your experience?

Looking at table 6d1 in the osg the total demand in 87amps for 16mm clipped direct.

If you did upgrade what is the usual price to upgrade to a 25mm supply?

Thanks any help would be great as I cant get my head round the theory of diversity and the realistic day to day use of it. Cheersss!!!

 

[revjames]

I dont think anyone calculates it, most put 25mm in to allow for 100A supply.

 

[batty]

Generally a 60 amp supply will do most average houses after all you are not likely to have everything on at one time. The only time I get supplies upgraded if people want a 10.5kw shower 50 odd amps on a 60 amp fuse does not give a lot for other things.

 

[markysparky]

Thanksguys,

Things are so juicy now, so the old supply cables of 16mm are not up to the job? If some one wanted a 9 or 10 kw shower, induction hob and double oven and normal household circuits could you just put 25mm tails in from meter? or would you have no choice and get supply upgraded. would the 60 amp blow if you didnt? or could it handle it with diversity?

 

[batty]

The reason I get them upgraded if you install a 50 amp shower and main fuse is only 60 amp its your responsibility as the installer to ensure main fuse will not blow so upgrade is a precaution.

 

[Lurch]

There's no point upgrading the tails if you're nt going to change the fuse. The fuse protects that cable, so if the 60A fuse is protecting the 87A cables then no problems there. You would only need to upgrade the tails if the main fuse was upgraded to 100A.