Diversity calculation check please

[oharaf]

Hi folks, have to connect a 13.8Kw oven in a domestic property.

13.8/230 = 60A

Checking the regs it says 10A + 30% of remainder so;

10A + (50 x 0.30) = 25A

there is no socket!!!

This just does not seem to ring true, it suggests that 4mm and 32 A MCB would suffice.

I was thinking more like 10mm and an 60A, after all it is bigger than most showers!!! The run is under 10m

When the whole thing is running on christmas day..........

 

[dingbat]

When the whole thing is running on christmas day..........

....the thermostats will operate within a few minutes and all will calm down.

But, in any case, the 1956 diversity rules were made for installations in, er... 1956!

If you are at all worried, you can use the cable size you first thought of.

 

[Taylortwocities]

I would opt for 10mm and 45A cpd. Assuming the supply can support the load, of course

 

[oharaf]

cheers chaps

just out of curiosity why 45A CPD?

 

[oharaf]

TT , had the service head moved the other week, got the DNO subby to up grade it to 80A in return for helping dig the trench

 

[Taylortwocities]

just out of curiosity why 45A CPD?

Just a rule of thumb thing.
Do check what the maker's instructions say. They often specify the fuse size.

Depends on cable routestoo but you'll never bust 45A on that cooker. It will also depend a bit on what consumer unit you have. Some makers do not do all the MCB sizes after 40A. some do 45A, some do 50A.

EDIT, you'll not find a 60amp MCB either....

 

[ricicle]

EDIT, you'll not find a 60amp MCB either....

http://www.tlc-direct.co.uk/Products/HGMT163.html

 

[Taylortwocities]

you'll not find a 60amp MCB either...

That one seems to have grown an extra three

EDIT: Although I have to admit that you used to be able to get 60amp MCBs for old Dorman Smith and Merlin Gerin boards, but not any more.
Crabtree too. But not 60898s.

 

[oharaf]

The TLC post is just the reason i asked actually!!! Saw the 60Amp MCB.

I know that MK do do a 50A, however you are right it is never going to draw all 60amps at one go for so long, cheers TT

 

[Spark123]

One word of warning - some consumer units are not rated to take a 63A MCB even though they are available (for the equivalent industrial range).
Hager domestic boards are rated for a 63A MCB.

 

[ban-all-sheds]

Checking the regs

Regs, or OSG?

it says 10A + 30% of remainder so;

10A + (50 x 0.30) = 25A

Use the table on the next page and you'll get 28A.

And check that the 10.8kW rating is at 230V - if it's 240V then you'll get 27A. Or 24A with the first method.

But it's all pretty academic - the use of diversity is not compulsory....

 

[oharaf]

Well folks, was there yesterday whilst the kitchen fitters were putting the oven in. There was the handbook so opened it up.

Manufacturer reccommends


6mm supply on a 45A MCB


any thoughts anyone?!?!?.....

 

[dingbat]

Manufacturer reccommends


6mm supply on a 45A MCB


any thoughts anyone?!?!?.....

As 6.0 sq mm will carry 47 A at Ref method C and there are no corrections to apply for a CB, unless you have some reason to de-rate the cable, it would be fine.

What did you install?

 

[ColJack]

This just does not seem to ring true, it suggests that 4mm and 32 A MCB would suffice.

or a 25A breaker and 2.5mm² cable...

this is the main reason that I disagree with applying diversity to calculate cable size for a cooker..

I still maintain my opinion that diversity is used to calculate the TOTAL load for an installation, and not for designing individual circuits..

if it says it's 13.8KW then I would design for 13.8KW and fit cable and breakers accordingly, in this case a 63A breaker and 10mm cable ( minimum, subject to installation conditions.. )

 

[oharaf]

10mm on 45A