2 hobs on a 6mm radial ????????

[Robojin]

Have I missed something here but is diversity not supposed to be use to make sure the max demand of the WHOLE install is under the DNO's fuse rating.Individual cable's and protective devices should be sized for the full expected load when designing, diversity has nothing to do with this stage of design.

Just had a look at pg95 in the OSG, as always open to interpretation, para 3 says use table 1A on individual circuit design making allowance for diversity, para 4 says when assessing whole installation don't add each individual circuit together to arrive at the demand but refer to 1B, para5 says that if you do add each individual together to assess total demand, you must apply a further allowance but not from table 1B as this the responsibility of the designer, presumably refer to the appropriate reg in the Red book then, ho hum!

 

[SPECIAL LOCATION]

Have I missed something here but is diversity not supposed to be use to make sure the max demand of the WHOLE install is under the DNO's fuse rating.Individual cable's and protective devices should be sized for the full expected load when designing, diversity has nothing to do with this stage of design.

The only way this circuit should go live is if the MCB is rated at less than the cable rating including any factors for the way it is installed (surface, buried etc.)

Erm....

IMHO you have missed something! :|

311.1 Maximum Demand and DiversityFor economic and reliable design, the maximum demand of an installation shall be assessed. In determining the maximum demand of an installation or part thereof, diversity may be taken into account.

"or part thereof" not whole inst' i.e. a final circuit.

and to elaborate on what Robojin said..

paragraph 3 is quite clear that current demands of a final circuit re points of utilisation and where appropriate allowances for diversiuty...

And the last paragraph o pg 95 refers to alternative methods..

but the bottom line is the responsibility of the installation designer!

(the name on the certificate)

Ultimately these figures are all used as part of the overall Max load calcs..

But individual circuits diversity is also appropriate in deciding circuit load..

thus MCB size... installation methods thus cable size etc...

A sub-main to an outbuilding could quite reasonably have a diversity applied..

yet at the main CU it is in reality just another "Final circuit"!