Rule of thumb.

[StokieSpark]

This diversity lark, what is the basic rule of thumb about it? add up all circuits and divide by 0.4?

 

[Des 56]

Thats one way of doing a good bit of guesswork,because with unknown loads,it is mostly just that guesswork

There are other ways
Follow the list in the on site guide
Apply the type of loading onto the installation that you think will be a maximum ( another guess)and use a clamp meter and measure it

Why they bother asking for max demand in a domestic is debateable

 

[Lizard King]

Careful not to divide by 0.4 as you will get considerably higher load than you started with....!

Seriously though, Appendix 1 of the On Site Guide is as good a place as any to start, for domestic circumstances. Where the premises are larger, i.e. multi-resident block, factories, offices etc, then it is really down to the experience of the designer/specifier to make the call. Usually this will involve making educated assessments of the likely current demand for each circuit (or each electrical 'service' if we're at an early high-level stage), adding these together and then applying a sensible diversity factor. Quite often the final diversity factor is negated (and often reversed!) by making an allowance for future spare capacity on the system (to the order of 20-25%).

LK

 

[ezzzekiel]

you should
take the highest rated circuit
then 40% of remainder

 

[Sintra]

Diversity

Lighting : 66% of total demand

Cookers : 10A + 30% balance + 5A for socket outlet

Electric showers :
100% for 1st shower
100% for 2nd shower
25% of the full load of any remaining showers

Immersion heaters : 100%

Underfloor heating : 100%

Storage heaters : 100%

Sockets & permanently connected equipment : 100% of demand of the largest load.40% of demand at every other point.

Maximum Demand

Current demand to be assumed for points of utilisation and current-using equipment

Socket-outlets other than 2A socket-outlets : rated current

2A socket-outlets : at least 0.5A

Lighting outlet : connected load with a minimum of 100w per outlet

Final circuits for discharge (flourescent) lighting : rated lamp watts x 1.8

Electric clock, electric shaver supply, bell transformer, current using equipment of less than 5w : may be neglected

Cooking appliances : the first 10A of the rated current plus 30% of the remainder of the rated current plus 5a for any socket outlet incorporated in the cooker switch

All other stationary equipment : British Standard rated current, or normal current
OSG p95-97