Diversity

Diversity can be more of an art than a science - so much depends on individual circumstances and as a result the published circuit-based guidance tends to be very conservative.


There are a variety of different approaches - trying a few different ones in the same situation can sometimes be illuminating. Some observe that final circuits are designed to satisfy wide range of criteria - not just the size of loads - which typically results in a larger number and/or higher rated circuits that strictly necessary - so ignoring the circuits you actually have and basing diversity calculations on the minimum possible number/size of circuits from just the load point of view can give more realistic results. Going further you can just base calculations on typical Watts per square metre of floorspace and ignore the division into final circuits altogether.


Your example sounds a little unusual (rather a lot of showers for what seems (judging but the power and lighting circuits) quite small office areas). You'd normally have more diversity to apply at each DB/submain so things don't normally add up anything like as fast as your 900A suggests. If you have a three units per floor and three floors then you'd have a total of 18 showers - even applying the OSG tables you'd only take 100% of the first two and just 25% of the remaining 16 - which even doing likewise for the other loads will come out far lower then just adding up the per DB totals. Plus of course, for this sort of size installation, you'll probably spread your single phase loads over three phases - so reducing your numbers by two-thirds.


  - Andy.

Diversity can be more of an art than a science - so much depends on individual circumstances and as a result the published circuit-based guidance tends to be very conservative.


There are a variety of different approaches - trying a few different ones in the same situation can sometimes be illuminating. Some observe that final circuits are designed to satisfy wide range of criteria - not just the size of loads - which typically results in a larger number and/or higher rated circuits that strictly necessary - so ignoring the circuits you actually have and basing diversity calculations on the minimum possible number/size of circuits from just the load point of view can give more realistic results. Going further you can just base calculations on typical Watts per square metre of floorspace and ignore the division into final circuits altogether.


Your example sounds a little unusual (rather a lot of showers for what seems (judging but the power and lighting circuits) quite small office areas). You'd normally have more diversity to apply at each DB/submain so things don't normally add up anything like as fast as your 900A suggests. If you have a three units per floor and three floors then you'd have a total of 18 showers - even applying the OSG tables you'd only take 100% of the first two and just 25% of the remaining 16 - which even doing likewise for the other loads will come out far lower then just adding up the per DB totals. Plus of course, for this sort of size installation, you'll probably spread your single phase loads over three phases - so reducing your numbers by two-thirds.


  - Andy.