The diversity of Diversity

“This is with good reason, as fairly often a non standard layout is not in fact the result of some brilliant masterstroke  of design by a hitherto unrecognised genius,  but rather some hapless cock-up by an over-keen diy type, and in that case serves as an alarm bell that there may  be more horrors to be found.”

Wise words and put in a very amusing way.

Many times I see one ring final (or radial) feeding sockets and one or two lighting circuits on a cheap rewire and in practice they last for years with few problems. 

Personally I like to see two socket circuits and two lighting circuits as an absolute minimum in any installation. That is just to reduce the chances of losing all sockets or all lights at any one instance.

If you had two identical properties with identical use then the one with two of each circuit would not use any more than the one with one of each circuit. It is dependant upon likely use total. 

Therefore applying diversity calculations often do not match.

That is why the floorspace consideration (plus intended type of use) seems more appropriate.

I recently did a rewire for a friend of mine with 5 rings and 5 lighting circuits but two of each would have been OK . It just added a bit more resilience in case of a fault (or powering a circuit down for additions and alterations).

Yes it`s ok to have two rings (or radials) on one MCB it is still one circuit. Although it is sometimes an indication that someone has created a spare way to create a shower circuit or something and modified what was originally in place. It can be done, for example, to reduce ring end to end cable lengths of a massively drop fed circuit thereby having its merits if you do not have a spare way in the consumer unit and normally you`d be happy with one circuit feeding all of those sockets (or lights) . 

Whilst having loads of different circuits can indeed make it possible for the total load drawn, the really big question is, what is the likely max current draw for anything over X time (X might be 5 mins, 10 mins etc etc etc) . How do you calculate diversity? that is the question.

“This is with good reason, as fairly often a non standard layout is not in fact the result of some brilliant masterstroke  of design by a hitherto unrecognised genius,  but rather some hapless cock-up by an over-keen diy type, and in that case serves as an alarm bell that there may  be more horrors to be found.”

Wise words and put in a very amusing way.

Many times I see one ring final (or radial) feeding sockets and one or two lighting circuits on a cheap rewire and in practice they last for years with few problems. 

Personally I like to see two socket circuits and two lighting circuits as an absolute minimum in any installation. That is just to reduce the chances of losing all sockets or all lights at any one instance.

If you had two identical properties with identical use then the one with two of each circuit would not use any more than the one with one of each circuit. It is dependant upon likely use total. 

Therefore applying diversity calculations often do not match.

That is why the floorspace consideration (plus intended type of use) seems more appropriate.

I recently did a rewire for a friend of mine with 5 rings and 5 lighting circuits but two of each would have been OK . It just added a bit more resilience in case of a fault (or powering a circuit down for additions and alterations).

Yes it`s ok to have two rings (or radials) on one MCB it is still one circuit. Although it is sometimes an indication that someone has created a spare way to create a shower circuit or something and modified what was originally in place. It can be done, for example, to reduce ring end to end cable lengths of a massively drop fed circuit thereby having its merits if you do not have a spare way in the consumer unit and normally you`d be happy with one circuit feeding all of those sockets (or lights) . 

Whilst having loads of different circuits can indeed make it possible for the total load drawn, the really big question is, what is the likely max current draw for anything over X time (X might be 5 mins, 10 mins etc etc etc) . How do you calculate diversity? that is the question.