"Andy Wade" wrote in message
...
Stefek Zaba wrote:

Fairy neurf. For an entire cooking installation - hob + oven(s) - it
snipped
'Tis a common source of confusion, especially with lighting circuits
where 1A allows no diversity on an individual circuit but 1B allows 66%
diversity (household) on the lighting load's contribution to the
installation maximum demand.

Andy

Diversity is all well and good, but...................

Who here prefers to make the installation as safe as they can? In my view,
diversity is good on loads that you know will only demand a surge lasting
for a few seconds, but it is not the safest for loads that can exceed the
safe limits for minutes at a time.

If you know that a total load runs safely at 32 Amps, then the installation
should reflect that fact, and be designed to allow for that safe total
loading. The matter of diversity rules could show that the total load of 32
Amps will only be demanded for five minutes at a time though, so why can't I
allow for the drop in the running load in my design? I know the cable and
switch gear can withstand a higher current flow for that length of time, so
this would make my installation much cheaper with the lower graded
equipment.

My honest view on diversity ruling is it is not totally safe. OK if a load
is known to only demand a start surge that lasts for 2, 3, 4 or 5 seconds at
a time, then drops immediately to its constant running level. For loads
which you know can demand that higher current for lengths of time verging on
minutes, then diversity rulings are tosh. If the load is known to demand
higher currents for sustained periods, then the design of the installation
should reflect this fact.