Stefek Zaba wrote:
Fairy neurf. For an entire cooking installation - hob + oven(s) - it
indeed seems entirely reasonable to me to consider the design load as
diversified, as you simply can't draw the flat-out load for any serious
length of time. For a 4-ring hob - well, it depends on your style of
usage! Chez nous, it's common enough to be doing large pans of pasta,
sauce, soup, and fried-things to feed medium-sized hordes of transient
teenagers; again the simmerstats mean that the full-on load won't last
long, but I'd still be chary of connecting through a 13A plug-n-socket
and a 1.25mmsq flex (OK, I sneaked that headroom-lowering bit of spec in
without any evidence just to bolster my point ;-) than a 20A DPsw and
2.5mmsq hob feed.
Oh I agree. I wasn't for a moment trying to suggest that it would be OK
to connect it via a 13 A plug or FCU. In any case the "came with flex
and fitted plug" bit of the story now seems to have been discredited. A
dedicated 16 A circuit is the minimum acceptable, and 20 A preferable.
(I doubt that the product standard would allow it to be fitted with a
1.25 or 1.5mm^2 flexible cord in any case.)
S'like that with diversity, innit - as the Good Book says, its values
are 'only for guidance because it is impossible to specify the
appropriate allowances for diversity for every type of installation...
As you hinted, the more independently switched loads there are, the
safer one's diversity assumptions become - it's the central limit
theorem in action, I guess. The OSG's cooker rule undoubtedly evolved
in the era when when the four-rings-grill'n'oven cooker was the only
sort and it's certainly stood the test of time for that type of
appliance. For a plain 4-ring hob alone I guess we'd agree that it's
getting a bit marginal.
The figures given in Table 1B therefore may be increased or decreased as
decided by the engineer responsible for the design of the installation
concerned.' Applying which, I'd be happy connecting a 5kW hob to a 13A
socket (well, FCU) for Granny, where Granny's been given such a hob as a
Christmas pressie, there's no heftier cooker circuit to use, and she's
living on her own;
Even that's dodgy. Granny will die; the house will be sold...
I'd be most *un*happy putting a 5kW hob on a 13A
accessory in a communal-use kitchen (student kitchenette, yoof hostel,
etc) - and to be fair the Good Book would be unhappy too, as it's not
'household' - and like the OP I'd be chary of the arrangement in a
bigger-than-single-person household.
Absolutely.
But thanks for the clue-by-four about the significance of Table 1A vs
1B, for all that!
'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
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