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John Rumm John Rumm is offline
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Default New Induction Hob - CU Change Needed?

On 17/03/2019 09:22, Kevin H wrote:

New kitchen planning underway. Looks like we're going to replace a
gas hob with an induction hob requiring a 32A connection back to the
CU (photo he https://goo.gl/CGJfg3)

The CU is pretty old (1995 when the house was built). There is a


It may be old(ish) but its a decent brand and appears to be in good
order. (although that non Mem/Eaton water heater MCB does not fit that
well, and leaves a larger than desirable gap in the facia)

spare position but on the non-RCD protected side. I assume using this
slot would not be acceptable practice?


You appear to already have a cooker circuit there with a 32A MCB on it.
Any reason why you are not using that?

If you use that then its a like for like swap of appliance, and you
don't need to meet new requirements for cable protection.

If you want a completely new circuit, then looking to see if there is a
RCBO that will fit that CU might be a more pragmatic answer. (especially
with the space afforded by removing the water heater MCB - so even a
double module RCBO would be ok).

(Another option for more RCD space would be to get a longer bus bar for
the RCD side, and shorted the non RCD side, so you move the split to the
right a bit - but the RCBO would be a better choice IMHO).

I've noticed that the current cooker is also on the non protected
side of the CU,


With a single RCD "split load" installation like that, its quite common
to want the cooker on the non RCD side. Cookers (and anything else with
a mineral insulated heating elements in close proximity to moisture) are
a common source of higher earth leakage currents that are prone to
"sensitising" RCDs or even nuisance tripping them. Also there are not
many likely electric shock scenarios with a bit of fixed equipment like
a cooker.

and given there is a combined isolation switch/13A
outlet next to the cooker I was wondering if regardless of the need
to add the induction hob this alone should be a reason to update the
CU, as that socket isn't protected by the RCD?


Its a reason to get shot of the combined "cooker point". Since the
socket really would benefit from RCD protection, and it also reduces the
nominal capacity of the circuit by 5A [1]

[1] http://wiki.diyfaq.org.uk/index.php/Diversity

Ignore the water
heater note - the immersion heater is no longer connected.

A final question. Any reason not to use 10mm on the 10m run to the
kitchen? Hob and oven won't be sharing a circuit.


Nothing inherently wrong with it, although it would likely be overkill
unless you have many de-rating factors to contend with. 6mm^2 is more
commonly used, and has the benefit of being easier to work with.


--
Cheers,

John.

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