Incoming fuse size, or second fuse with solar panels and batteries?

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Llanfair Caereinion, Nr Welshpool
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My attention has been drawn to this amendment but even before that the question arises when a consumer unit is rated at 100 amp, and the DNO fuse is also 100 amp, should there be a second fuse before the CU to stop over load when solar panels and batteries can supplement the supply so one can be drawing 120 amp for an extended time without the fuse rupturing?

For me OK I have a 60 amp DNO fuse, but looking at my install I can't see any way the extra power from solar and battery is not going to mean I can in the summer draw 100 amp without blowing the DNO fuse. So should there be a second fuse before the CU. I have an isolator before the CU should that be a fused isolator?

People with more batteries can one assume draw even more power for example when part of the EV system, I would assume my inverter is the limit in my case of what extra power can be provided, which means to know the limit one needs to read the manual for the inverter before upgrading a DNO fuse, simply can't see the DNO reading the inverters manual before replacing fuse.

I have seen a second CU fitted with my solar install, and loads of isolators, but no fuse, should there have been a fuse fitted, or is it all built into the inverter to stop once the current exceeds 100 amp?

I don't see it as a problem when solar installed, but could be latter when buildings are added to installing second shower etc. I am well aware with two kitchens, so two cookers and also three bathrooms so two electric showers I could easy overload the 60 amp DNO fuse, I assumed only 60 amp as the Wylex fuse box was only rated 60 amp, now I have a modern CU there was no reason if it was to rupture not to ask for a larger one to be fitted. But it would seem the solar panels and battery now means stuck with 60 amp fuse.
 
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