Can't see why you want 3 CUs. An outdoor socket does not require an outdoor CU. Even a shed does not require its own CU. Run the cable in from a spare way on the house CU direct to the sockets and the lights via a switched FCU.
The standard domestic circuit in Australia is 10 amps so the two plugs would have to plug into two different circuits, not 2 sockets on the same circuit.
2.5mm is the correct cable for UK socket circuits. However, as has been said, if it comes from a plug 1.5 is OK.
Look for a RCD in your consumer unit. It is a cutout with a test button.
Two in line won't give extra protection, it will mean both or either will trip on a fault leading to confusion.
Bulb has a smart meter experimental tariff:
1600 -1900 hrs (Dinner cooking time) 29.75p per kWh
2300-0700 hrs (overnight) 7.45p per kWh
other times 12.19p per kWh.
Standing charge 20.44p per day.
This is in SE London, other areas may vary slightly.
They have to be manufactured and sold to the suppliers and fitted. The suppliers pass this cost to all of us through increased bills.
The very minimum "visible" extra costs are the batteries you have to buy for the remote unit every now and then.
But look at it this way. If every one had smart...
You will also need to get permission from your DNO for such a large load. If the neighbours complain of dimming lights when you are welding without permission they may well cut you off.
Of course it won't be a transformer. Transformers are AC devices. LED strips require DC. Unless, of course he is using a transformer then I would not expect the LEDs to last long.
You surprise me. Most electronics these days has no means of isolation (apart from pulling the plug which may be hidden). There is often a standby mode but that is not isolation.
All good points of course, but strange no one has thought about instant isolation of a gas cooker where those things could also happen.
There should always be at least one standard telephone in a house which does not rely on an electricity supply.
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