Disagreement?On the note of the 230 or 240 disagreement lol!
You can use 240V as that is what all the manufacturers will quote on the equipment.Would I be correct is just using a safe margin for example if its a 13amp extension lead it will be 13 x 230v = total load not to exceed 2990watts or 13 x 240v = total load not to exceed 3120watts.
You will be perfectly safe with 3,000W.So to make it easy to understand I could assume a number to act as a safety zone that is less than both of the above numbers. Say 2800watts total load. So i could take any 13amp extension lead and use 2800 watts as its Max load figure. this way I'm lower than both 13 x 230 and 13 x 240 so therefore using 2800watts as my 'do not exceed' figure I in theory can overload the extension lead and all should be safe enough.
The point really is that you are using Watts which if you multiply Amps by 230V will give a lower Wattage so be extra safe.
We, on the other hand tend to use Amps so if you have a 3,000W Immersion heater this will be stated by the manufacturer as 3,000W @ 240V = 12.5A.
If you divide 3,000 by 230 it will give 13.04A but this is not correct because at 230V the Wattage will be less -
Actually 2,755W @ 230V = 11.98A