Andrew Gabriel wrote:

I would suggest you make up some rules for yourself for extension cords

Never use them as a substitute for getting the required number
of fixed sockets installed in the right places.
Always use high quality ones, not bargin basement ones.
Leads up to 12m long must be 1.25mm² conductors.
Leads up to 15m long must be 1.5mm² conductors.
Leads up to 25m long must be 2.5mm² conductors (which won't fit
into a standard 13A plug).
Don't use high current appliances like kettles and heaters with them.
Don't forget to get the installation inspected and tested regularly,

in each of the above cases, why?

NT