How much current safe for 30m extension?

I must admit to doing much the same when I was living in a London flat - for very similar sorts of reasons and only to rig up and put away each time I used it. It obviously depends on your physical arrangements as to whether it is totally reckless or not quite totally so.

What I did, however, was to take some polypropylene cord and tied figure of eight knots on the bight every foot or so, with the loop big enough to pass the plug through. You have guessed the rest - one end of the cord was tied to the window frame and the other to the garage and the power cable just ran down through the loops. That way, the weight of the cable was taken by loops in the tensioned cord - particularly important at the ends, where otherwise the cable would have had to be tied around something. Where I had to do a change in direction to avoid the cable rubbing against anything, I just took a piece of cord from the main cord and tied it off, to a tree branch, IIRC - and then tensioned the cords to get the run I wanted..

I don't know your layout and can only advise that doing things like this is inherently high risk - but, if you are going to do it anyway, this might help reduce that risk a little. If it goes wrong, as you have been clearly told - you will be wishing that you just bought an inverter or a small genny (IIRC, B&Q do a perfectly good one for under

If you do think about leaving the cord(s) (but not the cable) in place - with a pull through extra cord so that you can pull the cable down as and when you need it, be aware that man-made cords can be very affected by sunlight, by relatively modest sudden shock loads, by abrasion, by pressure at points of sharp change in direction, by the knots and by a whole lot more. So you need to select the cord carefully with a very high factor of safety and inspect it often. Also note that birds will sit on it and do what birds do to whatever is underneath - so routing it over a neighbour's patio is not a good idea - unless you live in London*.

This sounded interesting so I checked out B&Q's website by searching for "generator".

I found this

What was the £100 one you are refiing to?

Perhaps this one

Interesting. Do you know where I can find the manufacturer's website as I would be interested in reading so specs on this and related generators.

My approach is strictly for temporary use. It will be there for a day at a time. (Maybe just overnight for a single night if I over- run the job and I don't want to put the cable and the rest of it all away in the evening and get it all out again in the morning).

Sue, that appears to be a very neat solution. It sounds simple, cheap and effective.

I like that and I think I should do the same on a temporary (one day) basis.

One variation is that I will need to lift and suspend the wire where is passes the end of the building furthest from my flat and goes off into the air. At that point I think I will need to mount a pulley in the wall (with the help of the tennamts in that flat) and then loop some string around the pulley such that the lower part of the loop can be reached from the ground. That way I don't need them to be in when I want to raise the cable up.

The thing I must think about is security. I will never ever hear the end of it if the string permitted some local ne'er-do-well to pull up a heavier duty rope and then to scale the wall by using it!

Maybe I will lift up the lower end of the pulley string from my own third story (top floor) flat by oulling another string to the pulley's string. IYSWIM!

Yup, I can see that this if fraught with dangers. In fact I wonder if it might be easier to go into the loft and thread the wire as far as I can along the inside (partiton wall permitting) and then seeing what the down drop requirements are from there onwards!