Needed to test a 5 volt 20 amp power supply was working at full current and had no suitable resistive load. Google lead me eventually to a 3 minute youtube video:-
https://www.youtube.com/watch?v=WECW88rJYrE
Using some scrap 0.7mm O/D (and some 0.4mm) enamelled copper wire I was able to dump the 20 amps and later 35 amps as a test of a transformer.