I've seen it happen. Peeps buy a drum for the cable and wind all the spare on that. Saw a fella with MH, hooked up wound all spare on drum, put under van, (he was only short distanca from EHU) all melted during evening (was in winter) and blew most of the site, and done damage in van.Its like when your cable goes very stiff after a few years you can leave it coiled, have heater on for a few mins, then you can coil it up nice and easy.
Hi people new here and have been looking in wonderment of all this I have been missing, anyway my little trick so this doesn't happen to me is simple I wind my EHU back to front. ie caravan end first, that way I have to unwind it all to be able to plug it into van.
Quote: Originally posted by Gongoozler on 01/2/2010.... A single core of wire will have a magnetic field, but with 2 or 3 core mains cable the current will be flowing both ways and so the magnetic fields will cancel.
If this were true then solenoids as in a/c relays would not work and neither would induction heaters, the magnetic field is there and will attract ferrous metals but won't magnetise them (you'll need DC for that)
My experience of this was when I borrowed a reel of 8mm cable from my father to supply power for lighting in a temporary theatre, he wasn't best pleased when he found out I hadn't unwound the complete reel and all the time it was in use we were happily playing with the magnetic field it was creating in the centre of the drum
Quote: Originally posted by Rune Caster on 04/2/2010
Quote: Originally posted by Gongoozler on 01/2/2010.... A single core of wire will have a magnetic field, but with 2 or 3 core mains cable the current will be flowing both ways and so the magnetic fields will cancel.
If this were true then solenoids as in a/c relays would not work and neither would induction heaters, the magnetic field is there and will attract ferrous metals but won't magnetise them (you'll need DC for that)
My experience of this was when I borrowed a reel of 8mm cable from my father to supply power for lighting in a temporary theatre, he wasn't best pleased when he found out I hadn't unwound the complete reel and all the time it was in use we were happily playing with the magnetic field it was creating in the centre of the drum
Post last edited on 04/02/2010 15:40:16
When you wrap a mains cable around a drum you create two solenoids (ignoring the earth cable, but who needs one of them) with roughly equal but opposite currents. There will be some difference between the current in the live and in the neutral cable so the cancelation won't be perfect, hence the residue field in the middle of the drum.
If you had split the cable and wound the the live around one drum and the neutral around another one, thus seperating the two solenoids, you would have had much stronger magnetic fields to play with (but I suspect your dad would have been even less pleased with you).
[B.T.W. This type of cancellation is basically the same principle as used in balanced microphone cables to stop them picking up the local taxi radios.]
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Topic: melted my ehu cable
