Effect Of Cable Rolling

Depending on the size of the attached load, there might be a problem with heat dissipation from concentric turns. Extension leads, for instance, are intended to be used fully unwound from the reel, and if left partly-wound on the reel are usually subject to de-rating.

I have also seen it cause a severe voltage drop, worse than just the extra length of wire. Think of it as an air-core reactor.

The magnetic field is probably not the biggest problem (unless there is ultra sensitive things in the neighborhood) The problem (and danger !) lies in the heat production of the "coil" you make by "winding" the cable. Laying it out i zig-zag would be the best sollution, if you don't have the place to do this, make the windings (circles) as big as possible and CHECK the temperature of the cable when it is in use. I witnessed one time how a roll of cable just melted into one big "clump" of plastic and copper. And it was NOT because there was to much current flowing through that cable. It happened because of the generated heat.

For this reason the "fuse" you see on some extention-cable-rolls is not a current fuse, but a THERMAL fuse !

Does this sound safe, leaving an energized cable lying in coils on the ground?

Never use cable rolled in a coil, it will heat up and may cause a fire.

Magnetic field will almost not appear because the "coil" is bifilar. The major problem is the warming.

Unroll it before you apply any power unless you derate it by about 90% even if you are lucky and it doesnt melt or catch fire it will be so badly damaged you will have to throw it away

"Figure-eight" the extra wire. The magnetic will balance and the heat will be manageable.

We routinely perfom this with high voltage, running through 4/0 for every rock concert you've ever been to. Temporary power cables are often too short for desired runs and need be extended. "Figure-eight-ing" the coil prevents connectors from fusing together or burning the casing off the wires.