No that is not quite true. The high current in the cables generates strong magnetic fields, which is what causes and why I mentioned the cables "dancing around." A magnetic field, for example, is what causes a traditional type "clamp on" ammeter to operate, what we used to call an 'amprobe'. The magnetic field(s) generated by the current in the welding cables is nothing to sneeze at.
If you want to "see" this sometime, and if you have a good 200 or more amp DC welder, coil one of the cables up somewhat, and strike a big heavy current arc. The cables will MOVE!!
The transformer field is actually quite contained, by some measure. This is simply because the conductors are wrapped around the core, and the core poles are (such as E core) form what you might call a magnetic circuit. Something that is much better is a toroidal core (a doughnut core) These, used primarily for higher frequency transformers such as switch mode power supplies, computer supplies, just about any "wall wort" of late have very very little magnetic leakage because of the construction of the core
Arc gouging at 400A
Del,
I watched the videos, but came to a different conclusion. The magnetic field induced movement only happens when the conductors are very close together. The wires that are a foot or so apart don’t move. The magnetic field is defined by the current and the length of the wire. For a coil, add the number of turns. So the length of the cables, very close together provides the force to move them. They have to be very close together for this to work.
Now let’s think about a similar experiment the same distance (a couple of inches) from the welder transformer. Likely orders of magnitude more magnetic flux that close to the transformer. Lots of force to move something there. Very little magnetic flux in a wire compared to a transformer at the same current.
As you pointed out, a lot of the flux in a well designed transformer (Chinese?) is contained with in the transformer. However the wire experiment distance was a couple of inches. If we are going to compare, it needs to be apples to apples.
I still think that the magnetic field density at the same distance is much greater with a transformer than a single wire.
