Cable routing through slotted hole

There is no magnetic reason not to do this - the problem with cable bunches is purely thermal, so long as the net current in the hole sums to zero there will be no overall magnetic field.


As an aside about the mechanism ..


Note that the metal box hole problem is almost never an eddy current problem, despite misleading pictures in a few text books from organisations that should know better.

There will be no electric curent in any steel (or other metal) that is at right angles to the direction of current flow - - the slotted hole thing is required to prevent magnetic losses. (eddy currents are parallel to the currents that cause them, not at right angles - eddy current can be an issue in long runs of AWA however - but in the case the current in the armour really is parallel to the driving current in the core.)

If you want a picture, the effect is that all the little dipole magnets in the steel swing round like so many atom scale compasses, trying to magnetise the steel to form a complete nose to tail loop of N-S-N-S... surrounding the current, and then having to undo it and reverse direction  50 times a second and getting all hot and bothered doing so. When there is no net current, they do not feel the urge to surround it.


Once you have this off pat, you realise you can hacksaw cut between the holes in a cast iron or steel plate to break the magnetic path, and fill the cuts

in with solder or braze metal to restore the IP rating,  which if it was a current thing , would not work.


regards Mike.

There is no magnetic reason not to do this - the problem with cable bunches is purely thermal, so long as the net current in the hole sums to zero there will be no overall magnetic field.


As an aside about the mechanism ..


Note that the metal box hole problem is almost never an eddy current problem, despite misleading pictures in a few text books from organisations that should know better.

There will be no electric curent in any steel (or other metal) that is at right angles to the direction of current flow - - the slotted hole thing is required to prevent magnetic losses. (eddy currents are parallel to the currents that cause them, not at right angles - eddy current can be an issue in long runs of AWA however - but in the case the current in the armour really is parallel to the driving current in the core.)

If you want a picture, the effect is that all the little dipole magnets in the steel swing round like so many atom scale compasses, trying to magnetise the steel to form a complete nose to tail loop of N-S-N-S... surrounding the current, and then having to undo it and reverse direction  50 times a second and getting all hot and bothered doing so. When there is no net current, they do not feel the urge to surround it.


Once you have this off pat, you realise you can hacksaw cut between the holes in a cast iron or steel plate to break the magnetic path, and fill the cuts

in with solder or braze metal to restore the IP rating,  which if it was a current thing , would not work.


regards Mike.