Electronics/Interrupting electrical flow
Is there a device or a way to block/interrupt/disrupt the flow of electricity in a cable or cord without cutting into it, like with magnetism, probably?
Of course, magnets can be used to generate an electric current, and the direction of that current depends on the orientation of the magnets, so is it possible to set up a magnetic field that would just stop an electrical current because the magnetism makes the electrons want to flow the other direction? We've also probably all seen some movie where a spy clips a little device around a cable or wire and intercepts the signal without cutting it open and leaving any sign of tampering, so I wonder (if that's even legitimate) if something similar is possible with blocking or scrambling it like crimping a garden hose.
I was at my friends home the other day. He was showing me his solar panel installation. The power company installed a totally new meter box on the corner of his home. It is a switching system which monitors the power coming into his home whether from the solar panels or from the power company. When the sun is shining brightly and the solar panels are putting out more than the house is consuming it switches the extra power back into the power company and the meter gives the home owner credit for supplying power to the grid. If the solar panels can not supply sufficient power to the home then the power company makes up the loss. The power meter has the switching system for this installed into the meter box.
What you are talking about is something quite different but perhaps the same principles could apply. It would require the engineering of an alternate source that would be applied to cancel the power coming down the line. It could be done and would be an advanced engineering project to design such a device.
But, the best way is to install an ON/OFF switch; either mechanical or electronic, either hard wired or software or virtually driven.
Magnets could be used for doing this by installing magnetically operated reed switches that when the magnetic field comes near the reed switches they click off the flow of power. This would be a very simple and low cost system but does require the breaking of the power line and adding the magnetic reed relay elements into the electric delivery line.
There are many devices that clip over a power line and measure line parameters from sensing the current's magnetic field but these are for measuring current flow and cannot alter the flow of current in the power line.
But causing the power to be disrupted anonymously without tampering the physical line is quite difficult on its merits. However, if the power system was known to have an automatic control system at either end of the transmission line you could conceivably introduce an rf or digital signal onto the line which would jam or host control the main control panel.
Maybe this will give you some further ideas. Let me know if you need more.