Sabotaging the electric network is kind of a well established scheme: find a node of the network, put some explosive on the pole and take it down (or the like). The network is gone for a while.
Now imagine that this organization wants to avoid using explosives and plans to do the following: a large set of conjureds agrees on switching on a high power electric device in their houses (let's say an electric oven or a water boiler, drawing at least 3 kW) at the very same time, to the split second.
Is this a realistic plan to take down the network on (at least) an urbanized area of about 500 square km?
(background info: when I was at the University during a lecture on electricity generation the professor told us that in the '80es a comedian, during a TV show, proposed to complain against the government by switching off the TV when he said to do so. The professor claimed that if he had done it, it would have caused a nationwide blackout.)