Motor 101

The equation has not changed, but governments have tried to interfere with technology. By the way it is the CHANGE in torque is equal to the CHANGE in voltage squared.

Some time ago now, there was a "harmonization" of voltages in Europe and the UK. The UK was using 415V, much of the EU was using 380V, so the "harmonized" voltage became 400V as a compromise. The voltage supply levels in the different countries never actually changed, but equipment mfrs were supposed to all make their motors to be 400V 50Hz, with the understanding that they would be within operating tolerance with both 415V and 380V supplies. That way everything would appear to be "normal". If you have older motors however, they will still say what their original design voltage is. It probably doesn't matter much though.