Only true to say that N and E are at the same voltage if you are close to the point of junction, and exactly what close means depends on the pulse duration, and to a lesser extent what else is connected to earth but not to the neutral that will increase the capacitance to terra firma. But if you are more than perhaps 6 feet away the they can be 1000+ volts apart for a few microseconds during a kA surge.
But in the TT suppression there is a spark gap or at least a gas discharge device in the earth path, as semiconductors may fail short, but not fire the ADS properly In a TN system the semiconductors can go to ground and fuses will handle it.
Only true to say that N and E are at the same voltage if you are close to the point of junction, and exactly what close means depends on the pulse duration, and to a lesser extent what else is connected to earth but not to the neutral that will increase the capacitance to terra firma. But if you are more than perhaps 6 feet away the they can be 1000+ volts apart for a few microseconds during a kA surge.
But in the TT suppression there is a spark gap or at least a gas discharge device in the earth path, as semiconductors may fail short, but not fire the ADS properly In a TN system the semiconductors can go to ground and fuses will handle it.
