The circuit is arranged with diodes to prevent any direct connection from N to E... there's a small chance of the diodes shorting I suppose, but the size of the FE wire would mean it would blow like a fuse before any substantial current could pass. It is much the same as say, on a DC supply, allowing a device to use either 4.5v from alkaline cells or 5.0v from usb, using diodes to prevent the 5v supply trying to charge the alkalines.
The circuit is arranged with diodes to prevent any direct connection from N to E... there's a small chance of the diodes shorting I suppose, but the size of the FE wire would mean it would blow like a fuse before any substantial current could pass. It is much the same as say, on a DC supply, allowing a device to use either 4.5v from alkaline cells or 5.0v from usb, using diodes to prevent the 5v supply trying to charge the alkalines.
