Newer style NEMA 5-15 plugs are polarized. The neutral pin is larger than the live pin. You must have some very old 2 pin plugs, or you got hold of a plug made in China. The Chinese plugs have pins of the same size and are even more dangerous.<p>Also chances are the sparking isn&#x27;t due to the way the plug is inserted in the socket. It&#x27;s more likely due to the fact you have connected a capacitive load such as a computer power supply, and the fact the the mating parts of the receptacle are very close to the front making a spark more visible.