Mike L writes, On old fashioned lamp plugs, both prongs on the plug are the same size & the lamp works any way you plug it in. On new plugs the prongs are different sizes. I’ve been told this is to keep the polarity constant. What is polarity & why does it matter.

Polarity refers to the two conductors of an electrical circuit. These conductors are called poles, as in the poles of a magnet. One pole is a supply & the other is a return. The supply is the black or “hot” wire & the return is the white or “neutral”.

In modern receptacle outlets one slot is taller than the other. The tall slot should be connected to the neutral conductor & the short slot to the hot. That’s normal polarity.

Modern plugs match these receptacles & correspond to wiring in lamps, appliances & tools. A lamp is wired such that the neutral wire goes to the casing of the lamp socket & the hot wire goes to the tab or button at the bottom of the socket. The routing path is an important safety feature. If your installing a bulb without unplugging the lamp, you’re more likely to accidentally touch the socket casing than the socket tab. For a tool or appliance, the hot wire is fed through the switch. That means there’s only an inch or two of energized wire in the case of the tool or appliance. If the polarity is reversed, virtually all the wiring in the case (including all the motor windings if there’s a motor) is energized when it’s plugged in. Damaged insulation on a wire or a motor winding could energize a metal tool case, creating an electrocution hazard. Correct polarity is another way of putting the odds in your favor.

When replacing the cord or plug on an appliance, be sure to get the connections right: The neutral wire is the “identified” conductor. It may have ridges running along it’s length or a colored thread between the wire & insulation.