Polarization has nothing to do with switching, it has to do with SAFETY. In the old days when 3-wire (hot, common, ground) was not required, the polarized plug was intented to keep the case of the tool/appliance connected to the "common" (white) wire in order to help reduce the electrocution hazard to the operator. A typical plug/outlet looked like this:
The above 2-wire connection still posed a serious safety hazard because even though the "common" is the normal return path of current to the source, it can, and will be, at some potential above earth ground - that means you can very well be electrocuted by the "common" (white) wire. 2-wire devices are still perfectly legal provided that neither conductor is attached to the case or any other exposed conductive surface of the tool/appliance - sometimes you will find 2-wire tools/appliances still carrying the "double insulated" identifier which is what allowed a mfg to legally use a non-polarized connector on a device as the device did not have any exposed conducting parts deliberately connected to a current conducting wire/part. This still poses a problem because a mechanical fault can result in exposed conductive surfaces becoming energized and thus injuring/killing the operator. If you'll note the "W" designation on the above gif identifies the larger "common" blade. 2-wire male connectors (plugs) are still widely used on tools/appliances but 2-wire outlets are normally limited to only low-voltage DC (direct current) supplies and control/signal line connections.
The result was making the 3-wire connector device the new standard.
On the above you will note the "G" designation to identify the "Equipment Ground" terminal and "W" to identify the "common" terminal. The ONLY place the "common" and "EG - equipment ground" will EVER be connected is at the service entrance (or source if using a generator). The reason for this is that the common line (center tap from the utility transformer) must return to earth ground - at every downstream point from the service entrance, the "EG" MUST be isolated from the "common" conductor! I see so many people who "think" they know what they're doing making the assumption that it doesn't matter if it's white or green and many who don't have a clue which end is up when it comes to electrical creating extremely dangerous conditions.
If you don't know what you're doing, don't touch it!
What does this have to do with gun building? EVERYTHING because it has to do with SAFETY. You wouldn't hand a loaded and cocked gun to your 3 year old grandchild and walk away would you? Then why create a situation where you'll cause your 3 year old grandchild to be electrocuted? Think it can't happen ... think again! Grandpa "thought" he knew what he was doing and "thought" it was a waste of money to hire a qualified electrician to wire his workshop - A few months later his 3 year old grandson under his care died by electrocution in that workshop because of grandpa's combined ignorance and frugality.
Every year in the United States around 400 people DIE via electrocution and another 1,500 suffer serious/permanent electrocution injury because of improper installed wiring. Faulty wiring is also responsible for more than 110,000 fires resulting in more than 850 deaths and 4,000 serious/permanent injuries annually.
