On Sat, 30 Jan 2016 23:24:59 -0600, "dangerous dan"
wrote:

While looking at this wall plug,

Do you mean the wall outlet, the receptacle? I think so. (Or the
plug on the end of the cord?)

I noticed it has a designated side for white wire, and a designated side for black wire. In the past I never saw that on a plug and just put it on whichever side was handy.

Is there a valid reason for putting a specific color wire on a specific side? I personally wouldn't think so, but maybe an electrician would know a reason, or someone more knowledgeable.

That's why they call you dangerous dan. They haven't always been
labeled white and black but the screws were silver and brass colored
and people who connected them were supposed to know which went to
which. This goes back to the 50's and I think earlier. The
practical light bulb only goes back to 1870.