Just because a leg is grounded does not necessarily make that leg a "COMMON".
Please point to where I said this?
But I will say that I think it is very poor practice when you have your system grounded that you do not call it out in regards to it relation to ground. For the same reason I think it is poor practice to feed power to the bottom of contactors or fuses or use the shield as a current carrying conductor or other goofy things that are not explicity against code but are unintuitive.
Unless I have a very good reason to float a power supply I always tie the low or center leg to ground. This way I have predictable behavior for the fusing when there is a short circuit to ground or some other potential. Is it required? No of course not.
Please tell me what the negative is about my method?
Here is a negative for yours.
I have a panel with a 12VDC power supply for some analog circuitry that someone built a few years ago. They want to update a transducer and use a bipolar version that now requires a +/- 12VDC supply. Well, the guy who did the previous design liked your method of labeling wires, so 0v was actually labeled -12V. So now after I replace the single power supply that is in there with the new bi-polar supply, what am I going to label my actual-12VDC? Had the guy went with ANA-com or 0vdc etc, no problem. Now I either have a confusing mess or I need to make a bunch of new tags. In reality, provided the panel space is there I will probably just leave the old power supply on and put the new one on for just this purpose and label the leads something completely different.
Thinking that there is any convention or rule-of-thumb in electrical circuits that you can assume to always be true only proves that you are not yet old enough to have found out differently.
It really dissapoints me when someone resorts to using the age card and putting words in other peoples mouths to try and argue their points. I never said anything about "rules of thumb" or "can assume to always be true". I pointed out the negatives of doing it that way and why I don't like it. I didn't even say it was wrong, but only that I detest when it is done that way. I think if there is a better way, then why would you not use it?
I will tell you the same thing that I tell everyone else that has ever tried to use the age card with me to settle an argument. Just because you have been doing it that way for several decades doesn't make it right. I've seen a lot of people do a lot of dumb things for a very long time and swear by their success.
I'm old enough to understand that much!