I have followed this post with interest and there have been a lot of very good replies with good explanations.
But I keep thinking something is missing. And that is that the definition of a neutral conductor is misunderstood.
I know I am going to get a lot of flack about this but it is important understand grounding and neutrals and the differences.
By definition a neutral conductor [White] is a conductor that is connected at to the ground [Earthed, Grounded, Bonded ] at the source. That is not to be confused with the Grounding conductor [Green] while they are the same potential they are not the same and caution should be used when discussing or using them.
For uses of the term "ground" or "earth" in electricity but not in the context of mains wiring, see ground (electricity).
As the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures. Current carried on a grounding conductor can result in objectionable or dangerous voltages appearing on equipment enclosures, so the installation of grounding conductors and neutral conductors is carefully defined in electrical regulations. Where a neutral conductor is used also to connect equipment enclosures to earth, care must be taken that the neutral conductor never rises to a high voltage with respect to local ground
Ground or earth in a mains (AC power) electrical wiring system is a conductor that provides a low-impedance path back to the source to prevent hazardous voltages from appearing on equipment. (The terms "ground" and "earth" are used synonymously here. "Ground" is more common in North American English, and "earth" is more common in British English.) Under normal conditions, a grounding conductor does not carry current.
Neutral is a circuit conductor that normally carries current, and is connected to ground (earth) at the main electrical panel.
In the electrical trade, the conductor of a 2-wire circuit connected to the supply neutral point and earth ground is referred to as the "neutral. [1]
In a polyphase (usually three-phase) AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors, but may carry very little current if the phases are balanced.
The United States' National Electrical Code and Canadian electrical code only define neutral as the grounded, not the polyphase common connection. In North American use, the polyphase definition is used in less formal language but not in official specifications. In the United Kingdom the Institution of Engineering and Technology defines a neutral conductor as one connected to the supply system neutral point, which includes both these uses.
All neutral wires of the same earthed electrical system should have the same electrical potential, because they are all connected through the system ground. Neutral conductors are usually insulated for the same voltage as the line conductors, with interesting exceptions
If you are using a UPS with a Neutral then it is bonded to the chassis and would be the same electrical potential as the Ground connection that not to say they you can't have or use an isolated UPS or transformer but they would not have a Neutral but they would have a Ground connection. They must be clearly marked so there is no confusion as to the potential.
Excuse me for stressing the difference but I have seen people get severely shocked by not knowing and understanding the difference. You can spend many hours trouble shooting a system with a broken neutral the symptoms will keep changing depending on what's powered at the moment
NFPA require that all power sources have one leg bonded to the ground or chassis at the source and only at the source. While grounds or bonds connects at every point that it is exposed box, device whatever.
If you follow the code 24VDC power supplies need to have one leg connected to ground. Not that this is always followed I have seen a lot of problems with systems with multiple power supplies that were not bonded together. Spent many hours chasing down intermittent problems because of it.