Excessive Neutral Current
The basic aspects of our electrical system have been around for over 100 years. During this time we have developed a pretty good idea of how to generate, transmit, distribute, and maintain electric power.
The most typical type of distribution wiring is a three-phase wye system. Three-phase delta systems are also very common, especially for motor and heavy machinery loads. Nearly all commercial an industrial facilities have three phase power, a large portion of it distributed as a wye system.
With a wye system comes the expectation that if the three-phases have about the same amount of current, then the neutral will have very little current. If high currents are measured in the neutral, or at least higher than we expect, problems may result.
Current in a facility or business is dependent on the loads inside. Therefore, there are no significant external factors that affect how much current winds up in a panel or a neutral.