My house has a 200A main panel and receives power from a center tap transformer (240V split into 120V phases). The house consumes more than 10KW of energy. I have noticed in the past that outlets on one 120V phase will sit around 105V-110V and outlets on the other phase will be 120V-125V. Recently the main water line was replaced in the house and the voltage difference on outlets between the two phases spread further while the work was being performed (90V on one phase and 140V on the other). I found that the ground for the main panel runs about 75 feet from the main panel on the back of the house to where the main water line comes into the front of the house, and they had dug up and cut the pipe which was my ground, leaving only about 4 feet of grounded pipe buried. Once the work on the main water line was done voltage differences returned to their original levels.
From what I have read, it seems like the voltage difference between the two phases would be caused by a poor return path back to neutral. However, when the main water line work was being performed my ground was severely diminished which caused an even greater voltage imbalance which makes me wonder if I need a better ground.
I have inspected the connections I can see in the main panel by removing a cover below the meter cover (exposes the 3 main bar connections) and breaker cover (exposes breaker and ground-neutral bonded connections), and I do not see any corrosion or anything that looks like it isn't to code.
Questions: 1. I thought if you remove the ground from the system completely, the voltage should still be balanced (assuming normal conditions with nothing shorting to ground), so why did losing a good ground cause a larger voltage swing between the two phases? 2. It seems like my problem is in the main panel since loads on one phase of the house cause a voltage swing on the other phase of the house (across all circuits in the house). How do I measure (like with a multimeter) to determine whether I have a grounding problem or a neutral problem?
My uneducated guesses may have led me astray. The important question ...
What is a good procedure to identify the source of the issue?
Answer: use a clamp-on amp meter to measure current through main neutral (I had a reading of 0A but an imablance of more than 20A between the two phases) and measure the current through the grounding electrode (I had 20A going through it). This confirmed that I had a floating neutral which the power company had to come out and fix.