My compressor is on its own 240 breaker by itself. While testing all wiring to the garage we noticed that one of the feed wires to the breaker box from the meter approximately 100 ft from from each other was putting out 123 volts & the other side read 0.03 so only half the box is hot. About 5 yrs ago we switched from overhead wiring to under ground for both house & garage & are separate from each other & all has new wiring breakers & boxes. In the garage I currently have all breakers removed except 1 breaker that operates the led lights & outlet boxes, 1 breaker that is connected to a motor home, & 1 that runs the pump for our water well Which the pump is above ground. The compressor breaker is pulled because I feel the motor is fried it had power to all the wires in the back of motor but doesn't work. Now back to the well, every time the well kicks on it draws enough power to dim the lights in garage almost totally out. The pump on well is 120 volt. I'm thinking I have a bad underground main wire from the meter to the breaker box or could it be something else. The power on both each of the lead wires at the meter show 123 volts each. I appreciate any answer you can give. Thank you
This is probably a classic supply line problem. If the pump is on an opposite leg from the lighting, it's "using up" limited neutral capacity due to a poor connection Dangerous. If the pump is on the same leg as the lighting, well (no pun intended), it's taxing a bad hot connection. But I doubt that because the pump probably wouldn't even run. As Ed, 3ph and Harp have repeatedly said here, this situation sounds like an open or compromised neutral feed. Dangerous for everybody and everything. You're going to need to take measurements in various panels to make sure you have 240 across the hots and 120 to neutral and ground. Just recently it was suggested in a situation like this to first contact the power company as they will come out for free to make sure their connections are solid. Let us know what you find, we all learn from that.
I would first check at the feeder breaker, a loose connection there could be the issue , you have the sub in the garage open so you would have seen a problem there but make sure it’s not a buss /lug issue. Check the feed if you have both sides good there a break in the underground wiring is not uncommon, depending on the size of the cable it may be worth it to rent a cable tracer like the greenlee 521, these are really handy tools for finding faults (my rental place has them but it only takes a couple times to pay for one). The cable can be repaired in ground with a possibly 2 splice kit(s) no box needed.
If the voltage is bad at the breaker check the breaker itself and the buss a bad connection to the buss can damage the position or buss depending on the brand panel.