I have a separate garage that was built in 2001. It has a 100 amp sub panel that is fed from the main panel in the garage of my house. The panels are about 50' apart and the wire is in conduit. The sub was bonded between the ground and neutral bars but I have separated them and there is also a separate ground rod for it. There are only 3 wires between the two panels and not a 4th grounding wire.
I have a low voltage PLT license that I use for the trade I am in and have done quite a bit of high voltage wiring in houses that I have lived in.
A couple of weeks ago I was going to use a craftsman skill saw to cut a board and when I tried to start it, the saw didn't start just hummed like the brushes were bad. The strangest part is that the light on the garage door opener flashed on and off when I attempted to start the saw. Now all 7 120v circuits in my garage don't work. I have a 220v compressor that does work but none of the 120v circuits do including ceiling lights.
I have a digital multi meter and have checked voltage at the main breakers. It is consistent at 120v at both breakers. As I have investigated the situation I have found that 3 of the circuits when energized will cause the voltage to drop from 120v to 110v and the other leg goes up to 130v. Even after I have disconnected the wiring on those circuits I cannot get power to the other outlets or lights. With the power off, I have also checked with an ohm meter between the neutral and hot wire at the breakers and it shows open on all circuits. When I have the light switches on and plug in my irrigation controller the transformer hums loudly and the lights do seem to go on.
What am I missing? Where do I check next?