It is about 250 feet of 4/0 URD from PoCo transformer to meter base. Then about 40 feet of 4/0 URD from meter to house. And 425 feet of #2 URD from meter to pole barn where the light is located. I know that there is a substantial VD at the pole barn with any load running. But the light is the only load on the pole barn service at night when the issue occurs. I changed the light ballast and photo eye to 240 volt. Still shuts off when A/C in house starts or any other large load. It just baffles me that the A/C at the house affects the barn light.
