480v grounded 3 phase serving an oil well pump jack

[ActionDave]

I'm predicting it's a corner grounded service properly wired and the problem is with the equipment.

 

[hillbilly1]

In the picture, you can see each transformer has a wire connected to its tank. This wire is spliced to the utility grounded conductor and to what looks like a white conductor. It then looks like 2 black and 1 white conductor go down the pole as service entrance conductors. We don't see the service entrance equipment, which is where the GEC is likely located.

Looks like from the picture, it is corner grounded at the pole, though we can’t see it, the ground looks to loop around and terminate at each lug on the back side of the transformers, so there may, or may not be a GEC connected at the service, but as you say, we don’t have pictures of the service.

 

[Elect117]

It is corner grounded B.
I think the OP should look at if they have any rusted out boxes, connectors or poorly bonded metal conduits.

Motors are resilient and will work through a lot of issues. It can make it hard to track down stuff when it only fails every 6-8 months. Open deltas can also cause some issue on their own.

You are probably going to need to power monitor the service for a week or two in order to really know the answer.