Why is POWEReasy showing a warning?
Your site has observed high unbalance in voltage amongst the three phases. IEEE1159 requires voltage unbalance be maintained within a 3% range. High voltage unbalance can lead to lowering the life of three phase equipment.
When do you need to fix this and why?
This condition is coming from your supply. A 5% voltage unbalance is sufficient to reduce your motor life by half. To protect your three phase devices it is advised that you install suitable voltage regulation devices.