Phase converters in general typically don't require much maintenance, if at all.

If you regularly check a few components and keep up with anything you may see that's out of the ordinary, you shouldn't have any problems.

Be sure to check their ventilating slots and make sure they are open and unobstructed. Check automatic controls and have their contacts inspected at scheduled intervals (if applicable,) and last but not least have the bearings, which are factory sealed, greased periodically.

There you go, low maintenance.