The microwave turntable stopped because my square dish refused to become a circle

I placed a square glass dish in the microwave and started a short heating cycle.

The turntable moved one quarter turn and stopped.

The motor continued humming. The dish remained pressed against the side wall.

I stopped the microwave immediately.

The dish fit through the door and sat flat on the turntable, so I had assumed it fit the appliance. What I had not checked was whether its corners could complete a full rotation. Diagonally, the dish required more space than it did when aligned with the doorway.

I removed it carefully and transferred the food into a microwave-suitable round container that allowed the turntable to rotate freely. Before heating, I checked that the cover was vented as directed and that the container did not touch the interior walls.

The second cycle completed normally.

The square dish had not been too large in every direction. It was too large in the direction that appeared only after rotation. The microwave had discovered geometry one corner at a time.

I inspected the turntable and support ring after they cooled. Both were seated properly and undamaged. If the table had failed to turn with a clear, correctly installed setup, I would have used the appliance guidance rather than operating it repeatedly.

This was a useful distinction between “fits inside” and “fits while moving.” The same issue appears with rotating shelves, lazy Susans and any machine that needs clearance around an object, not just beneath it.

What should be checked before starting? Confirm that the container is appropriate for microwave use, rotate the unpowered turntable gently through a full circle if the manual permits, and leave clearance around corners, handles and covers?