ECN Forum Forums Code Related Discussion NEC & other Code issues Circuit conductor grouping

Are you saying the 12-3 has an "A" phase from one panel and possible a "B" phase from another panel?

This would result in neutral circulating current between the two panels.

Are the panels off the same transformer?

While not compliant, it would not result i induction issues.
IF I AM READING YOUR POST CORRECTLY.

But I would suggest rewiring to correct the issue.