  In PT symmetric systems, the notion of non-Abelian frame charges enables
multiband topological characterization of the degeneracy nodes through
examining the eigenvector frame rotations. Interestingly, some features of
these frame charges can be viewed as an analogue of electric charges confined
in conducting wires, only that they flow in momentum space along nodal lines.
However, these frame charges are not integers, and non-Abelian signatures
emerge when braiding between adjacent band nodal lines occurs, which flips the
direction of the flow. In photonic systems, we discover that the photonic
{\Gamma} point serves as the source or sink of such frame charge flow due to a
hidden braiding induced by the often-ignored electrostatic mode at
zero-frequency. We use biaxial photonic crystals as examples and show how
complex nodal line configurations can be explained as the topological
consequences of the frame charge flow from the {\Gamma} point to the Brillouin
zone boundaries. We further designed and fabricated meta-crystals to
experimentally observe these line nodes as manifestation of the non-Abelian
frame charge flow.
