I wander why Boundary Heat Source in "Conjugate Heat Transfer" cannot get connected with "Electric Currents,Shell" directly?

Hi everyone,
Recently, I found some question on simulating heat distribution of heat electrode circuit surrounded by air, using Conjugate Heat Transfer(,laminar) inflow model and electric currents,Shell model, but study result shows no change to temperature.
Where, Boundary Hat Source was choosen by General source (Qb: surface losses(ecs/cucn)).
Anybody know how to deal with this situation?
Thanks!