Can I ask your opinion in relation to neutral /earth on this rather untidy changeover arrangement located just downstream of the main isolator? There are 2no 3-pole contractors with mains in bottom left and generator in bottom right. On the stud adjacent they have connected gen neutral, DNO neutral and installation earth. The arrangement means a self-imposed conversion to an unauthorised TNCS. I can’t be sure if the existing supply is already TNCS.
