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.
Hmm It would be OK in Australia, where MEN is permitted, but not in the UK.
To be clear I have understood, the contactors are connecting the load to either the genset or the supply but never both at once - its not a parallel running phase synchronous unit ?
Ideally there should be a contactor pole in the neutrals as well - clearly the genset NE side needs to be solidly bonded, but really the DNO N E should not be.
If you just remove the link, so the genset needs the DNO link to earth it;s star point then there is a class of DNO side faults that upset operation on genset.
If the supply is already TNx derived, and the earthing is at least as chunky as the neutral then it will not do much harm in the short term though it violates ESQR , and it may inject diverted neutral current into the earthing network. If the supply is TT, then you may end up acting as the electrode for the substation transformer, and the preffered path for other peoples fault currents, which is not good. And it confuses any RCD on the supply side of the changeover, but I imagine there isn't one.
Hmm It would be OK in Australia, where MEN is permitted, but not in the UK.
To be clear I have understood, the contactors are connecting the load to either the genset or the supply but never both at once - its not a parallel running phase synchronous unit ?
Ideally there should be a contactor pole in the neutrals as well - clearly the genset NE side needs to be solidly bonded, but really the DNO N E should not be.
If you just remove the link, so the genset needs the DNO link to earth it;s star point then there is a class of DNO side faults that upset operation on genset.
If the supply is already TNx derived, and the earthing is at least as chunky as the neutral then it will not do much harm in the short term though it violates ESQR , and it may inject diverted neutral current into the earthing network. If the supply is TT, then you may end up acting as the electrode for the substation transformer, and the preffered path for other peoples fault currents, which is not good. And it confuses any RCD on the supply side of the changeover, but I imagine there isn't one.
