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.
Does the installation have its own earth electrode suitable for the generator when the supply is lost?
If it does have a suitable earth electrode, then it depends on whether the installation is PME as to whether danger is immediately possible
If it's already PME, and main bonding is suitably sized for that, then immediate danger is unlikely, It's a breach of legislation (if it's an LV supply under ESQCR and that should be noted) so there's a choice of C3 or FI - I'd go for the FI and reason being breach of legislation.
If it's not already PME, or bonding is not suitable, then the installation and service cable are susceptible to damaging diverted neutral currents at any time - Code C2, or C1 if signs of overheating of any protective bonding conductors already. Again note possible breach of legislation - if bonding not suitable sized for PME, appropriate ref to Chapter 54.
It if does not have a suitable earth electrode, then I'd be tempted to go for C1, citing no suitable means of earthing for an intended mode of operation (mains loss could remove the link between N and/or supply means of earthing and Earth), ref Regulation 551.4.3.2.1. And again note possible breach of legislation.
Does the installation have its own earth electrode suitable for the generator when the supply is lost?
If it does have a suitable earth electrode, then it depends on whether the installation is PME as to whether danger is immediately possible
If it's already PME, and main bonding is suitably sized for that, then immediate danger is unlikely, It's a breach of legislation (if it's an LV supply under ESQCR and that should be noted) so there's a choice of C3 or FI - I'd go for the FI and reason being breach of legislation.
If it's not already PME, or bonding is not suitable, then the installation and service cable are susceptible to damaging diverted neutral currents at any time - Code C2, or C1 if signs of overheating of any protective bonding conductors already. Again note possible breach of legislation - if bonding not suitable sized for PME, appropriate ref to Chapter 54.
It if does not have a suitable earth electrode, then I'd be tempted to go for C1, citing no suitable means of earthing for an intended mode of operation (mains loss could remove the link between N and/or supply means of earthing and Earth), ref Regulation 551.4.3.2.1. And again note possible breach of legislation.
