UK Backup 106A generator earthing arrangement questions

[kediss]

5 single phases to one huge property.



Backup generator which can take about 106 amps split between 2 phases - 1 phase will be wired through the 2 pole ats which has been pre installed with the earths linking through to the pme system ( think for a 32a backup generator ) and then the other phase has a 2 pole manual transfer switch with a commando socket rated to 63a but it’s a 30-40m run so you could potentially use another phase which feeds 2 db’s



I’m sure you can limit things on the generator to control distribution of power and how much but haven’t got to that yet.



Generator also has a 100ma rcbo and 2 main sw’s installed



Earthing arrangements : 5 separate pme supplies sharing neutral and earth.



Generator speced to have an earth rod installed.



Thinking about TT’n the whole lot and making an island while keeping the pme separate. and as I dont want different potentials from generators tt earth



What’s everyone’s opinions is that my safest route or can I connect the pme to a 106 amp generator? Wouldn’t want someone on the cable fixing it and getting a whack since there’s a path to earth if connected onto pme

 

[pc1966]

Generators of that size are normally TN supplies as N & E is linked within the generator, the fact you have an earth rod is not making it TT.

You do need the rod as an independent means of earthing since during loss of supply conditions you cannot assume the supply earth is present.

Since you are not allowed to link N-E at more than one point, and the main supply is already linked at the substation (either low impedance if TN/PME, or via substation Earth if TT), then all arrangements to switch power must switch both L1-L3 (as used) & N to preserve only one N-E link at a time. Those transfer switches should prevent any risk of back-driving the supply.

Where you might want to TT the arrangement is for safety as under loss of supply / out-of-specification supply it could be due to an open PEN fault and under those conditions the generator could be at an elevated potential w.r.t. true Earth so a risk for anyone working on it, such as checking operation or stopping/refuelling/starting, etc.

 

[Rockingit]

Not sure I'm fully understanding what the question is, here. Generator supply will be TN-S, the generator requires an earth rod for referencing (BS7430), and your changeover switching (auto or manual) also requires isolation of the [DNO] supply earth.