3 phase 70 KVA generator

[Engineer54]

Ive just been reading this guide, and it suggests that the suppliers earthing facility cannot be relied upon for ADS, when the genny is in operation.
Now in my mind, this means that your earthing for the genny is required to be at TN levels (very very low on large gen sets), or MCB's with residual earth fault protection are required. Can anyone add to this please, and point me to documentation?

Thanks

John

You don't necessarily need TN values (always better of course) on generators, the main consideration is that you ALWAYS provide a 4 Pole changeover switch on 3 phase systems and never a 3 pole with solidly linked neutrals. A good 10 ohm TT earthing system should generally suffice for a generator installation...

Most generators of any size will (or should) come with it's own pretty comprehensive protection facilities, including earth fault protection, either via a multi function protection relay unit or incorporated within the units MCCB/ACB.

 

[johnboy6083]

When I asked this question I overlooked a fundamental issue: the fact that your not relying on the rod for ADS, but to tie the genny down to earth potential.
The genny will already have a very low earth fault loop impedance because it will usually have a dedicated earth cable. I overlooked this too.
I was feeling ill though! Lol