earthing systems with standby generators

[gjaggers]

i have a 230v system connected to a tncs earthing arrangement and have been asked to connect a standby generator,i believe the generator should be connected to a tt earthing arrangement so how should i go about connecting the 2 two different earthing systems together
the boss has said just connect the earth rod to the tncs system ,a cardinal sin in my eyes!!!!!!
should i rearrange the tncs system to a tt type?

 

[IQ Electrical]

It is my understanding that your boss is correct, the DNO earth is required to be bonded to your earth electrode and hence to the generator starpoint.

I seem to recall a 3-pole changeover switch being acceptable on a DNO TN-C-S system changeover switch, 4-pole on TN-S.

It was explained to me that any utility work on the neutral conductor, cable sheath or substation earth electrodes already takes into account the risk of transfer potential due to unbalanced generators, poorly wired (reverse polarity) installations and genuine earth faults as part of published live working procedures.

As always, check on local DNO requirements and the ESQCR 2002 Regulations

 

[Guest123]

Well when the genny is running, assuming it is not a floating power supply (i.e. neutral isolated from earth in the genny?), the star point / neutral is connected to gen frame which is in turn earthed through the rod(s) you will have installed.

Think of a line to earth fault of a circuit supplied by the genny - the fault current will flow from the genny line, down through the circuit, through the fault, and will return through the SWA (or 3rd core) to the genny star point thus operating any protective devices in the geney. Generator outputs are by and large TN-S systems, because you are running an actual CPC in the cable, the fault current has no reason to go anywhere else other than back to its origin.

Any fault should not flow through the main supply earthing as they are not referenced together other than at their orgins via earth rods into the rock we all live on.

Likewise the rods on the gen frame ordinarily would not form part of the earth fault path of the geney system unless your installed CPC was damaged.

IMO leave all earthing connected together.