Generator earthing

davezawadi (David Stone):

In response to John, an Earth spike is not necessary if there is another adequate Earth connection. A defect in BS7430 which makes assumptions which are not necessaraly correct, it is assuming a very small generator which is free standing. I'd like to see the Earth "spike" at a 2.4 GW power station! Hugh, You latest post is correct. What size is the tractor generator, might be up to 100 kVA if a big tractor? It is still not 200A though. See above. Bigger tractor generators are usually 3 phase, and a local TX supply is too, are you sure it is real TN-S?

David,


I agree with Mike, this is not correct if it's a TN-S earthing terminal provided by the DNO. See Regulation 551.4.3.2.1:

551.4.3.2 Additional requirements for installations where the generating set provides a switched alternative to system for distribution of electricity to the public (standby systems)
551.4.3.2.1 Protection by automatic disconnection of supply shall not rely upon the connection to the earthed point of the system for distribution of electricity to the public when the generator is operating as a switched alternative to a TN system. A suitable means of earthing shall be provided.

The reason for this, is that the supply cable may break.


But good question whether it's "real TN-S".


The added difficulty with a DNO-provided earthing terminal is the need to provide a switched N-E bond as well as ensure adequate isolation from the live conductors of the grid as part of the supply changeover arrangements - which, if the generator has its own electrode completely, a simply "All lines and neutral" changeover switch is probably best to achieve all of this.


Regulation 21 of ESQCR would apply.

davezawadi (David Stone):

In response to John, an Earth spike is not necessary if there is another adequate Earth connection. A defect in BS7430 which makes assumptions which are not necessaraly correct, it is assuming a very small generator which is free standing. I'd like to see the Earth "spike" at a 2.4 GW power station! Hugh, You latest post is correct. What size is the tractor generator, might be up to 100 kVA if a big tractor? It is still not 200A though. See above. Bigger tractor generators are usually 3 phase, and a local TX supply is too, are you sure it is real TN-S?

David,


I agree with Mike, this is not correct if it's a TN-S earthing terminal provided by the DNO. See Regulation 551.4.3.2.1:

551.4.3.2 Additional requirements for installations where the generating set provides a switched alternative to system for distribution of electricity to the public (standby systems)
551.4.3.2.1 Protection by automatic disconnection of supply shall not rely upon the connection to the earthed point of the system for distribution of electricity to the public when the generator is operating as a switched alternative to a TN system. A suitable means of earthing shall be provided.

The reason for this, is that the supply cable may break.


But good question whether it's "real TN-S".


The added difficulty with a DNO-provided earthing terminal is the need to provide a switched N-E bond as well as ensure adequate isolation from the live conductors of the grid as part of the supply changeover arrangements - which, if the generator has its own electrode completely, a simply "All lines and neutral" changeover switch is probably best to achieve all of this.


Regulation 21 of ESQCR would apply.