Fixed generator questions

[Simon47]

I stand corrected (surprised no-one else has done it) on switching the earth ...
537.1.5 Where an installation is supplied from more than one source of energy, one of which requires a
means of earthing independent of the means of earthing of other sources and it is necessary to provide that not more than one means of earthing is applied at any time, a switching device may be inserted in the connection between the neutral point and the means of earthing, provided that the device is:
(i) a multipole, linked switching device arranged to disconnect and connect the earthing conductor for the appropriate source at substantially the same time as the related live conductors, or
(ii) a switching device interlocked with a multipole, linked switching device inserted in the related live conductors such that the earthing conductor for the appropriate source shall not be interrupted before the related live conductors and shall be re-established not later than when the live conductors are reconnected.
Switching devices provided in accordance with (i) and (ii) shall meet the requirements of Chapter 46 for a device for isolation.
So it's is permitted to switch the earthing, but going back to the OPs situation, I cannot see how it can be considered safe to do anthing other than switch the entire earthing system at the MET of the supplies. Only switching it for some items is ripe for creating hazardous voltage differences - and indeed it is effectively prohibited :
411.3.1.1 Protective earthing
Simultaneously accessible exposed-conductive-parts shall be connected to the same earthing system individually, in groups or collectively.
Also applicable will be :
444.5.1.1 Within a single building
All protective and functional earthing conductors of an installation within a building shall be connected to the main earthing terminal, as required by Regulation 542.4.1, except where this is precluded by the requirements of legislation or Part 7.
The bit in Part 7 that would apply is 722.411.4.1 (iii) which details a device that will disconnect the protective earth after disconnecting the live conductors in the event of a PEN fault.

Ah, here we are, the condition for switching the earth conductors :
543.3.3.101 No switching device shall be inserted in a protective conductor, except:
(i) as permitted by Regulation 537.1.5
(ii) a multipole, linked switching in which the protective conductor circuit is not interrupted before the live conductors and is re-established not later than when the live conductors are reconnected
(iii) a switching device interlocked with a multipole, linked switching device inserted in the live conductors such that the protective conductor circuit shall not be interrupted before the live conductors and shall be re-established not later than when the live conductors are reconnected, or
(iv) a multipole plug-in device in which the protective conductor circuit shall not be interrupted before the live conductors and shall be re-established not later than when the live conductors are reconnected.

But given that switches can and do fail, I would suggest that having any switch in the earthing system ought to be considered poor design unless it is completely unavoidable.

When I said that switching of the earth was not permitted, I could have been thinking of :
411.4.3 In a fixed installation, a single conductor may serve both as a protective conductor and as a neutral conductor (PEN conductor) provided that the requirements of Regulation 543.4 are satisfied. No switching or isolating device shall be inserted in the PEN conductor.
Although PENs are not generally permitted in consumer installations (by ESQCR)

 

[John-]

I stand corrected (surprised no-one else has done it) on switching the earth ...
537.1.5 Where an installation is supplied from more than one source of energy, one of which requires a
means of earthing independent of the means of earthing of other sources and it is necessary to provide that not more than one means of earthing is applied at any time, a switching device may be inserted in the connection between the neutral point and the means of earthing, provided that the device is:
(i) a multipole, linked switching device arranged to disconnect and connect the earthing conductor for the appropriate source at substantially the same time as the related live conductors, or
(ii) a switching device interlocked with a multipole, linked switching device inserted in the related live conductors such that the earthing conductor for the appropriate source shall not be interrupted before the related live conductors and shall be re-established not later than when the live conductors are reconnected.
Switching devices provided in accordance with (i) and (ii) shall meet the requirements of Chapter 46 for a device for isolation.
So it's is permitted to switch the earthing, but going back to the OPs situation, I cannot see how it can be considered safe to do anthing other than switch the entire earthing system at the MET of the supplies. Only switching it for some items is ripe for creating hazardous voltage differences - and indeed it is effectively prohibited :
411.3.1.1 Protective earthing
Simultaneously accessible exposed-conductive-parts shall be connected to the same earthing system individually, in groups or collectively.
Also applicable will be :
444.5.1.1 Within a single building
All protective and functional earthing conductors of an installation within a building shall be connected to the main earthing terminal, as required by Regulation 542.4.1, except where this is precluded by the requirements of legislation or Part 7.
The bit in Part 7 that would apply is 722.411.4.1 (iii) which details a device that will disconnect the protective earth after disconnecting the live conductors in the event of a PEN fault.

Ah, here we are, the condition for switching the earth conductors :
543.3.3.101 No switching device shall be inserted in a protective conductor, except:
(i) as permitted by Regulation 537.1.5
(ii) a multipole, linked switching in which the protective conductor circuit is not interrupted before the live conductors and is re-established not later than when the live conductors are reconnected
(iii) a switching device interlocked with a multipole, linked switching device inserted in the live conductors such that the protective conductor circuit shall not be interrupted before the live conductors and shall be re-established not later than when the live conductors are reconnected, or
(iv) a multipole plug-in device in which the protective conductor circuit shall not be interrupted before the live conductors and shall be re-established not later than when the live conductors are reconnected.

But given that switches can and do fail, I would suggest that having any switch in the earthing system ought to be considered poor design unless it is completely unavoidable.

When I said that switching of the earth was not permitted, I could have been thinking of :
411.4.3 In a fixed installation, a single conductor may serve both as a protective conductor and as a neutral conductor (PEN conductor) provided that the requirements of Regulation 543.4 are satisfied. No switching or isolating device shall be inserted in the PEN conductor.
Although PENs are not generally permitted in consumer installations (by ESQCR)

Thank you for your efforts. I think I’m still going to link them out and ensure a common earth arrangement through out. ?

 

[i=p/u]

Does it mention anything about the size of generator, upto 10kva and no class 2 items???

 

[John-]

Does it mention anything about the size of generator, upto 10kva and no class 2 items???

 

[John-]

what's the relevance of class 2 items please?

 

[John-]

I stand corrected (surprised no-one else has done it) on switching the earth ...
537.1.5 Where an installation is supplied from more than one source of energy, one of which requires a
means of earthing independent of the means of earthing of other sources and it is necessary to provide that not more than one means of earthing is applied at any time, a switching device may be inserted in the connection between the neutral point and the means of earthing, provided that the device is:
(i) a multipole, linked switching device arranged to disconnect and connect the earthing conductor for the appropriate source at substantially the same time as the related live conductors, or
(ii) a switching device interlocked with a multipole, linked switching device inserted in the related live conductors such that the earthing conductor for the appropriate source shall not be interrupted before the related live conductors and shall be re-established not later than when the live conductors are reconnected.
Switching devices provided in accordance with (i) and (ii) shall meet the requirements of Chapter 46 for a device for isolation.
So it's is permitted to switch the earthing, but going back to the OPs situation, I cannot see how it can be considered safe to do anthing other than switch the entire earthing system at the MET of the supplies. Only switching it for some items is ripe for creating hazardous voltage differences - and indeed it is effectively prohibited :
411.3.1.1 Protective earthing
Simultaneously accessible exposed-conductive-parts shall be connected to the same earthing system individually, in groups or collectively.
Also applicable will be :
444.5.1.1 Within a single building
All protective and functional earthing conductors of an installation within a building shall be connected to the main earthing terminal, as required by Regulation 542.4.1, except where this is precluded by the requirements of legislation or Part 7.
The bit in Part 7 that would apply is 722.411.4.1 (iii) which details a device that will disconnect the protective earth after disconnecting the live conductors in the event of a PEN fault.

Ah, here we are, the condition for switching the earth conductors :
543.3.3.101 No switching device shall be inserted in a protective conductor, except:
(i) as permitted by Regulation 537.1.5
(ii) a multipole, linked switching in which the protective conductor circuit is not interrupted before the live conductors and is re-established not later than when the live conductors are reconnected
(iii) a switching device interlocked with a multipole, linked switching device inserted in the live conductors such that the protective conductor circuit shall not be interrupted before the live conductors and shall be re-established not later than when the live conductors are reconnected, or
(iv) a multipole plug-in device in which the protective conductor circuit shall not be interrupted before the live conductors and shall be re-established not later than when the live conductors are reconnected.

But given that switches can and do fail, I would suggest that having any switch in the earthing system ought to be considered poor design unless it is completely unavoidable.

When I said that switching of the earth was not permitted, I could have been thinking of :
411.4.3 In a fixed installation, a single conductor may serve both as a protective conductor and as a neutral conductor (PEN conductor) provided that the requirements of Regulation 543.4 are satisfied. No switching or isolating device shall be inserted in the PEN conductor.
Although PENs are not generally permitted in consumer installations (by ESQCR)

I still need to check, but as the site supply cables are SWA, and speaking to the customer last night, there are only two change overs. One in the same building at the geneset, and the other near the mains intake that seems to do multiple boards.

My assumption, still need to check, is that the change over in the meter cupboard does all single phase disboards, also changes over the earth, but does not do the dis board in the building with the geneset installed. Maybe this one is fed directly from the gen set.

There will be fortuitous connections to earth via the SWA back at the mains intake, and possibly direct connections of earths, which means the building bonds may still be at similar potentials to that of the changed over earth when the genset is running, but there are two runs of supply cable between the Generator earth when the switch is in the Gen position: the CPC for the TP board that the Bond is connected to that then goes back to the street MET, then through Disboard and back out to the same building on the alternate supply cable via the change over to the SP disboard. If so it could still introduce a potential difference, all be it small. So assuming the above proves correct. I still see that not switching the the earths and instead linking them out is still the best option. Further, i will link together the two supply CPCs in the change over. This will introduce deliberate parallel paths, but so long as each CPC complies on its own, I don't see this as an issue.

I will also contact the manufacturer of the genset and ask for their advise also.

Thoughts welcome please?

 

[i=p/u]

Richard burns could tell ye , telectrix will tell ya if ya pay him