Although it probably does not apply, if the gensets may also be used islanded - i.e more than one turning, but not synchronous, then the earths need to remain linked, unless the loads are far enough apart that you cannot touch a class 1 appliance on two separate islands at the same time.

Note that the one NE link is a UK specific thing, and applies to load side (consumer) wiring, and not distribution wiring - so you may have transformers or gensets in parallel, especially if they are DNO managed,  with a bolted NE link each, but only if they then combine immediately - which is actually quite common if they are side by side e.g. twin transformers are fitted as an upgrade as the load rises- before going on to a common panel or breaker and then out to loads as TN-S  If you ever encounter one of these, great care should be taken that the N-N link/ EE link is/are capable of taking the full load current and not to unbolt any of it unless both sources are dead.

When the DNO patch in a generator at a substation to do back feeding of a small village or whatever, they disable the genset earth leakage trips, as there is no  sensible alternative - going round converting to TN-S  is not really an option.

Mike.

In this case the three generators all combine via a power management module for 'single' output (actually multiple outputs, but shared from whichever generators are running).

The issue is this system has no transformers for supply / load separation, instead the outputs utilise live-neutral tap-offs (eventually) to provide single phase outputs for running of equipment.  In this instance I would presume that the regulations would require removal of any additional N-PE links to provide only one 'system ground / earth' and to prevent unwelcome harmonic outcomes. 

Just for additional context, as this is a mobile facility there is no provision for connectivity into local power grid generation so the system will always operate independently, managed and maintained by the on-site engineers. 

In that case, there may be further considerations, although a TN-S approach is still perhaps the most appropriate. We'd probably not recommend TN-C-S in most mobile/transportable set-ups in the UK, but as Mike says they exist elsewhere.

Is there a possibility a generator could be unplugged, or cable severed and be running with Neutral disconnected from Earth - unless of course there's residual current protection and/or insulation monitoring provided directly at the generator output (because it would be effectively IT system under those conditions).

Does BS 7909 apply to the use-case?

In that case there may be merit in having the common NE link at the power management module and 5 wires to each genset (LLLNE) In such a case one can have an earth leakage relay enabled on each genset, though it is not that useful, it will detect winding to chassis faults, and all 3 gensets are configured the same without  a link rather than link in one 'master genset' only. Once you are on the distribution side of that module you are in strict TNS country and are allowed as many rods, bonds to tent poles and water pipes as you like bridging between CPC and terra firma, but neutral is to be treated as if it may be alive.

As it is a supervised system this may relax the rigour needed in terms of allowing the unusual, but it does need to be done in a way that the most likely configuration mistakes (such as avoiding having 2 master gensets or at all none if you have both types) are mitigated. Are the gensets connectorised or is it a case of  ring lugs and socket set at each new  location?

(I have seen some errors with things that bolt together in the field that are toe-curling - the desire to get stuff up and running as the daylight fails can do funny things to judgement.)

Mike.

In that case there may be merit in having the common NE link at the power management module and 5 wires to each genset (LLLNE) In such a case one can have an earth leakage relay enabled on each genset, though it is not that useful, it will detect winding to chassis faults, and all 3 gensets are configured the same without  a link rather than link in one 'master genset' only. Once you are on the distribution side of that module you are in strict TNS country and are allowed as many rods, bonds to tent poles and water pipes as you like bridging between CPC and terra firma, but neutral is to be treated as if it may be alive.

As it is a supervised system this may relax the rigour needed in terms of allowing the unusual, but it does need to be done in a way that the most likely configuration mistakes (such as avoiding having 2 master gensets or at all none if you have both types) are mitigated. Are the gensets connectorised or is it a case of  ring lugs and socket set at each new  location?

(I have seen some errors with things that bolt together in the field that are toe-curling - the desire to get stuff up and running as the daylight fails can do funny things to judgement.)

Mike.