On the N-E connection question, that came from here:
https://www.justgenerators.co.uk/generator-faq.html
https://www.justgenerators.co.uk/generator-faq.html
There are a few bits in there that I don't completely agree with. For starters, I think the statement that generator outputs are always floating is not always true given previous discussions of the effects of having the centre tap of the 110-0-110 winding earthed - and putting 55V onto the neutral.
Relevant extract below (my emphasis).
Most buildings now have an RCD built into the consumer unit. This is configured to operate from the mains supply with an earthed neutral, and not from a generator with a floating earth. To utilize this protection device, it is necessary to modify the generator so that it is configured in the same way as the mains supply. This is a simple modification for a qualified electrician, involving adding a link wire from the neutral terminal to the earth terminal. It is recommended to make this connection in the plug that is to be used to connect to the generator. This ensures that the generator is unmodified when it is disconnected from the house, and therefore remains safe.
The plug should be labeled “Do not connect to mains: Neutral-Earth link fitted”. The lead between the generator and the transfer switch is not protected by the RCD, it is therefore recommended to use a steel armored cable for this connection. Finally a local low-impedance earth spike needs to be installed.
Have I misunderstood that?
I don't think you've misunderstood, but I disagree with it - or at least it's not well articulated.
The RCDs in the house really don't care about earthed neutrals - they only measure imbalance between L & N currents. With a truly floating supply, the issue is that someone could touch a "live" conductor, and not enough current would flow to trip the RCD - but that's demonstrating the safety value of a floating (IT) supply.
The real risk is that without an earthed neutral, a L-E fault wouldn't trip the over current protection (OCP). Instead, the live would become earthed, and then the neutral is "live". That in itself is not dangerous as neutral conductors have to be protected to the same extent as phase conductors and it should not be possible to touch anything "live".
Where it gets interesting is when there's a second fault (e.g. a N-E fault) in a different circuit. You then have a fault path which going via the OCP in the phase conductor of one circuit and the neutral conductor of a different circuit. Lets say the first is a 32A ring final and the second is in a lighting circuit. You now have fault current from a 32A circuit passing through wiring designed for a 6A circuit which isn't ideal to say the least. With RCBO protected circuits or circuits on different RCDs in a split board, both would then trip. But an RCD serving both would not trip. Depending on the characteristics of the connected generator, it's not guaranteed that a 32A breaker would trip (in a timely manner, or at all) under such conditions.
That's why that page simply states the simplistic advice that the genny neutral must be earthed. Not because it must, but because it would be too complicated to explain the nuances of the different possibilities.
Clearly it's a lot easier if the genny is hardwired - you simply design the whole setup and wire the genny accordingly. But when it's a plug in connection, you need to account for what someone might come along and do in the future - clearly it would be "undesirable" to link N&E on the installation side of the power inlet to make any floating genny safe, given that it would cause a short for a centre-tap-earthed genny. And with a plug in connection, you cannot assume that the genny isn't floating.
Perhaps a "soft earth" (say, incandescent light bulb) between N&E which would glow dimly (55V) with a CTE genny, but provide enough current to trip an RCD with a floating genny ?
These questions are of interest to me as I intend adding an inlet and C/O switch at home, and have made the provision at church (C/O switch installed during other works, but inlet not yet connected). At home I have a reasonable degree of control as long as my faculties remain; but at church, and at home if I'm not around (or all there) to supervise then whatever I do needs to be safe with the "untrained person working on 'the plug fits so it must be OK'" theory of electrics.
