Understanding of regulation 444.4.6 when dealing with mobile site with multiple generators

I have a mobile site with three 35KW generators.  The system is designed to power share at peak times across two of the three, with the third for maintenance purposes to allow continuity of supply. Each generator is able to have the Neutral line connected to the Earth line via a removable link, and the distribution system is such that, as long as the cabling remains physically connected, the Neutral and Earth lines remain connected at all times irrespective of status of breakers through the system. 

My understanding of the regulations will require one single generator to retain the N-E link, and the other two systems will have the link removed to avoid the possibility of harmonics and doubling up of Neutral return lines.

As the system is mobile, currently each generator is earthed via earthing rods, and the various elements across the mobile sites are also earthed using their own earthing rods and grids, with these earthing grids interconnected via separate earthing cables, as well as the obvious system earth through internal wiring.

Reading through Regulation 444.4.6, it mentions that for TN and TT systems, the system should be earthed at only one point.  My current understanding of this is tied into the next line in the regulations, which states that for TN systems the Neutral line should only be bonded once with the Earth line, and in fact number of interconnected physical earth rods isn't what that statement refers to. If this is the case and 'the system' refers to the N-E connection, would individually earthed generators with only one generator having the N-E link in place satisfy what the regulations state? 

Parents
  • Except in certain special cases (e.g. downstream of an open-PEN detection device, see Regulation 722.411.4.1), PE conductors in TN, TT, IT, FELV and PELV systems can be Earthed (via electrodes to the general mass of earth) as many times as you like - and even cpc's of different circuits bonded together (for example, Regulations 415.1.2, 701.415.2, 444.5.2).

    Note: This in no way detracts from the requirement that, where ADS is used, a cpc must be run to each point in wiring, and be run in the same wiring system as the live conductors or in its immediate vicinity - i.e. each circuit must have a cpc of its own suitably sized for the circuit protection for ADS to operate in the required disconnection time, and for fault current thermal effects relating to the circuit's overcurrent protective device.

    The Neutral or earthed Line conductor may be Earthed at one point only, however ... for the following reasons:

    1. Effectively makes the Neutral a PEN (or earthed line a PEL) conductor ... this arrangement is effectively prohibited by Regulation 8(4) of ESQCR.
    2. multiple N-E connections may cause spurious operation of RCDs
    3. definitely leads to EMC/circulating current issues
  • Thank you for the referenced reply, very handy for additional context!  What you have put was certainly along the lines of thinking and has given me some more reading to support that argument. 

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