Earthing arrangement for small 6kVA SDMO 6000E Generator

[Miss Sunshine]

Hi everyone. We are doing an off-grid system for a small log cabin. It consists of a 6kVA generator as back up to a small battery set and 4.5 kWp solar PV array with a 3.0/4.4 kW Sunny Island. The problem I have is the generator has a floating earth. After some research I was going to link the neutral and earth in the generator and run a 16mm earth cable to a stake (or several stakes) in the ground. But after talking to SDMO they have said it may cause a problem with the MODYS control panel on the generator. Does any one know if this is correct as SDMO are being really slow with definite information on this and the customer has run out of patience?

I was thinking I could link the neutral and earth in the fuse board, before the RCD. This is after the generator and after the Sunny Island. Is this correct, will I damage anything and will I have to do anything at the generator end.

I haven't got much experience with generators and any help will be greatly appreciated.

 

[HandySparks]

I have no experience of this generator, however, looking at:
DIESEL 6000 E SILENCE AVR, Portable Power generator, Generating set - SDMO
and:
http://www.sdmo.com/images/shared/PPW/800/PPW-PR-DO-EN-51.pdf

it seems that a differential protection module (RCD) is available as an option on this generator. This wouldn't work properly unless the neutral was earthed before the RCD at the generator. So it looks as though earthing the generator neutral is possible.

You won't, of course, be installing a TT supply. It'll be TN-S with a rod for earth reference.

 

[Richard Burns]

Normally I would expect any quality generator of that size, even though it is small, should be able to have the neutral earth referenced.
It does seem strange that they offer earth rods and RCDs for the generators if they are unable to be earthed.
A floating earth system is not appropriate for a permanent installation to a building.
You have a complex arrangement there with two generators that makes it hard to specify the earthing arrangement to put in place and to ensure that a protective device will operate in the case of either supply being operative.

Generally solar systems are not earthed and derive an earth from the installation. The generator as a permanent installation should have the neutral earth referenced and with a suitable low resistance earth system connected to the general mass of earth.
I assume the installation is remote from any other systems and so will not need to take these into account.
The two generators should not be able to be operated in parallel to supply the cabin. The installation must have 30mA RCD protection as well but it is important that the earthing system is separated from the neutral prior to the RCD protection or it will have no effect.
A local Neutral earth separation at the consumer unit is possible but it would be important to ensure that there is no possibility of an interaction with the generator supply itself as this would be unprotected and could introduce a shock risk to the main installation.
The full requirements for ADS should be implemented including appropriate bonding if necessary.

 

[McN41R]

The generator must be neutral earthed and that we all agree upon a floating neutral cannot be allowed.
how it should be earthed should really be advised by the supplier of the generator.
perhaps you can:
-sketch you arrangement including the cables run between Phase, neutral and Earth.
- advise of your generator model.

A floating neutral is a serious problems and can cause fires without tripping RCD or MCB's I would rather cause complications with a control panel rather than burn down my cabin. I would advise in writing to SMDO that you have a floating earth and this is a fire risk that cannot be tolerated and you are putting down a temporary earthing reference point for the generator system until their technical staff can advise of the correct earthing procedure for their equipment.

pehaps the following will already answer the question, if the wiring arrangement has already advised by SMDO.

if you generator is connected by phase, neutral and Earth (not bonding) then the generator is probably using your consumer unit earthing arrangement.

if your generator is connected with a phase and neutral only then you must neutral earth bond at the generator star point with separate earthing spike.

regards
McN41R

 

[Miss Sunshine]

Thanks for the replies. The are all very helpful. Going to move forward with McN41R's advice and email SDMO about floating earth being a serious issue with potential fire risk and then set up temporary/permament earthing arrangement as we all agree this is the way forward. I can't see how it is going to effect the panel but the SDMO UK tech guy mentioned it and now I am paranoid about it damaging the control panel. Will keep you posted.