Off grid earthing system

[bill01803]

What earthing system should be used on an off grid install with a solar inverter, wind inverter, battery backup inverter and a 4.5kW floating earth generator?

 

[Richard Burns]

It depends on what the installation is powering.
With a floating earth generator it is hard to arrange a complete installation with anything other than a floating earth, however this is not safe if the installation is extensive.

 

[bill01803]

It is a house and farm buildings

 

[Wilko]

With a floating earth generator it is hard to arrange a complete installation with anything other than a floating earth ...

Hi RB - sorry in advance to ask dumb question - can the floating earth gen be reference to earth by externally connecting one of the floating outputs to gen body and earth stake?

 

[Richard Burns]

You need a solidly earthed point connected to all the supplies that can be used as a permanent earth reference.
You should be looking to get a low resistance earth probably by using wide and deep earthing at multiple points.
The generator would need to be assessed to ensure that it can be solidly referenced to earth on one pole, (yes Wilko it should be possible but the design of the generator must be safe for this to do) it would be best to get an internally earthed generator designed for the purpose.

 

[bill01803]

Leaving the generator out of it as it is plugged in and so can be disconnected, the supplies from the inverters don't appear have a reference to earth, I am waiting for a copy of the original cert to see what the installer claimed it to be.
As they are standard inverters presumably on a mains connected system it would rely on the dno for the earth reference, since this has been disconnected there doesn't appear to be one.

 

[Gavin A]

can you post up make and model of the inverters?

 

[bill01803]

The inverts are both Aurora Uno

 

[bill01803]

Update, spoke to Hyundai and the generator can be linked neutral to earth long as it is done external to the generator and labelled

 

[Gavin A]

The inverts are both Aurora Uno

are you sure this is off grid, and not a hybrid system with grid connect and battery back up?

AFAIK those inverters don't have off grid functionality - or is the generator and demand big enough that they're able to take their reference from the generator and just reduce the demand from the generator?

 

[bill01803]

I know the tails from the meter go into two neutral blocks and no further:- two uno inverters, an exide battery backup and the said 4.5kW hyundai generator with it's floating earth. also there is a couple of immersion heaters connected directly to the board from the solar/wind.
plus a token 3/8 stake outside the "renewables shed

 

[Worcester]

The question still remains what is generating the "grid reference" - what controls the batteries and genny? Sunny Island?

 

[bill01803]

The battery pack inverter must be in control, the geni is manual

 

[bill01803]

The battery supply is a Victron blue power multi plus 5kVA
Quote from manual
"The MultiPlus is provided with a ground relay (relay H, see appendix B) that automatically connects the Neutral output to the chassis if no external AC supply is available"

So it would appear something is not quite right

 

[UKMeterman]

What happens when on a sunny day the load in the house drops below the output of the inverters and they try to export?