Earth neutral bond for inverter before I get grid hook up on new build.

[jimseng]

Hello. I think I will have my inverter up and running way before I get round to getting the grid hook up on my new build. I assume this means I need an earth neutral bond and a ground spike to start with. Is this correct? 
In the long term I see that Sunsynk inverters have an internal relay to achieve this but I can't find one mentioned in the Growatt manual. I just thought I would ask for any pointers when I get round to installing this. Once I have the grid connected how would I go about setting this up for grid power failure?

Thanks

[markc]

In an off grid system you take the neutral and earth back to the inverter terminals, no need for any earth spike etc. - this is similar to an inverter in a motor home or boat etc.

[Dillsue]

1 hour ago, jimseng said:

Once I have the grid connected how would I go about setting this up for grid power failure?

If you've not bought your inverter, dont buy it yet. Wait til you have a plan for a permanent grid tied set up that can temporarily operate off grid. Grid tied and off grid inverters operate differently and you dont want to buy the wrong thing.

[jimseng]

Quote

Wait til you have a plan for a permanent grid tied set up that can temporarily operate off grid.

I do have a plan! I am just holding off on the grid for a while until I am closer to building regs sign off but the solar is going up much earlier. It would be a shame not to use it.  I am going to by a hybrid and run it off grid until the DNO turn up. 

Quote

In an off grid system you take the neutral and earth back to the inverter terminals, no need for any earth spike etc

So I won't need to change anything when I hook into the grid? 
 

[Dillsue]

2 hours ago, jimseng said:

I do have a plan! I am just holding off on the grid for a while until I am closer to building regs sign off but the solar is going up much earlier. It would be a shame not to use it.  I am going to by a hybrid and run it off grid until the DNO turn up. 

So I won't need to change anything when I hook into the grid? 
 

In your first post you asked "Once I have the grid connected how would I go about setting this up for grid power failure?" That doesnt sound like a plan to me!

 

Whatever you buy make sure it has a G98/G99 cert for legitimate connection to the grid, once it's available. That will ensure your inverter shuts down when there's grid failure. You'd need to work out how to get that inverter running without a grid connection but thats off grid wizardry and probably needs to be part of the plan if you want the PV up and running before you've got a grid connection.

[jimseng]

Quote

In your first post you asked "Once I have the grid connected how would I go about setting this up for grid power failure?" That doesnt sound like a plan to me!

What I am asking is what is needed in terms of earth neutral bonding as the Sunsynk manual states there is an internal relay to bond the earth and neutral when the grid shuts off in event of a power cut and the Growatt doesn't specifically mention this. There is a lot of talk about earth / neutral bonding but it is hard to distinguish what is for the American market and other countries and what is required for the UK.
I'm not sure I understand how my first post suggests I don't have a plan. I think I am mis-understanding something. Can you explain?
 

Edited Wednesday at 16:34 by jimseng

[JohnMo]

Do you have two inverters or one and what make is it? You keep mentioning two different makes

 

Is a string or hybrid inverter?

[JohnMo]

If your weather is anything like ours you PV will be producing nothing.

 

Just get your grid connection sorted.

[jimseng]

I haven't chosen an inverter yet and I am still specifically inquiring about the earth neutral bond requirements in the uk. And more specifically that one make (Sunsynk) mentions there is an earth neutral bond relay internally and the Growatt doesn't mention this so I thought I would ask what people do on this forum. 
As for the grid connection, I don't see the point in hooking it up and paying the standing charge months before I actually move into the house but if there is all that solar on the roof and the batteries are in I might as well at least use it to make the tea, just to curry favor with the builders. I should get enough for that at least, and possibly a cupcake.

[Dillsue]

2 hours ago, jimseng said:

I'm not sure I understand how my first post suggests I don't have a plan. I think I am mis-understanding something. Can you explain?
 

Sorry but I got the wrong end of the stick and assumed you were talking about general inverter functions rather than a specific feature.

[jimseng]

@Dillsue

I think I need to be a bit more specific when forming my questions. I just assume everybody telepathically knows what I am asking.

[Mattg4321]

The Sunsynk has an iirc 230v output that is triggered when the inverter is in islanding mode. This doesn't serve as the neutral-earth bond. 

 

You need to connect the output to the coil on a separate relay that will make the neutral-earth bond.

 

An earth rod will also be needed if this is a grid connected system.

 

Don't expect to find any explicit regulations in BS7671 as to how this should be done exactly, as they don't exist.

 

Any circuits that you want to be able to use in islanding mode/off grid, need to be connected to the load terminals on the inverter. You really need someone who knows what they are doing to connect this up. 

[JohnMo]

Or just go AC coupled battery (with gateway), a normal string inverter for PV. You will need an earth spike. Then just operate in island mode. Once you have a grid connection take out of island mode.

 

AC coupled will provide whole house with power. A hybrid inverter may only do a single circuit when no mains is connected.

[jimseng]

@Mattg4321 The Sunsynk has an internal relay, that was why I asked this question and you have confirmed what I was thinking, that many inverters don't, and I do need to fit my own system for this, probably if I go for the Growatt. I'll investigate.

[SteamyTea]

10 hours ago, jimseng said:

 

Is that to stop any chance of voltage leaking back down the grid when there is a fault?

[jimseng]

Quote

Is that to stop any chance of voltage leaking back down the grid when there is a fault?

I'm actually struggling to get to the truth! It seems from what I have read that professional installers don't get this right either. In the Sunsynk manual I read this to mean that the Sunsynk inverter internally bonds the earth and neutral on the load side when the gird fails as the DNO bond is lost. Although in the same manual it states (as Mattg4321 has pointed out) that the inverter provides a 240v connection to drive an external relay to achieve this...So which is it Sunsyk? Growatt do the same but the 240v signal is present when on grid and goes to zero on grid failure. (So one has to choose a NO or NC contactor accordingly.)
It seems that one can link the grid DB and backup load DB neutral together and use the permanent DNO bond. This is fine until the DNO earth neutral bond fails and any local bonding inadvertently serves as the bond for the entire local infrastructure. Although it seems this is only a problem in countries where people steal the cabling.

I'm still working through it but it seems I will likely go with the Growatt due to budget and fit an external contactor to provide the E/N bond in the event of grid power failure. 
 

[Alan Ambrose]

>>>  a ground spike

 

You should have one anyway while you're building and in some instances (car chargers etc) afterwards too. My DNO put a label on their feed to that effect and refused to connect up their own earth.

 

>>> Is that to stop any chance of voltage leaking back down the grid when there is a fault?

 

No, it's so you have an earth/neutral bond in both cases and never two bonds. It's not totally clear to me why two bonds would be a problem, but it's just possible that would risk some extra leakage current.

 

>>> AC coupled will provide whole house with power.

 

I guess it's possible to only power some circuits if you like - and that strikes me that's a useful option e.g. power to the whole house except the really heavy users: HP, car charger, oven etc.

 

 

[Mattg4321]

You won't necessarily have an earth rod anyway as it's not mandatory. Not even for EV chargers now as most have built in PEN fault protection, meaning earth rods are not required as long as you meet other regulations.

 

Neutral - earth bond is necessary for the proper operation of RCD protection. Stopping the voltage going back into the grid is a separate issue.

 

Hybrid inverter can do as many circuits as the power of the inverter will be able to run. Nothing to say it can only operate a single circuit.

 

I wouldn't take what Sunsynk say as gospel. They are certainly not experts when it comes to electrical installation - I've seen that Keith on their videos do some fairly dodgy things! Also, I seem to remember that some of their inverters will require NO and some NC relays!! FYI Sunsynk are rebranded Deye inverters.

[jimseng]

Quote

FYI Sunsynk are rebranded Deye inverters.

I had forgotten that, and had a quick look and remembered that they don't show up on the ENA database as G100 compliant. I think that is why I had forgotten. Shame because the pricing seems better than Sunsynk, with better availability.

[Kelvin]

15 hours ago, Alan Ambrose said:

>>>  a ground spike

 

You should have one anyway while you're building and in some instances (car chargers etc) afterwards too. My DNO put a label on their feed to that effect and refused to connect up their own earth.

 

>>> Is that to stop any chance of voltage leaking back down the grid when there is a fault?

 

No, it's so you have an earth/neutral bond in both cases and never two bonds. It's not totally clear to me why two bonds would be a problem, but it's just possible that would risk some extra leakage current.

 

>>> AC coupled will provide whole house with power.

 

I guess it's possible to only power some circuits if you like - and that strikes me that's a useful option e.g. power to the whole house except the really heavy users: HP, car charger, oven etc.

 

 

You don’t need an earth rod for car chargers nowadays as they have their own fault protection. However if you plan on batteries and a gateway you will need an earth rod so worth thinking about all that now. In my case I banged the earth rod in beside the garage and the cable runs back to the house where the gateway is. Fortunately I had worked on the principle of n+1 ducts so had a spare duct for cabling. 
 

My gateway powers the whole house. I couldn’t see the point of adding another CU for just critical loads. The car charger is wired at the meter side so the inverter doesn’t see it as a load. It is possible to connect high loads (like an ASHP) to a ‘smart’ port on the gateway so that it can be shutdown if you have a power cut and running low on battery storage. 
 

If this is stuff that you plan on doing then I’d put in a fully off-grid system and running it like that until the grid is connected then switch over.