Epever up5000-hm8042 and Floating Neutral

[Feenster]

I recently contacted EPEVER support concerning their UP5000-HM8042 hybrid inverter with the following question:
"The inverter will be used completely off grid with no mains power connection.
Can you send me a circuit diagram to show how the system should be earthed please?"

The reply was:
"Actually, we only recommend grounding the housing of your inverter, you can not grounding anyelse parts in your system. Especially the netural line, please do not grounding the Utility and AC Output netural line."

Surprised (because there is no mention of this anywhere in the manual and expecting that there should be a neutral-ground bond), I looked for more clarification, especially in relation to the neutral-ground bond issue and received the following:
"To prevent common-mode interference. The AC output terminal of the inverter designed with a safety capacitor (referred to as Y capacitor). The ground wire is the common point between L and N affected by the Y capacitor. The voltage between L or N to the ground is 110VAC. The Y capacitor meets safety requirements. So usually, human exposure to one of the root won’t result in electrical shock."

My question is, does anyone have any experience of inverters with floating neutrals? Are they safe if the ac output is fed to the distribution panel (fuse board) of the house?
(The set up is entirely off grid. There is no utility connected to the house. There is an earth rod. The existing inverter (MppSolar) has a neutral-ground bond)

 

[binky]

Interesting, but 110v will certainly give a shock
Site supplies are 110v , but that gives 55v shock, low enough not to kill in most circumstances. However, as they have a capacitor to provide a level of safety, then I would follow their instructions.

 

[runningpiglet]

Interesting, but 110v will certainly give a shock
Site supplies are 110v , but that gives 55v shock, low enough not to kill in most circumstances. However, as they have a capacitor to provide a level of safety, then I would follow their instructions.

The capacitors do not provide a safety function, on the contrary they only increase hazard. They are there purely for EMI/RFI interference reasons - which are important too. If the live and neutral from the inverters have no relationship to ground then any downstream RCD/RCBO/GFCI (USA speak) safety breakers will be ineffective. Fully floating, so-called IT (think of it as "independent of terra") systems have their own special requirements.

 

[binky]

You don't need an earth for a RCD to work, just an imbalance in the L N flow. We are one of the few countries to use a CPC (earth).

 

[Feenster]

I am in contact with EPEVER and will give a summary of what they have to say.

 

[Andy™]

id be treating it the same as a large generator. link the earth to the neutral giving a TNS supply and an earth rod

 

[Phoenix]

You don't need an earth for a RCD to work, just an imbalance in the L N flow.

You have to think how the inbalence is going to occur, in an ungrounded system, its probably not in a first fault situation, so you'll have the RCD not trip, and the system then grounded at a random position with a random impedance, which could mean your polarity is not what you expect it to be and if its downstream of the RCD (likely) then any second fault is not going to create that imbalence either. There is a reason why electrical separation for mutiple pieces of equipment is not permitted in installations not under the control of skilled persons, normally a means of detecting a first fault would be installed so that it can be rectified at the earliest possible oppertunity. Its not something that belongs in a domestic installation

We are one of the few countries to use a CPC (earth).

While some parts of the globe are a bit hit an miss on whether they run a cpc with final circuits, I suspect that very few run un-grounded power systems (other than perhaps small systems run from generators) as you start to end up with problems with undesirable voltages between the physical ground and the LV wiring, due causes such atmospheric conditions, or coupling from the HV side. What does sometimes vary is where they ground it.... corner grounded delta, anyone? or halfway along one of the delta connected legs, because, who would need all three of your phases to be the same voltage above ground?...not the americians, thats for sure....

 

[UNG]

Interesting, but 110v will certainly give a shock
Site supplies are 110v , but that gives 55v shock, low enough not to kill in most circumstances. However, as they have a capacitor to provide a level of safety, then I would follow their instructions.

Site supplies transformers have the centre point of the secondary winding connected to earth which limits any shock voltage to 55v so it cannot be assumed all 110v supplies will only give a 55v shock

 

[Andy™]

Site supplies transformers have the centre point of the secondary winding connected to earth which limits any shock voltage to 55v so it cannot be assumed all 110v supplies will only give a 55v shock

can be 63.5v to earth

 

[Feenster]

As I promised I will give a summary of what EPEVER had to say. They always replied promptly and were eager to help.
I sent them a few circuits to consider and after some feedback I made some modifications.

The circuit below is the one that they recommend for my particular set up, where I am completely off-grid and rely on a generator for back up. There is no neutral ground bond anywhere. The inverter has no ac input earth connection but the earth from the generator can be brought through the ac output earth on the inverter.
They reminded me many times that you "can not grounding the netural line, if you grounding the input netural line that will cause inverter can not work normal".
"For the Circuit 1 it is recommend, we think that is the best and safety connections, and sorry, that will not effect RCD, I thought it wrong before, it is no problem, RCD will work if earth leakage occurs."

 

[Feenster]

Circuit 2 is the same as Circuit 1 but with a neutral ground bond in the panel.





"Actually, it is not recommend to grounding the netural line, If you still want to grounding the netural line, you can not connect Main Grid to the inverter and can grounding like this:"

"You said you will not connect Grid right? So you can ignore it, but we still recommend you do not grounding the netural line."

 

[Feenster]

Circuit 3 has no n-g bond but has a changeover switch for ac utility mains.

"For the Circuit3, you can not connect like this, some customer connect like that, but the inverter will be damaged, that because of the switch between inverter output with Utility, because the switch has the swtich time, that will cause some power into output terminal, that maybe will damaged inverter."

 

[offgridAndy]

Do you have a battery in your off grid set up?
Is the battery negative grounded? On a common earth point?

 

[Feenster]

Do you have a battery in your off grid set up?
Is the battery negative grounded? On a common earth point?

I didn't put the batteries into the diagrams. The only earthing that EPEVER recommend is the inverter itself, as far as I can remember.