MPP HV2-5048 Earthing of output

[TyTower]

MPP HV2-5048 Earthing of output

I have this inverter on a 48v battery and producing 240 volts A/C.
Its wired up normally as is the 240v A/c output but I ran the output through a RCD first then to the outlet plug. All the earths are connected up to each other BUT I have not yet connected the main earth to the ground peg.

Before doing so I ran the inverter and measured the A/C voltage from the unconnected earth to the earth ground peg proper and found it had a 48v A/c potential.

Is this correct? Is it how it should show at this time ?
Or is that telling me something is amiss.?

[coulomb]

MPP HV2-5048 Earthing of output

I have this inverter on a 48v battery and producing 240 volts A/C.
...
Before doing so I ran the inverter and measured the A/C voltage from the unconnected earth to the earth ground peg proper and found it had a 48v A/c potential.

Is this correct? Is it how it should show at this time ?

This is a hybrid model, so I don't know much about them. If the AC input was connected to the mains at the time, then I would expect some voltage at the earth terminal. There are often small "Y" capacitors to earth from both live and neutral at the input and output of the inverter, so I'm surprised you didn't see more than 48 VAC at the earth.

So yes, this is expected, and you should connect the inverter earth to the house earth.

[antiscab]

When testing potentials, did you use the meter in LOZ mode?

Otherwise you will be measuring with 1MOhm of meter resistance. 48v measured at 1MOhm suggests 4MOhm of isolation between the two

[TyTower]

Firstly the inverter is not connected to the grid in any way.

Second I have no idea what the second post is about ?
What is LOZ mode?
I had the multimeter turned to 400 volts A/C with one probe on the joined up earth wires and one probe on the earth rod.

[antiscab]

Fluke explains it better than I:
https://www.fluke.com/en-au/learn/blog/ ... ultimeters

I'm suggesting the 48vac difference measured is more a ghost voltage than anything to be concerned about. A cheap way to do it without a LoZ capable meter would be to put a light globe across as well. if there's no current available, the voltage will just fall to 0.

Are you operating with a MEN?
An RCD won't work without one (though you could use a RVD, though they're somewhat more expensive)

[TyTower]

Dunno about ghost voltage . The way I found this was I touched the earth wire while sitting on a damp cement block and felt a definite tingle . Also if you would explain your Acronyms the first time you use them it would make it a bit easier to understand .
MEN?
I went searching and I guess this is what you meant . No I dont have neutral connected to earth in my Inverter or elsewhere as far as I know .
Should I have with this inverter?

[antiscab]

Yep fair point
MEN = multiple Earth neutral

I would use one, though if the inverter doesn't like the neutral being connected to earth for some reason (some don't), then residual voltage detector it would have to be

[TyTower]

Fluke explains it better than I:
https://www.fluke.com/en-au/learn/blog/ ... ultimeters

I'm suggesting the 48vac difference measured is more a ghost voltage than anything to be concerned about. A cheap way to do it without a LoZ capable meter would be to put a light globe across as well. if there's no current available, the voltage will just fall to 0.

Are you operating with a MEN?
An RCD won't work without one (though you could use a RVD, though they're somewhat more expensive)

Didn't know of that as my 50 years of experience has mostly been with DC
Thanks for the post! There does not seem to be any other ways to say thank you on this forum.

[paulvk]

An RCD measures the current in the neutral and active should the current become imbalanced by more than the RCD is set for it will trip,
so it will trip without an earth if their is enough parasitic current flow and sometimes this causes problems.
Also in the above diagrams having an earth stake at a sub board is rarely done the out buildings would have to be a long distance away
and doing so prevents you having an RCD up stream, with my inverters I only earth the neutral while the inverter is running
as the neutral and active are disconnected from generator/grid input in this mode I use a relay driven by the inverter dry contacts.

[TyTower]

Also in the above diagrams having an earth stake at a sub board is rarely done.... the out buildings would have to be a long distance away
and doing so prevents you having an RCD up stream,...... with my inverters I only earth the neutral while the inverter is running .......
as the neutral and active are disconnected from generator/grid input ......in this mode I use a relay driven by the inverter dry contacts.

I've put dots where I think you mean to stop but its not making full sense to me yet.
OK on the sub-boards . That has been my experience also but why does putting one on prevent an RCD upstream?

as the neutral and active are disconnected from generator/grid input

can you explain that bit for me please.

.

[paulvk]

I've put dots where I think you mean to stop but its not making full sense to me yet.
OK on the sub-boards . That has been my experience also but why does putting one on prevent an RCD upstream?

can you explain that bit for me please.

.

If there there is an earth on the neutral down stream from an RCD unbalanced current will flow as current will flow on the earth back to the MEN link so it will trip.

With my inverters they disconnect both incoming from grid/generator active and neutral when in inverter mode so the MEN link is no longer there
Note my inverters are the 4048 MS so no feed to grid you would have to check how your ones operate.

[TyTower]

If there there is an earth on the neutral down stream from an RCD unbalanced current will flow as current will flow on the earth back to the MEN link so it will trip.

Nope still not with it . Must be a bit thick . down stream meaning ?

If the inverter produced A/C goes through an RCD before the power points and the earthing has a neutral link where will current flow?

RCDLeakage.png (68.61 KiB) Viewed 544 times

[coulomb]

down stream meaning ?

After the RCD (on the load side of the RCD).

If the inverter produced A/C goes through an RCD before the power points and the earthing has a neutral link where will current flow?

Your diagram does not show a neutral to earth link on the load side of the RCD. If there is, then some of the neutral current will flow through the earth, bypassing the RCD, causing an imbalance and likely causing a trip even though there isn't a life threatening fault.

[TyTower]

OK I think I understand now thanks.
Downstream being from the viewpoint of power flowing in from the source -->load.

Of course that's not what my intention was anyway after the RCD but I guess if the plug outlet earth is joined to the earthing network as it should be then the RCD would operate correctly as it is shown above as no current flows to earth unless in a fault condition. Am I right in that?

Simple things can get very complicated and messed up in your head if you think about them too much..

[coulomb]

I guess if the plug outlet earth is joined to the earthing network as it should be then the RCD would operate correctly as it is shown above as no current flows to earth unless in a fault condition. Am I right in that?

Yes, exactly.

[TyTower]

This statement from MPP Solar concerned me so I include it here . I believe this relates to an old problem with panels that does not exist with modern panels. Earth leakage of the negative in the panels themselves.

This is the statement from MPP Solar's HV2-5048

PV panel selection for HV2 models
Because the HV2 is designed based on high PV input which should require uses to wire panels in series as much as possible, without exceeding the max PV input limit. When selecting panels, be sure to use “non-grounding” panels as otherwise this could cause a leakage current problem on the HV2 inverters which are non-isolated design.

I have two strings of 8 normal 250 watt panels properly earthed with bite in clips and separate green yellow grounding wire on the mounting rails down to the combiner box where I have a breaker and a lightening arresting clamp which is also earthed on each string before combining . Input voltage on each string is less than 300V DC.

The inverter ,the combiner box ,the panels and the RCD on my 240v outlets are all earthed to the ground rod . My Inverter runs as normal so far and I have seen no issues yet.

My Grid is not connected to this inverter but Australian Grid is 240 volts single phase . That entails the neutral wire being earthed/grounded in the meter box . So fingers crossed . Its only been properly earthed for about 2 weeks. The two grounding rods , mine and the grids are about 20 feet physically apart in the ground.

IMG_20210302_180751.jpg (1.67 MiB) Viewed 304 times

[T1 Terry]

I would recommend using an RVD, avaiable from Ian @ https://www.rvdsafe.com.au/ We use these a lot with inverters that don't have an auto switching neutral to earth connection when on is not sensed by the inverter circuitry. This will protect all output from the inverter including from a generator that is powering the inverter turning it into a switch through supply and battery charger. Generators have a floating supply much the same as inverters .... a bit tricky to get the head around initially, but it means there is no active and no neutral but rather line 1 and line 2 with 240vac (or there abouts) between the two supply wires. This means any thing connected across line 1 and line 2 is seen as a load, that includes a resistor load that flesh provides, a rodent, pet or person ..... The RVD looks for voltage on the earth after the unit, anything that connects between either line 1 or line 2 and an earthed contact, like an earth metal appliance, an earthed wall stud or a water puddle linked to an earth point, will trip the circuit breaker. The safer side of this system, either line 1 or line 2 and earth are no longer a circuit that carries voltage or current because both line 1 and line 2 float rather than one of them being connected to the earth wire creating a neutral and the other becoming the active ....... Takes a while to get the head around and probably even longer to follow my crap explanation

As an aside, there is a model in the RVD range that can also sense reversed polarity, a very common problem with using plug in power points, particularly caravan parks that are a bit remote because the owner tends to do the electrical work to save a few $$ and often gets it wrong .....

T1 Terry

[TyTower]

Further to the right of that picture the Inverter 240v single phase comes out into a fuse /RCD box which monitors any residual current leakage to earth on the 240v supply. Cost ? about $24 RVD cost $195 ,bit of a difference

[T1 Terry]

Further to the right of that picture the Inverter 240v single phase comes out into a fuse /RCD box which monitors any residual current leakage to earth on the 240v supply. Cost ? about $24 RVD cost $195 ,bit of a difference

But an RVD works on both MEN and floating systems where an RCD only works on MEN systems, has no reverse polarity protection so some devices can be damaged including the RCD itself ...... what price safety, sounds like an extra $170 is too much .....

T1 Terry

[TyTower]

You got that right.