Inverter as Shore Power and N-G Bonding question

[Dh3Ace]

Hello,

I have a few questions in regards to MEN (Neutral-Ground bond) for RV (class B conversion).

I’m designing my electrical system and i have the following question:

When using Power Assists the Multiplus-II would not do the Neutral-Ground bonding as it expects the “shore power” to have it.
I have seen when in “Inverter mode” the N-G is done at the Multiplus-ii but when in “charger mode” and/or Passtrhough the N-G bound is not done.

So here what i’m thinking in my setup:

Inverter 1 (feeding AC-In to multiplus) from vehicule battery (as shore power)
No shore power planned at the moment
Multiplus-II with house battery system (separate from inverter 1)

------


The Inverter 1 (does not N-G Boudning confirmed with Multimeter between AC-Neutral - AC Ground no connectivity)

So we must connect L/N to a RCD/GFCI Braker (better than a gfci outlet? or the same?)
Ground not connected to GFCI Braker and then to a busbar then to Chasis.

L connected to Multiplus AC-IN
N (from gfci) connected to “Ground” does the N-G bond then N connected to Multiplus AC-IN
G Connected to Multiplus AC-IN

EX:

Inverter N -----> N input GFCI - N output -------------------> N Multiplus-ii
Inverter L -----> L Input GFCI - N Input ------------------------> L Multiplus-ii
GFCI - N Input -------------> G Busbar
Inverter G -------------------------------------------------> G Busbar ----> G Multiplus-ii


My understanding is:

When the multiplus-ii is in “inverter mode” it is not using Inverter 1 N-G bound (as is offline even though AC-IN is bonded the inverter doesnt link the AC-IN N and G ? or am I wrong?).

When Inverter 1 turns on… the “Victron becomes in PowerAssits automatically if the setting is set ( i guess its stay that way once configured ?)”. Meaning it would use the 1st inverter up to let say: 10A that we can define.

if we use only 2A of load in our outlet.. the remaining 8A would charge the batteries. And then the N-G bound from the Inverter 1 would be used as the Multiplus-ii would not be doing the N-G bound via internal realy (per default config).

Am I understanding correctly? If we design it this way there should always be only 1 N-G bound even though the Inverter1 have N-G bound and Multiplus-II have N-G bound when in “inverter mode”, as long as we ensure that when inverter1 is online the mutliplus switch to PowerAssists there is always only 1 N-G bound?

Thank you

 

[Kirk]

In most RVs, the 120V neutral and ground are not bonded together by the inverter. The neutral and ground bond typically occurs at the shore power connection point at the park. When using the inverter, the neutral is often "floating" or not connected to the ground.

 

[Dh3Ace]

Isnt there some risks if the Inverter is "Floating"?

I beleive there should always be one N-G ground for safety reasons.

 

[Lou Schneider]

Isnt there some risks if the Inverter is "Floating"?

I beleive there should always be one N-G ground for safety reasons.

Many inverters produce balanced power where each leg is 1/2 the output voltage above ground and the tie to ground is the battery negative lead. In other words the inverter internals are tied to ground as long as the battery negative is grounded, but neither hot or neutral are at ground potential.

Balanced power is often used in places like hospitals where stray currents to ground can endanger patients hooked to the equipment.

 

[Gary RV_Wizard]

I was under the impression that the inverter, when actually inverting, bonds neutral to ground. But I don't have any authoritative source for that. Permanently installed generators (not portables) do that, though, and I thought hardwired inverters did the same, for the same reasons.
I see Lou was responding as I typed. He's more knowledgeable than I on this subject.

 

[Dh3Ace]

Many inverters produce balanced power where each leg is 1/2 the output voltage above ground and the tie to ground is the battery negative lead. In other words the inverter internals are tied to ground as long as the battery negative is grounded, but neither hot or neutral are at ground potential.

Balanced power is often used in places like hospitals where stray currents to ground can endanger patients hooked to the equipment.

Hmm not sure i understand fully

I know the inverter (when in offline) does not have continuity between AC Neutral and Ground. And also from other forums where people reached out to the inverter that it is not AC Ground Bonded.

Are you saying we should check if AC Neutral is connected to DC Negative? Though in the manual they clearly state to not run the inverter without the "ground screw" on the metal case connected. Which lead me to the fact that nothing is tied together unless in operatinal mode something change but i doubt.

 

[boatbuilder1]

In the marine world when the inverter is in the invert mode the neutral to ground is connected. The AC ground and DC negative are also connected at one point.

 

[Dh3Ace]

In the marine world when the inverter is in the invert mode the neutral to ground is connected. The AC ground and DC negative are also connected at one point.

Agreed, i think that what i'm trying to do but change Shore power to our "12V Inverter" feeding. So i guess i need to do the N/G Bound there. But with these Inverter that have no N/G bond internally from what I read an GFCI braker is required.

So in Mode "grid" aka when in "shore power" the (inverter 1)

The (Inverter 1) feeds the (inverter 2) which is feeding our ac oulets etc..

So between (inverter 1) and inverter 2 we need to:
Bond N/G and then G with DC - ( i think )
Inverter 2 is then in passthrough and doesnt use the Internal N/G relay it uses the AC In and AC Ground from Inverter 1

----

When we turn off the (inverter 1). The (Inverter 2) detects its in "off-grid" and then start inverting.
It opens its internal relay (N/G). Then making the N/G at the (Inverter 2)


So in both sittuation we only have "1 N/G Bond" at every single time. We are not thinking to connect to "real shore power" at the moment.

 

[Dh3Ace]

Many inverters produce balanced power where each leg is 1/2 the output voltage above ground and the tie to ground is the battery negative lead. In other words the inverter internals are tied to ground as long as the battery negative is grounded, but neither hot or neutral are at ground potential.

Balanced power is often used in places like hospitals where stray currents to ground can endanger patients hooked to the equipment.

Oh i found a video that talks about that, and if that the case then Neutral / Ground cannot be tied as the Neutral is not a true Neutral.

Interesting didnt knew that, though i will test using a multimeter to see how much volt L and G have to see if its 100% or 50% of the voltage.

 

[John From Detroit]

Standard house power cable is three wires parallel. two are insulated and the "Safety Ground" in the middle is not.

In electronics two metal plates with an insulating material between them is a Capicator.

So a run or standard ROMEX is in effect two caps like this ---||---||---

That is a capacitive voltage divider.

 

[Primerump]

Hello,

I have a few questions in regards to MEN (Neutral-Ground bond) for RV (class B conversion).

I’m designing my electrical system and i have the following question:

When using Power Assists the Multiplus-II would not do the Neutral-Ground bonding as it expects the “shore power” to have it.
I have seen when in “Inverter mode” the N-G is done at the Multiplus-ii but when in “charger mode” and/or Passtrhough the N-G bound is not done.

So here what i’m thinking in my setup:

Inverter 1 (feeding AC-In to multiplus) from vehicule battery (as shore power)
No shore power planned at the moment
Multiplus-II with house battery system (separate from inverter 1)

------

not sure why you intend to feed one inverter from another.. that doesn't make any sense.. primary power
should be from the house batteries and the vehicle battery system isolated.

then your primary power source is either:
1. shore
2. inverter
3. generator

The Inverter 1 (does not N-G Boudning confirmed with Multimeter between AC-Neutral - AC Ground no connectivity)

So we must connect L/N to a RCD/GFCI Braker (better than a gfci outlet? or the same?)
Ground not connected to GFCI Braker and then to a busbar then to Chasis.

L connected to Multiplus AC-IN
N (from gfci) connected to “Ground” does the N-G bond then N connected to Multiplus AC-IN
G Connected to Multiplus AC-IN

EX:

Inverter N -----> N input GFCI - N output -------------------> N Multiplus-ii
Inverter L -----> L Input GFCI - N Input ------------------------> L Multiplus-ii
GFCI - N Input -------------> G Busbar
Inverter G -------------------------------------------------> G Busbar ----> G Multiplus-ii


My understanding is:

When the multiplus-ii is in “inverter mode” it is not using Inverter 1 N-G bound (as is offline even though AC-IN is bonded the inverter doesnt link the AC-IN N and G ? or am I wrong?).

When Inverter 1 turns on… the “Victron becomes in PowerAssits automatically if the setting is set ( i guess its stay that way once configured ?)”. Meaning it would use the 1st inverter up to let say: 10A that we can define.

if we use only 2A of load in our outlet.. the remaining 8A would charge the batteries. And then the N-G bound from the Inverter 1 would be used as the Multiplus-ii would not be doing the N-G bound via internal realy (per default config).

Am I understanding correctly? If we design it this way there should always be only 1 N-G bound even though the Inverter1 have N-G bound and Multiplus-II have N-G bound when in “inverter mode”, as long as we ensure that when inverter1 is online the mutliplus switch to PowerAssists there is always only 1 N-G bound?

Thank you

standard practice ( and code ) is to have only ONE neutral ground bond at the power source, so in the case of shore power, the bond is defined there. this is to eliminate ground loops.
when on inverter power, the inverter becomes the source point and in compliance, the multiplus activates the ground relay as it's now the source point. when on generator power, it's now the source and so the multiplus de-activates the ground relay.

 

[John From Detroit]

If you understand the need for the safety ground being bonded to neutral on the mains... you understand why it is not needed with the inverter.