Should I Ground-Neutral Bond Inverter in Small RV

[max514]

I have a small popup camper in which I installed a small inverter to power the outlets from the battery when not connected to shore power or generator. It's really just to conveniently plug in low draw appliances in a conveniently located pre-existing outlets as opposed to using an extension cords or dedicated outlet(s) for the inverter. It is wired as follows:



The "Branch Circuit Breaker" is part of the RV's power center, a WF-8725 by WFCO. There is no EMS on this RV. The power center powers 4 outlets when connected to shore power so all I did was add a transfer switch between the first outlet of the circuit and the power center. When the RV is connected to shore power or a generator, the transfer switch powers the outlets from shore power/generator and when the RV is disconnected, it powers the outlets from the inverter. In order to avoid a charging loop, I ran new wiring directly from the battery to the inverter, bypassing the power center so as to not create a charge-discharge loop through the RV converter/battery charger. When off-grid, the battery powers the power center, which powers the 12V circuits of the RV and the battery powers the inverter which powers the AC outlets of the RV.

The AC Loads in the diagram consist of 4 GFCI outlets that were pre-installed in the RV. The Inverter is a Victron Phoenix 12/375VA, which has a floating neutral with the option to bond ground and neutral.

My first question is: should I Ground-Neutral bond the inverter? Would creating a return path to the inverter in case of a fault be more dangerous since it doesn't have an AC breaker or are the fuses on the DC side enough to protect me?

My second questions is: In either case, should I connect the inverter's ground screw to the chassis?

EDIT: If I ground-neutral bond the inverter, then it's already grounded to the chassis through the battery negative so it would be grounded twice. If I do not ground-neutral bond the inverter, then the ground screw would ground the frame of the inverter to the chassis but would not protect against a fault. Am I right?

My third question is: with shore power, the gound-neutral bond happens in the panel from which the power originates but my generator, a Honda EU2200i, has a floating neutral. Should I use a ground-neutral bond plug on the generator as well to allow the generator's breaker to trip in case of a fault?

These sound like obvious questions but I've been reading about this a lot and, while I've learned a great deal, I'm also more confused than when I started.

Thank you in advance for reading this long post. Your advice and the time you take to reply is sincerely appreciated!

 

[time2roll]

Since the Victron inverter has the option I would bond since the connection is made to a distribution panel.
If just plugging in an appliance direct I would skip the bond.

 

[Odom1957]

Neutral bond should be at the power source, so when you're on shore power, you'll have a floating neutral in the rv. When you are on Inverter, you'll have a bonded neutral.

If you run on a generator, then you should run a bonded neutral generator.

 

[max514]

So this is how I ended up proceeding:

Connected only shore power - tested GFCI - passed.

Connected only inverter - tested GFCI - got open ground. Opened the unit, bonded ground and neutral, tested, passed.

Connected only generator to RV - tested GFCI - got open ground. Made a ground-neutral plug, tested GFCI, passed.

Basically, made sure each source was ground-neutral bonded independently of each other so there is only one.

My last question is: now that the inverter has a ground-neutral bond, does the ground screw on the inverter (connecting chassis of inverter to chassis of trailer) count as a second ground-neutral bond since battery negative is connected to chassis of trailer too?

 

[Odom1957]

What you have done now is create 3 bonds, not one. That is wrong.

If shore power is connected, then you will have 2 neutral bonds active, which is wrong.

If generator is connected, you'll have 2 neutral bonds active, which is wrong.

You can ONLY have neutral bonded at one location, the power source.

You must disconnect the inverter bond when you are on shore power or generator power. If you have a way to connect generator and shore power simultaneously, then you must disconnect the bond not creating the power as well.

Most Victron units have a ground relay to accomplish this automatically in the inverter, but if yours does not, then you need to build a ground relay that is only active when the inverter is source power.

 

[time2roll]

The transfer switch isolates the N-G of the inverter. Sure the ground is always connected however the N is not connected when using the other power source.

 

[Zwy]

What you have done now is create 3 bonds, not one. That is wrong.

If shore power is connected, then you will have 2 neutral bonds active, which is wrong.

There is a transfer switch in place to change sources. This isolates each N-G bond from another.

If generator is connected, you'll have 2 neutral bonds active, which is wrong.

No, the generator would be similar to shore power, plug cord into the generator and transfer switch will isolate the N-G bond.

You can ONLY have neutral bonded at one location, the power source.

The power source providing power will be the one location.

You must disconnect the inverter bond when you are on shore power or generator power. If you have a way to connect generator and shore power simultaneously, then you must disconnect the bond not creating the power as well.

I doubt the member is using the generator with shore power, the cord from the RV plugs into one or the other.

Most Victron units have a ground relay to accomplish this automatically in the inverter, but if yours does not, then you need to build a ground relay that is only active when the inverter is source power.

No need, he has a transfer switch.

 

[max514]

@Odom1957: everything you replied is exactly right.

To specify, the cord from the RV plugs into the generator when off-grid OR to shore power when available. Never both.

The generator has a floating neutral by design so the G-N bond is accomplished by plugging in a plug on which N and G are jumped hot is not connected into one of the outlets.

The transfer switch does isolate the inverter from the other power source when in use. I tested for continuity and only ground is always connected. Both hot and Neutral are switched.

For the inverter, I'm not sure about this:

Now that the inverter has a ground-neutral bond, does the ground screw on the inverter (connecting chassis of inverter to chassis of trailer) count as a second ground-neutral bond since battery negative is connected to chassis of trailer too?

 

[Odom1957]

The chassis ground is not a neutral bond, it is a DC bond. It should be connected to the frame of the RV, or a DC bond (wherever you can get it from)

 

[max514]

The chassis ground is not a neutral bond, it is a DC bond. It should be connected to the frame of the RV, or a DC bond (wherever you can get it from)

Oh good! I should have looked when I was in there to know for sure but what if the AC ground is connected to the chassis of the inverter?

 

[time2roll]

Oh good! I should have looked when I was in there to know for sure but what if the AC ground is connected to the chassis of the inverter?

Regardless of how many points of AC ground to the frame and to the Neutral there is only one point of N-G bond and it is isolated by the transfer switch.

 

[Odom1957]

Regardless of how many points of AC ground to the frame and to the Neutral there is only one point of N-G bond and it is isolated by the transfer switch.

This is incorrect. If the inverter is bonded (neutral to ground) at the inverter, and you ground the inverter to the chassis, then you will always have a bond on the vehicle.

You shall never connect the neutral to ground in any way, except at either a neutral disconnect (which is uncommon in anything but marine) or with a relay inside a power generation device that has the ability to disconnect upon command.

Bonding issues like this create ELCI and GFCI faults that can be a PITA to track down and correct.

Victron inverters should have separate DC and AC bonds on their inverters, but I haven't checked them all.

 

[Zwy]

This is incorrect. If the inverter is bonded (neutral to ground) at the inverter, and you ground the inverter to the chassis, then you will always have a bond on the vehicle.

You shall never connect the neutral to ground in any way, except at either a neutral disconnect

You missed this part:

The transfer switch does isolate the inverter from the other power source when in use. I tested for continuity and only ground is always connected. Both hot and Neutral are switched.

(which is uncommon in anything but marine)

Really? I have a 3 pole double throw in my system where neutral is switched.

My camper AOI has a neutral switching transfer switch.

At my utility pole, the generator transfer switch is 3 pole and switches neutral.

I guess it is more common than you might think. I have an extra 3 pole double throw sitting in my storage shed for my shop if I decide to install solar for it.

or with a relay inside a power generation device that has the ability to disconnect upon command.

Not needed as the member is switching between power sources thru a transfer switch that switches neutral.

 

[max514]

So I opened the inverter today to check whether the ground screw on the chassis of the inverter is for the DC side only and I can see that the ground prong of the AC side is also connected to the chassis of the inverter. Since AC neutrals aren't connected to the chassis of the trailer anywhere, this is not a second G-N bond.

So there is still only one G-N bond at a time - on the inverter OR on the generator OR on shore power.

 

[Odom1957]

With no shore power connected, where is your neutral connected to ground? Inverter? Where is your ground bonded to the chassis? Nowhere?

 

[max514]

Victron made a provision for the G-N bond inside the inverter. You simply move the position of the ground wire to a different connector, as shown in the images below (from the inverter manual).

 

[Zwy]

With no shore power connected, where is your neutral connected to ground? Inverter? Where is your ground bonded to the chassis? Nowhere?

Inverter is N-G bonded.

AC ground is bonded to chassis.

So I opened the inverter today to check whether the ground screw on the chassis of the inverter is for the DC side only and I can see that the ground prong of the AC side is also connected to the chassis of the inverter.

With the transfer switch, there is only one N-G bond at any time from the power source being utilized. Nothing wrong with this system.

 

[defed]

i have a similar question, though different application (stationary non RV).

the neutral/ground is bonded in the main service panel. the inverter is connected to a manual transfer switch. it looks like only the hot is switched in the transfer switch, as i have continuity at the inverter neutral and ground even when the switch is on 'grid'. this means that i should NOT bond the n/g in the inverter, correct? the chassis ground has continuity to the AC in ground/neutral...does it still get connected to the grounding system?

 

[Zwy]

For stationary application with a grounding electrode, bond in main panel, do not bond inverter. What model inverter?

Inverter chassis ground is to be connected to equipment grounding busbar.

 

[defed]

For stationary application with a grounding electrode, bond in main panel, do not bond inverter. What model inverter?

Inverter chassis ground is to be connected to equipment grounding busbar.

i'm not 100% sure on which inverter yet, but looking at the victron multiplus2 48/3000. that's what i was thinking, it is bonded in the main panel...and because the transfer switch only cuts the hot, it will always be bonded through to the inverter...so do not bond them there. just wasn't sure if the inverter chassis had to go to ground busbar because it is already connected to the ground wire of the AC in (at least i think it would be, it is on my cheap inverter).