XW Pro Grid Support limitations?

[400bird]

In my case my contactor is a 3 pole, so I disconnect L1,L2 , and N so I have nothing but ground connecting my off grid system to the grid. Everything I have shares the same ground and a single ground rod. So since the N is disconnected from the grid panel when in off grid mode I made the N-G bond in the off grid panel like I said. Slightly more complex I know but this way the inverter without a doubt is not capable of either drawing or pushing power to the grid.

I think you're creating unneeded problems for yourself.
Your house already has the one neutral ground bond, in the main panel.

Is your off grid panel ever connected to the grid pabel? For example, when the transfer relays inside the XW close? In that case, I believe you have both of your neutral ground bonds connected together.

You can't push power to the grid on neutral and ground. That's just a single (unmetered) wire coming from the utility. If the hot lines are open, it can't push power to the grid. No need to disconnect the neutral.

 

[GXMnow]

I just dug into my XW manual and as I remember it explicitly states that there is no control over the N, switching or disconnecting, furthermore it states it does not connect it to ground and an external bond must be made.

The way the relays in the XW+ and XW-Pro appear to be the same. There is no setting to change how it controls the relays, other than some timing settings when using multiple units and/or and external contactor. The contacts that are open or closed in each operating mode are always the same.

The output neutral is always tied to the AC1 and AC2 input neutral. There is no time they are ever disconnected. The reason it breaks the neutral to the transformer is to eliminate any issue with the voltage of the 2 poles being out of balance and causing excessive current flow. When you are on grid in a split phase system, the utility transformer has it's center tap tied to the neutral. The L1 and L2 voltages should be identical, but they can vary by a small amount due to different loading, or even a winding being off a turn or two. If the transformer in the XW was also connected, and the voltage balance was not the same as the turns ratio (it should be exactly 1:1) then the XW transformer would fight the utility grid to try and balance the two legs. Even a tiny voltage difference could cause a huge amount of current to flow. That is why the neutral center tap of the XW transformer needs to be disconnected.

Many of the cheap split phase inverter/charger units on the market don't even have a connection point for the neutral on the input. I don't like that solution for a few reasons. If there is a balance error between the input L1, L2, and the transformer turns ratio, then the neutral will not be at the grid neutral potential. And ground bonding the output neutral will cause current to flow in the ground. It's not a good design.

 

[hogback]

To make sure I'm getting what you're saying @GXMnow , if you had a G N bond upstream (in a taking energy from the grid sense) of the AC1 terminals, this bond would not exist for the system when powering from the grid? I don't have any grid connection, but instead rely on the N G bond internal to the generator weather the generator is running or not. The generator is the only place in my system where the bond exists, and this usage seems to be suggested in the manual. Does AC2 work differently? I think I'm not understanding what you are saying is disconnected when grid is powering.... let me take a guess then... all Ns (load, ac1, ac2) are always bonded to each other internally in the xw, so a single N G bond on any of these will always suffice, but there is an additional internal relay to the xw that opens when taking power from ac1 or ac2, but this just applies to the xw's transformer, yes?

 

[Chris30559]

The way the relays in the XW+ and XW-Pro appear to be the same. There is no setting to change how it controls the relays, other than some timing settings when using multiple units and/or and external contactor. The contacts that are open or closed in each operating mode are always the same.

The output neutral is always tied to the AC1 and AC2 input neutral. There is no time they are ever disconnected. The reason it breaks the neutral to the transformer is to eliminate any issue with the voltage of the 2 poles being out of balance and causing excessive current flow. When you are on grid in a split phase system, the utility transformer has it's center tap tied to the neutral. The L1 and L2 voltages should be identical, but they can vary by a small amount due to different loading, or even a winding being off a turn or two. If the transformer in the XW was also connected, and the voltage balance was not the same as the turns ratio (it should be exactly 1:1) then the XW transformer would fight the utility grid to try and balance the two legs. Even a tiny voltage difference could cause a huge amount of current to flow. That is why the neutral center tap of the XW transformer needs to be disconnected.

Many of the cheap split phase inverter/charger units on the market don't even have a connection point for the neutral on the input. I don't like that solution for a few reasons. If there is a balance error between the input L1, L2, and the transformer turns ratio, then the neutral will not be at the grid neutral potential. And ground bonding the output neutral will cause current to flow in the ground. It's not a good design.

I think I understand what you're saying now, and it makes complete sense, the neutral break you referred to is between the actual transformer in the inverter and the input either AC1 or AC2 (it doesn't matter since all the N are tied together "I agree"). This bond is crucial to balance and sync up with the grid AC with the transformer inside the inverter and has nothing to do with the N-G bond. I see now you only brought that up to indicate the N taps in the inverter always stay connected to each other and never break, which will allow me to have the single NG bond in the grid panel. I do follow and agree. I understand that would certainly work for my case and to also answer 400bird's comment about the N being unmetered and unable to push power through to the grid, I Agree 100%. I guess the reason I did it the way I did was that I wanted true total isolation from the grid when in off grid mode, in which I am in 98% of the time. I don't truly have an argument as to why. to me using the 3pole contactor and adding the NG break relay was a simple enough solution to achieve this.

 

[GXMnow]

all Ns (load, ac1, ac2) are always bonded to each other internally in the xw, so a single N G bond on any of these will always suffice, but there is an additional internal relay to the xw that opens when taking power from ac1 or ac2, but this just applies to the xw's transformer, yes?

I think I understand what you're saying now, and it makes complete sense, the neutral break you referred to is between the actual transformer in the inverter and the input either AC1 or AC2 (it doesn't matter since all the N are tied together "I agree"). This bond is crucial to balance and sync up with the grid AC with the transformer inside the inverter and has nothing to do with the N-G bond. I see now you only brought that up to indicate the N taps in the inverter always stay connected to each other and never break, which will allow me to have the single NG bond in the grid panel. I do follow and agree.

Yes to both.

This function is required in the way the XW series operates to allow both on and off grid operation without fighting the neutral balance. No matter how the system is operating, only a single Neutral / Ground bond is required and there should never be a second one and there is no need for the neutral to be switched.

This is different to how some other inverters work. Several inverters in the Victron line do have a relay that ties the neutral and ground together when it is running in the off grid mode. But this is for mobile applications like an RV or boat. When they unplug from the grid connection, they lose their N/G bond and the relay then creates it. I have also seen RV transfer switch units that duplicate that function. This is only needed when the system fully disconnects from the grid, including breaking the neutral tie. Unless this is a mobile system, I would just always leave the neutral connected back to the grid and have the one constant bond back at the point of entry.

 

[BentleyJ]

This issue has come up recently and I was also under the impression Schneider uses dynamic neutral bonding via the 5th relay (smaller) attached to the PCB just above the AC connection terminals. On April 10th @hyw17 posted a paragraph from the Conext XW installation manual specifically stating that the inverter does not bond neutral to ground under any operating conditions. Pg69 attached for review.

So who whats to pull the front cover off their Schneider, disconnect the Neutral wires and do the continuity test both with qualified AC input and without? I would volunteer but our entire main panel is powered through the XW+ and really don't want to do all that at this moment.

 

[hogback]

So, if you were charging with just L1 and L2, and never even connected the N, it would charge fine, but you'd lose all 120V circuits on pass through during the charge, or would the internal wizards throw a fit?

 

[400bird]

This issue has come up recently and I was also under the impression Schneider uses dynamic neutral bonding via the 5th relay (smaller) attached to the PCB just above the AC connection terminals. On April 10th @hyw17 posted a paragraph from the Conext XW installation manual specifically stating that the inverter does not bond neutral to ground under any operating conditions. Pg69 attached for review.

Seem pretty cut and dry with these two lines:
"Conext XW+ does not connect the neutral to ground."

"In a system without a generator, or with a generator that does not provide a
grounded neutral, you must make the connection from neutral to ground..."

So who whats to pull the front cover off their Schneider, disconnect the Neutral wires and do the continuity test both with qualified AC input and without? I would volunteer but our entire main panel is powered through the XW+ and really don't want to do all that at this moment.

I don't need to pull the cover. I have AC in and AC out (two hot wires each) and a single Neutral connection that goes back to my main (grid side panel) if the XW opened the connection to the neutral, there's no way my system would function off grid.

 

[400bird]

So, if you were charging with just L1 and L2, and never even connected the N, it would charge fine, but you'd lose all 120V circuits on pass through during the charge, or would the internal wizards throw a fit?

I haven't tested it, probably the second option. It should function fine, but I suspect it is testing for the neutral connection.

 

[BentleyJ]

I have AC in and AC out (two hot wires each) and a single Neutral connection that goes back to my main (grid side panel) if the XW opened the connection to the neutral, there's no way my system would function off grid.

All the neutrals for AC1, AC2 & Load are hard wired together at the terminal block, that never changes. We are only talking about there potentially being a relay that makes or breaks a connection between N-G so unless there was a ground fault somewhere, your system would work normally with or without a N-G connection.

 

[400bird]

All the neutrals for AC1, AC2 & Load are hard wired together at the terminal block, that never changes. We are only talking about there potentially being a relay that makes or breaks a connection between N-G so unless there was a ground fault somewhere, your system would work normally with or without a N-G connection.

Right, my mistake. I think the other portion of my post is still valid. The XW doesn't have the capability to and never will bond ground to neutral.

 

[GXMnow]

So, if you were charging with just L1 and L2, and never even connected the N, it would charge fine, but you'd lose all 120V circuits on pass through during the charge, or would the internal wizards throw a fit?

If you only connected L1 and L2 with no neutral, I would expect the XW-Pro would never qualify the input as good power and it would leave the input contactor open, the neutral connected to the transformer center tap, and it would stay running off grid. And in that case, it would not be able to charge from the grid power.

If the neutral ground bond did hold it stable enough to read as the AC input as "qualified", it may try to connect, but as soon as there is any unbalanced load on the system, it would fault and drop off grid again.