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LV6548 Grounding issues

DanF

Solar Enthusiast
Joined
Nov 26, 2020
Messages
124
Location
Ohio
I have an issue with current flow on my ground wire.

My main panel has the neutral bonded (Sub panel does not).
The LV6548 inverters - AC Line IN is not bonded, AC Line OUT IS bonded internally. (Everything looks good here to me)

What I have found...
While running sub panel circuits without going through the inverters (Main panel to sub panel through the manual transfer switch) everything is fine.
While running sub panel circuits through the inverter while on battery backup (Power outage simulation) everything is fine.

While running sub panel circuits through the inverter but in normal (Power on main panel is on and routed through the AC input on the inverters by way of the manual transfer switch) I loose bonding and I have current flow through the ground. This is a bit baffling here. The inverter should only be acting as a switch and the bonding from the main panel should not be affected just by being routed through the inverters. When the inverters transfer over to backup mode they have an internal bond and all is well again.

Has anyone with the LV6548 inverters experienced this or checked for current at your main panel on your ground in a similar setup as mine?
 
Dan, I noticed nobody ever replied to this. Did MPP give you an answer?
I have not yet been able to put my inverters into split mode, but they work fine in parallel. I can so some testing if you need some comparisons for parallel mode.
 
Dan, I noticed nobody ever replied to this. Did MPP give you an answer?
I have not yet been able to put my inverters into split mode, but they work fine in parallel. I can so some testing if you need some comparisons for parallel mode.
Well, sort of.. they got way deep into the build and my drawings and made the situation more complicated than it should have been so I gave up on the back and forth. I ended up changing my ground from the panel directly to the inverters (It was in my junction box on a terminal strip with the other circuit grounds) This seemed to be the issue. Sorry I didn't clear that up earlier!

Dan
 
Well, sort of.. they got way deep into the build and my drawings and made the situation more complicated than it should have been so I gave up on the back and forth. I ended up changing my ground from the panel directly to the inverters (It was in my junction box on a terminal strip with the other circuit grounds) This seemed to be the issue. Sorry I didn't clear that up earlier!

Dan
Thanks for the update!
 
Well, sort of.. they got way deep into the build and my drawings and made the situation more complicated than it should have been so I gave up on the back and forth. I ended up changing my ground from the panel directly to the inverters (It was in my junction box on a terminal strip with the other circuit grounds) This seemed to be the issue. Sorry I didn't clear that up earlier!

Dan
Hi Dan, can I ask you to clarify your ground wire / neutral wire routing between the Main Panel (bonded) , Sub Panel (unbonded), and the inverter. It sounds like you're saying that both neutral and ground run directly from the Main Panel, to the Inverter, and then from the inverter to the sub as I attempt to show below. Said another way, there is no direct neutral or ground connection between the main panel and the sub-panel, and there is no switching connection on the neutral line or the ground line except in the inverter itself.

Thanks in advance.

Ed
 
Hi Dan, can I ask you to clarify your ground wire / neutral wire routing between the Main Panel (bonded) , Sub Panel (unbonded), and the inverter. It sounds like you're saying that both neutral and ground run directly from the Main Panel, to the Inverter, and then from the inverter to the sub as I attempt to show below. Said another way, there is no direct neutral or ground connection between the main panel and the sub-panel, and there is no switching connection on the neutral line or the ground line except in the inverter itself.

Thanks in advance.

Ed
You are spot on.. No neutral bond except at the main panel. I think there is a problem with the neutral being bonded from the factory with these inverters (Which is a problem). These inverters should have no bonding when using the mains power and this should switch to being bonded when not using the mains power. (Batteries, panels or both) I haven't confirmed that this happens yet..
Also, you should have the inverter cases bonded and a separate ground should run within 6' of the ground rod for the main panel from what I understand in the NEC.
The companies that make many inverters sell their products all over the world and so they don't get involved with local codes.

I am still trying to come up with a reading on how the MPP Solar inverters work, but haven't had time yet unfortunately because my wife has been ill. I know this is extremely important to many followers on this forum and for me as well. I'll do my best to try and do a video on my system and update everyone as time will allow.

I hope this helps,
Dan
 
Dan, could I ask you to look at the sketch below, and tell me if I've captured your setup accurately.
First, I know it's an LV6548, not LVX so please disregard that.
Secondly I know you have two LVX units, instead of one so I've made some adaptation there., and
Finally I know you use a 2-pole xfer switch instead of interlocked breakers so that's different too.

What I'm trying to understand is the neutral and ground routing. It looks to me that there's a neutral loop in the drawing with neutral flowing through the LVX and also straight to the subpanel. If the LV6548 switches neutral that isn't an issue, but I'm not sure if it does. The manual says in the PV warnings that the unit is "non-isolated", but I have no clue what that means. So basic question is should I remove the neutral run from the Junction box to the sub-panel, and rely on the neutral run through the LV6548 to carry neutral when I'm using Grid Power directly, or should I leave it in place?


Nowhere that I can find does it discuss the function of it's internal transfer switch. Have you tested the Neutral In, Neutral Out for continuity in bypass mode vs off grid mode? Have you tested Ground IN vs Ground Out for continuity in Standby mode and Inverter mode? Have you tested Neutral Out and Ground out for continuity in bypass mode vs inverter mode?

Oh, before you ask the subpanel will only have 120 volt loads in it so splitting the output of the LV6548 is Okay. I may in the future add a second unit to run one of the AC units or the wall oven, but in PA I don't really need AC, and we can function without an oven. Furnace, dryer, hot water are gas

Thanks

Ed
 

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Looks like a ground loop to me.
Ground flows from the main panel, through the junction box (where it serves as an EGC, but is not bonded) to the inverter (where the treatment of neutral is at issue and if that is what you're referring to then Okay), to the sub-panel (where it is isolated from neutral) to the chassis of the 2nd junction box (as an EGC).

There is indeed the potential for a "ground loop" between the inverter and the main panel if the inverter bonds neutral and ground when in off-grid mode. I think it is this call it "primary" loop that is causing the voltage on ground that @DanF was seeing, but his update above suggests it went away when he removed a direct ground run between the main & subpanel and only ran ground through the inverter so perhaps the unit doesn't bond, and no loop will occur. That as they say is the question.

What I wasn't clear about from Dan's explanation and what I'm looking at is the "secondary" loop where neutral is attached twice to the subpanel, once directly from the mains for use when the inverter is offline, and again through the inverter.
 
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