MPP LV6548 Ground/Neutral Safety?

[Zwy]

No, I would not consider them a 240V "generator". It has two separate sources that are connected in series.

Actually found the answer, as these units are mounted in parallel under NEC 250.30

"Multiple power sources of the same type that are connected in parallel to form one system that supplies premises wiring shall be considered as a single separately derived system and shall be installed in accordance with 250.30."

 

[Zwy]

you should familiarize yourself with the grounding requirements:

The Basics of Bonding and Grounding Transformers

Clearing up confusion on bonding and grounding solidly grounded transformers

www.ecmweb.com

Yes, if one reads that correctly, the EGC is not a bonding jumper in a SDS (separately derived system) . Therefore either the inverter would require a bonding jumper inside the inverter between N-G or a bonding jumper (sized correctly) to the first disconnect or over current device.

I had run across this article, although dated and for 480V systems, it still applies to a 240V split phase system employing a neutral switching 3 pole transfer switch. https://iaeimagazine.org/2009/septe...er-equipment-applications-and-considerations/


"Four-Pole Transfer System Considerations – Ground Fault

Separately derived systems require four-pole transfer equipment in order to provide the normal and alternate sources with mutually exclusive grounded circuit conductors (neutral), see figure 1. This is an important requirement since for separately derived systems the generator is required to be grounded perNEC250.30. The use of four-pole transfer equipment and resulting separation of the systems allow the overcurrent protective device to recognize load unbalance current and avoid nuisance ground-fault tripping. Figure 2 illustrates that this is accomplished by preventing the neutral current from having a parallel path through the equipment grounding conductor (EGC). Another benefit of using four-pole transfer equipment in a separately derived system is demonstrated in figure 3. When a real ground fault occurs the current is not allowed to return to the source using the grounded conductor (neutral). This allows the overcurrent protective device to accurately recognize the fault and protect the system. Failure to use four-pole transfer equipment for a separately derived system would adversely affect the equipment ground-fault protection and ability to recognize load unbalance. A more complicated and costly modified differential ground-fault system would have to be designed and installed."

 

[timselectric]

Actually found the answer, as these units are mounted in parallel under NEC 250.30

Series, not parallel. But, I would still consider them as a single power generator.
And only a "separately derived system" if used with a transfer switch that also separates (switches) the neutral. (Not the standard)

 

[Zwy]

Series, not parallel.

I've looked for a real definition, what I have found is 2 120V power supplies phased at 180 degrees with series connected loads at 240V.

The neutral is added to provide a path if 1/2 of the 240V is opened. So, is it really a true series system? If was a true series system, if 1/2 of the 240V is open, then the other side would not function without the neutral.

Maybe you have a better resource for a definition? Is a split phase system truly in series?

But, I would still consider them as a single power generator.

From the NEC definition of power source I would also as it produces split phase.

And only a "separately derived system" if used with a transfer switch that also separates (switches) the neutral. (Not the standard)

Most definitely, that is what this part of the discussion is all about, a system that is considered SDS with a switched neutral, 2 inverters in split phase.

 

[timselectric]

Maybe you have a better resource for a definition? Is a split phase system truly in series?

It really doesn't have anything to do with the split-phase part of the system. Each inverter creates 120v, on their own. If wired in parallel, you get 120v and double the rated amperage. When wired in series, you get 240v (twice the voltage of a single unit) and the rated amperage of a single unit.

 

[timselectric]

Most definitely, that is what this part of the discussion is all about, a system that is considered SDS with a switched neutral, 2 inverters in split phase.

I guess that I missed that. I thought that you were the first here to call it a separately derived system.

 

[Zwy]

It really doesn't have anything to do with the split-phase part of the system.

It should due to each inverter is 120V and each has a neutral and the inverters are in phase.

Each inverter creates 120v, on their own. If wired in parallel, you get 120v and double the rated amperage. When wired in series, you get 240v (twice the voltage of a single unit) and the rated amperage of a single unit.

I understand that part, to an extent. As alternating current, the reason we see 240V between L1 and L2 is due to the sine waves are phased 180 degrees, thus between the peak of one sine to the bottom of the other sine is 240V.

 

[timselectric]

It should due to each inverter is 120V and each has a neutral and the inverters are in phase.



I understand that part, to an extent. As alternating current, the reason we see 240V between L1 and L2 is due to the sine waves are phased 180 degrees, thus between the peak of one sine to the bottom of the other sine is 240V.

The reason you get 240v is because they are in series.
To clarify a bit more:
If they were in parallel you would only get 120v.
In phase with each other at 60Hz.
180 deg out of phase would be 120Hz.

 

[Roll2Videos]

FYI
mpp solar; USA Mpp Solar & watts247 are two different things

I think I’d lean in the watts247 direction for accurate info.
Other people explaining what they clearly don’t understand to someone who doesn’t know either seems a dubious task

“Due to the original design of this unit, when this unit works in battery mode, the N-G terminal of AC output will be short. When this unit works in the line mode, the N-G terminal will be open.”

^^^this seems to indicate it’s fine

You can only have 1 bond location. If you have 1 unit at 120V no problem. If you have two units at 240V making a N-G you will have two bonds in each unit.

 

[12VoltInstalls]

At 240 or 120V (USA) there is only one neutral…

 

[sv308]

Sorry to bring up an old thread but I have been attempting to get some clarification on this question.

I am using 2x SP6548 in split phase to get to 240v. I will use the Units and Panels as the primary source of power during the day but have the grid available for recharging the system if the panels are not performing well enough to do so by themselves

The proposed wiring will look like this -
I have an emergency disconnect directly after the meter.
It will service ac input power to the units and can continue doing so after i turn the main off at the sub panel which services the house.
the sub panel has a interlock kit on it that will let me switch between the grid input and a 60amp input that the ac output from the inverters will send power to.




The Neutral Ground bond is acheived at the main \ emergency disconnect panel
So i was not sure if i would need to remove the bonding screw from the units.
So after reading this thread i reached out to support from sungoldpower and i am just not sure if i trust their response 100%


so originally i provided them the drawing above and asked if i needed to remove the screw - they responded with


So i replied asking - What scenerio would involve me removing that screw - they responded with



So they advised you would NEVER remove the screw - which doesnt seem accurate.

any input on the proposed setup would be great - thanks!

 

[timselectric]

Sorry to bring up an old thread but I have been attempting to get some clarification on this question.

I am using 2x SP6548 in split phase to get to 240v. I will use the Units and Panels as the primary source of power during the day but have the grid available for recharging the system if the panels are not performing well enough to do so by themselves

The proposed wiring will look like this -
I have an emergency disconnect directly after the meter.
It will service ac input power to the units and can continue doing so after i turn the main off at the sub panel which services the house.
the sub panel has a interlock kit on it that will let me switch between the grid input and a 60amp input that the ac output from the inverters will send power to.

View attachment 176706


The Neutral Ground bond is acheived at the main \ emergency disconnect panel
So i was not sure if i would need to remove the bonding screw from the units.
So after reading this thread i reached out to support from sungoldpower and i am just not sure if i trust their response 100%


so originally i provided them the drawing above and asked if i needed to remove the screw - they responded with
View attachment 176708

So i replied asking - What scenerio would involve me removing that screw - they responded with

View attachment 176709

So they advised you would NEVER remove the screw - which doesnt seem accurate.

any input on the proposed setup would be great - thanks!

Remove the bonding screws in both units.
That's the only way to avoid double bonding, the way you are connecting everything.
Assuming that removing them stops bonding in those units.

 

[Robert Ibe]

Nevermind I found what I was looking for.

 

[BuffaloTrace]

Nevermind I found what I was looking for.

Who are you replying too?