LV6048 output neutral-ground bonding?

[Zwy]

Folks, I just heard back from MPP:


I do not follow his reasoning, but the bottom line is that MPP does not support connections between the input and output neutral.

So.... In the configurations we have been talking about with the LV6048 a transfer switch must switch the neutral

View attachment 83709

Really the only way to do it. Too many issues with N-G bond, and possible backfeed on the neutral. Which also makes this a SDS.

 

[Zwy]

Where and when have MPP given this advice ?
I only know of this fudge from Growatt discussions.

The infamous post #11 in this thread. Even a photo to boot. https://diysolarforum.com/threads/lv6048-output-neutral-ground-bonding.33719/post-417481

 

[Quattrohead]

Ah OK buried so deep.

 

[Quattrohead]

Folks, I just heard back from MPP:

I do not follow his reasoning, but the bottom line is that MPP does not support connections between the input and output neutral.

Folks, I just heard back from MPP:

I do not follow his reasoning, but the bottom line is that MPP does not support connections between the input and output neutral.

There should NEVER EVER be ANY connection between in and out of the line connections.
The inverter circuit is a floating transformer isolated unit that is designed with relays to take care of all the risks.
Bypassing this for any reason is extremely dangerous.

 

[MrM1]

Schneider and solark tie the input and output neutral together internally and they never try to create an NG bond. Consequently, you don't need or want an neutral switching transfer switch. It would look like this:


However, that creates a loop on the neutral line so I would do it like this:

View attachment 83609

So removing the Neutral from the Schneider SW out is the correct method? What if the grid is down? Isn't the Schneider SW the source of the neutral in that case for the critical loads? In the example above, Could you remove the Neutral In to the Schneider instead? Or does it need that for charging?

What is the problem with the Neutral Loop?

 

[FilterGuy]

So removing the Neutral from the Schneider SW out is the correct method? What if the grid is down? Isn't the Schneider SW the source of the neutral in that case for the critical loads? In the example above, Could you remove the Neutral In to the Schneider instead? Or does it need that for charging?

Since the neutral in and the neutral out are tied together internally, either of them can be used for 'IN' and either of them can be used for 'OUT' or more importantly, either of them can be used for In *and* Out. If you look at the diagram with the schnider, all neutrals lead back to the neutral bus in the main breaker box. So in the diagram I did, the Neutral in is also the Neutral out. You could remove the neutral in and use the Neutral out as well. I chose neutral in to use because it has the fewest connections.

What is the problem with the Neutral Loop?

As a loop, it becomes an antenna and can create RFI issues. This is similar to ground loop RFI issues, but you don't hear about this much because 'neutral loops' are pretty uncommon.

 

[FilterGuy]

Not strictly true, the bare wire the other 2 line wires are attached to between poles and strung to your house are grounded at every pole and are the ground/neutral wire to the house. It is one and the same.

It is a matter of definitions. The wire coming from the utility is considered a Grounded Neutral. (It is a current-carrying conductor that is bonded to earth ground). If we remain strictly with the definitions, a ground wire (or what the NEC calls the Equipment Grounding Conductor) will never carry current in normal operations. The 'bare wire' that comes from the utility is by definition not a ground wire.

No matter what you call it, the Neutral-Ground bond at the utility does not provide a low impedance fault path for a short between hot and the Equipment Grounding Conductor, so the NEC requires a Neutral-Ground bond at the service entrance.

BTW: I wish the NEC would change the name to something like "Equipment Safety Conductor" and reserve the words 'ground' or grounding' to tieing to earth. It would help prevent a lot of the confusion that exists in this space.

 

[mrzed001]

A few points:

1) On some of the lower power MPP units, they made a change a year or more ago that implemented the internal relay. I never found out how to identify new and old units and I don't know if similar changes were done on higher power units.

I think all newly made (last 2 years) original (not a clone) and more than 3kW MPP Solar inverters have that relay

2) The lv6048 manual on the MPP website says this about the dry contact:
View attachment 81656
It does not appear to be intended for a bonding relay.

It does.
I even put the outer relay product in this post:

Safety hazard w/ Growatt 5000ES (European version) when connected to American grid

I’ll be watching this thread with interest. At present I’m planning on a parallel Growatt setup for 240v loads only. Would be a shame not to be able to use 120v in the future. Also, the Growatt’s debatable UL compliant, certified or listed rating could also write my whole project off.

diysolarforum.com

3) On the smaller inverters, the control for the bonding relay used to be program 24. Program 24 does not exist on the newer units or on the LV6048.

It was menu point 38 if I remember correctly. Not in the new inverters.

4) This post in another thread implies there is an internal bonding relay:

LV6048 output neutral-ground bonding?

Just picked up an MppSolar LV6048 and noticed that they bond the output neutral to ground! Not clear why. If your split phase input is from a panel where ground and neutral are bonded, which is always the case if the panel is the first disconnect after the meter, you would like to preserve that...

diysolarforum.com

I even posted a pic from the double throw bonding relay:

Safety hazard w/ Growatt 5000ES (European version) when connected to American grid

I’ll be watching this thread with interest. At present I’m planning on a parallel Growatt setup for 240v loads only. Would be a shame not to be able to use 120v in the future. Also, the Growatt’s debatable UL compliant, certified or listed rating could also write my whole project off.

diysolarforum.com

The post also talks about how to disable the bonding relay.

If this inverter is used in like the circuit I showed above, the bonding relay would need to be disabled.

The off-grid bonding with relay is bad if you use a 240V inverter and an auto transformer.
Every other case it is perfectly where it should be.

 

[eabyrd]

It is a matter of definitions. The wire coming from the utility is considered a Grounded Neutral. (It is a current-carrying conductor that is bonded to earth ground). If we remain strictly with the definitions, a ground wire (or what the NEC calls the Equipment Grounding Conductor) will never carry current in normal operations. The 'bare wire' that comes from the utility is by definition not a ground wire.

No matter what you call it, the Neutral-Ground bond at the utility does not provide a low impedance fault path for a short between hot and the Equipment Grounding Conductor, so the NEC requires a Neutral-Ground bond at the service entrance.

BTW: I wish the NEC would change the name to something like "Equipment Safety Conductor" and reserve the words 'ground' or grounding' to tieing to earth. It would help prevent a lot of the confusion that exists in this space.

Why can’t we just say earthing like the ROW

 

[OffGridForGood]

I am not trying to answer the original question, however I as someone with Two MPP LV6048's I feel I need to point out two things:
First: The MPP LV 6048's are completely different than the MPP 6548's and the LVX 6048
Second: when you guys discuss "THE" Ground screw for the dynamic N-G bond remember in the LV 6048 this is TWO BONDING SCREWS! becase this unit is really twin 3kW inverters jambed into one box. I have posted pics prior. And because this is really two dynamic bonding relays, it begs the question how can this Not create a loop, even if only the short distance between the two side by inverters? Even if only One MPP 6048 not several, and with several this is 4 or 6 etc multiple N-G bonds during inverting.
I have taken my two units apart, and studied the internal workings. I can confirm: my units are from 2021 (unit 1|) and early 2022 (unit 2) vintage.
I can confirm they dynamically bond N-G during inverting only. This was tested multiple times with @FilterGuy help and guidance.
I can confirm removal of the screws removed the dynamic bonding, even under considerable load, near max rated.
I can confirm the G-in and the G-out are tied together internally in each unit.
I read all the postings in this 8-page thread, I can say although I understand the thinking behind it, the use of a MTS for Gen and Utility both operating as source to the MPP - itself feeding a subpanel (in my case with CLP Reliance 306) with careful attention to N and G loops (thanks @FilterGuy) has resulted in a great system that (seems) to operate perfectly from my perspective.
I can't comment on the MPP solar position that the N-in and N-out 'shouldn't be tied together' but their reason doesn't seem to hold water. (with N-bonded to G at the main panel what voltage are they talking about running back to the utilitiy line??? the transformer at the utility is an isolated transformer right? and N is BONDED to Earth-Ground, so zero potential?
Correct me if I am out to lunch. I got thick skin, and I prefer to be corrected and learn than spout crap uncorrected.

 

[OffGridForGood]

For anyone with a MPP 6048 (or interested in how these work internally) Ian has a YT vid where he systematically takes one apart (to repair a shorted board) and at 16:15 he shows you the TWO dynamically activated bonding screws in the units.
A couple members I think may be interested: @TheCoachStone @FilterGuy - you may find this video helpful.

www.youtube.com/watch?v=YWdNCllE1-c