Neutral Grounding at Inverter

[wmgeorge]

In a discussion on another Forum. Inverter being supplied with 230 volts no Neutral but EG wire. Outputting 115/230 vac as a transformer might with a center tap to source the 115 volts. They are calling the center tap, Neutral I contend that its Not a Neutral until its tied to the Main ground lug at the service panel. Attaching it to the panel EG does not qualify, opinions?

Yes I have Mikes 2020 PV Code book, the Illustrated one. Retired Master in Iowa

 

[tallgirl]

What's the inverter? Make and model.

It's possible there is no "neutral", in the sense of where 0 volts, relative to the two outputs, would be but without the inverter make and model that's just guessing.

 

[wmgeorge]

What's the inverter? Make and model.

It's possible there is no "neutral", in the sense of where 0 volts, relative to the two outputs, would be but without the inverter make and model that's just guessing.

Growatt SPF 8000T DVM-MPV but to be called correctly a Neutral it Must be Grounded and the only place I think it can be legally done is at the Main service panel Ground. Otherwise you could have two Neutrals in a system with a difference in potential, perhaps very slight admitted. I asked the OP for a picture of the UL Approval on the label.

 

[jaggedben]

The code requires neutrals to be grounded but that's not what makes it a neutral. What makes it a neutral is that the vector sum of the voltages to the phase conductors is zero (ideally, or practically close enough). So you are incorrect in as much as it's already a neutral before you ground it. You are correct in as much as the code always requires a neutral to be grounded at this voltage, so if it's not grounded then it needs to be. Also it's not allowed to use white wire if it isn't grounded, but again, it's required to be grounded. Typically it would be given a grounded neutral by running a white wire to its neutral terminal like anything else.

I'm not familiar with that inverter, and it matters how it's being used. But from a cursory look at the features online, it most certainly needs a neutral connection like any other piece of equipment that uses a neutral. Perhaps it doesn't need one if it is not being used in any off-grid scenario, but that doesn't seem to be the point of this inverter. In other words, connecting the neutral terminal on the inverter only to an EGC, as you seem to describe, is most likely wrong.

 

[wmgeorge]

If its not a legal Neutral as its not grounded and can not be White nor mixed with another legal system Neutral. How can there be both a grounded and ungrounded Neutral in premise wiring? It can be called a center tap neutral in respect to say a 230/115 transformer but can not be called Neutral and colored White. So your answer is just as confusing as the 2020 Code on PV systems. Lets hope the 22 or 23 Code clarifies. In the trade when we call a Neutral we are referring to the system White * grounded conductor.

 

[wmgeorge]

If its not a legal Neutral as its not grounded and can not be White nor mixed with another legal system Neutral. How can there be both a grounded and ungrounded Neutral in premise wiring? It can be called a center tap neutral in respect to say a 230/115 transformer but can not be called Neutral and colored White. So your answer is just as confusing as the 2020 Code on PV systems. Lets hope the 22 or 23 Code clarifies. In the trade when we call a Neutral we are referring to the system White * grounded conductor.

Added: Of course the easy way out is to tie the Inverter center tap or what they call neutral to the System Neutral... but is that allowed?

 

[ggunn]

Many commercial inverters do not require a neutral conductor. The provide a strap to tie their neutral connector to the equipment grounding conductor.

 

[wmgeorge]

Many commercial inverters do not require a neutral conductor. The provide a strap to tie their neutral connector to the equipment grounding conductor.

That makes sense so indeed it should meet the requirements for a grounded Neutral. I can understand some countries do not use the same wiring as us.

 

[wwhitney]

Growatt SPF 8000T DVM-MPV

The only SPF 8000T models I find for the US market are DVM-US and DVM-US MPV, did you mean one of those?

Growatt

Those are both listed as "off-grid storage inverters." I only glanced at the manual, but they have both input and output AC connections. So I'm thinking that the output side is always a microgrid supplied by the PV, batteries, and built-in transformer, and that the AC input side is only used for battery charging, and the inverter is not designed to operate grid-tied. In which case there would be no need for a neutral connection on the input side, as battery charging can be a 240V load. Not familiar with the product, so my conclusions may be off.

As an aside, would such a system require an interconnection agreement with the POCO?

Cheers, Wayne

 

[wmgeorge]

Wayne I do not have a clue, its not my system or inverter I was trying to get a straight answer I could pass on.

 

[jaggedben]

Many commercial inverters do not require a neutral conductor. The provide a strap to tie their neutral connector to the equipment grounding conductor.

I could be wrong about how this system is being used, but it appears to be an inverter designed to power L-N loads off-grid. Admittedly I do not have the patience to look up and read the manual, and the OP has not provided clarification on this aspect of the installation.

 

[jaggedben]

If its not a legal Neutral as its not grounded and can not be White nor mixed with another legal system Neutral. How can there be both a grounded and ungrounded Neutral in premise wiring? It can be called a center tap neutral in respect to say a 230/115 transformer but can not be called Neutral and colored White. So your answer is just as confusing as the 2020 Code on PV systems. Lets hope the 22 or 23 Code clarifies. In the trade when we call a Neutral we are referring to the system White * grounded conductor.

You can't have a legal ungrounded neutral under the NEC, but you could have multiple neutrals on the same site that aren't connected to each other except through the grounding electrode. It is unclear from your description if the inverter neutral is supposed to supply a separate system neutral, the same system neutral as the service, or no neutral. That matters.