Sunny Boy TL inverter without neutral

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Zee

Senior Member
Location
CA
I am in a pickle.

I just replaced a failed SHARP SUNVISTA inverter with a new SMA SB3800TL-US. I added the secure power supply.
No permit needed.
After almost a day of re-wiring and remounting everything....I realized there was never a neutral for the old inverter. It does not require one. ....I totally forgot about it!:dunce::slaphead:

Tech support says this new model will not run w/o a neutral. And it won't.

I would have pulled a new neutral from inverter to subpanel...but wiring seems to be inaccessible and either romex or MC cable.
(all I can see is solid #12 red, black, green going thru the back of the exterior stucco-mounted ac disco and then reappearing in the sub-panel with the 2p20 PV breaker in it....so I assume Rx or MC)
It goes behind a finished basement wall...i.e. impossible to access run.:rant:

Couple questions:
There happens to be an outdoor rated, surface mounted, bell box, 120Vac outlet below the inverter.
What would Code say about someone unnamed running a neutral, alone, in metal conduit, to that outlet's bell box and the assumed neutral wire inside it?
What would any actual physical or electrical issues be with that?

Tech support did verify that no current actually will flow on this neutral.

Tech support says i just need a ground reference on the inverter's neutral terminal. I thought of bonding that neutral terminal to ground with a jumper wire to ground...but will not do so because there are some unlikely, yet dangerous-sounding, potential issues:
"conduit could have current flowing in it under certain circumstances" ....:jawdrop:

Finally does the SPS use the neutral wire of the inverter output circuit? Would current ever flow on the neutral?

Replacing this with another type of inverter will be costly.
 
Last edited:

Carultch

Senior Member
Location
Massachusetts
I am in a pickle.

I just replaced a failed SHARP SUNVISTA inverter with a new SMA SB3800TL-US. I added the secure power supply.
No permit needed.
After almost a day of re-wiring and remounting everything....I realized there was never a neutral for the old inverter. It does not require one. ....I totally forgot about it!:dunce::slaphead:

Tech support says this new model will not run w/o a neutral. And it won't.

I would have pulled a new neutral from inverter to subpanel...but wiring seems to be inaccessible and either romex or MC cable.
(all I can see is solid #12 red, black, green going thru the back of the exterior stucco-mounted ac disco and then reappearing in the sub-panel with the 2p20 PV breaker in it....so I assume Rx or MC)
It goes behind a finished basement wall...i.e. impossible to access run.:rant:

Couple questions:
There happens to be an outdoor rated, surface mounted, bell box, 120Vac outlet below the inverter.
What would Code say about someone unnamed running a neutral, alone, in metal conduit, to that outlet's bell box and the assumed neutral wire inside it?
What would any actual physical or electrical issues be with that?

Tech support did verify that no current actually will flow on this neutral.

Tech support says i just need a ground reference on the inverter's neutral terminal. I thought of bonding that neutral terminal to ground with a jumper wire to ground...but will not do so because there are some unlikely, yet dangerous-sounding, potential issues:
"conduit could have current flowing in it under certain circumstances" ....:jawdrop:

Finally does the SPS use the neutral wire of the inverter output circuit? Would current ever flow on the neutral?

Replacing this with another type of inverter will be costly.

All conductors associated with a circuit, including the equipment grounding conductor, need to be routed in the same conduit. (not counting the obvious exception for parallel conductors in a system of multiple conduits). 300.3(B)

This particular model does not put any serious amount of current on the neutral, so an EGC-sized neutral will suffice. Be aware that some inverters may still put current on the neutral due to their internal power supplies, albeit usually much less than the full load amperes on the ungrounded AC conductors. Unfortunately, downsizing the neutral doesn't seem to help you anyways, because in this case, both the power wires and the EGC would have to be #12. But in a general sense, this strategy can help reduce the capacity required for the conduit.
 
Last edited:

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The Secure Power Supply delivers 120V line to neutral. But it is isolated from both normal inverter output and grid.
In the absence of a ground fault all neutral current will return to the SPS on its dedicated neutral and there will be no current on the inverters grid neutral connection.
 
I have always been a bit confused by the 3 phase inverter neutral thing. Seems like a while back, they didnt need a neutral, then it seemed like often you could use the neutral or not, now it seems like you need a neutral (obviously a broad generalized statement and there are differences between manufacturers). I wonder why they couldnt use the EGC in the inverter output circuit to get the reference? UL lets dimmers use the EGC for operational stuff :angel: It seems unnecessary to have to run that extra conductor, and its usually, in my experience, a full size neutral - what a waste......
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I am pretty sure that most/all transformerless inverters have to have a neutral, and virtually all residential sized inverters being built today are transformerless. FWIW, something I learned just yesterday is that Enphase microinverters will run without the neutral connected, but they don't run well.
 

Carultch

Senior Member
Location
Massachusetts
I have always been a bit confused by the 3 phase inverter neutral thing. Seems like a while back, they didnt need a neutral, then it seemed like often you could use the neutral or not, now it seems like you need a neutral (obviously a broad generalized statement and there are differences between manufacturers). I wonder why they couldnt use the EGC in the inverter output circuit to get the reference? UL lets dimmers use the EGC for operational stuff :angel: It seems unnecessary to have to run that extra conductor, and its usually, in my experience, a full size neutral - what a waste......

What I'd like to see the manufacturers do, is explain what their inverter does with the neutral in the manual. And whether there is a legitimate reason to connecting a full sized neutral, or whether it is completely sufficient to only run one that is sized to match the EGC.

In some cases, like Solectria central inverters, the manual specifies that the inverter doesn't need a neutral for its operation, however it could be a utility or AHJ requirement to have one for reasons not up to the inverter manufacturer.

For instance, the Fronius IG Plus 12kW inverters actually do need a full sized neutral. Because the three internal inverting units are all connected phase-to-neutral across 277V, and when the power is much less than 12 kW, not all of the inverting units will be operating. And thus, there would be full current on the neutral.

A lot of inverters either use the neutral for either voltage measurement purposes, or possibly for powering internal power supplies. And thus such a conductor would never see anything near the full load amperes, and it is sufficient to size it per the EGC.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
What I'd like to see the manufacturers do, is explain what their inverter does with the neutral in the manual. And whether there is a legitimate reason to connecting a full sized neutral, or whether it is completely sufficient to only run one that is sized to match the EGC.

In some cases, like Solectria central inverters, the manual specifies that the inverter doesn't need a neutral for its operation, however it could be a utility or AHJ requirement to have one for reasons not up to the inverter manufacturer.

For instance, the Fronius IG Plus 12kW inverters actually do need a full sized neutral. Because the three internal inverting units are all connected phase-to-neutral across 277V, and when the power is much less than 12 kW, not all of the inverting units will be operating. And thus, there would be full current on the neutral.

A lot of inverters either use the neutral for either voltage measurement purposes, or possibly for powering internal power supplies. And thus such a conductor would never see anything near the full load amperes, and it is sufficient to size it per the EGC.
FWIW, SMA tech support told me that their Tripower inverters only use the neutral for voltage sensing and therefore qualify for the reduced neutral under 705.95(B). I didn't find it in the manual so I called them.

Also FWIW, some AHJ's still require a full sized neutral for at least part of the interconnection circuit. Austin Energy, for example, requires a separate utility grade PV meter and a full sized neutral from the interconnection point through the PV meter to the next termination, which in most cases is the AC disco.
 

Zee

Senior Member
Location
CA
Thank you all for the excellent feedback.

Would anyone disagree with this statement:
The SMA SB3800TL-US, as it operates the Secure Power Supply ("standalone op."),
does not put any current on the neutral leaving the inverter
(inv. output circuit), but just on the short neutral from inverter to SPS outlet?

Interesting possibility:
tech support immediately recommended the brand spanking new Sunny Boy 5.0-US / 6.0-USSunny Boy 5.0-US / 6.0-US
. (Not to be confused with 5000, 6000)
The point being is "it can be set up for operation with no neutral."
I looked into specs and found that it can be setup for 240V Delta.
Would this be the setting for no neutral?
Could i reasonably expect this to work with standard residential split phase 120/240 Vac?


(of course, this would be 1. overkill, as a 3.5 kw inverter is enough here and 2. a ton of work to re-install......)
 

Zee

Senior Member
Location
CA
FWIW, a heads up: an after market "SPS" is available (through WESCO for example) that is all wired up and ready to go.
Outdoor rated, full metal, "in use" cover, WR and TR GFCI outlet, switch, with wiring and flexible conduit nipple ready to plug into the SMA SBxxxxTL inverter line.
Saves lots of labor.:thumbsup:
But I digress.
 

Zee

Senior Member
Location
CA
Correct. The kit is just the external hardware.
You still need an SMA inverter. The newer TL line is usually equipped with the SPS option.
 
I am pretty sure that most/all transformerless inverters have to have a neutral, and virtually all residential sized inverters being built today are transformerless. FWIW, something I learned just yesterday is that Enphase microinverters will run without the neutral connected, but they don't run well.

Yeah that's a good point: a transformer based inverter can get a neutral from the secondary.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I am pretty sure that most/all transformerless inverters have to have a neutral, and virtually all residential sized inverters being built today are transformerless. FWIW, something I learned just yesterday is that Enphase microinverters will run without the neutral connected, but they don't run well.

I'm pretty sure that Solaredge can be programmed to run without a neutral and at one point a crew reported an inverter operating with no neutral despite having not been programmed. (Although the inspector failed the job anyway because the neutral was on the plans and I never got a chance to verify what was really true.)

I would have sworn the SMA 240V TLs can also be so programmed but maybe I'm wrong.

As for the Enphase, what does 'not well' mean? That's tantalizingly vague. :lol:
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Also, Zee, did you try pulling a new wire? Solid #12 in conduit is not a code violation or an unheard of practice so you shouldn't just assume it's MC based on that.
 

Zee

Senior Member
Location
CA
Also, Zee, did you try pulling a new wire? Solid #12 in conduit is not a code violation or an unheard of practice so you shouldn't just assume it's MC based on that.

No I haven't tried to pull a new wire. Thanks for thought, i will take a look at feasibility.

At this point I see these options:

1. run a neutral, by itself, in a new separate conduit, to the pre-existing non-associated outlet nearby
2. replace the whole shebang with another inverter and program it to a 240 V delta grid
3. go back to customer's home, remove the inverter and say "oops .....sorry... don't pay me, and no there is no solution...your system will never work again...bye now!"

on 1. i want to be 100% sure there is no current even in SPS mode.
on 2. i need to know 100% if this 240 V delta set up works on residential 120/240 vac split phase.
on 3. let's not think such things
 

Smart $

Esteemed Member
Location
Ohio
...
1. run a neutral, by itself, in a new separate conduit, to the pre-existing non-associated outlet nearby
...
I believe it was noted earlier, that is a violation of 300.3(B)... unless you comply with 300.3(B)(3).
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I'm pretty sure that Solaredge can be programmed to run without a neutral and at one point a crew reported an inverter operating with no neutral despite having not been programmed. (Although the inspector failed the job anyway because the neutral was on the plans and I never got a chance to verify what was really true.)

I would have sworn the SMA 240V TLs can also be so programmed but maybe I'm wrong.

As for the Enphase, what does 'not well' mean? That's tantalizingly vague. :lol:

If an Enphase array has an open ground in, say, the AC disco, The inverters will run but the line to neutral voltages will drift, and when one of them drifts to the point where it gets out of the operating range of an inverter, the inverter will shut down. Of course, when that happens, it affects the L-N voltages, so it can make another inverter in the array either shut down or come back on line. It makes the monitoring data look very screwy, but now I know what to look for.
 

Zee

Senior Member
Location
CA
For retrofits:
I found two residential sized inverters that claim to operate on 120/240 V split phase w/o neutral. They do this by setting them to work on the 240 Delta grid.
Solectria TL line, and the new SMA 5.0 /6.0 TL.
Code compliance is a diff. issue.
Clearly i would not recommend no neutral as per above for a new install.

SolarEdge too (per Jaggedben) .....but i don't want to add optimizers to existing array (of SHARP 167's).....:eek:
Otherwise, half my new installs are SolarEdge.

Excited about latest Sunny Boy!:cool:
The new SMA 5.0/6.0 has 3 mppts! :thumbsup::thumbsup::thumbsup:
And....Some weird configuration will get "4 inputs" (MPPT?)
That new inverter can warrant a whole new thread.
Also:2000 watts of standalone power! Needs 20A outlet and wire.
 

Zee

Senior Member
Location
CA
Jaggedben, You were absolutely right: it was conduit behind the wall, and so I pulled a new neutral through it without too much difficulty. I really overthought this one!:happyno:
 
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