Adding a Neutral Conductor to existing QuadPlex

[Paco Solar]

Folks,
Background:
I have an existing 3-phase, ground-mtd. PV system in PA, being replaced with a new System, that I am designing now (new Modules and inverters). We are now under NEC 2017.
We'd like to utilize the existing wires (300' underground, then 400' aerial on poles) from the array to the Point of Interconnection (POI).
We are proposing inverters (solaredge 33.3k) that require a 4-wire (wye) service (which we have, at the service). At the transition from Underground to Aerial, the 4 conductors (3 + N) were transitioned to "quad-plex" so the Neutral (messenger) becomes uninsulated, and there is no EGC.

Question:
In order to provide the insulated Neutral conductor, we'd like add a single conductor, strapping it to the existing quadplex "bundle" The Inspector has a feeling that this is not compliant, but is open to us making the case. 300.3 (B) seems to go against this idea, (if the quadplex is considered a "cable") requiring that all conductors of the same circuit be "...contained within the same....cable...". Can anyone think of a Code section that might permit this idea? Has anyone ever seen this done before? Any alternate ideas? (The photo shows the riser pole, where the 4 UG conductors come up the pole and transition to the quadplex.)

Thank you!

 

[ggunn]

SolarEdge three phase inverters do not require a neutral connection; they only require that the current carrying conductors be referenced to ground. You have a neutral at the service, don't you? If it is bonded to ground you do not need to run a neutral conductor to the inverter(s).

 

[Paco Solar]

Hmmm... thanks for the feedback. The Tech's at SolarEdge tell me that the Neutral is required. They do permit it to be reduced in size, according to one of their white papers, but this inverter does require it to be there.

 

[pv_n00b]

SolarEdge three phase inverters do not require a neutral connection; they only require that the current carrying conductors be referenced to ground. You have a neutral at the service, don't you? If it is bonded to ground you do not need to run a neutral conductor to the inverter(s).

You can leave out the neutral if you have an EGC. The EGC is used to monitor the phase to neutral voltage since the EGC and neutral are bonded at the service. But you have to have one or the other, SolarEdge is not setup for an ungrounded 3W delta service.

 

[pv_n00b]

Question:
In order to provide the insulated Neutral conductor, we'd like add a single conductor, strapping it to the existing quadplex "bundle" The Inspector has a feeling that this is not compliant, but is open to us making the case. 300.3 (B) seems to go against this idea, (if the quadplex is considered a "cable") requiring that all conductors of the same circuit be "...contained within the same....cable...". Can anyone think of a Code section that might permit this idea? Has anyone ever seen this done before? Any alternate ideas? (The photo shows the riser pole, where the 4 UG conductors come up the pole and transition to the quadplex.)

Thank you!

I'm confused, what is the reason to need an insulated neutral and not the bare neutral? The inverter won't care.
My guess is that the previous contractor was able to combine the EGC and neutral into one conductor through the use of a number of exceptions in the NEC for remote services. I've done it but it requires some dancing.

 

[ggunn]

Hmmm... thanks for the feedback. The Tech's at SolarEdge tell me that the Neutral is required. They do permit it to be reduced in size, according to one of their white papers, but this inverter does require it to be there.

There has to be a grounded neutral in the service but it does not need to be connected to the inverter; maybe that's what they mean. I design a lot of systems with three phase SE inverters and I never connect them to the neutral. I don't have a data sheet for a 33.3kW SE, but the sheet for the SE50KUS shows for "AC Output Line Connectors" 3W + PE, 4W + PE. 3W means no neutral.

CAVEAT: I do not know for sure that the 33.3kW SE is not different, but for all the three phase SE inverters I use the neutral is optional.

 

[jaggedben]

I'm confused, what is the reason to need an insulated neutral and not the bare neutral? The inverter won't care.

There is an existing bare conductor they want to re-use as the EGC. If a neutral is also required it really cannot be bare because they'd contact each other creating a non-compliant load side N-G connection.

My guess is that the previous contractor was able to combine the EGC and neutral into one conductor through the use of a number of exceptions in the NEC for remote services. I've done it but it requires some dancing.

I don't believe it's been compliant for new installations since ... the 2002 NEC?

 

[pv_n00b]

There is an existing bare conductor they want to re-use as the EGC. If a neutral is also required it really cannot be bare because they'd contact each other creating a non-compliant load side N-G connection.

If the system works as it is and the AHJ does not require it to be changed I don't see why they can't continue to use the bare conductor as a combination neutral and EGC. If it's not broken don't fix it.

I don't believe it's been compliant for new installations since ... the 2002 NEC?

There is still one path to use this in cases where the circuit is outside and the transformer and panel are a long distance from each other. It involves going through the NEC and following several exceptions through multiple sections. One of the few places where the NEC allows a combination of grounded conductor and EGC. But it's there.

 

[electrofelon]

There is still one path to use this in cases where the circuit is outside and the transformer and panel are a long distance from each other. It involves going through the NEC and following several exceptions through multiple sections. One of the few places where the NEC allows a combination of grounded conductor and EGC. But it's there.

250.30(A)(1) exception #2.

As to the question in the OP, I see no issue with adding another messenger supported conductor. What would be the violation?

 

[Paco Solar]

There has to be a grounded neutral in the service but it does not need to be connected to the inverter; maybe that's what they mean. I design a lot of systems with three phase SE inverters and I never connect them to the neutral. I don't have a data sheet for a 33.3kW SE, but the sheet for the SE50KUS shows for "AC Output Line Connectors" 3W + PE, 4W + PE. 3W means no neutral.

CAVEAT: I do not know for sure that the 33.3kW SE is not different, but for all the three phase SE inverters I use the neutral is optional.

Thank you. Yes, the 33.3kw, 480V inverter is different than the 208 inverters. The datasheet for the 33.3k only lists "4-wire WYE (L1-L2-L3-N) plus PE" as the AC Connection. In this project, the Utility, as part of the Interconnection application for the new PV System is requiring a "fully-rated Neutral" from the inverter to the Point of Interconnection, so I don't believe the bare conductor will be permitted as the Neutral.

There does not appear to be a clear Code allowance for adding a single conductor to the quadplex cable that is currently strung.

 

[Paco Solar]

250.30(A)(1) exception #2.

As to the question in the OP, I see no issue with adding another messenger supported conductor. What would be the violation?

Thank you... just saw your comment. that is what we'd like to do... The following could be a violation, it would seem: (from the OP) "300.3 (B) seems to go against this idea, (if the quadplex is considered a "cable") requiring that all conductors of the same circuit be "...contained within the same....cable..." I just looked for a Code definition of "Cable," and there is no definition in Article 100 (2017)

 

[electrofelon]

Thank you... just saw your comment. that is what we'd like to do... The following could be a violation, it would seem: (from the OP) "300.3 (B) seems to go against this idea, (if the quadplex is considered a "cable") requiring that all conductors of the same circuit be "...contained within the same....cable..." I just looked for a Code definition of "Cable," and there is no definition in Article 100 (2017)

. Article 396 does provided definitions of what is acceptable. Plexing as support does seem to only be allowed for "factory assembled" cables which would seem to disallow plexing another conductor on to it. They do also refer to these as cables, although I don't think I buy the 300.3 B argument still. For field installations it appears you either need rings or saddles or field installed lashing. So in my opinion you could lash another conductor to an existing assembly but not twist it on with the others and use that as the sole support.

 

[ggunn]

Thank you. Yes, the 33.3kw, 480V inverter is different than the 208 inverters. The datasheet for the 33.3k only lists "4-wire WYE (L1-L2-L3-N) plus PE" as the AC Connection. In this project, the Utility, as part of the Interconnection application for the new PV System is requiring a "fully-rated Neutral" from the inverter to the Point of Interconnection, so I don't believe the bare conductor will be permitted as the Neutral.

There does not appear to be a clear Code allowance for adding a single conductor to the quadplex cable that is currently strung.

I see that on the data sheet, but you might want to check the installation manual. I have encountered inverters that didn't require a neutral where it wasn't shown on the data sheet but was in the manual. BTW, not requiring a neutral is not an exclusive feature of the 208/120V SE inverters; I use the SE80KUS and SE120KUS 480/277V inverters quite a lot and they do not require a neutral, either.

Also BTW, if you look at that line on the data sheets of other three phase SE inverters you will see variations; one I have says that it can connect to a 208V delta, which I don't think is correct; three phase conductors (no neutral) of a grounded wye is not the same as a delta. FWIW, SolarEdge documentation is at best inconsistent.

Does SE even make the 33.3kW inverter any more? The latest data sheet I have for inverters in that range are the SE30KUS and SE40KUS, which BTW show the neutral as optional. The data sheet I found for the SE33.3KUS is four or five years old. SE equipment changes often and their documentation struggles to keep up. I recommend calling SE tech support and asking them if your inverter actually needs a neutral.

 

[LarryFine]

. . . three phase conductors (no neutral) of a grounded wye is not the same as a delta.

Other than possible line-to-ground voltages, yes, it is. A load can not tell the difference.

 

[ggunn]

Other than possible line-to-ground voltages, yes, it is. A load can not tell the difference.

It's not a load, it's a source, and the voltages have to be referenced to ground. An inverter that doesn't connect to the neutral has a neutral to ground strap internally. If the service is a corner grounded delta, for example, that is a problem.

 

[Paco Solar]

I recommend calling SE tech support and asking them if your inverter actually needs a neutral.

Yes, good idea...I did that, and SE tech support tells me the 33.3kw does require the Neutral conductor. (for this project, the installer I am working with was able to procure the 33.3kw inverters, but you're correct...they are being phased out.)

 

[pv_n00b]

Yes, good idea...I did that, and SE tech support tells me the 33.3kw does require the Neutral conductor. (for this project, the installer I am working with was able to procure the 33.3kw inverters, but you're correct...they are being phased out.)

I hope you got a good deal on them to make up for having to run that new conductor. You can get a SE 30kW or 40kW and don't have to change a wire.

 

[Paco Solar]

. Article 396 does provided definitions of what is acceptable. Plexing as support does seem to only be allowed for "factory assembled" cables which would seem to disallow plexing another conductor on to it. They do also refer to these as cables, although I don't think I buy the 300.3 B argument still. For field installations it appears you either need rings or saddles or field installed lashing. So in my opinion you could lash another conductor to an existing assembly but not twist it on with the others and use that as the sole support.

Thank you... this seems to open the door for adding the desired conductor. If I was the Inspector I would want to know that the exist. messenger is capable of supporting the added weight of the additional conductor... not sure how that could be verified. It might be simpler to add a new messenger with a single conductor (i.e. duplex), and lash that to the existing quadplex

I hope you got a good deal on them to make up for having to run that new conductor. You can get a SE 30kW or 40kW and don't have to change a wire.

Good point. Perhaps we can switch to the 30kw and resolve the whole issue. Not sure why I didn't think of this before....

 

[ggunn]

Good point. Perhaps we can switch to the 30kw and resolve the whole issue. Not sure why I didn't think of this before....

I did, but I thought you said that you already had the 33.3kW. Availability of an SE30KUS could be a problem.

We have a need for an SE40KUS inverter but we cannot find one. Fun fact: an SE80KUS is just two SE40KUS inverters connected in a Synergy box; the SE80KUS is available but the SE40KUS is not, and there is no way to make an SE80KUS into an SE40KUS. Even if we only connect DC to one of the integrated SE40KUSs the NEC requires us to wire it as an SE80KUS, and we cannot extract one of the SE40KUSs and use it alone.

 

[ggunn]

I misspoke earlier, or at least I had old information. Apparently the SE80KUS and SE120KUS can connect to a delta service, but I don't know what their abbreviations mean for wye and delta grids.

Supported grids are WYE: TN-C, TN-S, TN-C-S, TT, IT; Delta: IT.