Adding a Neutral Conductor to existing QuadPlex

pv_n00b

Senior Member
Location
CA, USA
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.
The TN-C has phase conductors and a combined grounded conductor/EGC. Which is what the OP's overhead line is. The TN-S and TN-C-S have a grounded conductor and EGC that are separate, the difference being if the EGC is bonded to the grounded conductor at the source or derived after the source.
What it all comes down to is what inverters can work with and that falls into two categories:
  • Grounded services with a grounded neutral conductor at the service entrance
    • Phase conductors, neutral, and EGC run to the inverter (4W+EGC 3ph system)
    • Phase conductors and EGC run to the inverter (3W+EGC 3ph system)
  • Ungrounded services that do not have a grounded conductor
    • Phase conductors and EGC run to the inverter (3W+EGC 3ph system)
All inverters can work with the 4W+EGC system. Most inverters can work with grounded services with only 3W. The EGC can be used to test for the phase to neutral voltage. Most inverters cannot work with and will fail if installed with, a 3W ungrounded service. It is really important to understand and to be able to distinguish between inverters that can operate with a 3W grounded system but not with a 3W ungrounded system. So many people believe that if an inverter only needs a 3W+EGC that it can operate with a grounded or ungrounded service and this is an expensive misunderstanding.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
The TN-C has phase conductors and a combined grounded conductor/EGC. Which is what the OP's overhead line is. The TN-S and TN-C-S have a grounded conductor and EGC that are separate, the difference being if the EGC is bonded to the grounded conductor at the source or derived after the source.
What it all comes down to is what inverters can work with and that falls into two categories:
  • Grounded services with a grounded neutral conductor at the service entrance
    • Phase conductors, neutral, and EGC run to the inverter (4W+EGC 3ph system)
    • Phase conductors and EGC run to the inverter (3W+EGC 3ph system)
  • Ungrounded services that do not have a grounded conductor
    • Phase conductors and EGC run to the inverter (3W+EGC 3ph system)
All inverters can work with the 4W+EGC system. Most inverters can work with grounded services with only 3W. The EGC can be used to test for the phase to neutral voltage. Most inverters cannot work with and will fail if installed with, a 3W ungrounded service. It is really important to understand and to be able to distinguish between inverters that can operate with a 3W grounded system but not with a 3W ungrounded system. So many people believe that if an inverter only needs a 3W+EGC that it can operate with a grounded or ungrounded service and this is an expensive misunderstanding.
Very informative, thanks, but what do the abbreviations mean? FWIW, I only design systems with inverters connected to grounded neutral wye systems and I omit the neutral whenever I can.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
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.
I've just started reading about SolarEdge's Synergy units, but the installation manual says "Each Synergy Unit operates independently and continues to work in case others stopped operating." So could you just get an SE80KUS and install only one Synergy Unit with the Synergy box (Synergy Manager)? I would think that would justify wiring under the NEC like an SE40KUS.

And then if you're able to buy Synergy Managers by themselves, you could use the other Synergy Unit with a Synergy Manager as another SE40KUS for another project. Unless SolarEdge is doing something weird like programming the Synergy Manager to only work with Synergy units of specific serial number.

Cheers, Wayne
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I've just started reading about SolarEdge's Synergy units, but the installation manual says "Each Synergy Unit operates independently and continues to work in case others stopped operating." So could you just get an SE80KUS and install only one Synergy Unit with the Synergy box (Synergy Manager)? I would think that would justify wiring under the NEC like an SE40KUS.
I thought of that, too; I asked the Principle Engineer at SolarEdge tech support; he says we cannot do that.
 
Yeah that is IEC terminology that we don't use in the states much. I always forget the letters and have to look it up when it comes up. Briefly, from the Wikipedia article:

IEC terminology

International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT.

The first letter indicates the connection between earth and the power-supply equipment (generator or transformer):

"T" — Direct connection of a point with earth (Latin: terra)
"I" — No point is connected with earth (Latin: īnsulātum), except perhaps via a high impedance.
The second letter indicates the connection between earth or network and the electrical device being supplied:

"T" — Earth connection is by a local direct connection to earth (Latin: terra), usually via a ground rod.
"N" — the earth connection is supplied by the electricity supply network, either separately to the neutral conductor (TN-S), combined with the neutral conductor (TN-C), or both (TN-C-S). These are discussed below.
 
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