Neutral on a 120?240V High Leg Delta

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Now im just confused because the colors just dont match up...:? I know that the voltages I measured with our electrician are correct but the wires and colors just arent matching up... This building has 3 main disconnects on the inside. 2 1950's square D 600A and 400A single phase discos and this 400A 3 phase disco all going out into the bundle of wires shown into the pictures.

Can anyone make any sense of this?
It is almost certainly a high leg delta. All of the measured voltages match.
You do not see that when looking at the delta fused disconnect only because it does not feed any 120V loads.

You should have a total of four wires coming down your service mast, three hots and a neutral. The neutral in the three phase disconnect is probably there just to provide the EGC connection.
 

Ctay005

Member
Location
Orem, Utah, USA
It is almost certainly a high leg delta. All of the measured voltages match.
You do not see that when looking at the delta fused disconnect only because it does not feed any 120V loads.

You should have a total of four wires coming down your service mast, three hots and a neutral. The neutral in the three phase disconnect is probably there just to provide the EGC connection.
This is what the voltages seem to show but the wires were clearly color coded incorrectly in this case.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
This is what the voltages seem to show but the wires were clearly color coded incorrectly in this case.
Black Red and Blue may have been OK before the requirement to identify the high leg with orange was introduced.
The neutral should have been marked white though.
 

Smart $

Esteemed Member
Location
Ohio
This is what the voltages seem to show but the wires were clearly color coded incorrectly in this case.
High leg was not always required to be marked orange. In the earlier days Blk, R, Blu, W were commonplace phasing colors.

If you go into the 120/240 panels, it would not surprise me to see Black Red White... :jawdrop:
 

jaggedben

Senior Member
Now im just confused because the colors just dont match up...:? I know that the voltages I measured with our electrician are correct but the wires and colors just arent matching up... This building has 3 main disconnects on the inside. 2 1950's square D 600A and 400A single phase discos and this 400A 3 phase disco all going out into the bundle of wires shown into the pictures.

Can anyone make any sense of this?
High leg was not always required to be marked orange. In the earlier days Blk, R, Blu, W were commonplace phasing colors. If you go into the 120/240 panels, it would not surprise me to see Black Red White... :jawdrop:
Yes, if someone marked the high leg red in the three phase disco, but the single phase panels are black, red, white, then red in the single phase would be the same as blue in the 3-phase. Or rather, hopefully that would be the extent of the mix up. I've seen red and black get reversed in single phase systems too.
 

Ctay005

Member
Location
Orem, Utah, USA
Just wanted to post a quick update and get your opinions on this system.

I think what we are going to do with this system is use a wye/delta transformer and hook the pv to the wye and then hook up to the delta normally. This should prevent the imbalance from being an issue and I will be able to use some 208v solaredge 3 phase inverters on the wye side of the transformer. Is there anything i should know about using a transformer or is it pretty straightforward?


Thanks again for all the help so far on this design. This 3 phase stuff has been making my head spin!
 

Smart $

Esteemed Member
Location
Ohio
... Is there anything i should know about using a transformer or is it pretty straightforward?
...
Pretty straightforward to me. That said, I know what I don't know, but I do not know what you do not know, or do know for that matter... so how about you tell us about what you do not know? ... :p:D
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Just wanted to post a quick update and get your opinions on this system.

I think what we are going to do with this system is use a wye/delta transformer and hook the pv to the wye and then hook up to the delta normally. This should prevent the imbalance from being an issue and I will be able to use some 208v solaredge 3 phase inverters on the wye side of the transformer. Is there anything i should know about using a transformer or is it pretty straightforward?


Thanks again for all the help so far on this design. This 3 phase stuff has been making my head spin!
Are you sure that the service will accept a balanced connection? Some high leg services have a much smaller t'former on the high leg.

As to the transformer question, I strongly recommend you speak with the tech support guys at the inverter manufacturer. They deal with this stuff all the time.
 

Ctay005

Member
Location
Orem, Utah, USA
Pretty straightforward to me. That said, I know what I don't know, but I do not know what you do not know, or do know for that matter... so how about you tell us about what you do not know? ... :p:D
Theres still a lot i dont know! That's why I'm coming here!

So the transformer i was referred to is a 480v delta primary with the center tap 240v delta secondary. Will the 4 wires (L1, L2, L3, N) coming out of the inverters hook up to a delta primary of the xfmr without issues? The spec sheet for the inverter (Se33.3k) says its made for a 480v wye with a neutral.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Theres still a lot i dont know! That's why I'm coming here!

So the transformer i was referred to is a 480v delta primary with the center tap 240v delta secondary. Will the 4 wires (L1, L2, L3, N) coming out of the inverters hook up to a delta primary of the xfmr without issues? The spec sheet for the inverter (Se33.3k) says its made for a 480v wye with a neutral.
You can't connect that inverter to that transformer; the transformer is delta and the inverter is wye. You can connect a delta inverter to a wye transformer but not the other way round.
 

pv_n00b

Senior Member
Location
CA, USA
Theres still a lot i dont know! That's why I'm coming here!

So the transformer i was referred to is a 480v delta primary with the center tap 240v delta secondary. Will the 4 wires (L1, L2, L3, N) coming out of the inverters hook up to a delta primary of the xfmr without issues? The spec sheet for the inverter (Se33.3k) says its made for a 480v wye with a neutral.

The forum is pretty helpful at answering specific questions but I would not trust us to design the interconnection for you. If it doesn't work you are going to have to pay to fix it and not any of us. If I were you I would get an engineer involved to help you design what is turning out to be a bit of a complex interconnection. You will learn a lot in the process and the people involved will have skin in the game. Good luck and keep learning.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
And a center tapped (high leg) 240 secondary would be the wrong voltage as well as the wrong configuration. If the previous comment is correct you want a 480Y/277 secondary unless the primary is that already.
 

Smart $

Esteemed Member
Location
Ohio
Theres still a lot i dont know! That's why I'm coming here!...
The best in the profession visit here, and even as they as individuals are not all knowing. It is the combined knowledge that is daunting.

That said, perhaps stating the system parameters, values set in stone stuff first, then speculations. Let's start with the service voltage and configuration...? Array details? Are inverter make/model set or not, and if yes, make/model, otherwise inverter make/series preference...?
 
In most cases I have encountered the way to deal with a 240V high leg service is to connect to the A and C phases and the neutral as if it were a split/single phase service, ignoring the B (high leg) phase. Most utilities do not care about the imbalance, as the high leg may not even be used at all.
:thumbsup: That would be my first try. Some people get all focused on balancing, but if everything is big enough and the poco doesnt care......
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
:thumbsup: That would be my first try. Some people get all focused on balancing, but if everything is big enough and the poco doesnt care......
Actually, sometimes the POCO does care and they do not want you to land anything on the B phase.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Pulling the info together it looks like the OP has a 480V three phase wye inverter he wants to interconnect with a 240V three phase high leg service. Is that correct?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
That color scheme looks like a 120/208 WYE system. You should use your voltmeter to confirm the actual situation. The high leg is supposed to be marked orange, and now is required by the NEC to mark it orange per 110.15. I suggest re-marking it orange, to distinguish it. Or marking it orange in addition to red, if somehow red is a local requirement. Anything you can do to make the high leg stand out is encouraged.

As for voltage drop, indoors vs outdoors makes no difference. What matters is distance, wire metal material, wires per phase, effective operating temperature, and to a slight extent, the fact that it is AC wire in metal conduit.

If it is my choice, I would parallel, when the calculations prescribe sizes that large (greater than 500 kcmil). Generally all KCMILs are close to equal, when curtailing voltage drop. Although smaller wires have slightly less effective resistance. Ampacity is a significantly different story, as smaller wires have disproportionately more ampacity per KCMIL.
That is not really what the code says....it says orange OR other effective means.
 

Ctay005

Member
Location
Orem, Utah, USA
The best in the profession visit here, and even as they as individuals are not all knowing. It is the combined knowledge that is daunting.

That said, perhaps stating the system parameters, values set in stone stuff first, then speculations. Let's start with the service voltage and configuration...? Array details? Are inverter make/model set or not, and if yes, make/model, otherwise inverter make/series preference...?
Heres the system overview as I have it so far.

2x SolarEdge Se33.3k inverters
218 Hanwa 315 QPro modules
Hooking up to a 240v High leg service

The question is in finding a legal interconnection betweeen the 480 wye output of the inverters and the 240v high leg service.

I tried getting a hold of the POCO to see if they would allow a connection to the AC phases and ignoring the B phase like has been suggested (and just using 1 phase inverters) but nobody at Rocky Mtn Power was able to give me an answer. The SolarEdge guys dont seem to know much about this service and they recommended trying the single phase route across the phases or just going all on the A and C phases. Again this depends on if the POCO approves...

We will have an EE look over everything before we submit the interconnetion application.
 
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