240 delta with high leg solar installation

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Smart $ said:
Did you solidly ground the wye point on the 480Y/277 side?

The utility side is 240 delta high leg with a grounded-neutral center tap? (The service; not the transition transformer)


If yes to both,
the inspector needs his head examined (more appropriately, his credentials revoked).
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If no to either or both, the inspector may have a point. :D
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Playing Devils advocate, does the same logic apply in reverse? if you make an error should your credentials be revoked? I am all ways amazed how people think. If the person at the inspection can not explain his or her own work, why is the inspector wrong?
 
wouldn't 450.6C and 250.30 apply to the transformer install?

I'm not saying the OCPD in the service panel will not function to shut down in a ground fault,,,,BUT,,,,, doesn't the grounding and bonding requirement still apply? (I haven't seen an Exception to it, in the code)

edit to add, 2014 NEC used.
 
acrwc10 said:
wouldn't 450.6C and 250.30 apply to the transformer install?
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250.30 would. I don't think 450.6 is relevant. There's only one transformer here. 705 and 690 govern the installation of the inverter.

I'm not saying the OCPD in the service panel will not function to shut down in a ground fault,,,,BUT,,,,, doesn't the grounding and bonding requirement still apply? (I haven't seen an Exception to it, in the code)

edit to add, 2014 NEC used.
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From the OP's descriptions the system is grounded and bonded adequately, at least in regards to the general concepts (i.e. inverter-side neutral is grounded), leaving aside details of conductor sizing and installation, etc. It might be that what's he's calling the 'GEC', that bonds to the neutral secondary to the service ground bar, should be called a 'Bonding Jumper' instead. Physically, it would serve the same purpose. Perhaps the inspector's objection is just a quibble over the naming and number of green wires, but it doesn't seem so.
 
acrwc10 said:
Playing Devils advocate, does the same logic apply in reverse? if you make an error should your credentials be revoked? I am all ways amazed how people think. If the person at the inspection can not explain his or her own work, why is the inspector wrong?
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If I make an error on such a basic issue, one that should be an obvious prerequisite for said credentials, and I am still adamant on my position after it is pointed out, along with several other indicators that I'm wrong (e.g. stamped, plan-checked drawings)... heck yeah!
 
once again playing Devil's advocate, Art 250 lays out the requirements for when the transformer/separately derived system requires "grounding". The input/primary side is the PV, that side is grounded, the OP says its a 480/277Y. The secondary is a 240 Delta (not grounded, no neutral) connected to a 240v 4wire system. where in the code does it say you can solidly connect an ungrounded to a grounded system? The output characteristics of the two systems don't match. I'm not saying they won't work, I'm just saying "per the letter of the code" it seems to be a violation. The system is grounded or ungrounded. Maybe a code change to address it?
 
A high-leg delta is not an ungrounded system. That doesn't change because the grounded conductor is not brought to one side of a transformer, it's still a grounded system. Also the two systems are not 'solidly connected'. If the engineer says that the setup is ok and especially if Solaredge agrees then it should be fine.

The code is permissive, if it doesn't address something that doesn't mean you can't do it. Where in the code does it say you cannot power a delta with a wye, or vice versa? What code section are you thinking that it violates?
 
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ggunn said:
If the connection is through a transformer, it is not a solid connection.
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Connecting a secondary of one transformer to the primary of another is a solid connection. If the secondary of the source transformer is grounded, the entire secondary system is grounded, including the primary of the supplied transformer. In the OP's scenario, the inspector seems to be saying the primary of the downstream transformer (relative to the utility) is not grounded. That is quite simply not true.
 
Smart $ said:
Connecting a secondary of one transformer to the primary of another is a solid connection. If the secondary of the source transformer is grounded, the entire secondary system is grounded, including the primary of the supplied transformer. In the OP's scenario, the inspector seems to be saying the primary of the downstream transformer (relative to the utility) is not grounded. That is quite simply not true.
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If the PV inverter is supplying 480/277 Y that is the primary side, of the transformer, the current is not flowing to the PV from the utility. The output of that same transformer is an "ungrounded" 240 Delta, this would by default be the "secondary" side of the transformer. Can we agree that is true?

Now if that same "ungrounded" 240 Delta secondary is supplying/tied to the "Grounded" 240 Y system. That makes it a violation, your transformer output is required to be grounded.
 
acrwc10 said:
If the PV inverter is supplying 480/277 Y that is the primary side, of the transformer, the current is not flowing to the PV from the utility. The output of that same transformer is an "ungrounded" 240 Delta, this would by default be the "secondary" side of the transformer. Can we agree that is true?
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No. :happysad:

Technically neither side is primary. You are [subjectively] correct in that more energy will be transferred from the 480V side to the 240V side. However, without utility voltage there would be no transfer. Now consider a typical transformer with no load. Both sides have voltage but only one side has potential without the other and that is the side that is considered the primary.


Now if that same "ungrounded" 240 Delta secondary is supplying/tied to the "Grounded" 240 [DELTA] system. That makes it a violation, your transformer output is required to be grounded.
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[FIFY]

You are talking about a separately derived system. This is not a separately derived system. This is two interconnected electric power production sources... and one is a utility source. Additionally, this interconnected system is grounded. It just happens to be grounded somewhere other than at the 240V:480/277V transformer of discussion.
 
acrwc10 said:
... The output of that same transformer is an "ungrounded" 240 Delta, this would by default be the "secondary" side of the transformer. ...

...
That makes it a violation, your transformer output is required to be grounded.
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Where does the word 'output' appear in the code? I don't see it anywhere in 250.20, for example. That section just says that 'systems' need to be grounded.
The 240V system is grounded at the service, and that's all it needs to be a grounded system. There is no requirement for a system to be grounded in two places, in fact that would often be a violation of 250.6.
 
acrwc10 said:
If the PV inverter is supplying 480/277 Y that is the primary side, of the transformer, the current is not flowing to the PV from the utility. The output of that same transformer is an "ungrounded" 240 Delta, this would by default be the "secondary" side of the transformer. Can we agree that is true?

Now if that same "ungrounded" 240 Delta secondary is supplying/tied to the "Grounded" 240 Y system. That makes it a violation, your transformer output is required to be grounded.
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I understand what you are getting at, but basically, the NEC doesnt consider the utility side of the transformer the "separately derived side" just because energy is (usually) flowing in that direction. The NEC sees the inverter like any other load The utility side is "already grounded" so even if the grounded conductor were present a the utility side of the transformer (which it isnt 99.7% of the time in the <600 volt world), bonding it there again would create a parallel path for neutral current.
 
Smart $ said:
You are talking about a separately derived system. This is not a separately derived system. This is two interconnected electric power production sources... and one is a utility source. Additionally, this interconnected system is grounded. It just happens to be grounded somewhere other than at the 240V:480/277V transformer of discussion.
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Maybe I am misreading you, but the 480/277V side of the isolation transformer is separately derived from the utility. The neutral of the 480/277V side is grounded at the transformer and the neutral of the 240/120V high leg side is grounded at the service. No violation.
 
ggunn said:
Maybe I am misreading you, but the 480/277V side of the isolation transformer is separately derived from the utility. The neutral of the 480/277V side is grounded at the transformer and the neutral of the 240/120V high leg side is grounded at the service. No violation.
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Exactly.

I was referring solely to the 240V delta high leg system when I said it is not a separately derived system. But I believe we both know this is only when using the NEC definition. If we backed up the service point to the primary side of the [now former] service transformer, the 240V delta high leg system would be separately derived.
 
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BenJChaney said:
Post #10:
On the service side of the xfmr, there is no neutral connection. There is one on the inverter side, but not service side. The GEC is tied continuously from the array, through the inverter, through the disconnect,through the xfmr which is also tied to the neutral on the inverter side of xfmr, through the disconnect, and tied the the ground/neutral bar at the service. I'm including a photo of the label on the transformer.
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It seems like there are three or four interpretations of this setup going on, a sketch would really help.

Back in post #4 Smart$ said:"Did you solidly ground the wye point on the 480Y/277 side?"

I bolded GEC because I'm not sure it is such as described.
I would call the green part, up *to* the PV disco, an EGC.

Then it becomes a GEC (and solidly grounded?) by going from PV disco to a grounding electrode, and not doing the stuff in red.

Are the X1, X2, and X3 conductors from the 240 delta side of the xfmr grounded in the MSP?
Shouldn't the xfmr for the PV be grounded along with the PV neutral?

To the OP- you might want to look at page 12. My apologies- it doesn't seem to help.

Figure 3: AC grids supported by SolarEdge three-phase inverter
https://www.wholesalesolar.com/cms/solaredge-se14400us-208-installation-manual-3800765590.pdf

With SMA inverters, your only option for high-leg (stinger) are:
L-L:
SB 5.0-US
SB 6.0-US
L-N:
SI 4548-US 120 V
SI 6048-US 120 V
http://files.sma.de/dl/1380/COMMONTXCONFI_AUS161222W.pdf
 
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PVfarmer said:
...
I bolded GEC because I'm not sure it is such as described.
I would call the green part, up *to* the PV disco, an EGC.
...
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That is for sure a point of contention. Will require OPer's input to ascertain.

The inverters are connected to the 480/277V 3Ø 4W wye side of the transformer.
 
PVfarmer said:
It seems like there are three or four interpretations of this setup going on, a sketch would really help.

Back in post #4 Smart$ said:"Did you solidly ground the wye point on the 480Y/277 side?"

I bolded GEC because I'm not sure it is such as described.
I would call the green part, up *to* the PV disco, an EGC.

Then it becomes a GEC (and solidly grounded?) by going from PV disco to a grounding electrode, and not doing the stuff in red.

Are the X1, X2, and X3 conductors from the 240 delta side of the xfmr grounded in the MSP?
Shouldn't the xfmr for the PV be grounded along with the PV neutral?

To the OP- you might want to look at page 12. My apologies- it doesn't seem to help.

Figure 3: AC grids supported by SolarEdge three-phase inverter
https://www.wholesalesolar.com/cms/solaredge-se14400us-208-installation-manual-3800765590.pdf

With SMA inverters, your only option for high-leg (stinger) are:
L-L:
SB 5.0-US
SB 6.0-US
L-N:
SI 4548-US 120 V
SI 6048-US 120 V
http://files.sma.de/dl/1380/COMMONTXCONFI_AUS161222W.pdf
Click to expand...


If this configuration is counting on the interconnected OCPD in the service to open in a ground fault then have the inverter recognize the power outage to shut down, "how long would be an acceptable time for this to be energized before it is completely shut down?"
 
PVFarmer, Let's please not get into the PV grounding electrode system (690.47) unless the OP comes back and clarifies that that is what the inspector's objection is really about. The array could have a GEC but it's entirely irrelevant to what's been mentioned so far.
 
acrwc10 said:
If this configuration is counting on the interconnected OCPD in the service to open in a ground fault then have the inverter recognize the power outage to shut down, "how long would be an acceptable time for this to be energized before it is completely shut down?"
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See UL 1741.
 
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