Solar install turning out really bad - looking for some help/advice please.

[HX_Guy]

The 370 is from the inverter LCD display and also the SolarEdge online portal...



And here is the AC voltage at the inverter...

[inetdog]

SolarEdge has actually said that 350-370 is normal operating voltage (without me even mentioning that mine is running at 370).
I then told them that I did notice mine is around 370, and they explained that if the AC voltage is higher than 240V, the DC voltage will also be higher...and my AC voltage is in fact around 243V.

Makes sense. And the idea that the voltage output of the optimizers would be higher than normal to make up for voltage loss in the connectors just does not seem credible to me.
With normal panels, you could be looking at an open circuit voltage on the order of 500V, but when the optimizers are open circuited or isolated from the SE inverter they drop their output to 1V.

PS: If you have high resistance in a long run of AC between inverter and the POCO transformer, then a no load voltage at your service panel of 243V may actually go significantly higher than that at the inverter terminals, and that is what determines the needed DC.
Also, how well do you trust the calibration of your meters? Or is the 370 figure from the readout of the SE inverter?

[HX_Guy]

SolarEdge has actually said that 350-370 is normal operating voltage (without me even mentioning that mine is running at 370).
I then told them that I did notice mine is around 370, and they explained that if the AC voltage is higher than 240V, the DC voltage will also be higher...and my AC voltage is in fact around 243V.

[Alisobob]

Absolutely it needs to be redone, and not just this one, but all of them in my opinion.

The bigger issues is the connectors he made that are now under panels throughout the roof!!

You might remember me suggesting you never let this guy touch your house again......

This is exactly why...

[sensij]

Absolutely it needs to be redone, and not just this one, but all of them in my opinion.

The bigger issues is the connectors he made that are now under panels throughout the roof!!

I had been wondering why your system voltage was running so high, when 350 V would be typical. Perhaps there is enough voltage drop in the bad connections that it was compensating to get to 350 V at the inverter. That might be a question for SolarEdge, it seems like they've been responsive to your technical questions.

[HX_Guy]

Absolutely it needs to be redone, and not just this one, but all of them in my opinion.

The bigger issues is the connectors he made that are now under panels throughout the roof!!

[inetdog]

Are you kidding me??

I was up on the roof making a change to the DC combiner box and while working on it, by accident I notice...WTF did that wire just move? Oh yea...a freaking wire that's supposed to be crimped tight just slid right out of the connector! A wire that has up to 500V going through it. This is a connector that the genius installer crimped together with a plier, instead of the proper MC4 connector crimper that costs a whopping $35 on Amazon! How the hell is this guy licensed and in business?!?

I hate to say it, but for safety I would say that you either need to recrimp with the correct tool (which may or may not be possible or acceptable now that the connector is deformed) or replace all of the connectors. <sigh>

[HX_Guy]

Are you kidding me??

I was up on the roof making a change to the DC combiner box and while working on it, by accident I notice...WTF did that wire just move? Oh yea...a freaking wire that's supposed to be crimped tight just slid right out of the connector! A wire that has up to 500V going through it. This is a connector that the genius installer crimped together with a plier, instead of the proper MC4 connector crimper that costs a whopping $35 on Amazon! How the hell is this guy licensed and in business?!?

[HX_Guy]

OK, last comment from me on this particular train of thought.

I would be uncomfortable with the 6 AWG that is currently installed, since I think a higher temp correction (at least 60 deg C, maybe higher) would be appropriate for the attic run. I realize this is a slightly different opinion than much earlier in the thread, but the temperature discussion has changed my mind. (edit: yes, even considering the fact that your "actual" current is unlikely to ever be 45 A, and is more likely peaking in the low-mid 30's). To me, the path of least pain would be to re-run from the combiner box to the inverter with 2 AWG per the existing permit. Replace the white wire with black, while you are at it. It sounds like the AHJ would have been ok with that, and not objected to the missing 4th string. By going with 2 AWG, you've got wire sized that will be safe under any reasonable projection of your attic temp. Use a splice or replace the terminal block at the DC disconnect of the inverter, I don't have a strong opinion.

I hear you Sensij and I agree that's probably the path of least pain..if I ever hear back from the installer after the whole failure. I haven't heard back yet since the permit failure.

[PVAndy]

Thanks Volusiano, the electrical stuff is so over my head, I love when it's explained well like that so thanks for that.

The 12,400 is DC STC (40 x 310w panels). For AC the permit says 11.4kW AC though that seems like the maximum amount, not for my specific system.
I say that because looking at the SolarEdge spec sheet, it shows a max DC STC of 15,350 with a nominal AC output of 11,400.

http://www.solaredge.com/files/pdfs/products/inverters/se-single-phase-us-inverter-datasheet.pdf

Going by what you said, 11.4kw (AC) / 240V = 47.5A...with the 80% rule, that's 59.4A...but again that's the max the inverter will put out if I maxed out the DC input I assume, right?

So how do I figure out the AC system rating for my actual system if the 11.4kW seems to just be something they plugged in from the spec sheet?

I assume I'm late to the game and this has already been answered. When you calculate overcurrent protection, disconnects, and wire sizes you go by the inverter AC rating. It has nothing to do with the size of the DC system.

Andy
PV Design Engineer
NABCEP Certified Installation Professional

[sensij]

That would require both a new permit AND rewiring, I don't see the advantage to that plan.

If we were to submit a new permit, then as we talked earlier, should the 3 strings @ 45A be fine since they are running through the attic?

OK, last comment from me on this particular train of thought.

I would be uncomfortable with the 6 AWG that is currently installed, since I think a higher temp correction (at least 60 deg C, maybe higher) would be appropriate for the attic run. I realize this is a slightly different opinion than much earlier in the thread, but the temperature discussion has changed my mind. (edit: yes, even considering the fact that your "actual" current is unlikely to ever be 45 A, and is more likely peaking in the low-mid 30's). To me, the path of least pain would be to re-run from the combiner box to the inverter with 2 AWG per the existing permit. Replace the white wire with black, while you are at it. It sounds like the AHJ would have been ok with that, and not objected to the missing 4th string. By going with 2 AWG, you've got wire sized that will be safe under any reasonable projection of your attic temp. Use a splice or replace the terminal block at the DC disconnect of the inverter, I don't have a strong opinion.

[HX_Guy]

This agrees with Ben25's suggestion.

Pair 1: 30 A * 1.25 = 37.5 A
Pair 2: 15 A * 1.25 = 18.75 A

6 AWG THWN-2 base ampacity = 75 A
4 conductor correction of 0.80 [310.15(B)(3)(a)]
75 A * 0.80 = 60 A is the CCC corrected ampacity
37.5 A / 60 A = 0.625, which means a temp correction of 0.65 (61-65 deg C) should be OK.

That would require both a new permit AND rewiring, I don't see the advantage to that plan.

If we were to submit a new permit, then as we talked earlier, should the 3 strings @ 45A be fine since they are running through the attic?

[sensij]

Heard back from the manufacturer. They said we could either run two sets of #6 conductor (which would require new permits and rewiring)

This agrees with Ben25's suggestion.

Pair 1: 30 A * 1.25 = 37.5 A
Pair 2: 15 A * 1.25 = 18.75 A

6 AWG THWN-2 base ampacity = 75 A
4 conductor correction of 0.80 [310.15(B)(3)(a)]
75 A * 0.80 = 60 A is the CCC corrected ampacity
37.5 A / 60 A = 0.625, which means a temp correction of 0.65 (61-65 deg C) should be OK.

[sensij]

Heard back from the manufacturer. They said we could either run two sets of #6 conductor (which would require new permits and rewiring) or we could use a short piece of #6 spliced to #2 inside the combiner box (would require rewiring and also not sure if the inspector would accept that if it's not shown on the permit?).

The #6 spliced to #2 should be allowed by the exception in 310.15(A)(2). I could see this being approved during inspection even if it isn't in the permit, as long is the splice is done with a listed connector and properly crimped.

(2) Selection of Ampacity.
Where more than one ampacity applies for a given circuit length, the lowest value shall be used.

Exception:
Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

Informational Note: See 110.14(C) for conductor temperature limitations due to termination provisions.

[HX_Guy]

Heard back from the manufacturer. They said we could either run two sets of #6 conductor (which would require new permits and rewiring) or we could use a short piece of #6 spliced to #2 inside the combiner box (would require rewiring and also not sure if the inspector would accept that if it's not shown on the permit?).