Enphase IQ series +7 inverter

[jaggedben]

I read solarpro article calculated worst case with 1.25 multiply but I got worst case 199.18A line current excluding Envoy which is still less than 200A. Am I missing something?

I thought it would be close but that's even closer than I thought it would be.

But now if you apply the vector calculation to the overcurrent devices which are referenced in 705.12(D)(2)(3)(c) - this was Wayne's suggestion - you come out over 200A. It's the 208A Wayne calculated back in post #24.

 

[jaggedben]

Post #1 attachment the conductor connecting the main bldg service disconnect ground bar with the AC solar panel is removed.

Instead neutral from neutral bar is brought to the AC solar panel. Both panels ground bus are grounded with grounding electrode system.

The result of all tha above is attached sketch this post.

Understand that bonding of neutral and ground is depending on AHJ in AC solar panel.

Would the attached sketch on this post be code compliant?

The sketch is code compliant if the AHJ considers the AC solar panel to be another service disconnect. If they don't, then they'll probably ask that there be an EGC or bonding jumper to the AC solar panel instead.

 

[wwhitney]

3. Panel sizing. Total inverters I have is

a. Phase A (L1 and L2) from two aggregators: 66x290W = 19.14 kW.

b. Phase B (L1 and L2) from two aggregators is 66x290W = 19.14kw.

c. Phase C (L1 and L2): 49x290W = 14.21kw.

So with only 181 inverters, these could be arranged so that 3 combiners have 33 microinverters each, and 3 combiners have 27/28 microinverters each. Then the latter 3 combiners could be connected to 50 amp 2-pole breakers. In which case the vectorial sum of the (3) 60 amp 2-pole breakers and the (3) 50 amp 2-pole breakers would be only 190.5 amps per busbar.

There's still the issue of the Envoy. If you can get 55 amp 2-pole breakers, then you could use (3) 60 amp 2-pole breakers for 33 microinverters each; (2) 55 amp 2-pole breakers for 31 microinverters each; (1) 40 amp 2-pole breaker for the remaining 20 microinverters, and a (1) 15 amp 2-pole breaker for the Envoy on the same 2 phases as the 40 amp 2-pole breaker. Then the vectorial sum for each busbar would be 115*sqrt(3) = 199.2 amps.

Cheers, Wayne

 

[ggunn]

705.12(D)(2)(3)(c) in the 2014 NEC seems pretty clear to me. If you have three single phase inverters connected to a panel phase to phase through 120A breakers, each busbar has 240A of OCPD on it. If the rating of the panel is 200A (and if the busbar ratings are the same as the panel rating, which isn't always the case), you have busted the limit. If the inverters are connected phase to neutral, you haven't.

 

[wwhitney]

If the inverters are connected phase to neutral, you haven't.

By this I assume you mean if you have (3) 120A single pole breakers, rather than (3) 120A double pole breakers?

While 705.12(D)(2)(3)(c) doesn't explicitly say to add the ratings vectorially (nor, BTW, does it explicitly say to add them per busbar), adding them vectorially in 3 phase systems is the only reasonable choice, as that is how the currents add on the busbars. To me that is the same as if instructed to add a column of numbers, some positive, some negative, I would add them with signs, not just add up their magnitudes. It goes without saying.

Cheers, Wayne

 

[hhsting]

Maybe the natural way who knows but when something goes wrong and judge says which code section you used to justify all this and if its not in the code specifically spelled out then in the end liability rest on you and you did be busted. All of this load side, vectorial addition, or PV system being service disconnect having MBJ or not neutal to ground bond is just not specified or defined in code NEC 2014. Even AHJ for this project cannot make decision they said NEC 2014 is not clear in all this and that their is no local amendment. How is it possible that code panel just not think this thru

 

[hhsting]

I understand 2017 says something different and 2020 would say something different about PV system disconnect however AHJ where this project is at enforces NEC 2014 and they refuse to take 2017 or would be 2020 into account about following:

Nec 2014 690.13(C) says each PV system disconnecting means shall not be required to be suitable as service equipment.

Shall not is mandatory not be required to be suitable as service equipment AC PV system. This means no neutral to ground bond since its not service equipment based on the terminology no?

Now that leaves a question where in NEC 2014 it says you can get bonding jumper from main building service disconnect ground bus to the PV system AC disconnect?

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[ggunn]

By this I assume you mean if you have (3) 120A single pole breakers, rather than (3) 120A double pole breakers?

Yes, of course. You wouldn't put a breaker on the neutral. The language looks pretty straightforward to me. Look at a busbar and sum the ratings of all the breaker poles that land on it. They can't sum to more than the busbar rating. It makes no difference whether you have a three phase or a single phase system. Note that unlike the other sections of this part of the code, it's the breaker ratings that count rather than 125% of the inverter output current.

I have dealt with several AHJ's on this issue and that's the way all of them interpret it.

 

[ggunn]

Yes, of course. You wouldn't put a breaker on the neutral. The language looks pretty straightforward to me. Look at a busbar and sum the ratings of all the breaker poles that land on it. They can't sum to more than the busbar rating. It makes no difference whether you have a three phase or a single phase system. Note that unlike the other sections of this part of the code, it's the breaker ratings that count rather than 125% of the inverter output current.

I have dealt with several AHJ's on this issue and that's the way all of them interpret it.

There's one exception. One AHJ (and only one) has us put those silly "lightning arrestors" on every bus of an AC aggregation panel, connected through a breaker, but they don't count that breaker toward the 100% limit.

 

[wwhitney]

The language looks pretty straightforward to me. Look at a busbar and sum the ratings of all the breaker poles that land on it. They can't sum to more than the busbar rating. It makes no difference whether you have a three phase or a single phase system.

Sure, but the part about summing only the breaker poles that land on a particular busbar is implicit, it's not part of the text. I would similarly say the part about summing vectorially for 3-phase is implicit. I would hope that an AHJ that understands the purpose of the rule, and the way currents add, would agree with me, but obviously there's no guarantee.

Cheers, Wayne

 

[ggunn]

Sure, but the part about summing only the breaker poles that land on a particular busbar is implicit, it's not part of the text. I would similarly say the part about summing vectorially for 3-phase is implicit. I

I haven't done the math but I would hazard a guess that if you considered all the breakers loaded to capacity the current through the busbars would turn out the same either way. If you put a single phase inverter on two busbars of a single phase panel, the inverter delivers its rated current into both phases. If you put an inverter onto two busbars of a three phase panel, it still delivers its rated current into those two phases.

 

[ggunn]

I haven't done the math but I would hazard a guess that if you considered all the breakers loaded to capacity the current through the busbars would turn out the same either way. If you put a single phase inverter on two busbars of a single phase panel, the inverter delivers its rated current into both phases. If you put an inverter onto two busbars of a three phase panel, it still delivers its rated current into those two phases.

And another thing...

705.12(D)(2)(3)(c) doesn't even mention current at all. The only thing it addresses is the ratings of the breakers, both load and supply. What one does have to do is to extrapolate that since a two pole breaker on the A and B phases does not contribute to the loading on the C phase busbar, it's not just a matter of totaling up all the breaker ratings in a panel irrespective of which and how many of the busbars the breakers land on.

 

[hhsting]

Sure, but the part about summing only the breaker poles that land on a particular busbar is implicit, it's not part of the text. I would similarly say the part about summing vectorially for 3-phase is implicit. I would hope that an AHJ that understands the purpose of the rule, and the way currents add, would agree with me, but obviously there's no guarantee.

Cheers, Wayne

Even AHJ has to justify thru NEC code language that they are enforcing. If its not in the NEC specifically spelled out or in their local amendements specifically spelled out then AHJ has no say in it. See post # 46.

 

[hhsting]

I understand 2017 says something different and 2020 would say something different about PV system disconnect however AHJ where this project is at enforces NEC 2014 and they refuse to take 2017 or would be 2020 into account about following:

Nec 2014 690.13(C) says each PV system disconnecting means shall not be required to be suitable as service equipment.

Shall not is mandatory not be required to be suitable as service equipment AC PV system. This means no neutral to ground bond since its not service equipment based on the terminology no?

Now that leaves a question where in NEC 2014 it says you can get bonding jumper from main building service disconnect ground bus to the PV system AC disconnect?

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The above got hidden in thread

Sent from my SM-G935U using Tapatalk

 

[jaggedben]

I understand 2017 says something different and 2020 would say something different about PV system disconnect however AHJ where this project is at enforces NEC 2014 and they refuse to take 2017 or would be 2020 into account about following:

Nec 2014 690.13(C) says each PV system disconnecting means shall not be required to be suitable as service equipment.

Shall not is mandatory not be required to be suitable as service equipment AC PV system. This means no neutral to ground bond since its not service equipment based on the terminology no?

Now that leaves a question where in NEC 2014 it says you can get bonding jumper from main building service disconnect ground bus to the PV system AC disconnect?

"Shall not be required" is not the same as "shall not be permitted". If you want to treat the PV system supply side disconnect as service equipment, that's a sensible thing to do and (unlike the 2020 NEC) the 2014 NEC does not clearly prohibit it. It's really open to interpretation. At one point I posted a full list of all the code sections that could be used to argue 'for' or 'against'. It's not an argument that can be conclusively won. Only the AHJ's opinion matters in the end.

As far as what applies if you don't treat it as a service disconnect, it's pretty clear that you still need an effective fault current path and to bond everything per the basic requirements of article 250. Call it a supply side bonding jumper or an EGC, then follow the rule for that. Note that the requirements for bonding 'at the service' could still apply even if you decide not to call the disconnect service equipment.

 

[pv_n00b]

An entertaining thread. Y'all realize that when we do three phase math and use the square root of three in the calculations that we are doing vector math, right? So we do it all the time. The square root of three takes into account that the three source currents in a balanced system do not add directly. What we don't do much anymore is the single phase on a 3-ph system math. Back in the old days when we only had single phase inverters for systems less than 200kW we did it a lot more.

The current through the inverter CB in an AC combiner panel is the current output by that individual inverter, but the combined current on the busbar, through the main CB, and through the conductors out of the panel are the vector sum of the inverter currents.

An example in a balanced 3-ph system:
For 3 single phase 100kW inverters connected line to line at 480V.
The inverter output current will be 100000/480=208A
If three of these are balanced on a 480V 3-ph panel then each inverter CB would be 300A and the busbar current would be 300000/480/sqrt(3)=361A. It would not be 208*3 or 300*3.

For the same total size 3-ph inverter(300kW) the inverter output current would be 361A and the busbar current would be the same.

With 3-ph inverters the summation of the L-L outputs of the single phase currents happens inside the inverter and we don't have to deal with it, but if we do the summation in an AC combiner then we have to treat the inverter output currents as single phase and the currents in the AC combiner as 3-ph currents. Does the NEC call this out? No, it's not a textbook and it's not teaching vector math. This is stuff an electrician or engineer is going to have to know and apply if they are going to be working with single phase generation on 3-ph systems. It's often something that people get wrong when they are making the leap from working on single phase systems to 3-ph systems. All this being the case it's not that hard to find an AHJ who does not grok how the currents add as vectors.

 

[pv_n00b]

"Shall not be required" is not the same as "shall not be permitted". If you want to treat the PV system supply side disconnect as service equipment, that's a sensible thing to do and (unlike the 2020 NEC) the 2014 NEC does not clearly prohibit it. It's really open to interpretation. At one point I posted a full list of all the code sections that could be used to argue 'for' or 'against'. It's not an argument that can be conclusively won. Only the AHJ's opinion matters in the end.

As far as what applies if you don't treat it as a service disconnect, it's pretty clear that you still need an effective fault current path and to bond everything per the basic requirements of article 250. Call it a supply side bonding jumper or an EGC, then follow the rule for that. Note that the requirements for bonding 'at the service' could still apply even if you decide not to call the disconnect service equipment.

There's a pretty spirited fight going on over the 2020 NEC on this point. It's been going back and forth between making the PV disconnect on a supply side interconnection have a neutral-ground or not. Seems to be settling on the no bond side of things but a vocal group is still trying to change it to require a bond.

 

[wwhitney]

There's a pretty spirited fight going on over the 2020 NEC on this point. It's been going back and forth between making the PV disconnect on a supply side interconnection have a neutral-ground or not. Seems to be settling on the no bond side of things but a vocal group is still trying to change it to require a bond.

So if you have a neutral-ground bond in a supply-side PV disconnect, don't you have to keep the PV grounding conductor separate from the regular electrical service grounding conductor? Is this hard to achieve in practice?

Cheers, Wayne

 

[ggunn]

An entertaining thread. Y'all realize that when we do three phase math and use the square root of three in the calculations that we are doing vector math, right? So we do it all the time. The square root of three takes into account that the three source currents in a balanced system do not add directly. What we don't do much anymore is the single phase on a 3-ph system math. Back in the old days when we only had single phase inverters for systems less than 200kW we did it a lot more.

The current through the inverter CB in an AC combiner panel is the current output by that individual inverter, but the combined current on the busbar, through the main CB, and through the conductors out of the panel are the vector sum of the inverter currents.

An example in a balanced 3-ph system:
For 3 single phase 100kW inverters connected line to line at 480V.
The inverter output current will be 100000/480=208A
If three of these are balanced on a 480V 3-ph panel then each inverter CB would be 300A and the busbar current would be 300000/480/sqrt(3)=361A. It would not be 208*3 or 300*3.

For the same total size 3-ph inverter(300kW) the inverter output current would be 361A and the busbar current would be the same.

With 3-ph inverters the summation of the L-L outputs of the single phase currents happens inside the inverter and we don't have to deal with it, but if we do the summation in an AC combiner then we have to treat the inverter output currents as single phase and the currents in the AC combiner as 3-ph currents. Does the NEC call this out? No, it's not a textbook and it's not teaching vector math. This is stuff an electrician or engineer is going to have to know and apply if they are going to be working with single phase generation on 3-ph systems. It's often something that people get wrong when they are making the leap from working on single phase systems to 3-ph systems. All this being the case it's not that hard to find an AHJ who does not grok how the currents add as vectors.

I think you are mistaken (a la Kirchoff), but I will look this over when I have more time. In the meantime it is a non-sequitur when it comes to 705.12(D)(2)(3)(c); there is no mention of current in the article, only the ratings of load and supply breakers.

 

[hhsting]

An entertaining thread. Y'all realize that when we do three phase math and use the square root of three in the calculations that we are doing vector math, right? So we do it all the time. The square root of three takes into account that the three source currents in a balanced system do not add directly. What we don't do much anymore is the single phase on a 3-ph system math. Back in the old days when we only had single phase inverters for systems less than 200kW we did it a lot more.

The current through the inverter CB in an AC combiner panel is the current output by that individual inverter, but the combined current on the busbar, through the main CB, and through the conductors out of the panel are the vector sum of the inverter currents.

An example in a balanced 3-ph system:
For 3 single phase 100kW inverters connected line to line at 480V.
The inverter output current will be 100000/480=208A
If three of these are balanced on a 480V 3-ph panel then each inverter CB would be 300A and the busbar current would be 300000/480/sqrt(3)=361A. It would not be 208*3 or 300*3.

For the same total size 3-ph inverter(300kW) the inverter output current would be 361A and the busbar current would be the same.

With 3-ph inverters the summation of the L-L outputs of the single phase currents happens inside the inverter and we don't have to deal with it, but if we do the summation in an AC combiner then we have to treat the inverter output currents as single phase and the currents in the AC combiner as 3-ph currents. Does the NEC call this out? No, it's not a textbook and it's not teaching vector math. This is stuff an electrician or engineer is going to have to know and apply if they are going to be working with single phase generation on 3-ph systems. It's often something that people get wrong when they are making the leap from working on single phase systems to 3-ph systems. All this being the case it's not that hard to find an AHJ who does not grok how the currents add as vectors.

The problem is AHJ enforces NEC and local amendments not a textbook or theory electrical engineer because NEC does not go into all that.

For example if one calculates 100kvA on single phase breaker 480V as 100/.48/1.732 = 120.2A and size breaker as 150A then AHJ has no code section to enforce and say 100/.48 =208A and next size is 250A. AHJ cannot enforce this and their is no code section for calculation. All of that makes it tough for the AHJ.