Paralleling less then 1/0

[Shawn pavich]

So here is the situation the new inverters we have been using only come with 2 strings they are solar edge single phase but on most of the projects on the plans call for 3 or more strings we have just been paralleling let's say we have 3 strings we would with 10 awg wire we would parallel one string to number 6 from the roof to inverter to make 2 strings these are optimizers for each panel I dont know if we can do that according to 310.10 H nec if we can can you show me in the code book were it says we can paralleling less then 1/0 I did read the ex in 310 I did not see anything about photovoltic thanks in advance

 

[Smart $]

Can't quite make out your details as described, but FWIW, paralleling is when conductors are connected to the same terminal or terminal bus at each end. What you are doing sounds to be more like splicing or tapping.

 

[ggunn]

So here is the situation the new inverters we have been using only come with 2 strings they are solar edge single phase but on most of the projects on the plans call for 3 or more strings we have just been paralleling let's say we have 3 strings we would with 10 awg wire we would parallel one string to number 6 from the roof to inverter to make 2 strings these are optimizers for each panel I dont know if we can do that according to 310.10 H nec if we can can you show me in the code book were it says we can paralleling less then 1/0 I did read the ex in 310 I did not see anything about photovoltic thanks in advance

I'm trying to discern what you are asking about, which isn't easy, but in any case what you are talking about is not related to parallel conductors.

 

[Dennis Alwon]

I don't see any exception in 310 or 690 to allow parallel with sizes smaller than 1/0 for your install. As smart stated you may not have a parallel run

 

[Shawn pavich]

Ok thanks were I work everybody calls it paralleling we have been using the wrong term.so if I have six strings hit a combiner box positive and negative then from the positive terminal and neg term with #2 awg then land in a inverter what is the proper name for that we have been calling it paralleling thanks most of my electric knowledge is in res. you commercial guys don't look down on me hahaha

 

[Carultch]

Ok thanks were I work everybody calls it paralleling we have been using the wrong term.so if I have six strings hit a combiner box positive and negative then from the positive terminal and neg term with #2 awg then land in a inverter what is the proper name for that we have been calling it paralleling thanks most of my electric knowledge is in res. you commercial guys don't look down on me hahaha

Electrically, I understand why you call it parallelling. A better way to say it is, combining in parallel.

What you do not have, is parallel conductors of the same feeder (or other circuit). Parallel sets of conductors to comprise a feeder or other circuit of larger ampacity, are required to be 1/0 and larger. Two 1/0 copper wires, in separate raceways, comprises a 300A feeder. You are not allowed to do parallel sets of #10 copper wire, and think that you make a 60A feeder.

With SolarEdge inverters/optimizers, you are permitted to combine up to TWO strings, without fuses. Both strings require the ampacity to be sized for the larger of the two. If you have three or more strings per inverter, which is uncommon with the SolarEdge inverters, a DC combiner is required, with fuses on both positive and negative sides (because it is an ungrounded system).

 

[Shawn pavich]

Thanks a lot for the enlightenment I can see how most can not really tell what the hell I was trying to get across on my first post I will do better at explaining the situation on any other future post thanks

 

[Smart $]

...what is the proper name for that we have been calling it paralleling...

Parallel equipment... not parallel conductors.

 

[ggunn]

With SolarEdge inverters/optimizers, you are permitted to combine up to TWO strings, without fuses.

Not just with Solar Edge; any time you combine more than two PV strings you must have string fuses. And no, you cannot combine two strings and then combine that with another string without fusing them all individually.

 

[ptonsparky]

Thanks a lot for the enlightenment I can see how most can not really tell what the hell I was trying to get across on my first post I will do better at explaining the situation on any other future post thanks

Try using some punctuation, it lets us breath while reading, and saves lives.

"It's time to eat, Grandma." Has a different ring to it than "It's time to eat Grandma."

 

[Strathead]

Ok thanks were I work everybody calls it paralleling we have been using the wrong term.so if I have six strings hit a combiner box positive and negative then from the positive terminal and neg term with #2 awg then land in a inverter what is the proper name for that we have been calling it paralleling thanks most of my electric knowledge is in res. you commercial guys don't look down on me hahaha

I think I would call it combining.:slaphead:

 

[Carultch]

Not just with Solar Edge; any time you combine more than two PV strings you must have string fuses. And no, you cannot combine two strings and then combine that with another string without fusing them all individually.

Correct. The intent of the reason to no longer permit "bare combining" DC circuits together when combining more than three circuits, is so that two or more active circuits do not gang up and overload one faulted circuit.

The SolarEdge technical team says that this condition doesn't happen with their technology, and has submitted a proposal to allow "bare combining" multiple strings of power optimizer circuits. The rule was written for direct module circuits, that don't have a DC control device, and are perpetually energized until the sun goes down. But until that proposal gets accepted, the NEC rule limits you to no more than two strings without OCPD.

Another application of this rule, is in a situation commonly found around 100 kW. Two combiners are near in size, and are combined in the inverter without fuses or other OCPD. The DC feeder and combiner DC disconnect is upsized to the larger of the two circuit ampacity requirements.

 

[GoldDigger]

I wonder just how SE manages to set current and voltage levels for each of the strings independently when they are combined into one inverter input?
Possibly they set a loose voltage requirement and let the modules adjust that voltage slightly while producing their available power and keeping the two string voltages identical?

 

[Carultch]

I wonder just how SE manages to set current and voltage levels for each of the strings independently when they are combined into one inverter input?
Possibly they set a loose voltage requirement and let the modules adjust that voltage slightly while producing their available power and keeping the two string voltages identical?

Quite likely.

The single phase inverters have a nominal operating DC input voltage of 350V, and a maximum operating voltage of 500V. Each centered on both sides of ground. However, I've seen actual inverter data can indicate higher voltages.

The way that I understand it, is that each optimizer tracks the amount of power on its module, and within the string, it contributes a voltage proportional to its module's power as a fraction of the total power of the series string. Multiple strings in parallel, all add up to the same target voltage.

So suppose 10 modules in series, each at 250W nominal, each adding up to the target voltage of 350V. If all modules produced uniform power, that would be 35 Volts each, and at STC, a current of 7.14 Amps.

Now suppose that only 5 modules produce the full power, and the other 5 modules produce 125W. That's 47V for the optimizers at full power, and 23V for the optimizers at half power, each producing 5.36A of current. 47V*5 + 23V*5 = 350V. 250*5+125*5 = 1875W; 1875W/350V = 5.36A.

I believe it errors on the side of above nominal operating input voltages (360V, 370V, etc), in order to keep the current lower than the maximum within the strings.