Two questions regarding wire sizing from array to controller

[zanydroid]

I'm not sure the parallel conductor rules in the NEC apply here, as only one side of each wire run is connected in parallel. There are 2 separate sources, with separate wire runs, that are joined at one point. Not the normal parallel conductor setup where both sides of a run are connected together.

Sure that is fine but there's then no need to call it out in English as it's a well known PV wiring technique that does not require fusing. 3P and up would require fusing but not specifically for just the wire.

And it was described by OP as "doubling up 12s" which is pretty ambiguous, and this forum often suggests non-NEC paralleling.

 

[JustPractical]

So if I used a plug combiner to combine the "2P" part of each array, I could then run 10awg off that back to the house in pvc, and then to a disconenct, and then to 10awg on the inside?

 

[pvgirl]

So if I used a plug combiner to combine the "2P" part of each array, I could then run 10awg off that back to the house in pvc, and then to a disconenct, and then to 10awg on the inside?

Yes

 

[zanydroid]

So if I used a plug combiner to combine the "2P" part of each array, I could then run 10awg off that back to the house in pvc, and then to a disconenct, and then to 10awg on the inside?

You can, however my calculations showed that your panels are a few milliamps over. Do you need to file planset for permits? It would be hard to show the wire sizingcalculations with a straight face

 

[pvgirl]

You can, however my calculations showed that your panels are a few milliamps over. Do you need to file planset for permits? It would be hard to show the wire sizingcalculations with a straight face

Note NEC 220.5(B):

(B) Fractions of an Ampere​

​

Calculations shall be permitted to be rounded to the nearest whole ampere, with decimal fractions smaller than 0.5 dropped.​

PV Current calculations, per NEC 2020 690.8(B), largest of 2 methods:
690.8(A) Current 9.63 Isc amps * 2 in parallel * 1.25 = 24.075 amps

1. Without Adjustment and Correction Factors:

24.075 amps * 1.25 = 30.09375 amps or 30 amps​

2. With Adjustment and Correction Factors:

24.075 amps / 0.88 temp correction @ 40c for 75c conductor / 0.80 adjustment for 4 conductors in conduit = 34 amps​

24.075 amps / 0.91 temp correction @ 40c for 90c conductor / 0.80 adjustment for 4 conductors in conduit = 33 amps.​

temp corrected for outside part of runs worst case.​

Both within the ampacity of 10 AWG using a 75c or 90c conductor.

 

[zanydroid]

Note NEC 220.5(B):

(B) Fractions of an Ampere​

​

Calculations shall be permitted to be rounded to the nearest whole ampere, with decimal fractions smaller than 0.5 dropped.​

PV Current calculations, per NEC 2020 690.8(B), largest of 2 methods:
690.8(A) Current 9.63 Isc amps * 2 in parallel * 1.25 = 24.075 amps

1. Without Adjustment and Correction Factors:

24.075 amps * 1.25 = 30.09375 amps or 30 amps​

2. With Adjustment and Correction Factors:

24.075 amps / 0.88 temp correction @ 40c for 75c conductor / 0.80 adjustment for 4 conductors in conduit = 34 amps​

24.075 amps / 0.91 temp correction @ 40c for 90c conductor / 0.80 adjustment for 4 conductors in conduit = 33 amps.​

temp corrected for outside part of runs worst case.​

Both within the ampacity of 10 AWG using a 75c or 90c conductor.

Thanks for the clarification.

Which of those is ampacity needs to be under the 30A overcurrent protection limit and which of those are allowed to go over it?

 

[pvgirl]

Thanks for the clarification.

Which of those is ampacity needs to be under the 30A overcurrent protection limit and which of those are allowed to go over it?

Based to 690.9(B) for over current device rating is total Isc * 1.56 (multiplied by 1.25 twice) which is (1) in my calculations which is 30 amps.

 

[zanydroid]

Based to 690.9(B) for over current device rating is total Isc * 1.56 (multiplied by 1.25 twice) which is (1) in my calculations which is 30 amps.

Do you mean that (1) needs to pass the 30A OCPD limit (which it does rounding down to whole amps) and (2) needs to pass the 75C or 90C temp rating (depending on what the terminals/other equipment on the circuit path can handle)

 

[pvgirl]

Do you mean that (1) needs to pass the 30A OCPD limit (which it does rounding down to whole amps) and (2) needs to pass the 75C or 90C temp rating (depending on what the terminals/other equipment on the circuit path can handle)

Calculation (1) sets the size OCPD if needed and would correspond to the OCPD limits for small conductors, conductor ampacity must be the largest of (1) or (2), if (2) is larger then the 75c or 90c columns can be used. Unless all the terminations are rated for more than 60c, the 60c ampacity for conductor must greater or equal to (1) as well.

 

[JustPractical]

Question #4: Regarding running the ground - I had thought the whole ground array was to be attached to a grounding rod set near the array. No?

 

[Supervstech]

Question #4: Regarding running the ground - I had thought the whole ground array was to be attached to a grounding rod set near the array. No?

You can, but the ground is ALSO supposed to connect to the main panel grounding buss.

 

[pvgirl]

Question #4: Regarding running the ground - I had thought the whole ground array was to be attached to a grounding rod set near the array. No?

Not required or recommended to have an additional ground rod at the ground mount array. All metal parts of the panels and ground mount, must be bonded together, and a ground wire must run with the PV wires to the inverter where it is tied to the houses grounding system. Consult manual of the ground mount system you are using for proper bonding instructions. 6 AWG ground wire must be used where it's exposed, 10 AWG can be used in conduit with you PV wires.

 

[Zwy]

Question #4: Regarding running the ground - I had thought the whole ground array was to be attached to a grounding rod set near the array. No?

No.

EGC for array runs back to system grounding.

You can waste your time pounding in a ground rod at the array, it is permitted but can lead to a voltage gradient pulse if lightning strikes close by. The only requirement in NEC is the EGC to system grounding.

 

[JustPractical]

Not required or recommended to have an additional ground rod at the ground mount array. All metal parts of the panels and ground mount, must be bonded together, and a ground wire must run with the PV wires to the inverter where it is tied to the houses grounding system. Consult manual of the ground mount system you are using for proper bonding instructions. 6 AWG ground wire must be used where it's exposed, 10 AWG can be used in conduit with you PV wires.

Interesting. I know grounding and bonding can sometimes be a bit of a rabbit hole. I had gone with the practical "why bring any potential problems back into the house to run them through system ground."; BUT...I know the mantra "one ground in the system to avoid ground differntial problems" so makes sense.

Thanks to everyone for the help. I'll only be using this installation for about two years, but may as well do what I can right.

 

[wheelman55]

OP. If you are going to use a junction box at the array, then wire to a disconnect at the equipment, I recommend that you use these Polaris NSI connectors inside the junction box.

They come in various sizes.

Polaris connectors

Click on the video link and also download their brochure which is a bit down the page that I sent.

These connectors are amazing

 

[JustPractical]

OP. If you are going to use a junction box at the array, then wire to a disconnect at the equipment, I recommend that you use these Polaris NSI connectors inside the junction box.

They come in various sizes.

Polaris connectors

Good advice. For exposed connections, they are great.

 

[wheelman55]

And use the Polaris Grey. They are the ones to use for fine stranded wire.

 

[GuyG]

I’m getting a suspicion that Mike Holt has infiltrated this website and is posting under the alias @pvgirl ; she knows her stuff. ?

 

[cs1234]

@pvgirl is some sort of AI being trained to answer solar questions. The future is now!

 

[pvgirl]

@pvgirl is some sort of AI being trained to answer solar questions. The future is now!

Sorry not an AI just autistic.