Is a fused combiner box required for my installation?

[D0T-C0M]

Please refer to the attached one line diagram of my PV system.

My system consists of 28 panels arranged in 4 strings of 7 panels. For simplicity I’ll call each string of panels string#1, string#2, string#3, string#4.

In my hybrid all-in-one inverter there is 2 charge controllers called PV1 and PV2. Each charge controller has independent input terminals to accept 2 strings of panels so strings #1 and #2 will be run to charge controller PV1 and strings #3 and #4 will be run to charge controller PV2. String #1 and #2 are paralleled at the inverter on PV1 and String #3 and #4 are paralleled at the inverter on PV2.

My inverter limits the input current on PV1 and PV2 to 20amps max on each charge controller. The solar panels have a Isc=11.66A and a max series fuse rating of 25A.

Am I correct to understand that the electrical code does not require any over current device (i.e. fuse or breaker) for installations with 2 strings in parallel due to the fact that the fault current cannot exceed the max fuse rating size of the panels nor does it exceed the amperage rating of the cables?

Am I also correct to assume that I do not require a combiner box as I am only paralleling 2 strings and all that is required is a 4 pole DC disconnect switch for String#1 and String #2 and a 4 pole disconnect switch for Strings #3 and #4?


Solar oneline.png

[Mike90250]

If you say so. I can't read the micro print you posted in the pic.

Generally, good practice is to have a DC breaker on each PV string, so it can be turned off and compared to the other matching strings. Saves a LOT of troubleshooting time when it comes to it.

[D0T-C0M]

I'm not sure what you are referring to when you say 'if I say so"? I' m asking if I'm correct in assuming that I dont require fuses or combiner boxes with the setup I have.

In regards to your comment saying its good practice to install breakers to make troubleshooting strings easier, remember I only have 2 strings so If my diagram is legal then just open the 4-pole disconnects and check your open circuit voltages and short circuit current on each string at the disconnect.

My question is my diagram legal to the code in regards to not using fuses or a combiner box?

[SunEagle]

I'm not sure what you are referring to when you say 'if I say so"? I' m asking if I'm correct in assuming that I dont require fuses or combiner boxes with the setup I have.

In regards to your comment saying its good practice to install breakers to make troubleshooting strings easier, remember I only have 2 strings so If my diagram is legal then just open the 4-pole disconnects and check your open circuit voltages and short circuit current on each string at the disconnect.

My question is my diagram legal to the code in regards to not using fuses or a combiner box?

First off I see 4 parallel strings in that drawings so yes you will need to add fuses or a combiner box to your setup.

Second, as to what your NEC or AHJ feels is correct. That is a hard question since there are multiple NEC codes that are followed depending on the state and city you reside in. Again it still falls down to what the AHJ feels is acceptable and what they feel you need to change or improve.

[sdold]

It looks like the Sol Ark has two PV inputs (PV1 and PV2), and his drawing shows two parallel strings on each, so I think he would be compliant as long as he doesn't need to add rapid shutdown. The way they draw the terminals makes it seem as if there are four MPPT inputs, or that they are all just one parallel input, but I think it's two. I had to go to the Sol Ark site to see this since it's not obvious in the image above.

[bcroe]

If your inverter internally ties the 4 strings together, you need individual string fusing.
Some inverters (like mine) have the option of adding fuses there, instead of solid
jumpers. If not, consider bringing the strings into a combiner for a single large feed.

High voltage DC disconnects are quite large and expensive, far more than DC fuses.
This would cut disconnects down to just one with only 2 poles. Lots of 3 poles out
there, used from 480VAC 3 phase stuff, 4 poles I have not seen. Here this more
economical for a long run. Since strings here have varying orientation, a single
LARGE feed is more efficient than a lot of SMALL feeds taking turns carrying most
of the current.

Fuses can also provide the option of disconnecting individual strings. Bruce Roe

[D0T-C0M]

In my hybrid all-in-one inverter there is 2 charge controllers called PV1 and PV2. Each charge controller has independent input terminals to accept 2 strings of panels so strings #1 and #2 will be run to charge controller PV1 and strings #3 and #4 will be run to charge controller PV2. String #1 and #2 are paralleled at the inverter on PV1 and String #3 and #4 are paralleled at the inverter on PV2.

Sorry if I was not clear but the sol-ark inverter has 2 charge controllers PV1 and PV2. Each controller has 2 inputs. So string1 and string2 are connected to PV1 and string3 and string4 are connected to PV2. String1 and string2 are paralleled together at the PV1 terminals and string3 and string4 are paralleled at the PV2 terminals. PV1 and PV2 are isolated from each other

[D0T-C0M]

If your inverter internally ties the 4 strings together, you need individual string fusing.
Some inverters (like mine) have the option of adding fuses there, instead of solid
jumpers. If not, consider bringing the strings into a combiner for a single large feed.

High voltage DC disconnects are quite large and expensive, far more than DC fuses.
This would cut disconnects down to just one with only 2 poles. Lots of 3 poles out
there, used from 480VAC 3 phase stuff, 4 poles I have not seen. Here this more
economical for a long run. Since strings here have varying orientation, a single
LARGE feed is more efficient than a lot of SMALL feeds taking turns carrying most
of the current.

Fuses can also provide the option of disconnecting individual strings. Bruce Roe

Yeah I'm not going with a high voltage disconnect. I was told I needed one disconnect for the whole array, not 2 separate disconnects and I priced an Eaton DCU2101URM and they want $2500 so forget that. I talked to an installer and midnight solar sells a
MidNite Solar MNPV8HV-DLTL 4X for about $600-$700 which has 4 strings entering the combiner with 2 separate 30A strings out. This is probably what I'm going with as it will provide a single means to disconnect the whole array in one disconnect plus I only have to run 4 wires to my inverter instead of 8 so I will save a couple hundred bucks

[bcroe]

Yeah I'm not going with a high voltage disconnect. I was told I needed one disconnect for the whole array, not 2 separate disconnects and I priced an Eaton DCU2101URM and they want $2500 so forget that. I talked to an installer and midnight solar sells a
MidNite Solar MNPV8HV-DLTL 4X for about $600-$700 which has 4 strings entering the combiner with 2 separate 30A strings out. This is probably what I'm going with as it will provide a single means to disconnect the whole array in one disconnect plus I only have to run 4 wires to my inverter instead of 8 so I will save a couple hundred bucks

That will force the fusing down to one feed, and the disconnect switch, to be
at the same location. Might be fine for you, they are 230' apart here. A 361
(30A) or 362 (60A) 600V disconnect switch can be had for under $100 on
Evil Buy. A 4 string combiner could be a pretty simple thing. Bruce Roe

[SunEagle]

My question still stands. Is that drawing approved by your AHJ and POCO or is it something you would like to install?

Remember if you don't get approval you might be building something illegal and I will not support that type of work.

[PVAndy]

My question still stands. Is that drawing approved by your AHJ and POCO or is it something you would like to install?

Remember if you don't get approval you might be building something illegal and I will not support that type of work.

Check these out. We use them all the time. https://www.industrialcontroldirect....isconnect-268/

Andy

[khanh dam]

MIDNITE SOLAR MNPV12 PV
would be $200 a lot cheaper. does your AHJ require that large external disconnect on the $600 box?

[D0T-C0M]

MIDNITE SOLAR MNPV12 PV
would be $200 a lot cheaper. does your AHJ require that large external disconnect on the $600 box?

Yes the local authority requires one disconnect (lever) that isolates the whole array.

My question still stands. Is that drawing approved by your AHJ and POCO or is it something you would like to install?

Remember if you don't get approval you might be building something illegal and I will not support that type of work.

I haven't started buying or building anything until I get approval. The drawing I provided was one that came in the inverter manual that I submitted to the electrical inspector. I modded it to remove the batteries (future install) and removed the rapid shutdown stuff as this is not applicable when using a ground mount and added the 2 dc disconnects. They haven't responded yet but I talked to a local installer and he says they require one disconnect lever to disconnect the whole array.

[heimdm]

I think the thing to remember is that your AHJ (electrical inspector/NEC) has different requirements than the POCO/Utility. In many cases the AHJ cares about the DC disconnect (usually on the inverter), to shut down the array voltage in an emergency type situation. POCO requires the AC disconnect because they want to isolate the PV away from their grid. In many cases, not only does the POCO require the AC disconnect but they want the big level with the ability to LOTO (lock out tag out).