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**Mike90250** · 09-25-2017, 12:45 AM

Whoa, You have to have a way to disconnect the PV from the inverter, for testing or troubleshooting. You need a 500V rated DC breaker , or DC disconnect switch

Wires, Yep, you got lots of them. 10ga PV wire is pointless, you are paying for UV & Weather & Abrasion protection that you don't need. When your wire goes into the conduit, you could transition to 8 ga Alum wire. Cheaper than copper, but you need to insure all the connections / splices etc are rated for alum wire. You will need larger conduit, count the wires and size the conduit properly. But it saves $$

**diegodog** · 09-25-2017, 01:12 AM

Originally posted by Mike90250

Whoa, You have to have a way to disconnect the PV from the inverter, for testing or troubleshooting. You need a 500V rated DC breaker , or DC disconnect switch

Wires, Yep, you got lots of them. 10ga PV wire is pointless, you are paying for UV & Weather & Abrasion protection that you don't need. When your wire goes into the conduit, you could transition to 8 ga Alum wire. Cheaper than copper, but you need to insure all the connections / splices etc are rated for alum wire. You will need larger conduit, count the wires and size the conduit properly. But it saves $$

Disconnect is built into the inverter.

Great idea on ditching the PV wire for the underground run.

Thanks

**max2k** · 09-25-2017, 01:28 AM

Originally posted by diegodog

Hello,
...
(3) SMA 6300 watt inverters (4 dc inputs possible - maxes out at 600 volts) - incorporated dc disconnect
(60) Hyundai 45.1 volt 8.8 amp panels
Using 10 AWG pv wire
Wiring in series
10 panels per string
2 strings per inverter
6 strings total.
grid-tie

looking reasonable IMO. Where are you planning to put your inverters- near arrays or on the building? There're 2 options:

- run L1, L2, N AC and 6AWG for lightning protection. Advantage- simpler circuit, disadvantage- thicker wires: 6300W SMA inverter has AC output rating of 25A multiplied by 3 gives 75A which would require 6AWG for L1, L2 and N which will be hard to pull through and probably more expensive.

- run 2x6 DC wires from each string + 6AWG for ligtning protection. Advantage- 450V DC would have about x4 times less losses compare to 240AC with the same wires. Given max current of 8.8 A and 80% reduction due to > 6 current carrying conductors in the conduit you only need to pass 11A so even 14 gauge will be satisfactory and 12 of them will be easier to pull. This option would obviously require inverters mounted on the side of the house.

Originally posted by diegodog

Question 1
My plan currently is to run each string straight to the inverter (incorporated dc disconnect). No junction boxes, combiners, fuses, breakers. Each string gets a line straight from its last panel to its own input on the inverter with nothing in between. 451 volts and 8.8amps. This is a lot of wire obviously. Is there a better way to save on wire or is it better to keep it the way I'm planning. . Any disasters ahead? Missing something completely? Boneheaded?

Panel's wires are PV type wire while the 'home run' wires are THWN-2 so somewhere at the array you need a box with terminals switching from one to another..

Originally posted by diegodog

Question 2
Grounding: I'm using the old school lug method (tin coated) as I have no rails for weeb or other fancy options. To be honest I'm completely confused on the grounding front. Once all the panels are connected with the grounding wire where is its first stop? To the rod in the ground under the meter or into the inverter? If the answer is rod in the ground should I use the one close to the building or should I put one out in the field somewhere? If I go from panels to rod in the field does it need to work back to the ground rod at the building or it terminated in the field? Is 6 AWG what is needed for the job?

you need to use special stainless steel grounding lugs to connect grounding wire to the panel's frames to prevent aluminum corrosion of the panel frames. You have to make sure your 6AWG copper wire never touches panel's frames directly. Someone with experience on ground mounted arrays might help with the solution.

Are those concrete blocks have any rebar you could connect to? If so I'd connect panel frames with 6AWG and then to the rebar below. Then I'd run 6AWG between rebars and through the trench to the building grounding rod.

Originally posted by diegodog

Question 3
What is the path the AC current takes after the inverter. I'm not sure if I go from the inverter to my breaker box or if it goes to the current AC disconnect or if I need a 2nd separate AC disconnect. Can you give me an idea on the equipment that AC currnet hits (in order) as the power runs through the AC side with this setup.

Planning on using 10 awg and 30 amp breakers. I have 15 open slots on my panels 200 service.

Thanks again for everything

What rating your MSP busbar has? The service is 200A but internal bus bar could be lower/higher. Basically you can 'overload' that by 20% IIRC which is only 40A if it has 200A rating. You can probably replace your 200 A main breaker with 160A one to get some room for your inverters 75A combined output. This assumes your solar output is on the opposite end of bus bar relatively to the main breaker.

You can wire each inverter individually to its own 30A 'double' MSP breaker using 10 AWG essentially creating 3 completely independent solar systems.

or you can combine 3 inverter AC outputs together using some AC combiner box and then 'backfeed' the combined L1, L2 into single 'double' 80A breaker in your MSP. 75A wires would need to be 6AWG, but luckily for short run between combiner box and the MSP.

**tyab** · 09-25-2017, 05:10 AM

digodog - Here is a partial answer to #2 and covering GEC (grounding electrode conductor) and GE (ground electrode). You are required to electrically tie all the panels together and have a local ground electrode at the ground mount. Since your not using any sort of listed rail system, you are forced to use #6 solid copper wire to every panel approach. Think of it this way - one long continuous wire starting on one panel to the next in a long big S shape, with the wire finally heading into two ground rods, both 8' deep and the rods are at least 6' apart right at the ground mount. Those ground rods can be put into the ground up to a 45 degree angle so find that area where you have deeper rock to pound them in. There are other ways to do a ground electrode, see 250.52(A) if the ground rods simply will not work for you. This will be your compliant 690.47(D). Its important that the #6 wire be continuous unless you are familiar with the ways specified in 250.62(C)(1). As stated above, you can't let the copper touch the panel frames, so you need a listed lug that attaches to the frame - the panel frames will have one or more designated grounding holes. You can go expensive WEEB lugs - which will give a great connection or given you are trying to keep costs down you can use this:

Southwire | Homepage

https://www.garvinindustries.com/fittings/grounding-clamps-straps/lay-in-lugs/4-14al

Choose Southwire for your wire and cable needs - we offer high-performance products that are built to last.

They are bi-metal rated and here is what they look like on my system (I used them to bond various items).

https://www.flickr.com/photos/149650...3/31920780421/ (see the far right).
https://www.flickr.com/gp/149650329@N03/3vLP20 (middle)

They take a #12 stainless bolt - just make sure your panel hole can take that #12. Panel specs should have this info. You will need to get the stainless hardware, use mcmaster.com for a super wide selection. Hex bolt, external tooth washer on one side, external tooth washer and nut on the other. That lug has teeth on the bottom to help it compress into the aluminum coating to ensure a good bond (just not as good as the more expensive WEEB style). But they are only a buck and are UL listed.
Would also suggest using some aluminum anti-oxide on the aluminum to aluminum contact with the lug and on the external tooth washers to help keep that contact electrically good over time - something like this:

https://www.amazon.com/Ideal-30-030-Anti-Oxidant-Compound-Squeeze/dp/B000LDE7V4

I would suggest using anti-seize on the stainless bolts threads - this stuff is really good and a little goes a long ways but any stainless anti-seize will do.

MRO Solution 2400 - Marine Grade Anti-Seize Lubricant - 8 oz.

https://www.albanycountyfasteners.com/Anti-Seize-compound-2400-Marine-Grade-p/1050-106.htm

Check out the deal on MRO Solution 2400 - Marine Grade Anti-Seize Lubricant - 8 oz. at Albany County Fasteners

**ButchDeal** · 09-25-2017, 08:42 AM

Originally posted by diegodog

Question 3
What is the path the AC current takes after the inverter. I'm not sure if I go from the inverter to my breaker box or if it goes to the current AC disconnect or if I need a 2nd separate AC disconnect. Can you give me an idea on the equipment that AC currnet hits (in order) as the power runs through the AC side with this setup.

Most AHJs require a single AC disconnect to shut the entire system down, so you will need an AC combiner.

Originally posted by diegodog

Planning on using 10 awg and 30 amp breakers. I have 15 open slots on my panels 200 service.

Thanks again for everything

30a breakers are good in the AC combiner, then disconnect, then to your MSP But here is where it gets tricky.

You can't just land 3 X 30A breakers on your MSP, you need to combine them. Regardless depending on your MSP you cant feed 90a into it, you are most likely going to need a special MSP or a line side tap.

**diegodog** · 09-25-2017, 11:59 AM

Hey guy's I'm very thankful for the info. Some I understand and some I don't (will be studying the next few days). My knowledge level is very basic as I 'm finding out.

It looks like I made a mistake by buying the tin plated lugs. I watched a solar tutorial from Penn State University and they recommended Stainless or Tin coated as the tin to copper connection does not suffer from galvanic corrosion. The tin lugs do have the toothed washer to get passed the coating on the aluminum frame . For 60 bucks I better switch out to stainless to be safe as the damage caused by the corrosion is fast and devastating from what I have seen.

Inverter's are going on the back corner of the building right next to the Meter/ACDisconnect (Never occurred to me they could be placed at the array) however the building works better as I will have feet and feet of snow on the ground for months at a time to contend with. The back side of the building receives little sun so that's another advantage.
I'm completely broken on the electrical side. I was fairly sure I was lost and then I read your guys answers and now know for certain I am!

For getting wire to the inverter I like Max2K #2 idea (because that's the one I understood!)

- run 2x6 DC wires from each string + 6AWG for ligtning protection. Advantage- 450V DC would have about x4 times less losses compare to 240AC with the same wires. Given max current of 8.8 A and 80% reduction due to > 6 current carrying conductors in the conduit you only need to pass 11A so even 14 gauge will be satisfactory and 12 of them will be easier to pull. This option would obviously require inverters mounted on the side of the house.

With my limited understanding of things I need to get DC power to the one side of the inverter. So a straight shot to the inverter from right off the panels seems like the safest most straight forward option for a rookie. 12 wires (6 strings x 2 wires). I like the idea of stepping the wire down a size (after checking the charts for distance) to save a few $$. Since the DC disconnect is on the inverter I'm assuming If I kept it 10awg I would go from the panel to the DC disconnect/inverter with no equipment in between. If I step down a size on the wire I would need a junction box after the panels then a straight shot to the DC disconnect/inverter. Is this a correct line of thinking? If so it makes sense to me and I can get this line buried before the snow hits.

Panel's wires are PV type wire while the 'home run' wires are THWN-2 so somewhere at the array you need a box with terminals switching from one to another..
I don't understand this one. Does this mean I cannot connect the dc disconnect/inverter up to the PV wires coming off the panels directly? I have to switch them to THWN-2? Was this statement made assuming the inverter was at the panels and not the building? I may also be completely lost and not getting what your putting down.

One question on the grounding and I'm going to stop as the electric box talk got me scared.

You guys gave awesome information on the grounding. Thanks to both Max2K and Tyab.

Here is my plan
For grounding I'm using 6 awg all around. I will hook all the panel frames together with 6 awg. Once the panels are hooked together I will send (1x) 6 awg to a grounding rod in the field by the panels. Then I will send (1x) 6 awg to a 2nd grounding rod in the field by the panels but making sure they are the proper distance apart. And finally I will send (1x) 6 awg along the run to the barn to go to the inverter. Is this a correct understanding and blending of what you guys were saying?

Let me stop there so I don't get to far ahead of myself.

Butch I need to study more on the electric panel over the next few days so I can better understand what your saying. I'm sure I'll have a question or two!

Mike, Butch, Tyab and Max2K I thank you very much for responding and helping me accomplish as much as possible before calling in the electrician. I'm very grateful.

**max2k** · 09-25-2017, 12:58 PM

Originally posted by diegodog

...
With my limited understanding of things I need to get DC power to the one side of the inverter.

yes, to one of its 3 sides at the bottom- SMA has plugs on all 3 sides. Internally DC wires are on the left side and AC output wires are on the right side, both under black plastic cover at the bottom. I wired DC to mine through bottom left holes, this way water won't be able to get in there. You'll also need to put wires in the conduits so plan accordingly.

Originally posted by diegodog

So a straight shot to the inverter from right off the panels seems like the safest most straight forward option for a rookie. 12 wires (6 strings x 2 wires). I like the idea of stepping the wire down a size (after checking the charts for distance) to save a few $$. Since the DC disconnect is on the inverter I'm assuming If I kept it 10awg I would go from the panel to the DC disconnect/inverter with no equipment in between. If I step down a size on the wire I would need a junction box after the panels then a straight shot to the DC disconnect/inverter. Is this a correct line of thinking? If so it makes sense to me and I can get this line buried before the snow hits.

I'm not sure where are you getting this 10awg from- panel wires are very different and much more expensive type called PV wire. Your longest run sounds like 160' + 107' + 60' = 327'. This run can be done with cheaper THWN-2 wire. To switch from one type wire to another you need to install some terminal box at the array where PV wires would go in but conduit with THWN-2 would go out into the trench. I'm not recommending particular brand/model because I have no experience with those. In order to have less than 3% of losses on that distance you need your wire to have resistance less than 451V / 8.8A * 0.03 = 1.5 Ohm for both wires: 327' x 2 = 654' total distance. 14 AWG has 1.6 Ohm over that distance:https://www.cirris.com/learning-cent...lculator-table which is acceptable IMO as this is the distance from the far most corner of the array. Inverter connector can take 14 gauge wire. If you use 12 gauge for DC run it would have about 1 Ohm resistance over the same distance which will introduce 2% loss. 3/4' PVC SCH80 conduit would allow you to have 12 x 12 gauge wires or 17 x 14 gauge wires inside. Here comes $1 million question- do you need EGC green wire in that conduit or not. I'd try to ask your electrician as it is up to your local rules really. From pure academic point of view it's not needed but your local AHJ can sometimes bend the space and laws of physics a little. I think pulling additional wire after you already put 12 other in the conduit would be much more difficult.

Originally posted by diegodog

Panel's wires are PV type wire while the 'home run' wires are THWN-2 so somewhere at the array you need a box with terminals switching from one to another..
I don't understand this one. Does this mean I cannot connect the dc disconnect/inverter up to the PV wires coming off the panels directly? I have to switch them to THWN-2? Was this statement made assuming the inverter was at the panels and not the building? I may also be completely lost and not getting what your putting down.

with inverter at the building your DC run in the trench/conduit is done using THWN-2 wire while panels use Photo voltaic (PV) wire- much thicker sun / abrasion resistant / expensive wire. You don't want to run PV wire in the conduit.

Originally posted by diegodog

For grounding I'm using 6 awg all around. I will hook all the panel frames together with 6 awg. Once the panels are hooked together I will send (1x) 6 awg to a grounding rod in the field by the panels. Then I will send (1x) 6 awg to a 2nd grounding rod in the field by the panels but making sure they are the proper distance apart. And finally I will send (1x) 6 awg along the run to the barn to go to the inverter.

I'd connect this last 6AWG piece not to the inverter but to the building grounding rod directly 'bonding' building rod with array grounding rods. I'd connect inverter ground to building MSP grounding bar with normal green EGC wire. Here again local AHJ might just require the green EGC to extend all the way from inverter to your panels even if it doesn't make much sense. Since you want to pass the inspection you will have to have it there.

**tyab** · 09-25-2017, 01:50 PM

This should be doable with a load side connection on his 200 amp MSP and yes we have to use a sub-panel. The sub-panel has to have a 225 amp busbar to make it work - here is the layout.

- Downrate the MSP to a 125 amp OCPD (circuit breaker).
- Install a 100 amp OCPD in the lower right corner.
- Run a properly sized feeder (105 amps + adjustments - thank you 2014 code! - 2011 code would have required 2/0 copper) from the 100 amp OCPD to MLO sub panel that is 225 amps.
- Have a 225 amp MLO (main lugs only) subpanel. If you want it can be a OCPD subpanel but then you are paying the high cost to installed a 100 amp main breaker in this - less expensive to use a MLO panel.
- Put in three 35 amp OCPD one per inverter in the subpanel. No location requirements for these in the subpanel but convention would be lower.

Details:

First the SMA 6000 has a rated AC output of 25 amps (from the datasheet). Thus are total output of 75 amps has to be dealt with but its different between the MSP and the sub panel.

Starting from the main service panel.

We are going to backfeed a total of 75 amps from the three inverters. 75 * 1.25 = 93.75, round up and we use a 100 amp OCPD in the lower right corner. This falls under 705.12(D)(2)(3)(b) and thus we have to down rate the MSP breaker from 200 amps to 125 amps. These breakers are not cheap, but that is the way it goes - either that or go to a line side tap.

You run a properly sized feeder (105 amps plus adjustments) to the MLO subpanel. 105 amps since we will have backfeed OCPD of 105 amps total between the thee 35 amps OCPD's

The main lugs only subpanel has to be rated for 225 amps. Why? You have a 100 amp OCPD feeding the subpanel and in the subpanel you have 3 x 35 amps OCPD backfeeding. This requires us to follow 705.12(D)(2)(3)(c) and thus we are forced to use a 225 amp subpanel.

Each inverter has 25 amps output. 25 * 1.25 = 31.25, round up to next trade size and use a 35 amp OCPD for each inverter.

Have three 35 amps OCPD's in the subpanel - no location requirement since we are under 705.12(D)(2)(3)(c).

Now what happens if you need a safety switch between the MSP and the subpanel? This is messy since a 200 amp safety switch does not cover - we are 5 amps over according to the NEC. That means a 400 amp switch. Ouch. It may be less expensive to put a 100 amp main breaker in the MLO subpanel and then you can use a 200 amp safety switch. Hopefully you don't need this and can save that cost.

There are a bunch of sticker requirements for the downrated MSP breaker, the 100 amp breaker you put in the MSP in the lower right corner, outside AC disconnect. etc.

**diegodog** · 09-25-2017, 02:06 PM

Thanks Max2K!

It's clear to me now!

I had the 10 awg PV wire on the brain because the panels have the 10 awg pv wire on them, so I boxed my thinking off and just ran (wildly) with that idea. I figured if its whats on the panels and is plenty heavy enough to make that distance with little no no loss why not play it safe. However, with the amount of line I will be running I'm going to run the THWN-2 wire as you suggested. The way I was going to do it is foolish and wasteful. Thanks a million for the great advice.

You will also notice those concrete blocks and 6x6's I used for my stand and mount. It's built like that out of pure ignorance. When you don't know what your doing you go BIG to over compensate the lack of knowledge. If mother nature wants to take my panels for a ride she is gonna have to work!

I will run the the EGC green wire and let the electrician decide. No way I want to fight with a wire pull.

I'd connect this last 6AWG piece not to the inverter but to the building grounding rod directly 'bonding' building rod with array grounding rods. I'd connect inverter ground to building MSP grounding bar with normal green EGC wire. Here again local AHJ might just require the green EGC to extend all the way from inverter to your panels even if it doesn't make much sense. Since you want to pass the inspection you will have to have it there.

10- 4. I understand the above. Luckily I have no real inspection. The electric company said they are only checking their equipment, they don't care what I do with mine. There are 0 inspectors here. We have built the barn (pictured here) and a house on the other side of the field and the only inspection was an old timer, who never even got out of his car, to make sure we have vent pipes for the plumbing! So your really at the mercy of the electrician which is another reason I want to understand what I'm putting on my property and why I like to go as far as I can before I call anyone in.

Thanks again Max2K. I grasp what needs done now to get to the inverter and it makes logical sense to me.

I will be back later with a comedy called from the inverter to the MSP (took me a minute to figure out MSP) and see what you guys think.

Once again I am very thankful to you guys(gals) and this resource. Its quite and amazing amount of knowledge and help received here.

**DanS26** · 09-25-2017, 02:11 PM

If you have already purchased your inverters and wiring.......then ignore the comments below.......

A design using just two inverters is possible using just 5 wires carrying DC from combiner boxes at the array to the inverters at the building. Combine 3 strings each into two home runs. Instead of 13 wires of 107 ft each (6 pos 6 neg 1GEC) you then only need 5 wires of 107 ft (2 pos 2 neg 1GEC). Wire savings alone will almost pay for an inverter plus you can use a fused combiner box at the array making for a much safer installation.

The Fronius inverters will accommodate this design...not sure if the SMA inverters will handle combined strings.

You seem to be cost conscious so you may want to redesign to save lots if not too late.

**diegodog** · 09-25-2017, 02:35 PM

Tyab + Butch I'm going to need a second on that. LOL! I need a little time to digest before I have a reply.

My absolute immediate concern is getting the wiring to the inverter (including ground) from the panels before the winter comes. Which is soon northern ME. Once the wiring is all complete up to the inverter everything else can be done in -30 and 10 feet of snow. The main service line runs in the attic (from the back corner (meter) to the front corner (MSP)) so I wont have to bury the lines going from the inverter to the MSP I will run it along with he main line that supplies the barn now if it comes down to that). I think I'm very close with the help from the above postings to being able to get the necessary wire from the panels to the inverter and have it grounded properly.

You can wire each inverter individually to its own 30A 'double' MSP breaker using 10 AWG essentially creating 3 completely independent solar systems.

It appears this is a no go. If I only had 20 panels and 1 inverter could I do it with a 30A double breaker? I start to get confused from that point as I would think if I had the space I could do it. This probably means I'm missing a key detail somewhere along the way.

Thanks again guys for all the help.

**diegodog** · 09-25-2017, 02:45 PM

Originally posted by DanS26

If you have already purchased your inverters and wiring.......then ignore the comments below.......

A design using just two inverters is possible using just 5 wires carrying DC from combiner boxes at the array to the inverters at the building. Combine 3 strings each into two home runs. Instead of 13 wires of 107 ft each (6 pos 6 neg 1GEC) you then only need 5 wires of 107 ft (2 pos 2 neg 1GEC). Wire savings alone will almost pay for an inverter plus you can use a fused combiner box at the array making for a much safer installation.

The Fronius inverters will accommodate this design...not sure if the SMA inverters will handle combined strings.

You seem to be cost conscious so you may want to redesign to save lots if not too late.

Unfortunately is too late.

I do like the idea of the fused box at the array so I can shut down the panels if necessary, however can't you just unplug the panels if something occurs between the panels and inverter to take all current off the home run?

Thanks for the post and information !

**max2k** · 09-25-2017, 02:47 PM

Originally posted by tyab

... Each inverter has 25 amps output. ....

Instead of that- how about using Midnight MNPV6 Disco AC Micro Combiner? It can handle 3 inverters with up to 60A breakers each (OP needs only 30 really) with output bus rated to 168A combined. It has handle which simply switches all those internal breakers on or off mechanically at the same time. No subpanel required, I believe it can be wired directly to MSP 80A breaker for PV system in MSP. IIRC 80A breaker is listed for continuous 80A current, no need to apply 125% rule. Besides, in OP case that breaker will never see more than 60A in real life. OP just need to replace main breaker in MSP with 160A one to satisfy MSP bus bar requirements.

**max2k** · 09-25-2017, 02:54 PM

Originally posted by diegodog

Unfortunately is too late.

I do like the idea of the fused box at the array so I can shut down the panels if necessary, however can't you just unplug the panels if something occurs between the panels and inverter to take all current off the home run?

Thanks for the post and information !

No, unplugging at that voltage / current will create DC arch which will melt whatever you unplugged. The correct way to go about this:
- disconnect your AC first. This will stop current consumption from your array by inverters dropping current on DC side close to 0 as well.
- disconnect DC using inverter's DC disconnects, just in case

- go to the array and break the string you're going to work on somewhere in the middle by disconnecting one of the MC 4 connectors. This will ensure no matter what you touch in that string won't be able to shock you as you have 2 breaks now- one at the inverter and one somewhere in the string so your body can't close both breaks at the same time.

If you don't do the last step the array will remain energized as long as there's any kind of sun light and will produce 450V DC with enough current to kill you so be careful.

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