Noob needs more help (pics inside)

[DanS26]

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 !

Sorry to hear that.

IMO a fused "pass through" box at the array for each string would be a wise investment. A fault anywhere along your 6 strings from array to the building as you have it designed now will cause an arcing/blazing mess and shut down your entire production. Not worth the risk IMO.

[diegodog]

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.

10-4 - My lingo is not helping. By unplugging the panels I meant going to each individual MC 4 connector just to be sure. I will try to not speak so generically next time. Either way this is a great reminder.

[max2k]

10-4 - My lingo is not helping. By unplugging the panels I meant going to each individual MC 4 connector just to be sure. I will try to not speak so generically next time. Either way this is a great reminder.

no worries, you're coming up to speed very quickly. You just need to break the string in 1 spot, no need to disconnect all 10. It doesn't matter where you'd break it too- any convenient location will do.

Of course, if you manage to get under remaining voltage somehow it will still be dangerous but it would be hard to do- you'd need to get inside another MC4 connector and then reach out to the other end of the unbroken part of the string and get yourself connected there as well. IMO at that point after so many efforts you'd deserve what is coming . What makes this way safe is that panels have 2 ends and all connected in series with closed connectors- to get inside MC4 you need to unplug it first breaking string yet again. There's just no exposed contacts there except in the terminal box.

You'll even be fine if someone would turn AC/DC disconnects back at the house as the string will still be broken. I always prefer to work if I can ensure no idiot can turn things back on ignoring warning signs. I saw it happened once- someone just came, took the sign off and turn the switch ON. Luckily person who was working saw it and was not touching anything at the moment. He expressed his opinion about that in a very colorful way .

[max2k]

Sorry to hear that.

IMO a fused "pass through" box at the array for each string would be a wise investment. A fault anywhere along your 6 strings from array to the building as you have it designed now will cause an arcing/blazing mess and shut down your entire production. Not worth the risk IMO.

OP would have unsplit wires coming from terminal box(es) at array all the way to the inverters There's just no chance for any arching along the way.

[DanS26]

OP would have unsplit wires coming from terminal box(es) at array all the way to the inverters There's just no chance for any arching along the way.

I'm thinking burrowing/chewing animals.....or how about freeze/thaw action....or how about digging or plowing.... a manufacturing defect......you get the picture.

[max2k]

I'm thinking burrowing/chewing animals.....or how about freeze/thaw action....or how about digging or plowing.... a manufacturing defect......you get the picture.

OP would need to put wires in SCH80 PVC conduit and dig the trench deep enough so that would help against most of that. Manufacturing defects (wire broken under insulation) can start arch and burn out entire run at the defect spot possibly damaging PVC conduit. Not sure how fuses would help in that case though- until it shorts out completely of course. While ominous nobody reported this kind of problem here yet so these must be extremely rare.

[diegodog]

Wire will be in conduit the entire run.

If I hit the line with the tiller or plough I would think there will be much bigger issues. I just assume I get crispy if I do it. It is not in a farming area so hopefully I don't do anything that outrageous but .....

[max2k]

Wire will be in conduit the entire run.

If I hit the line with the tiller or plough I would think there will be much bigger issues. I just assume I get crispy if I do it. It is not in a farming area so hopefully I don't do anything that outrageous but .....

Nothing will happen to you as what you're building is 'ungrounded' system meaning none of DC wires is tied to the ground. This also means your digging tool cutting the wire won't actually put current through your body to the ground as there's no return path for it. It might get sparky for a second though .

[DanS26]

The OP must be smiling now or else beating his head up against a wall......here we are recommending fused connections and/or Schedule 80 conduit buried 18 inches in solid rock (see post #1).........heck just lay that high voltage DC on top of the rocks in conduit of course.......no one will bother it........

[diegodog]

So here is a bit on the MSP placed on the inside for the barn. 200 amp main breaker at the top.

[diegodog]

The OP must be smiling now or else beating his head up against a wall......here we are recommending fused connections and/or Schedule 80 conduit buried 18 inches in solid rock (see post #1).........heck just lay that high voltage DC on top of the rocks in conduit of course.......no one will bother it........

HAHA!!

I was able to get about 1 foot down for the wire ditch!!!! Some sections I can get down a bit more. It will be shallow none the less. I ran ethernet/coax from the main house to the barn about 1000 feet away. Ran the entire thing in conduit even though the lines were direct bury. Seems too risky to just throw it in there. There are sections of that run which are only 1-2 inches down due to the ledge (bedrock). The ledge causes massive headaches for any type of construction. And makes every job complicated.

I originally tried going below the freeze line for the 10 piers (6.5 feet down) due to the heaving issues. Took about 6 months before I gave up on that dream. As one dream gets crushed it normally opens up a better situation. Hopefully these slabs will be able to heave quite a bit since they are all independent from each other aside from the wiring. This project has been horrible for me as I know enough to get into trouble each step of the way and then hit a brick wall.

Building the house and barn were cake compared to this. I didn't realize about the mess I have with the breaker box as well. Though all those empty slots were going to be the ticket. Nope! Just another brick wall!!!

Thanks again guys.

[DanS26]

OP......not to complicate an already complicated project....but are you aware or have investigated expansion joints for your long conduit run? Since your conduit will not be very deep you will need to take the freeze/thaw cycle into greater consideration. Big loops at the connections at least. Your electrician probably knows this but maybe not.

[Mike90250]

I would NOT put big loops in. Hell to pull wire through. Lay it in the trench, like a snake. If there is any curve in the bundle of PVC, alternate the bend, so you have a lazy S pattern in the trench, zig zags from left wall to right wall. Bed it in sand. Or follow local construction advice/practice

[DanS26]

I would NOT put big loops in. Hell to pull wire through. Lay it in the trench, like a snake. If there is any curve in the bundle of PVC, alternate the bend, so you have a lazy S pattern in the trench, zig zags from left wall to right wall. Bed it in sand. Or follow local construction advice/practice

Mike, I meant 4" loops at the connections in the inverters and J boxes at the array. Standard electrical practices in cold weather areas.

[diegodog]

Here is my "learned enough to be dangerous post of the day" Thank to Max and Tyab for getting me thinking on this track and learning a ton!

6 strings of panels. Each string is 451 volts 8.8 amps
SMA inverter (x3) 25A max out put on the AC side

We have the 25A x 3(inverters) = 75A * 1.25 for safety = 93.75A - 100 AMP breaker will be needed in the MSP

My MSP is 200A I multiply 1.2 x 200 and get 40A as the Max I can connect to the MSP which does not work (I need to do 100 AMP in the MSP) according to the above calculation.

Here is my question and the part I'm not getting.

My panels will put off a max AMP of 6 strings x 8.8A. That is 52.8 AMPS (at absolute full throttle).

Why would I double the amount needed up to 100 AMP for something that will max out and most likely never hit at 52.8 AMP. I can see leaving some safety up to 60 AMP but going to 100 AMP and crippling my MSP from 200A to 125A seems like a bad idea.

What am I missing?

If someone is on the side of follow the book go 100AMP can you please explain exactly the risk of how the 52.8 AMPS on the 60 AMP breaker causes disaster and how the 100 AMP breaker would perform better? Is there a scenario which you could throw out to help me see why one would go 100AMP

Thanks again!!!