Noob needs more help (pics inside)

[max2k]

OP really needs a line side tap.

How that would be done in practice? I wonder if the tap wires could run directly into AC disconnect combiner bus as it already has breakers for each inverter, just to reduce number of panels/subpanels/etc on the wall.

[max2k]

...
Very doubtful.
I wouldn't say it's impossible, but it's really unlikely. I'd be pissed at the electrician if they did a 200A main breaker in a 125A bus-bar panel.
(and wonder how the heck it happened)
...

what about OP middle screenshot from msg #25? If that is his MSP and I'm reading it correctly it is 125A panel.

[sensij]

what about OP middle screenshot from msg #25? If that is his MSP and I'm reading it correctly it is 125A panel.

Looks like 225 A to me, based on the lug ratings. I don't think the middle picture is telling us anything about the bus bar.

[sensij]

IF you have a 225A bus bar with a 200A main breaker you could have a larger main breaker.
225A * 1.2 = 270A
270A - 100A = 170A.
There isn't 170A main breaker, so you'd go with a 150A (*IF* you have a 225A bus bar)

2014 NEC uses 125% of inverter output rating for the 120% rule calculation, not the breaker size as previous cycles required. For 225 A bus, that means a 175 A main breaker could be ok, instead of dropping all the way to 150.

[max2k]

2014 NEC uses 125% of inverter output rating for the 120% rule calculation, not the breaker size as previous cycles required. For 225 A bus, that means a 175 A main breaker could be ok, instead of dropping all the way to 150.

Good to know, thank you. At least something more realistic as using already increased breaker rating to rate bus bar was kind of ridiculous - that 25% 'head room' in breaker rating was not going to heat the bus bar anyway.

[ButchDeal]

How that would be done in practice? I wonder if the tap wires could run directly into AC disconnect combiner bus as it already has breakers for each inverter, just to reduce number of panels/subpanels/etc on the wall.

That is how we usually set them up.

[DanS26]

OP you should have a "load analysis" performed before downsizing the main breaker. If 150 amps is not enough then a line side tap (if allowed) could be installed.

You stated the meter and first disconnect is 60 ft away from the main service panel in the same building. You also stated that the main service panel has a ground rod driven. Are there two ground rods driven on opposite corners of this building? If so the rod at the main service panel which is really a sub panel should be removed.

[diegodog]

You guys are awesome!!

I spent the entire night trying to find documentation on what my bus bar rating was and couldn't find that. Is there a way other than looking at the sticker (I'll get more pictures) to see what I have? I see 100A, 125A, 200A on the stickers. Nothing that clearly said bus bar rating = x. Any particular place I take get a close up photo of that would help identify it for sure. Would be very happy if Sensij was correct and it was 225A.

I'm in a unique situation where there are 0 inspectors. There is 1 electrician. Closest Walmart is 100 miles away. So there are no issues in that respect. There is simply an old lady down at a small building that you send your property tax check to. I have yet to find a town without the property tax lady I have to visit once a year.

It looks like I downgrade the MSP or I can do the line side tap. I'll need to study up on what exactly the line side tap is and see if I grasp it.

Going back down to pre-school level again if you guys don't mind.

Can I use a simple junction box to make the splices between the PV wire and the THWN-2? Do I need anything fancy in there? I assume I need more than wingnuts and electrical tape.

Thanks again guys.

[max2k]

You guys are awesome!!

I spent the entire night trying to find documentation on what my bus bar rating was and couldn't find that. Is there a way other than looking at the sticker (I'll get more pictures) to see what I have? I see 100A, 125A, 200A on the stickers. Nothing that clearly said bus bar rating = x. Any particular place I take get a close up photo of that would help identify it for sure. Would be very happy if Sensij was correct and it was 225A.

sensij is most likely correct but it would help if you could post more pics with your panel stickers at better angle.

I'm in a unique situation where there are 0 inspectors. There is 1 electrician.

there are 2 possible issues here:

- safety. While some parts of the Code may sound draconian it also reflects results of analysis of the previous problems so when making compromise you need to understand possible consequences. One problem with the Code is it tries to address every possible case out there and sometimes I think it makes things more complicated than they need to be. Code authors rightfully assume that the rules won't be understood, they just need to be followed. Like in your case- what bad could happen if you leave 200A main breaker and feed your PV from another end of the MSP busbar through 100A breaker? I'm aware of 120% limit but in this arrangement I don't see any part of bus bar to get under current load above 200A, ever. Any load can only be connected between those breakers and as such the current partially would come from main breaker side of bus bar and another portion of it - from PV breaker side, there won't be place on the busbar where they'd flow together. Given that load 'connections' to busbar are made through multiple breakers between 2 'source' breakers they will be spreading the total load on the busbar even further.

The Code though needs to assume nothing and prevent case where someone would actually try to feed some other subpanel with 300A breaker off the MSP busbar where at the point of contact the total 275A current will exceed busbar rating above safe limit. I possibly can be missing some other scenario here so hopefully other members would be able to come up with one where this would be a problem besides not being up to Code.

- how are you going to deal with POCO? They usually use inspections as the means to ensure the install was done up to the Code so they don't have to come out and look for themselves. Since you really need for your POCO to recognize your install and update your billing settings (so you could take advantage of net metering) I wonder how this will be handled in your case.

Can I use a simple junction box to make the splices between the PV wire and the THWN-2? Do I need anything fancy in there? I assume I need more than wingnuts and electrical tape.

I'd try to find something with the terminals/bolts rated for outdoor use and not just splices. I'd not use electrical tape for insulation, it doesn't last, especially outdoors. You want to build your system once and forget about it, not to fix some bad connections every 3 months.

[diegodog]

I will try to grab more pictures tonight with better shots of the MSP and stickers. I've been scanning online and if I had to guess I would say the bus bar is 200AMP. But that's simply a guess.

Yeah I wish the code book had some pretty pictures with my exact set up with a step by step guide. The MSP panel issue I'm running into was unexpected. I thought it was as easy as 3x 30 AMP double pole breakers. LOL!! I also get the feeling once you have done this a few times its in actuality somewhat simple. Its that first go around that is the problem and all those little nagging questions that slow things down like "Hey you can't hang those the electricity has no where to go..", Can I just wing nut it?

As you can imagine there are not many people around here. The electrician is a guy named Bob. He works with no shirt on no matter the weather, smokes about a pack an hour and leaves one to wonder if he works up here due to no inspections. I will say though the barn has had no fires or explosions due to his previous work so that's a relief! I would assume this is not that complicated for a professional electrician but I want to have a general idea of what's going on as my family works in the barn.

The electric company told me "we don't care what you do on your side we only care about our side" I'm not originally from around here so the answer was surprising but I didn't push it as I like the freedom to blow myself up if I so choose so I support the electric company in allowing me to do that if I want to. I assume they would place their meter out there along with the disconnect that's currently there and drive off. They never inspected anything other than outside at the meter when the main service was brought in. It surreal almost after dealing with big city rules in the past. I know I'm out my league here so I would never even think about hooking any of this up but I want to know what Bob is doing at all times as well. The less Bob touches the better! I just want him for the dangerous parts!!

Yeah I agree on going a bit further and doing a nice junction box.

Hopefully I have some pictures and data sheets out here on this panel I have in the next 24hrs or so.

Also excited to watch some videos and do some reading on the Tap ButchDeal is talking about. Sounds fun and dangerous. Sounds like maybe a 2nd panel box and a piece of rebar connecting the two would do the trick!

Was going to paint the tops of the PT wood frames today to put the first layer in between the cooper in the wood and the aluminum frames but we got rain! The EPDM that I'm placing on top of the painted wood will be here this weekend. Once I find some decent junction boxes hopefully this part can go quickly.

Thanks again!

[diegodog]

Here is the product data sheet for the MSP.

[sensij]

Here is the product data sheet for the MSP.

There you go. 200 A, so 7700 W inverter max if you leave the 200 A main breaker. You'd have to drop all the way to a 125 A main to install 3 x 6 kW inverters. A pair of 7.7 kW inverters would have been reasonably well matched to those panels, and would have been ok with 150 A main.

Looks like line side tap is probably the way to go for you, if you have access to the conductors between the meter and the panel.

[max2k]

There you go. 200 A, so 7700 W inverter max if you leave the 200 A main breaker. You'd have to drop all the way to a 125 A main to install 3 x 6 kW inverters. A pair of 7.7 kW inverters would have been reasonably well matched to those panels, and would have been ok with 150 A main.

Looks like line side tap is probably the way to go for you, if you have access to the conductors between the meter and the panel.

just to satisfy my curiosity - have you seen anywhere explanation why PV cannot be simply fed to the side of the busbar opposite to the main breaker? IMO such connection would never exceed 200A busbar rating all the way up to 200A PV output even with 200A main breaker in place.

If that doesn't present any danger OP could just install that Midnight AC Disco/combiner next to his MSP, wire its output to the end of busbar and would be done with this interconnect dilemma.

[sensij]

just to satisfy my curiosity - have you seen anywhere explanation why PV cannot be simply fed to the side of the busbar opposite to the main breaker? IMO such connection would never exceed 200A busbar rating all the way up to 200A PV output even with 200A main breaker in place.

This is only true if the sum of the load breakers does not exceed 200 A. Usually, the sum of the breakers is higher since the loads aren't all concurrent, but crucially, if all the loads did fire off at once, the main breaker should protect the panel. Since the load side of the equation isn't designed to respect the 200 A bus-bar rating, it means the source side must.

[max2k]

This is only true if the sum of the load breakers does not exceed 200 A. Usually, the sum of the breakers is higher since the loads aren't all concurrent, but crucially, if all the loads did fire off at once, the main breaker should protect the panel. Since the load side of the equation isn't designed to respect the 200 A bus-bar rating, it means the source side must.

sure, let's say we have 4x 100A load breakers installed between 200A PV output connection and 200A main breaker on some abstract system. If they all 100 A loads consume at full rating 200A PV out would go to the closest pair and 200A from main breaker- to the pair closest to it. I'm having trouble to picture where along the busbar more than 200A would flow. In my mind the worst case would be single 400A breaker as it would at least need 400A rated lugs to connect to the bus bar.