Hawaiian Tie In

[jaggedben]

The wiring diagram in Post #11 would be a true supply side connection IF the breaker in the rightmost panel, which connects upstream of the main disconnect, were dedicated to PV only. If there are also loads downstream of that breaker is it not supply side.

It's probably a matter of semantics, but I disagree. The backfeed that is allowed at that connection is subject to the rules for supply side connections. For example if the service conductors were not rated for sum of the two service breakers, it would be non-compliant to backfeed more than their rating, even if all the load side aspects were compliant.

 

[GoldDigger]

It's probably a matter of semantics, but I disagree. The backfeed that is allowed at that connection is subject to the rules for supply side connections. For example if the service conductors were not rated for sum of the two service breakers, it would be non-compliant to backfeed more than their rating, even if all the load side aspects were compliant.

I may not be reading the schematic correctly, but it appears to me that there are loads as well as PV downstream of the isolated breaker at the right hand main. If that is the case, then the isolated breaker is just one of two main breakers and the PV connection is downstream of that main.
As I stated earlier, if there are no loads, only PV downstream of the isolated breaker, then it is a supply side connection.
A little more labeling on the schematic would help me.

 

[jaggedben]

I may not be reading the schematic correctly, but it appears to me that there are loads as well as PV downstream of the isolated breaker at the right hand main. If that is the case, then the isolated breaker is just one of two main breakers and the PV connection is downstream of that main.
As I stated earlier, if there are no loads, only PV downstream of the isolated breaker, then it is a supply side connection.
A little more labeling on the schematic would help me.

I don't think we're reading the diagram differently. It's how we're describing the rules. Again, in my opinion there are three connection points in series, and the breaker in the main is a supply side connection. It's also subject to Article 230 etc as a service disconnect, but the part of 705 that applies is the supply side section. I've had to argue this point in the past with AHJs who wanted to apply load side rules to MLO service panels. Generally 705 doesn't have that much additional to say about it that isn't covered in chapter 2, but the example I gave above is a possibility.

 

[GoldDigger]

I see what you are saying, and I think that my view is based on the fact that with an MCB panel with a load side connection to the bus of that panel that bus connection is the PV interconnection point.
Using your categorization the connection between the one and only MCB and the service wiring could be called a supply side connection. In some sense it is, but I do not know of anyone who would categorize that PV installation as having a supply side connection.

 

[Designer101]

That's not what Hawaiian Tie-in means to me. It means when you have a service panel that is just a main breaker, and a sub inside the house, you insert a new sub in between to create a place to interconnect. I suppose it could just as well mean what you're describing since in any case it's slang and I have no idea where it comes from.

Anyway...

What you're describing is a perfectly valid approach, but it has nothing to do with anything being 'supply side'. It is valid because the panel satisfies 705.12(B)(2)(3)(c).* (The use of a subfeed kit instead of a breaker is a bit of a loop hole that is addressed in the 2020 NEC, but as long as there isn't an additional source in the main it's not much of an issue.)

*2017 NEC reference. 2020 numbering is different.

 

[Designer101]

Ben,

I tried to connect 125A of solar into main panel by relocating all loads into sub panel by feeding through lug kit 4/0.
i tried to send this for electrical engineer for stamp but this is what i received as a his redlines. i even referenced the code section there
I am not sure how to convince the EE.

 

[wwhitney]

The markup comments are wrong about "opposite end from main breaker". And I believe on the #2 wire size--it has a 75C ampacity of 115A, so if the calculated "load" does not exceed 115A, it can be protected by a 125A breaker (next size up rule). (2) 10 kW inverters would be 83A continuous @ 240V, and after 125%, that's 104A < 115A. So I believe that's OK.

However, he's not wrong on the 70A comment given the arrangement you've drawn and the current NEC rules. They are unnecessarily strict for the case of two breakers/connections (other than the main) in a panel, and I submitted a PI that would have the effect of loosening them.

So under the current rules, you have to use the "connection to a feeder" allowance to do what you want. Your main panel has a 200A main breaker, and either feed through lugs or a 200A branch breaker to supply a 200A feeder. You then splice that 200A feeder (possibly within the main panel, or a separate enclosure) into two feeder segments--one going to your new load panel, which needs a 200A main breaker, and one going to your generation panel (or a disconnect first, if local regulations require a separate disconnect).

I believe the feeder segment to the generation panel (or disconnect) could be #1 Cu conductors landing on a 125A main breaker in that panel, if you can comply with the 25' tap rules. My recollection is that for taps, you can't use the next size up rule. If using a separate disconnect with OCPD, then from the disconnect to the generation panel could certainly be #2 Cu.

Cheers, Wayne

 

[jaggedben]

I agree with Wayne. It's a subtle point that using subfeed lugs to a panel with a main breaker is really a loophole in the 'sum of all breakers' rule ( 705.12(B)(2)(3)(c)). While one could make a legalistic argument for your design under the 2017 NEC, it's really violating the rule in spirit as far as electrical theory goes. And further, the 2020 NEC added language about subfeed lugs that makes your design explicitly prohibited.

And while a further understanding of electrical theory may lead one to agree with Wayne that the rules are unecessarily strict, for now those are the rules.

 

[Designer101]

The markup comments are wrong about "opposite end from main breaker". And I believe on the #2 wire size--it has a 75C ampacity of 115A, so if the calculated "load" does not exceed 115A, it can be protected by a 125A breaker (next size up rule). (2) 10 kW inverters would be 83A continuous @ 240V, and after 125%, that's 104A < 115A. So I believe that's OK.

However, he's not wrong on the 70A comment given the arrangement you've drawn and the current NEC rules. They are unnecessarily strict for the case of two breakers/connections (other than the main) in a panel, and I submitted a PI that would have the effect of loosening them.

So under the current rules, you have to use the "connection to a feeder" allowance to do what you want. Your main panel has a 200A main breaker, and either feed through lugs or a 200A branch breaker to supply a 200A feeder. You then splice that 200A feeder (possibly within the main panel, or a separate enclosure) into two feeder segments--one going to your new load panel, which needs a 200A main breaker, and one going to your generation panel (or a disconnect first, if local regulations require a separate disconnect).

I believe the feeder segment to the generation panel (or disconnect) could be #1 Cu conductors landing on a 125A main breaker in that panel, if you can comply with the 25' tap rules. My recollection is that for taps, you can't use the next size up rule. If using a separate disconnect with OCPD, then from the disconnect to the generation panel could certainly be #2 Cu.

Cheers, Wayne

well using lug kit didnt work as the ahj thinks it will viloate the UL listing though i was able to get it through electrical stamp connecting 200A SUB PANEL THRUGH LUG KIT.I cant derate any of the two main breaker so this is a problem already.
Using load side tap is a good idea I saw into code section the feeder taps per 705.12(B)(2)(1)(B), can we do that using main disconnect instead of 25 ft or 10 ft tap rules?( the language says AN OVERCURRENT DEVICE ON THE LOAD SIDE OF THE POWER SOURCE CONNECTION SHALL BE RATED NOT GREATER THAN THE AMPACITY OF THE FEEDER). can I use 400A rated load center protected by 200A main breaker and two breakers one for Solar 125A and one for existing feeder breaker 200A into NEW 400 A RATED SUB PANEL.

 

[B rye]

I am running into a somewhat similar situation in SDGE CA. Solaredge is saying I can avoid an MPU by using 705.12(b)(3)(3) on a 100/100 center fed panel needing 60A of backfeed by relocating all loads to a new sub and adding a 100 feeder to said sub. He is saying they have gotten it approved with another client in Utah. I just think it may be hard to get SDGE on board with it. Any insight would be greatly appreciated.

 

[jaggedben]

well using lug kit didnt work as the ahj thinks it will viloate the UL listing though i was able to get it through electrical stamp connecting 200A SUB PANEL THRUGH LUG KIT.I cant derate any of the two main breaker so this is a problem already.
Using load side tap is a good idea I saw into code section the feeder taps per 705.12(B)(2)(1)(B), can we do that using main disconnect instead of 25 ft or 10 ft tap rules?( the language says AN OVERCURRENT DEVICE ON THE LOAD SIDE OF THE POWER SOURCE CONNECTION SHALL BE RATED NOT GREATER THAN THE AMPACITY OF THE FEEDER). can I use 400A rated load center protected by 200A main breaker and two breakers one for Solar 125A and one for existing feeder breaker 200A into NEW 400 A RATED SUB PANEL.

Can't read all your notes because the picture resolution got shrunk, but as far as I can see it's fine by the electrical code. I don't think you need the fused disco between the 400A sub and the solar sub, unless that's a utility requirement or it's your only accessible disco for rapid shutdown.

BTW, this design is what I learned to call a 'Hawaiian Tie-In'. Adding a sub in series with an existing feeder.

 

[jaggedben]

I am running into a somewhat similar situation in SDGE CA. Solaredge is saying I can avoid an MPU by using 705.12(b)(3)(3) on a 100/100 center fed panel needing 60A of backfeed by relocating all loads to a new sub and adding a 100 feeder to said sub. He is saying they have gotten it approved with another client in Utah. I just think it may be hard to get SDGE on board with it. Any insight would be greatly appreciated.

Why would SDGE have any say about it? PG&E wouldn't. This is local AHJ stuff. If the service is rated 100A you should be able to backfeed 60A. Under 30kW in CA the utility can't really refuse to interconnect.

 

[B rye]

Why would SDGE have any say about it? PG&E wouldn't. This is local AHJ stuff. If the service is rated 100A you should be able to backfeed 60A. Under 30kW in CA the utility can't really refuse to interconnect.

In my experience SDGE seems to give out NEM rejection for anything they don’t like on the one line you provide with the Application.

 

[jaggedben]

In my experience SDGE seems to give out NEM rejection for anything they don’t like on the one line you provide with the Application.

Sounds like something that should be taken up with the CPUC. But I don't know the ins and outs of the relevant regulations, or if it's been tried.

 

[1solarrae]

Does anyone have any pictures of what this looks like done?