Hybrid System , PV, Battery, Generator, ATS Confused Designer? Parallel feeders &ocpd

[Smart $]

Which I take to mean, "I'll argue about anything." I know this about you.

Not everything

The first drawing showed one SI per phase (to neutral) on a three phase system and three SB's phase to phase on the protected loads panel, which isn't a problem.

I know, but look at the manual when more than three SI's are used on a 3? system.

Where did the diagram come from? It appears to be made by and from SMA...????

 

[sandsnow]

In all fairness to sandsnow's perspective (to which I've only been taking the position of devil's advocate to stimulate the discussion), when SI's are 3?-connected, more than one per phase must connect to the system through a multicluster "box", and no more than one SI per phase per cluster. It seems if this multicluster interface is needed for more than one SI per phase on 3?, a similar "device" is needed for more than one SI per leg on split phase....

Another question I have is where the diagrams posted by the OP'er came from. I've been all over the website and cannot find any similar diagram depicting two SI's per leg on split phase system.

SMA sent us those drawings. They said they were not avail. on the website. Didnt say why. Send me a pm and i will send you the pdf

 

[Smart $]

SMA sent us those drawings. They said they were not avail. on the website. Didnt say why. Send me a pm and i will send you the pdf

PM sent.

An underlying point: there is no indication that I could find of being able to connect 4 SI's to a split phase system in the instructions... so its not covered by the UL listing.

 

[ggunn]

PM sent.

An underlying point: there is no indication that I could find of being able to connect 4 SI's to a split phase system in the instructions... so its not covered by the UL listing.

As an academic question, would there still be a problem if it were an off grid system with no AC input to the SI's from the grid or from a generator?

 

[Smart $]

As an academic question, would there still be a problem if it were an off grid system with no AC input to the SI's from the grid or from a generator?

If I may, from Sandsnow's perspective, no. Each SI would be considered a separate power source, not all that different from multiple PV inverters.

 

[GoldDigger]

If I may, from Sandsnow's perspective, no. Each SI would be considered a separate power source, not all that different from multiple PV inverters.

But a pure GT inverter is designed to operate completely independently and be synchronized solely by the grid input. That means that you only have to worry about load balancing and ampacity.
Multiple off-grid or hybrid inverters, on the other hand, need special interconnections to be able to operate in parallel as "separate power sources."

 

[sandsnow]

As an academic question, would there still be a problem if it were an off grid system with no AC input to the SI's from the grid or from a generator?

There are SMA drawings showing complete off grid use. It's a pain for me to post it. If you want it, send me a PM with your email.

Remember the Code applies regardless of grid status. Enforcement is another story. 690.1

 

[sandsnow]

If I may, from Sandsnow's perspective, no. Each SI would be considered a separate power source, not all that different from multiple PV inverters.

Right

 

[Smart $]

But a pure GT inverter is designed to operate completely independently and be synchronized solely by the grid input. That means that you only have to worry about load balancing and ampacity.
Multiple off-grid or hybrid inverters, on the other hand, need special interconnections to be able to operate in parallel as "separate power sources."

That's what is in question. Operating in parallel, with the grid being the power source for off-grid side loads when in grid mode, may not be part of the listing specification. Listing has to overide 240.8 to be used in parallel... or essentially identify each SI is to be considered a "black box".

 

[jaggedben]

... when SI's are 3?-connected, more than one per phase must connect to the system through a multicluster "box", and no more than one SI per phase per cluster. It seems if this multicluster interface is needed for more than one SI per phase on 3?, a similar "device" is needed for more than one SI per leg on split phase....

The last sentence is incorrect (see below). One SI can serve as the 'master' for 2 'slaves' in a 3? system or 3 'slaves' in a double split phase system. Controlling anything beyond that is simply beyond the SI's onboard capability, so that's why the multicluster is required.

there is no indication that I could find of being able to connect 4 SI's to a split phase system in the instructions... so its not covered by the UL listing.

I'm not sure how you missed it. Search the manual for "double-split phase" and you'll find the capability explicitly described on pg 16, and in several other locations with various specific instructions.

 

[Smart $]

The last sentence is incorrect (see below). One SI can serve as the 'master' for 2 'slaves' in a 3? system or 3 'slaves' in a double split phase system. Controlling anything beyond that is simply beyond the SI's onboard capability, so that's why the multicluster is required.



I'm not sure how you missed it. Search the manual for "double-split phase" and you'll find the capability explicitly described on pg 16, and in several other locations with various specific instructions.

You are correct.... especially that I missed it. There's even an illustration glaring me in the face as I write (page 21), and the informational note mentions using a multicluster box for additional units. :slaphead:

However, the problem is still as Sandsnow points out. The configuration illustrations, i.e. including the one's provide via email show the SI's connected directly to the load side of the transfer switch. So there is only one ocpd on the grid side for whichever source is connected. The proposed installation has one ocpd for each SI. Perhaps the answer is to power the four SI's with one two-pole breaker... :blink:

 

[TrickleCharge]

Has anyone encountered a 70A 4 pole siemens or murray breaker that would comply with 240.8? Again this is a residential application. Im guessing kind of like the 200A main that has 4 poles but I have never seen anything else in my 32 years of doing this (inside joke). However, when reading the requirements of 240.8 that states that individual circuit breakers shall not be connected in parallel THEN go over to 408.36 Ex 2 which states individual protection shall not be required for a panelboard protected on its supply side by 2 main circuit breakers having a combined rating not greater than that of the panelboard.......So what is it then? To go with 2 mains to supply the sub panel or to not go because of running the ocpd in parallel???? Any input?

 

[Smart $]

Has anyone encountered a 70A 4 pole siemens or murray breaker that would comply with 240.8?

No.

Here's a link to Murray breaker catalog pages...

http://w3.usa.siemens.com/powerdist...t-catalog/Documents/sf-11-sect-03-013-024.pdf

Again this is a residential application. Im guessing kind of like the 200A main that has 4 poles but I have never seen anything else in my 32 years of doing this (inside joke). However, when reading the requirements of 240.8 that states that individual circuit breakers shall not be connected in parallel THEN go over to 408.36 Ex 2 which states individual protection shall not be required for a panelboard protected on its supply side by 2 main circuit breakers having a combined rating not greater than that of the panelboard.......So what is it then? To go with 2 mains to supply the sub panel or to not go because of running the ocpd in parallel???? Any input?

The problem, as I understand it, isn't with the off-grid side.

Regarding grid side, can you install a two-pole 150A (see MPP type on page 3-19 of the linked catalogue), run a 140A+ feeder, then meet the tap rules of 240.21(B)(1) for taps not over 10ft in terminating to SI's?