Paralleled Output to (1) AC PV DISCONNECT from (2) AC PV INVERTER OUTPUT COMBINERS

[Pressure]

I am designing a system, that will require (2) AC PV Inverter Output Combiners. Each combiner will be rated at 800A with a 800A Main OCPD, and have 752A at the continuous use rating. I would like to then parallel the output of each combiner to a single 1600A Fused AC PV Disconnect. Each Combiner will require (3) Sets of [(3) 400kCMIL AL and (1) #1/0 AWG EGC CU in 2.5" Conduit to the 1600A AC PV Disco.

The question is in regard to the paralleling of the (2) power sources and their distances from each other. I am calculating a 2.02V drop @ 0.42% for the first combiner, and a 5.79V drop @ 1.21% for the second combiner. I do not believe this violates any paralleled conductor rules, but I could be wrong. Can I potentially increase the conductor size of the second combiner to bring it closer to the Vdrop of combiner 1, or do I need to have both combiners next to each other and have the same size and length of conductors for each?

Any insight into best practices for this situation would be appreciated. Thanks.

 

[ggunn]

Parallel sets of conductors must be connected to each other at both ends, so a difference in voltage drop between the two output circuits before they are combined is not relevant.

 

[Pressure]

Thank you for verifying. Greatly appreciated.

 

[wwhitney]

If I understand your one-line diagram correctly, you have no parallel conductors. Parallel conductors are electrically connected to each other at both ends.

In grid-tied operation, each inverter will just sync to the grid voltage it sees at its terminals, which will be the grid voltage at the main AC disconnect plus whatever voltage rise occurs on the particular path to that inverter. It doesn't matter if one group of inverters sees a voltage that is 4V higher than another group of inverters; all that matters is that each inverter sees a voltage within its operation window.

Cheers, Wayne

 

[electrofelon]

Make sure you meet an applicable tap rule and any article 705 modification to it.

 

[ggunn]

Make sure you meet an applicable tap rule and any article 705 modification to it.

With a system that big it's unlikely that it will be under 705.12.

 

[electrofelon]

With a system that big it's unlikely that it will be under 705.12.

Sorry we are still on the 2017 here. But still, even if it's a supply side connection, there are still load side rules that may apply.

 

[Pressure]

Would you all like to know what I'm up against? I'm in preliminary for the system, and working on the design.

I have an (E) 3000A Siemens SB3 Switchboard with a 3000A Main OCPD. It is being fed by (8) Sets of [(4) 500 MCM in 4" Conduit] I have reached out to Siemens, but that was last Friday. I am looking to see if I can add (4) Lugs to each phase for a Supply-Side Connection with (4) sets of 600 MCM. We will see what their engineers say about that option. It looks like the bussing could handle it, but that's not my call. This falls under 2023 NEC 705.11(C)(2) Existing Equipment. 2023 really adds a bit of clarity to the Supply -Side Connections.

My first request was to the utility to see if there was a possibility of landing in the (E) XFMR. Unfortunately they only allow a max 8 sets of conductors on the secondary.

The last option that I hinted at to the utility was to bring in a new XFMR just for the PV and backfeed the med voltage lines. I don't hold out high hopes for that one.

 

[ggunn]

The last option that I hinted at to the utility was to bring in a new XFMR just for the PV and backfeed the med voltage lines. I don't hold out high hopes for that one.

Unless the site is metered on the MV side of their transformer, they are unlikely to approve it unless they have provisions for a Feed In Tariff (FIT) connection to the grid.

 

[electrofelon]

Would you all like to know what I'm up against? I'm in preliminary for the system, and working on the design.

I have an (E) 3000A Siemens SB3 Switchboard with a 3000A Main OCPD. It is being fed by (8) Sets of [(4) 500 MCM in 4" Conduit] I have reached out to Siemens, but that was last Friday. I am looking to see if I can add (4) Lugs to each phase for a Supply-Side Connection with (4) sets of 600 MCM. We will see what their engineers say about that option. It looks like the bussing could handle it, but that's not my call. This falls under 2023 NEC 705.11(C)(2) Existing Equipment. 2023 really adds a bit of clarity to the Supply -Side Connections.

My first request was to the utility to see if there was a possibility of landing in the (E) XFMR. Unfortunately they only allow a max 8 sets of conductors on the secondary.

The last option that I hinted at to the utility was to bring in a new XFMR just for the PV and backfeed the med voltage lines. I don't hold out high hopes for that one.

Is there a metering section in the switchboard or is it metered at the transformer? Hopefully Siemens will be helpful in getting you the correct number of terminations. There is the possibility of adding stacking lugs, lugs to the other side (if not already done), and stuff like that which is IMO is perfectly fine, but others will say nanny state stuff like you can only use lugs officially approved by the manufacturer. Another option is to use an oversized 12 port polaris connector and "pass thru" the 8 conductors, which leaves you 4 for the PV, IPLD750-12 should do it (but confirm cable OD).