PV System Interconnection

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INGMRS

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Hello,


I'm doing the interconnection design of a 1200A photovoltaic system, the customer has a relatively old 2000A switchboard for the main disconnect medium, which is also 2000A.


In my design, I am using 5 inverters with an OCPD of 225A each, and they are connecting in a switchboard of 2000A, the feeder of this control panel has been interconnected with the panel of my client.


I have two doubts:


1. Is it allowed to interconnect my pv system to the main breaker of my client?


2. As I understand, I have to design my pv system up to 1.20% of the main breaker, right?


The issue is that the switchboard of my client is of 2000A, that means that I can connect only a PV system of 400A. then, I think that I have to change the switchboard of client from 2000A to 3000A with a 2000A main breaker, right?


What do you think about this, do you have any recommendation?


Thanks, and regards.
 
INGMRS said:
Hello,


I'm doing the interconnection design of a 1200A photovoltaic system, the customer has a relatively old 2000A switchboard for the main disconnect medium, which is also 2000A.


In my design, I am using 5 inverters with an OCPD of 225A each, and they are connecting in a switchboard of 2000A, the feeder of this control panel has been interconnected with the panel of my client.


I have two doubts:


1. Is it allowed to interconnect my pv system to the main breaker of my client?


2. As I understand, I have to design my pv system up to 1.20% of the main breaker, right?


The issue is that the switchboard of my client is of 2000A, that means that I can connect only a PV system of 400A. then, I think that I have to change the switchboard of client from 2000A to 3000A with a 2000A main breaker, right?


What do you think about this, do you have any recommendation?


Thanks, and regards.
Click to expand...
My recommendation is that you get the relevant NEC codebook and become very familiar with section 705.12. all your answers are in there.
 
INGMRS said:
Hello,


I'm doing the interconnection design of a 1200A photovoltaic system, the customer has a relatively old 2000A switchboard for the main disconnect medium, which is also 2000A.


In my design, I am using 5 inverters with an OCPD of 225A each, and they are connecting in a switchboard of 2000A, the feeder of this control panel has been interconnected with the panel of my client.


I have two doubts:


1. Is it allowed to interconnect my pv system to the main breaker of my client?


2. As I understand, I have to design my pv system up to 1.20% of the main breaker, right?


The issue is that the switchboard of my client is of 2000A, that means that I can connect only a PV system of 400A. then, I think that I have to change the switchboard of client from 2000A to 3000A with a 2000A main breaker, right?


What do you think about this, do you have any recommendation?


Thanks, and regards.
Click to expand...

You should be looking at a supply side connection. Hopefully the existing switchboard easily allows it.
 
INGMRS said:
In my design, I am using 5 inverters with an OCPD of 225A each, and they are connecting in a switchboard of 2000A, the feeder of this control panel has been interconnected with the panel of my client.
Click to expand...
Sounds like the connection has already been made? Can you describe how and where the connection has been made?

The issue is that the switchboard of my client is of 2000A, that means that I can connect only a PV system of 400A. then, I think that I have to change the switchboard of client from 2000A to 3000A with a 2000A main breaker, right?
Click to expand...

not sure where you are getting 400 for the max.

Perhaps a one line diagram would help.
 
INGMRS said:
Hello,


I'm doing the interconnection design of a 1200A photovoltaic system, the customer has a relatively old 2000A switchboard for the main disconnect medium, which is also 2000A.


In my design, I am using 5 inverters with an OCPD of 225A each, and they are connecting in a switchboard of 2000A, the feeder of this control panel has been interconnected with the panel of my client.


I have two doubts:


1. Is it allowed to interconnect my pv system to the main breaker of my client?


2. As I understand, I have to design my pv system up to 1.20% of the main breaker, right?


The issue is that the switchboard of my client is of 2000A, that means that I can connect only a PV system of 400A. then, I think that I have to change the switchboard of client from 2000A to 3000A with a 2000A main breaker, right?


What do you think about this, do you have any recommendation?


Thanks, and regards.
Click to expand...

The rating of the inverter OCPD is not the number that counts, it's 125% of the maximum inverter output current, but assuming they are the same, (5)(225A) = 1125A. If your panel and panel OCPD are both rated at 2000A, as I see it your only options are a) downsize the panel main breaker to less than 1275A and land your PV on a 1200 breaker in the panel, or b) connect your PV on the supply (line) side of the main breaker.

There is one more option which is probably moot - you could leave the main breaker at 2000A, restrict the load breakers in the panel not to exceed 800A in total, and land on a 1200A breaker, but if you could do that you could also use option a) which would be less restrictive on the load breakers.
 
INGMRS said:
Hello,

This is a simple diagram of the interconnection.

Regards,
View attachment 21676
Click to expand...


There are a number of problems here. Please read 705.12 for load side connection rules. You cannot just tap the load side of the service disconnect unless everything on the load side of it is rated for the total current from the grid plus the maximum output of your inverters. As drawn you are feeding 3200A to a 2000A panel.

Your best option IMO is to tap the service conductors between the grid and the service disconnect for your PV interconnection.
 
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As several people have said, your best choice is a supply-side interconnection. The way you are asking your question seems to indicate you might not be that experienced with PV and the size system you are dealing with is not where you want to learn. Best to bring in someone to help you out.

I have to point out though that it seems like a lot of people still think that the 120% rule applies to switchboards and it has not since the 2014 NEC. It only applies to panelboards. Load side interconnections to switchboards can interconnect PV up to the rating of the switchboard with the appropriate documentation to show that the load will not exceed the rating of the switchboard and that the AIC rating is not exceeded. Don't get stuck on the 120% rule when dealing with switchboards.
 
pv_n00b said:
As several people have said, your best choice is a supply-side interconnection. I have to point out though that it seems like a lot of people still think that the 120% rule applies to switchboards and it has not since the 2014 NEC. It only applies to panelboards. Load side interconnections to switchboards can interconnect PV up to the rating of the switchboard with the appropriate documentation to show that the load will not exceed the rating of the switchboard and that the AIC rating is not exceeded. Don't get stuck on the 120% rule when dealing with switchboards.
Click to expand...
(Isn't that changing in 2020 though, most likely?)
 
jaggedben said:
(Isn't that changing in 2020 though, most likely?)
Click to expand...

Based on the last draft I saw it is changing for the better. In the 2017 NEC it's not called out how to do a load side interconnection in a switchboard, the NEC just says the 120% rule only applies to panelboards and leaves everything else out. In 2020 it looks like it's going to have a provision that allows load side interconnections to equipment to be done under engineering supervision and not have to comply with any of the usual load side interconnection rules. So the rules are going to be there if people want to apply them but if they can tag in an engineer then the engineer can do whatever they want as long as it does not overload the equipment.
 
pv_n00b said:
I have to point out though that it seems like a lot of people still think that the 120% rule applies to switchboards and it has not since the 2014 NEC. It only applies to panelboards. Load side interconnections to switchboards can interconnect PV up to the rating of the switchboard with the appropriate documentation to show that the load will not exceed the rating of the switchboard and that the AIC rating is not exceeded. Don't get stuck on the 120% rule when dealing with switchboards.
Click to expand...

:thumbsup:

But...... could it be argued that 2014 705.12(D)(2)(1) applies to the "feeder bus" in a switchboard? (dont have 2017 still, so not sure if that language has changed).
 
electrofelon said:
:thumbsup:

But...... could it be argued that 2014 705.12(D)(2)(1) applies to the "feeder bus" in a switchboard? (dont have 2017 still, so not sure if that language has changed).
Click to expand...

People can argue anything in the NEC, that's what makes it such fun! The term "bus" is not used in (1) and the term "feeder bus" is not used in the NEC. But if (3) applies to busbars then do you have to apply (1) and (3) to everything that has a busbar? Also If a busbar is a feeder then is any connection also a tap and fall under (2)? Personally, I don't consider conductors inside listed equipment to be feeders, and most AHJs seem to agree. It causes too many problems. The only time I see people try to make a busbar a feeder is when they want to apply the feeder tap rules to a busbar tap circuit.
 
pv_n00b said:
People can argue anything in the NEC, that's what makes it such fun! The term "bus" is not used in (1) and the term "feeder bus" is not used in the NEC. But if (3) applies to busbars then do you have to apply (1) and (3) to everything that has a busbar? Also If a busbar is a feeder then is any connection also a tap and fall under (2)? Personally, I don't consider conductors inside listed equipment to be feeders, and most AHJs seem to agree. It causes too many problems. The only time I see people try to make a busbar a feeder is when they want to apply the feeder tap rules to a busbar tap circuit.
Click to expand...

Im with you, just throwing it out there....
 
pv_n00b said:
As several people have said, your best choice is a supply-side interconnection. The way you are asking your question seems to indicate you might not be that experienced with PV and the size system you are dealing with is not where you want to learn. Best to bring in someone to help you out.

I have to point out though that it seems like a lot of people still think that the 120% rule applies to switchboards and it has not since the 2014 NEC. It only applies to panelboards. Load side interconnections to switchboards can interconnect PV up to the rating of the switchboard with the appropriate documentation to show that the load will not exceed the rating of the switchboard and that the AIC rating is not exceeded. Don't get stuck on the 120% rule when dealing with switchboards.
Click to expand...

Hello pv_n00b,

Thanks for your response,


The way like i am asking is maybe because it is not my first leanguage and i cant communicate what i want assertively, and probably as you said my experiences with PV systems are not so accurate, that is the reason that i am asking in this forum to the experts in the code rules.
I will have a meeting next monday with people with more evident experience in this area, maybe i can get another point of view.


For retrofeed of the original doubt, In the next drawing you can see the power connection of my client:

original diagram.jpg

Before to ask in this forum i have talked with people from eaton, because the switchboard of my client is from them, they made a proposal, they propose to install a new switchboard to collect all the inverters and a new structure attached to the switchboard of my client to interconnect the PV System to the electrical system of the client. Something like this:

eaton proposal.jpg

I Had doubts about the interconnection and rating capacity of the switchboards, but i was not clear with the 120% rule, and that was the reason to open thread.


I was thinking that one option was to change the switchboard of my client from 2000A to 3000A of capacity.


Regarding the capacity of the system, my client has a maximum demmand of 800kW (according to one year measurement each15 minuts demmand data), so its maximum consume of current is about 963A for 480V, much less than the 2000A of OCPD capacity.


Regards.
 

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  • eaton proposal.jpg
    eaton proposal.jpg
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How is the connection to be made? It's hard to read that sketch but looks like you intend to connect with a 1200 amp breaker? Has it been verified that there is space for this breaker? Keep in mind switchboards often have multiple ampacity busbars so you would need engineering supervision.
 
pv_n00b said:
Based on the last draft I saw it is changing for the better. In the 2017 NEC it's not called out how to do a load side interconnection in a switchboard, the NEC just says the 120% rule only applies to panelboards and leaves everything else out. In 2020 it looks like it's going to have a provision that allows load side interconnections to equipment to be done under engineering supervision and not have to comply with any of the usual load side interconnection rules. So the rules are going to be there if people want to apply them but if they can tag in an engineer then the engineer can do whatever they want as long as it does not overload the equipment.
Click to expand...

Is there a clear line of demarcation between panelboards and switchboards? It seems to be a continuum to me.
 
electrofelon said:
How is the connection to be made? It's hard to read that sketch but looks like you intend to connect with a 1200 amp breaker? Has it been verified that there is space for this breaker? Keep in mind switchboards often have multiple ampacity busbars so you would need engineering supervision.
Click to expand...

Hello,

The proposal of eaton ( they told me it has been implemmented in other proyects) is something something like this:

structure to interconnect switchboard aftermarket.JPG

Regards,
 
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