Looking for interconnection options

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Leviathan

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Arizona
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Solar Operations
Hi All,
I'm typically used to designing small residential systems (~5-20kW) and I've been tasked with something that I'm unfamiliar with. I need to install a 35kW system and this customer has a 400A switchboard. I'm looking for advice from people who are more experienced as to how you'd approach a job like this and, particularly, the best interconnection method. We would typically install a 400A solar-ready panel for something like this but, as it stands now, I don't believe that's an option. The customer has 2x200A panels. Thanks, in advance for any information or advice. Like I said, this is foreign territory for me. I can provide additional information if it would be helpful.

Screenshot 2022-03-12 145223.png
 
I suck at PV but I believe you can do a line side tap. BTW, I sometimes answer questions I don't know the answer to because, for some reason, when someone else sees a response they are more likely to reply. LOL
 
As these things go that's a pretty good existing setup, giving you potential options fo supply side or load side taps. That said, there's a few additional thing's we need to know.

First, what is the actual continuous current output of the inverters? If 160A or less, you could consider a load side tap. If more it needs to be lineside. The code does not care about a kW rating, especially if that's DC.

Second, do the remote panels fed by this one already have main breakers at them? If yes, that simplifies the load-side option, as otherwise you'd need to install overcurrent protection after your tap.

Finally, what's the deal with the two sets of conductors coming off the fuse-block on the right? Is that a proper parallel conductor installation? If not, you might want to fix that before inviting any inspector to look at it.
 
jaggedben said:
As these things go that's a pretty good existing setup, giving you potential options fo supply side or load side taps. That said, there's a few additional thing's we need to know.

First, what is the actual continuous current output of the inverters? If 160A or less, you could consider a load side tap. If more it needs to be lineside. The code does not care about a kW rating, especially if that's DC.

Second, do the remote panels fed by this one already have main breakers at them? If yes, that simplifies the load-side option, as otherwise you'd need to install overcurrent protection after your tap.

Finally, what's the deal with the two sets of conductors coming off the fuse-block on the right? Is that a proper parallel conductor installation? If not, you might want to fix that before inviting any inspector to look at it.
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The continuous pull is going to be 120A or less. And yes, the panels all have main breakers on them. Also, after taking a look at the photos I have, it seems that there are actually 2x 125A panels connected to the right fuse-block :confused:. I appreciate your quick reply and insight. It's more valuable than you realize.
 
One option would be to replace the lugs on the load side of the meter with triple lugs, and run another conductor set to another grouped disconnect per 230.40 exception #2, or another non- grouped disconnect per 230.40 exception #3. The latter often works out well for ground mounts cuz you can just throw a 200 main breaker panel at the array site and run service conductors/ three wire to it.
 
Ask the panel manufacturer if they have a line side kit for this panel. I have done this several times with Sun Valley service entrances. Kit is basically 3-hole lugs, but with instructions and a certification that "adding our adapter kit does not void the U/L listing of this product.".
 
mdOPSP said:
The continuous pull is going to be 120A or less.
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Just to be clear, the code requires that you design to 125% of the inverter maximum current as published by the manufacturer irrespective of how much DC you plan to feed it.
 
BillK-AZ said:
Ask the panel manufacturer if they have a line side kit for this panel. I have done this several times with Sun Valley service entrances. Kit is basically 3-hole lugs, but with instructions and a certification that "adding our adapter kit does not void the U/L listing of this product.".
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The class 320 meter sockets we get around here do not come with lugs, we have to provide them. I admit I have never even looked to see if the manufacturer provides an "approved list" of lugs, but none of the inspectors around here would question any listed lug. I usually use crimp lugs in 320 sockets, stacked back to back, two on each 3/8 stud. I have also bolted on multi port mechanical lugs. Last time I did that was because one of the load side sets was 500MCM and I can currently only crimp up to 350.
 
mdOPSP said:
The continuous pull is going to be 120A or less. And yes, the panels all have main breakers on them. Also, after taking a look at the photos I have, it seems that there are actually 2x 125A panels connected to the right fuse-block :confused:. I appreciate your quick reply and insight. It's more valuable than you realize.
Click to expand...

A load side option might be to set a subpanel to the right and rewire the two 125A feeds to it, while also tying in the solar there. It would need to be at least a 300A rated panel. But that might be easier than shutting down the service to do a line side tap.

Arguably you could just polaris the feeds and tap to a fused disconnect, but the AHJ might have more questions. I see the subpanel avoiding those questions.

I'd bet that those two 125A feeds are improperly double lugged, and I doubt you'll find manufacturer specified triple lugs for an older piece of equipment like that. Both options above fix that issue for the inspector.
 
jaggedben said:
A load side option might be to set a subpanel to the right and rewire the two 125A feeds to it, while also tying in the solar there. It would need to be at least a 300A rated panel. But that might be easier than shutting down the service to do a line side tap.

Arguably you could just polaris the feeds and tap to a fused disconnect, but the AHJ might have more questions. I see the subpanel avoiding those questions.

I'd bet that those two 125A feeds are improperly double lugged, and I doubt you'll find manufacturer specified triple lugs for an older piece of equipment like that. Both options above fix that issue for the inspector.
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Yes it would be good to do an interconnection that fixes that presumed double lug issue. Is the following what you are thinking?

Run a 200A feeder off the right fuse block to a new Main lug sub panel. Move the 125s to there and also put the PV breaker (s) there. Qualify the bus using the 120% rule or the "sum of all OCPDs except the OCPD protecting the busbar" rule. The 120% rule would result in a smaller allowed bus rating, but that panel would likely be 400A rated anyway so it may not matter.
 
Yes that's what I was suggesting.

I think in theory, if the 125A feeds are properly terminated outside taps of unlimited length, you don't need the sub. Just polaris everything. But if you look at recent threads that's pretty fraught with code ambiguity and potential AHJ misunderstanding.
 
I would tap the feeder conductors coming off the left fuse block. I would use Burndy BIBD350-2 insulated multi-tap connectors. Remove the feeder conductor from the fuse block, strip an inch of insulation off the middle of the exposed feeder conductors and slide the connector down the conductor, and tighten it up at stripped section. That way you don't have to cut the wire. Then run your new feeder conductors from the 2nd port on the taps to a 200A rated PV combiner panel. If the utility requires a lockable visible break disconnect, run the new feeders to that first. Could't be easier!
 
jaggedben said:
Finally, what's the deal with the two sets of conductors coming off the fuse-block on the right? Is that a proper parallel conductor installation? If not, you might want to fix that before inviting any inspector to look at it.
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Yeah, separating the A and B phases like that in separate metal conduits is generally not allowed, in a parallel conductor circuit even more so. I would be worried about having an inspector look at this and require it to be corrected. If you touch it you own it.
 
pv_n00b said:
Yeah, separating the A and B phases like that in separate metal conduits is generally not allowed, in a parallel conductor circuit even more so. I would be worried about having an inspector look at this and require it to be corrected. If you touch it you own it.
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Sounds like they are properly separated feeders, but there questions about how they are terminated at both ends.
 
jaggedben said:
Sounds like they are properly separated feeders, but there questions about how they are terminated at both ends.
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Only if the run is underground in non-metallic conduit (300.3(B) exception). We can assume that's what's happening but I would make sure before I poked at it.
 
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