Inverter feeder tap 705.12(B)(1)

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tortuga

tortuga

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Greetings everyone, I have another PV scenario
This one is a existing building that has a 120/240 200A main and 4/0 AL going to a gutter.
Then there are 4 fused 60A disconnects tapped off the gutter and a 100A panel tapped at the end.
The first fused disconnect is empty and would be an ideal place to pipe the inverter to.
However the sum of the OCPD's on the feeder is 220A, but no OCPD is "greater than" the 4/0 AL ampacity.
Does this comply with 705.12(B)(1)(b)?
705-12B1.png
 
To comply with 705.12(B)(1)(b) there would have to be a 200A OCPD installed inline in the 4/0 feeder between the PV POI and the first 40A fused disconnect to limit the current that can be on the 4/0 feeder. Assuming that the feeder is 90C rated and does not need derating for COU it's only rated for 205A. Not much of a margin there to add more supply.
Typically where 705.12(B)(1)(b) works best is tapping into a feeder conductor feeding a panelboard with main OCPD.
 
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You can upsize the 4/0 feeder and redo all the taps. Then you are compliant with 705.12(B)(1)(a).
 
If you could extend (through the gutter) the load conductors in the last 40A disconnect to be supplied by the currently unused 40A disconnect, then you could connect the PV in the last 40A disconnect. That complies with 705.12(B)(1)(b), as there is only one feeder segment downstream of the last 40A disconnect, which supplies a subpanel with a main breaker. This relies on the reasonable reading of 705.12(B)(1)(b) that the "load side of the power source connection point" refers to the load side relative to the primary source (what I called downstream).

Cheers, Wayne
 
Thanks everyone, all good options It seems I cant help but think of the most expensive way "just change the whole service"

wwhitney said:
If you could extend (through the gutter) the load conductors in the last 40A disconnect to be supplied by the currently unused 40A disconnect, then you could connect the PV in the last 40A disconnect. That complies with 705.12(B)(1)(b), as there is only one feeder segment downstream of the last 40A disconnect, which supplies a subpanel with a main breaker.
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Moving taps around would be brilliant thanks Wyane!
Seems strange that 705.12(B)(1)(b) does not address the disconnects tapped between the service main and the inverter 'source output'.
705-12B1b.pngWhat if down the road someone swaps them out to their full 60A with a new loads?
I guess that's well down the road for next time.

pv_n00b said:
You can upsize the 4/0 feeder and redo all the taps. Then you are compliant with 705.12(B)(1)(a).
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Right, I am hoping to avoid sizing the wireway, as its a really old and small.
ggunn said:
If it makes a difference, you'd only have to upsize the feeder from the PV tap out to the rest, not the part from the PV tap back to the service.
Click to expand...
Good idea

Thanks again all
 
tortuga said:
Seems strange that 705.12(B)(1)(b) does not address the disconnects tapped between the service main and the inverter 'source output'.
What if down the road someone swaps them out to their full 60A with a new loads?
Click to expand...
Good question. I think I may need to amend my suggestion and interpretation of 705.12(B)(1). I'll try to comment further when I've had a chance to think about it more.

Cheers, Wayne
 
tortuga said:
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Seems strange that 705.12(B)(1)(b) does not address the disconnects tapped between the service main and the inverter 'source output'.
Click to expand...

I think 705.12(B)(2) address that with its reference to 'all taps.'

tortuga said:
What if down the road someone swaps them out to their full 60A with a new loads?
I guess that's well down the road for next time.
Click to expand...
Maybe put some signage. Not a code issue.
 
jaggedben said:
I think 705.12(B)(2) address that with its reference to 'all taps.'
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So are you suggesting that in the last diagram tortuga posted, if all the conductors are 4/0 Al, 705.12(B)(2) says that the top three horizontal segments are taps and have to comply with one of the tap rules in 240.21(B)?

Cheers, Wayne
 
wwhitney said:
Why would that be a problem? Either NEC code language wise, or Kirchoff wise?

Cheers, Wayne
Click to expand...
Right it would not be as any change would require a load calc and they would never go over 180A of load on existing AL 4/0 feeder
wwhitney said:
The top three horizontal segments are taps and have to comply with one of the tap rules in 240.21(B)?
Click to expand...
Right they are already existing 240.21(B)(1) feeder taps, probably from from the late 60's
Similar to this illustration mike uses;

1644509547469.png
 
tortuga said:
Right it would not be as any change would require a load calc and they would never go over 180A of load on existing AL 4/0 feeder
Click to expand...
But even beyond that, as each of the 3 taps with loads is protected by the fuses in the supplied disconnect, it doesn't matter that with the PV interconnection, a greater current can now reach that tap. Doesn't matter in terms of overload, it could make the minimum tap conductor size larger per 705.12(B)(2).

Now if one of those three segements were full size (4/0 Al) prior to addition of the PV, so it wasn't a 240.21(B) feeder tap, and went on to supply two further disconnects via taps, then the addition of the PV raises the possibility of overloading that 4/0 Al segment, if the sum of the supplied disconnect fuses exceeded 180A.

tortuga said:
Right they are already existing 240.21(B)(1) feeder taps
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OK, but the question was if there currently weren't, because they were the same size as the feeder (4/0 Al), does 705.12(B)(2) mean they become 240.21(B) feeder taps once you add the PV interconnection in the far disconnect? I think it should, but the language is not so explicit, and the idea is fairly subtle, not obvious on the first reading.

Given the scenario in the second paragraph above, this seems like the correct reading, as with the 4/0 Al segment now considered a tap, it would preclude its supplying two different disconnects.

Cheers, Wayne
 
wwhitney said:
So are you suggesting that in the last diagram tortuga posted, if all the conductors are 4/0 Al, 705.12(B)(2) says that the top three horizontal segments are taps and have to comply with one of the tap rules in 240.21(B)?

Cheers, Wayne
Click to expand...
Yes that's what I was suggesting. And when calculating, say, 10% for a 10ft tap, that would be 10% of (200+125% of inverter outpuy). But if the conductors are all 4/0 AL then they all meet 240.21(B) requirements with no issues. (I assumed the horizontal segments were smaller wire because why would someone bring 4/0 AL to a 60A disco. But I guess if they didn't know the rules...)
 
wwhitney said:
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OK, but the question was if there currently weren't, because they were the same size as the feeder (4/0 Al), does 705.12(B)(2) mean they become 240.21(B) feeder taps once you add the PV interconnection in the far disconnect?
Click to expand...
As badly worded as it is, I think it's clear that's the whole point of 705.12(B)(2).
 
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