Solar Sub Panel with only solar breakers

[roblsmith3]

I am running into some issues with inspectors on the following situation.... we have 2x SolarEdge 9k inverters with 25A max output. We are combining the inverter outputs in a 100A 3 pole "solar sub panel" that will only house the 2x 40A 3 pole breakers and an 80A 3 pole MCB. This subpanel is then connected to the main conductors of the main panel via a "load side tap" using Buchanan B Taps. My question is, "Does the 120% rule still apply to this solar subpanel....limiting the backfeeding in the panel to only 30A?" If not, what part of the NEC 2011 allows me to use this subpanel as a "solar only" sub panel? Thank you for your responses in advance.

 

[GoldDigger]

The exact wording of the NEC prior to [2014] allows the interpretation that your inspector is making, even though it makes little sense. Most AHJs allow it, with some requiring a placard prohibiting the installation of any load breakers in the AC combiner panel.
The same inspectors may also apply the 120% rule to the feeder wires.
Also, what is a "load side tap"? Is it off the bus after the main but without a breaker?

 

[roblsmith3]

Yeah, we always put a placard on our "solar only" sub panels and it has been fine in all jurisdictions. This is a new inspector and I really don't want to have to get a 200 amp subpanel just to feed 62.5 amps (25x2x1.25)

 

[roblsmith3]

Yeah, we always put a placard on our "solar only" sub panels and it has been fine in all jurisdictions. This is a new inspector and I really don't want to have to get a 200 amp subpanel just to feed 62.5 amps (25x2x1.25). Any direction on what exact Code this is?

 

[jaggedben]

Yeah, we always put a placard on our "solar only" sub panels and it has been fine in all jurisdictions. This is a new inspector and I really don't want to have to get a 200 amp subpanel just to feed 62.5 amps (25x2x1.25)

You shouldn't have to. Special order two 35A breakers and change your main to a 70A breaker and then you can use a 125A panel under the 120% rule.

(Funny, I have this exact system on my planset to-do list right now.)

 

[jaggedben]

BTW, the load side tap is problematic if you're not planning any other modifications to the feeder you are tapping.

The 2014 code would allow it if there is a (second) overcurrent protection device downstream of the tap (i.e. towards the loads). If it feeds a MLO panel, as most sensible installers would have done, then you'll have to someone stick protection in between.

Under previous codes, the conductor could be subject to the 120% rule, and more often than not it will not be sized big enough for that.

 

[shortcircuit2]

Yeah, we always put a placard on our "solar only" sub panels and it has been fine in all jurisdictions. This is a new inspector and I really don't want to have to get a 200 amp subpanel just to feed 62.5 amps (25x2x1.25). Any direction on what exact Code this is?

705.12(D)(2) Bus or Conductor Rating

Read 705.12(D)...if you had used a 2 position panel with no provisions for additional breakers, just your PV inverter inputs...it would be OK IMO.

705.12(D)(2) also impacts the load side tap to the "Conductor" as jaggedben pointed out.

 

[shortcircuit2]

I am running into some issues with inspectors on the following situation.... we have 2x SolarEdge 9k inverters with 25A max output. We are combining the inverter outputs in a 100A 3 pole "solar sub panel" that will only house the 2x 40A 3 pole breakers and an 80A 3 pole MCB. This subpanel is then connected to the main conductors of the main panel via a "load side tap" using Buchanan B Taps. My question is, "Does the 120% rule still apply to this solar subpanel....limiting the backfeeding in the panel to only 30A?" If not, what part of the NEC 2011 allows me to use this subpanel as a "solar only" sub panel? Thank you for your responses in advance.

I'm not sure this load side tap would comply with 705.12(D)(1)...Dedicated Source Interconnection?

Then...the connection at the main panel should also be subject to 705.12(D)(7)...and be connected "opposite" the Main...

Could you give us more info on the details of the Main Service Panel where your "tap" is made?

 

[jaggedben]

I'm not sure this load side tap would comply with 705.12(D)(1)...Dedicated Source Interconnection?

Then...the connection at the main panel should also be subject to 705.12(D)(7)...and be connected "opposite" the Main...

Could you give us more info on the details of the Main Service Panel where your "tap" is made?

If the tap is made according to 240.21(B) then it should have an overcurrent device, which would satisfy 705.12(D)(1) in my opinion. He did mention an 80A main breaker.

The 'opposite the main' provision depends on the ratings of the main panel and breaker, but yes it could apply.

 

[roblsmith3]

Line Diagram

Line Diagram

Here is the Line diagram that I used for permitting if it helps explain the situation a little better. Still curious about advice and the code section pertaining to solar subpanels. Thanks.

 

[jaggedben]

Here is the Line diagram that I used for permitting if it helps explain the situation a little better. Still curious about advice and the code section pertaining to solar subpanels. Thanks.

The 2011 code makes no distinction between subpanels containing only sources and those with loads. 705.12(D) governs all. If your AHJ wants to make you change that sub to a 150A to meet the 120% rule, you've no strong argument against him. Best you can do is point them at the 2014 code, which allows your design because the total number of breakers, not including the (utility) breaker feeding it, do not exceed the rating.