120% Rule Options

[Cmy]

Discussing grid tied inverters and AC amps out, Hedges wrote about the 120% rule and breaker choices. Liking the Growatt 11.4 grid tied, 48 amps AC out means an existing 200a breaker needs to be changed.

My meter has three lugs wired to three 200a panels. One 200a panel connects to a 100a sub panel in the future solar building. That wiring is being changed to carry 225a. To meet the 120% rule should I -

Change the 200a main to 225a or 175a? Can a Homeline 200a panel be changed to 225a bolt on main under code? Is the 200a's meter line considered busbar for the 120% multiple? Assuming a 175a main is ok in a 200a panel, this looks the easiest with still enough amps for the addition. 200a x 1.2=240-175=65a for the 11.4's AC out.

Change the 100a sub panel to a new 225a or 175a panel while keeping the 200a main. Or does the 120% rule apply to main or both panels?

Split (tap?) the 200a feed before the 200a main panel, one leg to the panel and the other to the solar building's new panel. Giving the solar building a direct connection, with disconnects, to the meter?

Other options??

 

[Hedges]

I think meter's lugs could be considered a busbar and subject to 120% rule, not sure inspectors have decided to do that.

In my case I used Polaris connector as busbar (meter only had single lugs), and I think Polaris is good for 400A?
200A meter --> 200A main breaker --> Polaris --> [three panels/switches in parallel]

I would suggest taking one of the three connections ("Line Side Tap", I think they're called) and putting that through a 200A main breaker only box, or a 200A fused disconnect. Then fan out to feed your inverter and the 200A panel you just disconnected.

I think a daisy chain of panels are all subject to 120% rule if PV backfeeds the last one.

 

[hwy17]

One 200a panel connects to a 100a sub panel in the future solar building. That wiring is being changed to carry 225a. To meet the 120% rule should I -

If the panel only has a 200A main breaker and one 200A load breaker on it to go to the solar building, it should be possible to exempt it from 120 rule with labelling indicating not to add other loads to it.

It's a passthrough panel in that case and cannot become overloaded by the back feeding.

 

[Cmy]

I don't claim to fully understand the 120% rule but one definition referred to the main service panel capacity. I appear to have three main service panels each connected directly to the meter. Two wired through the back of the meter panel, through the exterior brick, and into the back of two 200a main panels.

The third 200a panel, wired through the side of the meter panel, and underground to the end of the mother in law addition. As that panel supports a pair of mini splits, oven, and small washer/dryer, it is not a pass through but not using 200 amps.

Changing that 200a to a 175a main would be an easy change, will ask the utility and see what they say. County, not city, so the utility does . Maybe time for a local electrician's input.

Panel in question, larger conduit 200a from meter, smaller 100a to future solar. The 100a line is fed by a dual 100a plug in. Had hoped to change to 174a plug in. Can a Polaris sit in its own box? Utility will probably want more disconnects here.

 

[Hedges]

120% rule for a panel is simple enough. Main breaker at one end plus PV breaker(s) at other end can total up to 120% of busbar rating.

I put Polaris inside the relatively spacious box that has 200A main breaker only, no busbars. Of course could go in any box.

Polaris is obviously acting as a busbar, could carry main plus PV current if those two connected at one end.
In my case, I had 200A main breaker from grid feeding it and 2 awg from Polaris to a couple boxes. Had to discuss "feeder taps" with inspector, and after he reviewed code pages he accepted it and applied "approved" sticker.

Seems to me 200A main plus 100A safety switch for PV totals 300A sources, so if I were him I'd limit 3/0 branches off Polaris to same feeder tap rules, 10' max and in conduit. Not that distance has anything at all to do with safety; they just threw us a bone by letting us have 10' of wire protected at far end instead of near end. I ain't worried; 2 awg if overloaded will trip breaker at far end. If it gets a fault anywhere in the 10' of conduit, 2 awg is plenty to fast-trip the 200A main breaker. Although 8 awg ground is considered sufficient for my 100A circuit, I used 6 awg because 6 awg is proper for 200A. Otherwise, the 8 awg ground would have to fast trip it.

Panel in question, larger conduit 200a from meter, smaller 100a to future solar. The 100a line is fed by a dual 100a plug in. Had hoped to change to 174a plug in.

Meaning what? There are 200A branch breakers, also taps for the breaker panel that aren't breakers. These plug onto 4 busbar fingers instead of 2.

 

[Cmy]

Looking for least disruptive, code passing, change to get more amps for the inverter's 48a. Easiest changing the dual 100a breaker to more amps and the main 200a breaker to 175a.

Volt55 suggested a pass through panel though I but want two load breakers - if allowed. Or a box is added to the 200a feed and tap the new line for the inverter. Wired a cabin and have rewired panels but polaris and taps are new.