200 amp meter main with a location for a pv breaker as a main disocnnect

[jaggedben]

If you have 36 250 W panels at 30 V ea, use two Sunny Boy SB4000TL-US inverters ...

Which would require two 25A breakers. Still doesn't solve the original problem.

 

[Zee]

TallGirl, yes, micros are great for those accustomed to ac wiring only and also great for contractors who hate math.
Lots of those.
I love math and can do the calcs.

Ok, i don't really know how sensitive they are, i will trust your expertise.

The fact remains that, that would be very hard work on a steep roof.
And i will be up there. So i will use a string inverter in this case.

I do, and have, applied micros where it makes sense.
For example, some jurisdictions have onerous req.s for dc discos.... which i just skip if i have micros.
Some roofs are easy to work on.
Some systems are small. I will make great use of the new SMA micros on a 1.5 KW array.

GGUNN, and TallGirl, i appreciate the warning on 5 panel strings. Those are impossible.:happyno:

Agent Moller and Jben, funny thing is: that is exactly what i will do, 2 @ SMA SB4000TL-US inverters.
10+10 on one.
10+6 on the other.

It is in fact 2 @ 25 A brkrs===>50 A brkr needed.

In terms of the 50 A vis a vis the 200 A MSP,
I will either see if it flies per inspector (actual amps of 33.3 A BUMPED UP TO 125% CONTINUOUS ARE ONLY 41.6 A)
or i will downsize the main brkr to 175 A, from 200 A.

I really don't care what the customer decides to do with the 200 A main breaker i will leave with him after I finish.....
I know my labeling of pv breakers ("DO NOT RELOCATE") and breaker placement opposite feed, and actual amps are all within safe limits.

That is because if there were a dual-MPPT, 7600 Watt inverter (max amps 32A) i could easily hook up this 9 kW array to it.

 

[ggunn]

In terms of the 50 A vis a vis the 200 A MSP,
I will either see if it flies per inspector (actual amps of 33.3 A BUMPED UP TO 125% CONTINUOUS ARE ONLY 41.6 A)
or i will downsize the main brkr to 175 A, from 200 A.

Section 705.12(D)(2) of the NEC is very clear on this issue; it is the backfed breaker size that is used in calculating the 20% rule, not the "actual amps" of the interconnection. If your inspector passes a 50A backfed breaker in a panel whose busbars are rated at 200A and whose main breaker is 200A, he is not doing his job.

BTW, 41.6A is still too much.

 

[tallgirl]

Zee,

SMA is from Germany and I know there is a lot of work going on in Europe at the moment with "low voltage ride-through". That's likely the reason that the inverters aren't current-limiting at lower voltage -- because that is precisely the wrong thing to do in order to insure the grid stay up.

I know you guys are constantly struggling against panel ampacity limits, but I'm starting to think that some amount in a bid for upgrading a service is just going to have to be the norm. My system was "huge", at 2.8kW DC when it went in 6 years ago, but that would be smaller than the minimum system sizes many of the installers I know will even consider. Squeezing an extra 30A2P into a panel is no big deal, but y'all are installing systems 2 and 3 times that size, for probably the same amount of money, and you can't throw in $1,500 for a panel upgrade? Your behavior is a lot like what happens with battery-backed systems -- too much panel, too little battery.

 

[Zee]

Zee,

SMA is from Germany and I know there is a lot of work going on in Europe at the moment with "low voltage ride-through". That's likely the reason that the inverters aren't current-limiting at lower voltage -- because that is precisely the wrong thing to do in order to insure the grid stay up.

I know you guys are constantly struggling against panel ampacity limits, but I'm starting to think that some amount in a bid for upgrading a service is just going to have to be the norm. My system was "huge", at 2.8kW DC when it went in 6 years ago, but that would be smaller than the minimum system sizes many of the installers I know will even consider. Squeezing an extra 30A2P into a panel is no big deal, but y'all are installing systems 2 and 3 times that size, for probably the same amount of money, and you can't throw in $1,500 for a panel upgrade? Your behavior is a lot like what happens with battery-backed systems -- too much panel, too little battery.

Aha...., thanks, good to know about "low V ride thru".

Yes, I used to mess with line side ties and try to save janky, crammed full, old, 100AMP meter/main panels.
I now hate line side ties.
Have done many.... and they are lots of work, difficult to do in a professional/compliant manner, and many utilities won't even allow them.
Now , my first choice is always to upgrade the main panel, IF NEEDED.
And, it usually works out: if a customer needs so much PV that you overload the panel per 120% rule, then their usage is so high that they could use a panel upgrade in any case, if not now but the near future.


In this case they have a difficult situation: a "grandfathered" in location for meter/ main not likely to stay if we were to permit the new panel, which we must.

 

[tallgirl]

Aha...., thanks, good to know about "low V ride thru".

Yes, I used to mess with line side ties and try to save janky, crammed full, old, 100AMP meter/main panels.
I now hate line side ties.
Have done many.... and they are lots of work, difficult to do in a professional/compliant manner, and many utilities won't even allow them.
Now , my first choice is always to upgrade the main panel, IF NEEDED.
And, it usually works out: if a customer needs so much PV that you overload the panel per 120% rule, then their usage is so high that they could use a panel upgrade in any case, if not now but the near future.


In this case they have a difficult situation: a "grandfathered" in location for meter/ main not likely to stay if we were to permit the new panel, which we must.

Rebates and tax credits, plus the declining prices in PV anyway, are driving a lot of larger systems. It would take me around 6.5 to 7kW to net out to zero, including my Leaf. I can go to 7.2kW only because I have a hybrid system and 30 amps of PV goes with 30 amps of load, so I don't have the "double-dipping" problem seen with pure grid-tied systems.

 

[texie]

Hello Gents,
I need to feed 9 KW of PV into a 200A service. Currently 200 main brkr/200 rated. With distribution.
I need at least 2p50A for PV. As we all know, 40A max allowed.

No, i cannot use a single, 32A AC rated output inverter (eg SMA SB8000US, Fronius 7500). This is due to split orientations and string sizes. Panels: 30 South and 6 East.

Service upgrade to 400A? Expensive.

Any knowledge of a 200 A meter/main panel I could have the electricain (I am just doing the pv) replace the current one with? Point would be to have a spot for the (N) pv brkr as a main disconnect brkr.

Your knowledge appreciated!

btw- this bugs me so much: if panels simply had a spot for an add'l main....the whole 120% rule would be a non-issue. And it is a big issue.

I'm pretty sure that Square D has a combo meter main that comes with a 200 amp main breaker installed and has a space available for an additional 50 amp max. main breaker. Would this solve your issue?

 

[Zee]

I'm pretty sure that Square D has a combo meter main that comes with a 200 amp main breaker installed and has a space available for an additional 50 amp max. main breaker. Would this solve your issue?

Yes, it would.

Tallgirl, yes we are very often bumping up against meter/main panel limits with these larger systems. Maybe i'll just have to get them one of your type of hybrid systems.

 

[ggunn]

I'm pretty sure that Square D has a combo meter main that comes with a 200 amp main breaker installed and has a space available for an additional 50 amp max. main breaker. Would this solve your issue?

If that means that the busbars are rated at 250A, that would work.

 

[tallgirl]

Yes, it would.

Tallgirl, yes we are very often bumping up against meter/main panel limits with these larger systems. Maybe i'll just have to get them one of your type of hybrid systems.

Zee,

I love battery-backed systems, honest I do, but I wouldn't go that route unless your customer absolutely needed one. They are a maintenance headache for a few hours a year worth of benefit.

 

[jaggedben]

If that means that the busbars are rated at 250A, that would work.

It means there is a pre-configured space for a second main breaker that is not on the busbar. In other words, a supply-side connection.

 

[texie]

It means there is a pre-configured space for a second main breaker that is not on the busbar. In other words, a supply-side connection.

Here is the Square D info on combo meter mains. It shows the optional 50 amp disconnect for various units depending on whether you want ringless or ring style and QO and HOM. I guess the question would be is this really a line side connection? I've seen one and the 200 and the 50 have separate factory wires going to the meter section. It would seem to me that this would be compliant for the OP. http://www.schneider-electric.us/documents/customers/retail-consumer/meter-mains.pdf

 

[ggunn]

It means there is a pre-configured space for a second main breaker that is not on the busbar. In other words, a supply-side connection.

That's a great idea.

 

[jaggedben]

Here is the Square D info on combo meter mains. It shows the optional 50 amp disconnect for various units depending on whether you want ringless or ring style and QO and HOM. I guess the question would be is this really a line side connection? I've seen one and the 200 and the 50 have separate factory wires going to the meter section. It would seem to me that this would be compliant for the OP. http://www.schneider-electric.us/documents/customers/retail-consumer/meter-mains.pdf

Yes, it would be a compliant supply side connection. 705.12(A) really doesn't have too many restrictions; until 2011 it didn't even explicitly limit the size of the PV output to the rating of the service.

If it's done inside UL listed service equipment then all the better.

Bit of a shame that the second breaker only allows 10 more amps than backfeeding the main busbar. But they probably designed that additional 50A spot with an air-conditioner in mind, not PV.

It seems there's also some products on that list that allow up to 6 service disconnecting breakers, although without branch circuit distribution. That sort of thing could also work if put in line ahead of another load center. Could be very good for an MSP upgrade in situations where there's a single-main-breaker enclosure that feeds a distribution panel inside the house.

 

[PWDickerson]

Zee, if you can con the inspector into accepting two 4kW inverters feeding a 40A backfeed breaker, you might want to consider a different stringing scenario. 9+9 on inverter #1 and 6+12 on Inverter #2 would give you ratios of 12.5% on both inverters, which will eliminate any clipping.

Another solution would be to use a 4 kW SMA TL-US and a 3.6 kW Power-One PVI-OUTD-US. The Power-One is also a dual MPPT unit. Combined max current is 31.7 amps, which fits on a 40 amp breaker. The Lower range of the MPPT voltage input for the Power-One is 120 volts, so it can handle the 6-panel string just fine. I would string 6+11 on the Power-One, and 9+10 on the SMA. This gives ratios of 18% and 19% respectively. This is a great option if you don't mind having inverters from 2 different manufacturers.

 

[PWDickerson]

It is in fact 2 @ 25 A brkrs===>50 A brkr needed.

Actually, the correct size for the backfeed breaker would be 45 amps (unless the breaker manufacturer doesn't make it, then 50A). The breaker is sized based on 1.25 * the sum of the continuous currents from the inverters, not the sum of the breakers in the AC combiner panel.

 

[ggunn]

Actually, the correct size for the backfeed breaker would be 45 amps (unless the breaker manufacturer doesn't make it, then 50A). The breaker is sized based on 1.25 * the sum of the continuous currents from the inverters, not the sum of the breakers in the AC combiner panel.

The 120% rule in the main panel is calculated from the sum of the sizes of the first breakers backfed by the inverters, not from 1.25 X the max current from the inverters. That in fact is the sum of the backfed breakers in the AC combiner panel. The rating of the breaker in the main panel isn't a factor, even if it happens to be smaller than the sum of the breakers in the subpanel. It may be weird, but that's the way the code reads.

 

[GoldDigger]

The 120% rule in the main panel is calculated from the sum of the sizes of the first breakers backfed by the inverters, not from 1.25 X the max current from the inverters. That in fact is the sum of the backfed breakers in the AC combiner panel. The rating of the breaker in the main panel isn't a factor, even if it happens to be smaller than the sum of the breakers in the subpanel. It may be weird, but that's the way the code reads.

The formula based on the rated continuous current output for backfeed calculation (120% rule) applies only for systems with battery storage.

 

[PWDickerson]

The intent of the language in 705.12(D)(7) requiring the 120% rule calculations be made using the first overcurrent device in panelboards wired in series is to clarify that it is not necessary to use progressively larger feeder breakers in the 120% rule calculations. Bill Brooks, John Wiles, and other experts agree that the rating of the main breaker in an AC combiner panel (or the feeder breaker in an upstream panel in the case of an MLO combiner) should be used in the 120% rule calculations for upstream panels.

 

[GoldDigger]

The intent of the language in 705.12(D)(7) requiring the 120% rule calculations be made using the first overcurrent device in panelboards wired in series is to clarify that it is not necessary to use progressively larger feeder breakers in the 120% rule calculations. Bill Brooks, John Wiles, and other experts agree that the rating of the main breaker in an AC combiner panel (or the feeder breaker in an upstream panel in the case of an MLO combiner) should be used in the 120% rule calculations for upstream panels.

The exact language of the Code section (2011), that the first(closest to the GTI) overcurrent device is the one which must be used all the way through seems to require that the sum of the branch breakers at the combiner be used upstream rather than the size of the combiner main breaker. That is contrary to what you say the experts agree on, and therefore seems to call for a revision to the Code language.
If it said "previous" rather than "first", then the interpretation you refer to might be justified.