Main Service panel breaker config

Looking at my 2014 NEC, I have 2 new stickers to put inside my service panel. One of them makes the 125 percent clearer....to most.... I think. But that got me thinking about how to run the wires into the service panel and breaker position (I know it goes on the bottom last position opposite the main breaker).

Here is the new warning to be on a sticker:
WARNING
THIS IS EQUIPMENT IS FED BY MULTIPLE SOURCES
TOTAL RATING OF ALL OVERCURRENT DEVICES
EXCLUDING MAIN SUPPLY OVERCURRENT DEVICE
SHALL NOT EXCEED AMPACITY OF BUSBAR

and the other:
WARNING
INVERTER OUTPUT CONNECTION
DO NOT RELOCATE THIS OVERCURRENT DEVICE

I have 2 inverters. An SB4000 and a SB5000. Each breaker of 20 amps is sufficient for overcurrent protection inside the main service panel. I have a 100 amp main breaker, a busbar rated for 120 amps and 80 amps worth of breakers excluding the solar. So I have 45 amps additional I can add according to the NEC. My question is should I combine both inverter AC outputs at the AC disconnect and run one 3 conductor wire (L1, L2 and N) to the REC meter then to the breaker panel. Inside the breaker box we have two columns of breakers. Each column is fed by a utility wire. 120, 120 and neutral. I think the inverters L1, L2 and N outputs correspond to the each of the 3 wires coming into the main panel. I was thinking to keep things balanced, I would run L1 to the left column into a single pole 20 amp breaker, L2 to the right column 20 amp single pole breaker and neutral of course in these inverters is ungrounded or unused. I think I have to combine the two inverters at or before the REC meter I have anyway as it only has doesn't have 2 sets of hookups for L1, L2 and N. If I ran one combined wire from the AC disconnect after combining the 2 inverters AC out at that point, what type of breaker (40 amp) would one use and where would L1, L2 plug into? would that be a double pole double throw plugged into either the left or right column inside the box. Or would my idea to use 2 20 amp breakers above work? Suggestions/pointers/criticism most welcome. Mike

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,800 admin
    Re: Main Service panel breaker config
    michaelc wrote: »
    Here is the new warning to be on a sticker:
    WARNING
    THIS IS EQUIPMENT IS FED BY MULTIPLE SOURCES
    TOTAL RATING OF ALL OVERCURRENT DEVICES
    EXCLUDING MAIN SUPPLY OVERCURRENT DEVICE
    SHALL NOT EXCEED AMPACITY OF BUSBAR

    Either I do not understand what it is trying to say, it is incorrect, or they have changed the code...

    Unless this is for a commercial installation (vs residential).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • michaelcmichaelc Solar Expert Posts: 36
    Re: Main Service panel breaker config

    I am just soliciting suggestions on ways to wire my two sunnyboy inverters into a meter, then into my houses breaker panel. The rest is just fluff and I should have just kept it simple. I have 3 conductors from each inverter labeled L1 L2 and N like any GT inverter I am guessing. The meter the utilities will give me to plug into the socket, also has contacts for 3 conductors, L1, L2 and N. So I plan on combining the two inverters outputs together in the AC disconnect box which the utility requires. So from that point I will have 3 conductors that go to the meter, and then come out of the meter and labeled L1, L2 and N. How exactly is the popular way to wire these into a main service panel (my houses breaker box) using circuit breakers. I know the breaker(s) go in the bottom last position according to the NEC. I have 3 10 amp wires at this point to wire in. N is a no brainer. It is the L1 and L2 that I am curious about. My breaker box has two columns as most boxes do. There are breakers plugged into both sides. There are slots at the bottom. I have 100 amp main main breaker and 120 amp bus. I have 80 amp total load according to the amount of breakers in the box. I noticed they are fairly evenly divided (in current rating) in each column so as to balance the loads. I am wondering how to "plug" the 3 conductors (well 2 since N is known) into and into what column. I can't find any diagrams on the web that show physically how to do this, just schematics.
  • SkiDoo55SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    Re: Main Service panel breaker config

    Will throw out a couple things to research
    i believe you need to provide current protection for the rated output of each inverter. If I looked up correct model you would have the following,
    SB4000. @ 16.6 amp x 120% = 19.9 or 20 amp breaker
    SB5000 @ 20.8 amp x 120% = 24.9 or 30 amp breaker
    these would be in a Inverter Combiner Box before your production meter.
    9000 watt combined Inverter output = @ 37.5 amp x 120% = 45 or 50 amp breaker in your main panel, which would put you over your main bus bar combined rating. You would use a double pole 240 breaker on one side which picks up L1 and L2 buss bars.
    don't forget your ground wire from inverter's to combiner thru meter socket to main panel. Wire has to be rated to carry the current of the circuits protective device rating.
    You may not have full rated arrays for each inverter, but they want it set up correctly for the inverter capacity to prevent additions to the solar array in the future. Inverter will limit it's output regardless of the watt input.

    You should also, use the SMA string sizing tools available to determine your arrays based on local min/max temps. Need minimum voltages to turn on and max Voc and max Vmp. String tool will show if you will fall in working ranges or exceed any values.

    if you are not sure of what is code I would consult a knowledgable electrician.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
  • michaelcmichaelc Solar Expert Posts: 36
    Re: Main Service panel breaker config
    SkiDoo55 wrote: »
    Will throw out a couple things to research
    i believe you need to provide current protection for the rated output of each inverter. If I looked up correct model you would have the following,
    SB4000. @ 16.6 amp x 120% = 19.9 or 20 amp breaker
    SB5000 @ 20.8 amp x 120% = 24.9 or 30 amp breaker
    these would be in a Inverter Combiner Box before your production meter.
    9000 watt combined Inverter output = @ 37.5 amp x 120% = 45 or 50 amp breaker in your main panel, which would put you over your main bus bar combined rating. You would use a double pole 240 breaker on one side which picks up L1 and L2 buss bars.
    don't forget your ground wire from inverter's to combiner thru meter socket to main panel. Wire has to be rated to carry the current of the circuits protective device rating.
    You may not have full rated arrays for each inverter, but they want it set up correctly for the inverter capacity to prevent additions to the solar array in the future. Inverter will limit it's output regardless of the watt input.

    You should also, use the SMA string sizing tools available to determine your arrays based on local min/max temps. Need minimum voltages to turn on and max Voc and max Vmp. String tool will show if you will fall in working ranges or exceed any values.

    if you are not sure of what is code I would consult a knowledgable electrician.


    Thank You so much skidoo55. Also thanks for looking up the inverter numbers and doing the calcs. I am on the cusp of being over on the bus. I played with SMA design tool and came up with string sizes of 18 for the sb5000 and 10 for the 4000. I also was asking in another thread of I could use my disconnect, a squared D D223NRB as a combiner. I think I can. Thanks again. Mike
  • solar_davesolar_dave Solar Expert Posts: 2,394 ✭✭✭✭
    Re: Main Service panel breaker config

    OK so my AHJ required a single point of attachment to the disconnect. No 2 wires under a single lug in at any point. This is what they required for combining a pair of grid tie inverters. They then goto the production meter and the disconnect switch, one like you mentioned, and then to a single 240v breaker in my panel. The main panel had to be derated to 175 amps at the main breaker.
  • michaelcmichaelc Solar Expert Posts: 36
    Re: Main Service panel breaker config
    solar_dave wrote: »
    OK so my AHJ required a single point of attachment to the disconnect. No 2 wires under a single lug in at any point. This is what they required for combining a pair of grid tie inverters. They then goto the production meter and the disconnect switch, one like you mentioned, and then to a single 240v breaker in my panel. The main panel had to be derated to 175 amps at the main breaker.

    Very neat panel farm in your house. I have one of square D units so ill use it. I emailed our permit guy to see if he feels two wires not together on one lug. How do you derate your panel at the main breaker which I assume yours is 200? Mike
  • solar_davesolar_dave Solar Expert Posts: 2,394 ✭✭✭✭
    Re: Main Service panel breaker config
    michaelc wrote: »
    Very neat panel farm in your house. I have one of square D units so ill use it. I emailed our permit guy to see if he feels two wires not together on one lug. How do you derate your panel at the main breaker which I assume yours is 200? Mike

    Pretty simple, you get a 175 amp main breaker to fit the 200 amp panel. That will get you up to 65 amps of back feed capacity. (200 * 1.20) - 175 = 65 amps. That will met NEC code.

    Of course the AHJ will have to approve the 175 main for the loads on the panel. You might know they would not do that on mine and I had to upgrade the service feed from the street transformer to 400 amps and have a pair of 200 amp panels attached, one is derated to 175 amps. Granted my loads were pretty high to start with, dual 3ton AC units, electric range, electric dryer, pool pump just to name the major 240V loads. I didn't quibble too much because we were adding a new office/shop building with a 125 amp sub panel and a 60 amp sub-panel in the garage to charge the 2 Chevy volts as well right after the solar add. Doing it as part of the solar project also allowed me to take the 30% tax credit on the panel work.

    BTW we did drop the electric range for nat gas and upgraded the AC units to a much higher seer rating heat pumps. The new office/shop has a 3 zone mini split on it for both heat and AC.

    Seems like 9000 watts of solar in Northern California is a bit extreme, perhaps some conservation is in order.
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