breaker size??'s

I'm about to re-wire stuff in my batt. room and don't really understand what size breakers I should be useing and where. Within a month or so the goal is to have 1000-1250 watts of PV and 4 380/ah L16's on 12V system. I have a lug type 200A fuse for batt to inv. which will be on 4/0 wire. I have a 6 hole dist. block that I will feed with 0awg and hopefully feed from there. My confusion is what to do on the lines from solar array, which will be in a combiner box with appropriate breakers, and line from classic 150 to batts. Classic manual is not clear on breaker size? says must meet some UL spec, chinese to me, What I do have on hand is a 60A breaker and wondering if that would suffice on CC line?? and should I have something on PV input line?? What do we base breaker size on?? line size or amount of current that will be in line?? What should I have on PV line in? and is it for protection or convieneice as shut of? PV comes to house on #4 reduced to #6 in metal box in batt.room. CC is fed with#6.
Marc
4x240w panels,Classic 150 CC, 4x380AHR L16's, antique Trace 12V inverter

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: breaker size??'s

    Circuit protection sizing, short form:

    1). Check the manual for the equipment involved. PV's will have a "series fuse rating", charge controllers will have a recommended fuse/breaker size for output (based on their maximum continuous current rating), inverters will have a recommended fuse/breaker size for input (based on maximum output power at minimum input Voltage), AC branch circuits are according to capacity & wire size (standard wiring practice).

    2). NEC calculation: continuous current * 1.25 * 1.25 round up to nearest available size.

    3). All circuit protection must be rated for the current type, continuous current amount, and maximum Voltage on the circuit. It is particularly important to make sure the ratings are correct and for Direct Current on DC circuits.

    Fuses/breakers on PV are there to protect against two or more panels feeding into a shorted one, as the whole circuit (including the PV) should be designed to handle the Isc of the panels. It is not strictly necessary to have CP on the combined output of the PV array, although some jurisdictions may require it and/or an "accessible" disconnect.

    Fuses/breakers on charger controller to battery circuit is there to protect against the battery dumping massive current through wiring if the controller should fail.

    Fuses/breakers on battery to inverter circuit likewise; to protect against massive current in the wiring should the inverter fail or for some other reason draw too much current.

    Note that the wiring always must be able to handle more current than the fuse/breaker. That makes the latter the first thing to go in an over-current situation.

    Any help?
  • VicVic Solar Expert Posts: 3,112 ✭✭✭✭
    Re: breaker size??'s

    Hi shockman Marc,

    The Classic manual is quite good, most manuals do not have the level of detail that the MidNite Classic manual has. The manual should be on the Disc that came with the Classic, when new. In the later pages of the manual is a table that lists wire and breaker sizing info. In the following manual, it is Table 14 -- Breaker Sizing --, Page 76 :

    http://www.midnitesolar.com/pdfs/classicManual.pdf

    This manual is about 8 MB.

    For a Classic 150 on 12 V, the wire size for the output of the breaker is #4AWG, protected with a 100 A breaker (DC-rated)

    For the input, up to 60 A is probably OK, but depends upon the exact ratings for the wire that is used.

    Hope this may help, Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: breaker size??'s

    Remember that the input current is based on Imp/Isc of the array--And with MPPT type charge controllers, the array voltage is frequently much higher than the battery voltage--So a reduced size array series breaker can make sense.

    I.e.; 100 volt array * 40 amp Imp = 4,000 watts

    4,000 watts/58 volt battery charging = 69 amp Ibatt-charging (nominal)

    Note, because the Vmp*Imp of the array is highly variable (i.e., cold temperatures, edge of cloud effects, refections from snow, water, sand), the NEC requires 1.25*1.25 (=1.56) up sizing of the wiring/breakers/controllers.

    69 amps * 1.56 = 108 amps wiring/breakers/controller

    And, because MPPT actually control their maximum output current... You can use the controller output rating as the max continuous..

    I.e., if you use an FM-80 with 80 amp maximum output based on the above mythological 4kW solar array, you would only need:

    80 amps continuous * 1.25 = 100 amp rated circuit+breaker

    -Bill "clear as mud" B. :roll:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shockmanshockman Solar Expert Posts: 113 ✭✭
    Re: breaker size??'s

    Okay were getting into math here, I see Tylenol in my near future! So I'm thinking if I use my 60A breaker(one those cute little red pop ups with little lever on side!you know the one) on input from array it can also serve as nice shutoff, and use a 100A one on CC to batt. I should be good to go?? does it matter on this one that cable is 6AWG?
    4x240w panels,Classic 150 CC, 4x380AHR L16's, antique Trace 12V inverter
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: breaker size??'s

    Using this table (NEC):

    http://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    6 AWG is good for ~55-75 amperes (in conduit).

    If you use Boating electrical charts, some suggest you can use 6 awg for short wire runs (to keep voltage drop low). Note that SAE wire gauge (as opposed to American Wire Gauge) is about 12% smaller vs AWG wire gauge:

    http://www.westmarine.com/webapp/wcs/stores/servlet/WestAdvisorView?langId=-1&storeId=11151&page=Marine-Wire

    Another chart which has suggestions:

    https://www.eol.ucar.edu/rtf/facilities/isff/LOCAL_access_only/Wire_Size.htm

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • VicVic Solar Expert Posts: 3,112 ✭✭✭✭
    Re: breaker size??'s

    Marc,

    Believe that I know of the cute breaker ... very little respect for those at this location.

    Midnite and Ouback offer very good breakers. These are the industry standard for PV installations, and are not too expensive. The following are often used in PV Combiners and on the input to a CC -- these are DIN-Rail types:

    http://www.solar-electric.com/mnepv.html

    For the output, a Panel Mount is good. If it were me, I'd use the Panel Mounts for both the input and output. Very nice, mount to a panel with screws and have superior mechanicals IMHO:

    http://www.solar-electric.com/pamodccibr.html

    The PM breakers mount conveniently in a MidNite box like this:

    http://www.solar-electric.com/mnedc-quad.html

    This is a very solid approach. Using a breaker as a switch requires a breaker that is fairly rugged, and having one that mounts from the front, like the PMs is a great advantage compared to the DIN-Rail types.

    AND, when it is possible, would recommend switching DC breakers with NO current flowing through them to help save the contacts. The Classic CC has the Mode function ... just switch Mode to OFF and switch the PV in (first) and the CC output breaker (if needed next). When powering-up the CC turn on the Battery breaker frist and the PV in last.

    Realize that you already have the "cute" breaker, and none of the above items linked are free, but the prices are very reasonable. All just opinions. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • shockmanshockman Solar Expert Posts: 113 ✭✭
    Re: breaker size??'s

    Vic, thanks for the tips, too bad I wasn't all over this sooner, I just received an order from NAWS, oh well guess I'll have to place another! hard to find this stuff up here. What is the knock on the "cutzie" I got it from the local battery guy.
    While reading instructions for my MS combiner box, I read about polarity of the din rail breakers and found out that if useing them between CC and batts. that they should be wired, what I would naturally consider to be backwords, which then caused me an epiphany!!!! I have one of these on my Air Breeze, it is on pos. line to batts with + on mill side. Now I'm wondering if that is correct?? or should it be turned around???
    Further to BB post cause I'm useing 6AWG CC to batts, should I reduce breaker from 100A ?
    4x240w panels,Classic 150 CC, 4x380AHR L16's, antique Trace 12V inverter
  • BB.BB. Super Moderators, Administrators Posts: 32,006 admin
    Re: breaker size??'s

    Ask the question differently... What awg should the wire be?

    I.e., maximum continuous current, any surge current, wiring distance. Operating voltage (and how much voltage drop will your load/system support).

    In the end, most people use much heavier cables for the DC power distribution to keep voltage drop down (12-48 volt systems have many times more current than 120 VAC systems==10 to 2.5x as much. Power=Volts*Amps ... 1/10th the voltage, 10x the amperage).

    Picking the breaker is (usually) secondary here (important, but cannot really do a good job of sizing until the rest of the details have been worked out).

    Will a 100 amp breaker be "OK" on a 6 awg cable--Yea--Not ideal, but if you have exposed wiring (instead of a bunch packed tightly in conduit)--It will probably be fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: breaker size??'s

    This is a very hardcore electrician code calculator, targeting people training for their journeyman license.

    http://www.electriciancalculators.com/codecalc_3/publish.htm

    "Table 310.16 & Voltage drop" is the primary calculator for wire and breaker sizing.
    "Raceway and trough fill" is for conduit sizing.

    The calculator tries to stick to the code book as much as possible, and where it can't, it goes conservative (so the code book is insanely conservative, the program is slightly more so). The notes tab documents any deviations from the code book. 150/60 MPPT charge controllers are usually 60 amps on the PV side and 80 amps on the battery side. 80 amp charge controllers need 100 amp breakers on the battery side (80*1.25). For combiner box breakers, it is is simplest to match the series fuse rating on the PV panel, of which 60-cell panels (the most common) are 15A (Panels also come as 72, 80, 96 cell). Charge Controller PV-side breakers are best at the sum of the combiner box ratings (5x15A strings = 75A, round up to nearest trade size of 80).

    The Engineer that James knows said it was insane to use bigger than 10AWG pre-combiner and 6AWG post-combiner (60A). I'm using 6AWG pre-combiner and 2AWG post combiner (lucky I didn't insist on going all the way to 1/0). I have most of the wiring distance pre-combiner because it is easier to run in the attic (long wire runs get heavy) and James is pretty anal about keeping stuff out of the sun (He preferred to run in attic). Phoenix gets a lot of 110+ degree summer days, a few over 115. Generator conduit and post-combiner PV conduit are exposed to the morning sun. Worked out well. It is expansion friendly.
  • VicVic Solar Expert Posts: 3,112 ✭✭✭✭
    Re: breaker size??'s
    shockman wrote: »
    Vic, thanks for the tips, too bad I wasn't all over this sooner, I just received an order from NAWS, oh well guess I'll have to place another! hard to find this stuff up here. What is the knock on the "cutzie" I got it from the local battery guy.
    ?

    Hi shockman,

    Sorry for the reply delay ... and doing construction.

    I assume that you are referring to a breaker similar to this:

    http://www.bluesea.com/products/7087/285-Series_Circuit_Breaker_-_Panel_Mount_100A

    I have one of these, but have never used it. IMHO, they ARE better than nothing. They are a Thermal Breaker, and seem a bit flakey mechanically. They are easy to deal with, can mount in any position, etc. The published Specs seem a bit thin to me. The AIC (max current interrupting spec) is a bit low -- 3000 A, and looks like it relies on an obscure SAE Spec that is not freely available. (SAE 1625, IIRC).

    That is all, just opinions. These are fairly common in RV/Auto after-market applications, so they are not the end of the world. Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • shockmanshockman Solar Expert Posts: 113 ✭✭
    Re: breaker size??'s
    Vic wrote: »
    Hi shockman,

    Sorry for the reply delay ... and doing construction.

    I assume that you are referring to a breaker similar to this:

    http://www.bluesea.com/products/7087/285-Series_Circuit_Breaker_-_Panel_Mount_100A

    I have one of these, but have never used it. IMHO, they ARE better than nothing. They are a Thermal Breaker, and seem a bit flakey mechanically. They are easy to deal with, can mount in any position, etc. The published Specs seem a bit thin to me. The AIC (max current interrupting spec) is a bit low -- 3000 A, and looks like it relies on an obscure SAE Spec that is not freely available. (SAE 1625, IIRC).

    That is all, just opinions. These are fairly common in RV/Auto after-market applications, so they are not the end of the world. Good Luck, Vic

    Yup! thats the one!!! and your right, very easy to use when not useing an E-panel. I will go ahead and use one (100A) on the controller to batts. line.
    4x240w panels,Classic 150 CC, 4x380AHR L16's, antique Trace 12V inverter
Sign In or Register to comment.