Miscellaneous questions about breakers...mostly

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Hairfarm
Hairfarm Solar Expert Posts: 225 ✭✭✭
in Solar Beginners Corner #1
Greetings,

As a newbie and first-time installer of PV, I still have a few miscellaneous questions. I'm trying to tie all of the knowledge together to complete my system-on-paper before the install. Most of my questions have to do with breakers. To be honest I'm not really sure what the rule of thumb is for sizing breakers/fuses. From what I recall it's 1.5 times the current roughly(?)

1) I'll be running 810 watts (6x135 watt panels - Each panel produces 17.7 volts @ 7.6 amps) Three sets of two in series, then paralleled for 35.4V, 22.8 amps. The three panel strings will each be going into a combiner box. 3 positive and 3 negative. I will use a 15 amp breaker for each of the three positive strings coming in.
Question: Is this the right breaker size to use?

2) My CC is an Outback Flexmax 80. Will an 80 amp breaker between the cc and the battery bank be enough? If so why?
I was thinking of one of these 80 amp models. http://www.solar-electric.com/mr60ampdccib.html Would this work?

3) Do I need any other breaker/fuses between my panels and my CC, or are the three 15-amp breakers (referred to above) in the combiner box sufficient to cut of the panel power to the CC, if needed?

4) I have a 300 amp fuse between my battery bank and my 2000 watt (4500 surge) inverter on a 4/0 wire specified in my manual. In addition to this I have a 350 amp DC cutoff switch on the 4/0 wire as well. Is this all I need? The distance from my batteries to 2000w inverter is 5 feet.

5) Must I use a true sine wave (Good AC) generator to charge my batteries since my inverter/charger is a true sine wave too? Or can I use a modified sine wave (Bad AC) generator through my true sine wave inverter/charger just as well? I have a Honda EU 2000.

6) Can someone recommend a decent battery monitor, or is the built-in software on my Flexmax 80 enough to tell me what I need to know?

7) Btw, what exactly tells me that my batteries are discharged past 40%? Will the Outback Flexmax 80 tell me this?

That about wraps it up. I have read all of my manuals for the CC, inverter, and panels, but breaker/fuse sizes still confound me.:confused: Can't wait to get my hands dirty on this install. I'm sure it will lead to tears of joy as well as tears of despair.:cry:

Thanks again to the posters on this forum. What a resource!

Hairfarm
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
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    Re: Miscellaneous questions about breakers...mostly

    I only have a minute here,, but a Honda Eu 2000 is a real sine wave genny. Most gennies are actually.

    Tony

    PS welcome to the forum, and I and others will write more later I'm sure.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #3
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    Re: Miscellaneous questions about breakers...mostly
    Hairfarm wrote: »
    Greetings,

    1) I'll be running 810 watts (6x135 watt panels - Each panel produces 17.7 volts @ 7.6 amps) Three sets of two in series, then paralleled for 35.4V, 22.8 amps. The three panel strings will each be going into a combiner box. 3 positive and 3 negative. I will use a 15 amp breaker for each of the three positive strings coming in.
    Question: Is this the right breaker size to use?

    Most likely. The breaker size may be specified on the back of the panel or on a spec sheet.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #4
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    Re: Miscellaneous questions about breakers...mostly
    Hairfarm wrote: »
    As a newbie and first-time installer of PV, I still have a few miscellaneous questions. I'm trying to tie all of the knowledge together to complete my system-on-paper before the install. Most of my questions have to do with breakers. To be honest I'm not really sure what the rule of thumb is for sizing breakers/fuses. From what I recall it's 1.5 times the current roughly(?)

    In general, with US/North American rated breakers and fuses... Take the maximum expected continuous current and multiply by 1.25 for the NEC safety factor (1/80%). Breakers and fuses should not blow at less than 80% of rated load. And will blow at 100% or more of rated load (can take minutes to hours--or never at 100%--depends on temperature, etc.).
    1) I'll be running 810 watts (6x135 watt panels - Each panel produces 17.7 volts @ 7.6 amps) Three sets of two in series, then paralleled for 35.4V, 22.8 amps. The three panel strings will each be going into a combiner box. 3 positive and 3 negative. I will use a 15 amp breaker for each of the three positive strings coming in.
    Question: Is this the right breaker size to use?

    You need to look for the data sheet and find the Series Fuse or Protection rating. Generally, it will be around 1.25x Isc (short circuit current) rounded up to the next standard size.

    Also note that there are AC and DC ratings for breakers... Some have one or the other, or both (and DC rating will usually be a lower rated voltage). Many DC breakers have +/- polarity ratings too (as well as "this side up" requirements).

    With UL/NRTL rated solar panels, if you cannot find the rating, I, personally, would not worry about using 15 amp breakers/fuses.
    2) My CC is an Outback Flexmax 80. Will an 80 amp breaker between the cc and the battery bank be enough? If so why?
    I was thinking of one of these 80 amp models. http://www.solar-electric.com/mr60ampdccib.html Would this work?

    First, you need to define the maximum current (800 watts of solar is way less than 80 amps). Next you need to up rate the wiring/breaker by 1.25x (NEC derating). Then look for the next larger breaker.

    Note: Normally an 80 amp breaker will eventually pop if operated at 80 amps. I believe the Outback (and perhaps some Midnite) breakers are "specially rated" to operate at 80 amps. So--it "depends".
    3) Do I need any other breaker/fuses between my panels and my CC, or are the three 15-amp breakers (referred to above) in the combiner box sufficient to cut of the panel power to the CC, if needed?

    That should be fine... However, there is the DC GFI requirement by NEC (main breaker plus ground current detect breaker between panel DC return and earth ground). I don't like it (I prefer to hard ground DC negative at the battery to earth/safety ground). Your building inspect may require the DC GFI (if you are inspected). That DC GFI breaker is not supposed to used as a DC Disconnect.
    4) I have a 300 amp fuse between my battery bank and my 2000 watt (4500 surge) inverter on a 4/0 wire specified in my manual. In addition to this I have a 350 amp DC cutoff switch on the 4/0 wire as well. Is this all I need? The distance from my batteries to 2000w inverter is 5 feet.

    What is the voltage rating of the battery bank? What is the maximum continuous AC Wattage do you want the inverter to supply?
    5) Must I use a true sine wave (Good AC) generator to charge my batteries since my inverter/charger is a true sine wave too? Or can I use a modified sine wave (Bad AC) generator through my true sine wave inverter/charger just as well? I have a Honda EU 2000.

    As stated in an earlier post, most generators are sine wave (although, some have pretty bad sine wave forms).

    And, a few of the "off brand" of AC Inverter/Generators don't really say what their output is (one was MSW).
    6) Can someone recommend a decent battery monitor, or is the built-in software on my Flexmax 80 enough to tell me what I need to know?

    I don't know anything about the Flexmate--So you will need to read up on it... However, I believe it is suppose to do battery monitor functions.
    7) Btw, what exactly tells me that my batteries are discharged past 40%? Will the Outback Flexmax 80 tell me this?

    I Don't know--The only two Battery Monitors I am aware of that have a programmable output are (some of) the Xantrex and Victron models.

    The rest of the models usually have an LCD or LED display that will give you 0-100% State of Charge (and other) readings.

    Good Luck and let us know hot it works out!

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #5
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    Re: Miscellaneous questions about breakers...mostly
    Hairfarm wrote: »
    6) Can someone recommend a decent battery monitor, or is the built-in software on my Flexmax 80 enough to tell me what I need to know?

    7) Btw, what exactly tells me that my batteries are discharged past 40%? Will the Outback Flexmax 80 tell me this?

    The flexmax is not a battery monitor. Outback makes a good battery monitor called the 'Flexnet DC'. Other good monitors are the trimetric and victron. All of these battery monitors need a shunt in the negative battery circuit.

    Be absolutely certain to have an 80 amp fuse or breaker between the battery and the flexmax. When a flexmax dies it may be a dead short accross your battery.

    Perhaps you should consider buying a Midnite e-Panel. Comes with AC and DC breakers, a shunt, a DC ground fault, a bypass switch, and it meets code.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Hairfarm
    Hairfarm Solar Expert Posts: 225 ✭✭✭
    #6
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    Re: Miscellaneous questions about breakers...mostly

    BB -
    You need to look for the data sheet and find the Series Fuse or Protection rating. Generally, it will be around 1.25x Isc (short circuit current) rounded up to the next standard size. With UL/NRTL rated solar panels, if you cannot find the rating, I, personally, would not worry about using 15 amp breakers/fuses.

    It seems that 10-15 amp breaker would be in that range then.
    First, you need to define the maximum current (800 watts of solar is way less than 80 amps). Next you need to up rate the wiring/breaker by 1.25x (NEC derating). Then look for the next larger breaker.
    Note: Normally an 80 amp breaker will eventually pop if operated at 80 amps. I believe the Outback (and perhaps some Midnite) breakers are "specially rated" to operate at 80 amps. So--it "depends".

    Looks like I missed the part in my CC manual that stated that I should use an 80 breaker on the wire that leads to the + positive on the battery bank.
    "Hairfarm - I have a 300 amp fuse between my battery bank and my 2000 watt (4500 surge) inverter on a 4/0 wire specified in my manual. In addition to this I have a 350 amp DC cutoff switch on the 4/0 wire as well. Is this all I need? The distance from my batteries to 2000w inverter is 5 feet."

    What is the voltage rating of the battery bank? What is the maximum continuous AC Wattage do you want the inverter to supply?

    It is a 12 volt system. The largest load I will have (115v x 9.4max load amp) is a 1/2hp AC shallow well pump that could start-surge from 3500 to 4000 watts. My inverter/generator is a 2000watt (4500 surge). The pump would be my largest load. I would make sure no other loads were in effect before starting the shallow well pump. It operates continuously at 115 x 9.4 = 1081 watts.
    That should be fine... However, there is the DC GFI requirement by NEC (main breaker plus ground current detect breaker between panel DC return and earth ground). I don't like it (I prefer to hard ground DC negative at the battery to earth/safety ground). Your building inspect may require the DC GFI (if you are inspected). That DC GFI breaker is not supposed to used as a DC Disconnect.

    There is no building inspector for my off grid cabin. Can you please tell me exactly how a hard grounded DC negative at the battery will "look" like? Which part of the battery bank do you ground, the two load points? Do I really need to go the GFI route for a remote offered cabin?

    By the way, it seems as though this image show a DC GFI being used as a DC disconnect. (see red circle with arrow) Is this wired as a DC disconnect or is it wired correctly?
    Attachment not found.
    "BB - I Don't know--The only two Battery Monitors I am aware of that have a programmable output are (some of) the Xantrex and Victron models.""

    ""vtmaps - Perhaps you should consider buying a Midnite e-Panel. Comes with AC and DC breakers, a shunt, a DC ground fault, a bypass switch, and it meets code.""
    Thanks for the recommendations guys. Those are bit more expensive that I'm prepared to spend. However, the Victron looks like it's more in my price range.

    Lastly, Cariboocoot referenced an insulated stainless steel bolt mounted in wood to be used as a "poorman's" connector for a group of 3 battery lugs. What is an insulated bolt? Is it a bolt that has a coating?

    I know I'm tossing a lot out here, but my cabin is remote and if I don't get all the right parts, I'm stuck having to waste time reordering parts online and driving 75 miles to the nearest Home Depot to get a forgotten component. I only have weekends to work on this as well, which will further delay the install.

    Thanks for the guidance everyone. :)

    hairfarm
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #7
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    Re: Miscellaneous questions about breakers...mostly
    Hairfarm wrote: »
    Can you please tell me exactly how a hard grounded DC negative at the battery will "look" like? Which part of the battery bank do you ground, the two load points? Do I really need to go the GFI route for a remote offered cabin?

    By the way, it seems as though this image show a DC GFI being used as a DC disconnect. (see red circle with arrow) Is this wired as a DC disconnect or is it wired correctly?

    The GFI is two circuit breakers ganged together. The 1 amp breaker _is_ the bond between Battery neg and ground. When a fault current of more than an amp occurs, the breaker is tripped and it disconnects the PV pos from the system.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #8
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    Re: Miscellaneous questions about breakers...mostly
    Hairfarm wrote: »
    It is a 12 volt system. The largest load I will have (115v x 9.4max load amp) is a 1/2hp AC shallow well pump that could start-surge from 3500 to 4000 watts. My inverter/generator is a 2000watt (4500 surge). The pump would be my largest load. I would make sure no other loads were in effect before starting the shallow well pump. It operates continuously at 115 x 9.4 = 1081 watts.

    So, my calculation would be:
    • 1,081 watts continuous * 1/0.85 inverter eff * 1/10.5 VDC cutoff voltage * 1.25 NEC derating = 151.4 amp minimum rated wiring+breaker/fusing

    Obviously, rounding up to 175 wiring/fusing or even 200 amps would be OK (again, sizing the wiring for the maximum fuse/breaker rating).
    There is no building inspector for my off grid cabin. Can you please tell me exactly how a hard grounded DC negative at the battery will "look" like? Which part of the battery bank do you ground, the two load points? Do I really need to go the GFI route for a remote offered cabin?

    A "hard ground" would be a heavy wire (6 awg or heavier) from the negative battery bus to a 8-10' ground rod driven at the edge/out side of foundation of the cabin (near where the PV wiring enters the side of the cabin). Any water pipes, gas pipes, etc. would also be tied to this ground rod.

    Personally, I am not a fan of the DC GFI--And code is changing (I do not know how yet).
    By the way, it seems as though this image show a DC GFI being used as a DC disconnect. (see red circle with arrow) Is this wired as a DC disconnect or is it wired correctly?
    Attachment not found.

    It is wired as a DC GFI--the reason it is not a "DC Disconnect" is because if you open the DC side for the PV array, it also opens the DC Battery to Earth Ground connection too... The code would want another DC Disconnect (breaker, knife switch, etc.) for a true "DC disconnect". (the lifting of "safety ground' is a 100% no-no in any safety grounding system I have every seen).
    Lastly, Cariboocoot referenced an insulated stainless steel bolt mounted in wood to be used as a "poorman's" connector for a group of 3 battery lugs. What is an insulated bolt? Is it a bolt that has a coating?

    Nothing fancy--Just using a block of wood for insulation with a bolt (or stud) in it to hold everything from moving.

    A better choice would be some sort of bus bar with insulated mounts. Something like these:
    wind-sun_2245_17173400

    But people make bus bars out of flattened water pipe too.

    I would prefer brass bolts and hardware over stainless (better electrical properties). However, if you use stainless steel hardware, make sure you use anti-seize compound. Stainless bolts/nuts will "gall" and bind/twist apart surprisingly easily without good lubricants.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Hairfarm
    Hairfarm Solar Expert Posts: 225 ✭✭✭
    #9
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    Re: Miscellaneous questions about breakers...mostly
    The GFI is two circuit breakers ganged together. The 1 amp breaker _is_ the bond between Battery neg and ground. When a fault current of more than an amp occurs, the breaker is tripped and it disconnects the PV pos from the system.

    --vtMaps

    That explains it in a way even I can understand ;) It basically sounds like an AC GFCI breaker, except used for a DC system.
    Nothing fancy--Just using a block of wood for insulation with a bolt (or stud) in it to hold everything from moving.
    A better choice would be some sort of bus bar with insulated mounts. Something like these: But people make bus bars out of flattened water pipe too.

    BB, I need a buss bar that can accommodate 4/0 wire for my inverter and 2/0 wire to each of my batteries. I can't seem to find one that will take wire that large. The ones you referenced seem to go only to 1/0 wire size.
    I want to wire my batteries like this:
    Attachment not found.


    I would need two buss bars (+ -) that I can attach two 4/0 wires(from buss bar to inverter) and 2/0 wire (from batteries to buss bars) and a ground wire as well. Can you please recommend a product (buss bar, power distribution block, "poormans" set up, etc,) that can accommodate that? Not sure why I'm stuck on such a simple concept, but I feel like I'm over-thinking this?

    2 steps forward, one step back!


    Thanks guys!


    Hairfarm
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #10
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    Re: Miscellaneous questions about breakers...mostly
    Hairfarm wrote: »
    BB, I need a buss bar that can accommodate 4/0 wire for my inverter and 2/0 wire to each of my batteries. I can't seem to find one that will take wire that large. The ones you referenced seem to go only to 1/0 wire size.
    I want to wire my batteries like this:
    ...
    I would need two buss bars (+ -) that I can attach two 4/0 wires(from buss bar to inverter) and 2/0 wire (from batteries to buss bars) and a ground wire as well. Can you please recommend a product (buss bar, power distribution block, "poormans" set up, etc,) that can accommodate that? Not sure why I'm stuck on such a simple concept, but I feel like I'm over-thinking this?

    Your illustration does not make it clear, but the wire lengths (total of + and -) from each battery to the bus bars must be equal, or as close as possible to it.

    The simplest route, although not necessarily the least expensive, would be to buy blocks of copper (or maybe aluminum if you are careful) of a suitable size and then just drill holes in them for through bolts (brass or SS) which will hold ring terminals crimped to the end of each wire.
    SMA SB 3000, old BP panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #11
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    Re: Miscellaneous questions about breakers...mostly

    I am sorry, I do not have any sources other than searching the net for bus bars or making them your self (or using crimp on terminations).

    Personally, I would advise against aluminum bus bars (to much problem with surface oxidation which forms in seconds when exposed to oxygen). But, I guess, people have done aluminum bus bars before.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Hairfarm
    Hairfarm Solar Expert Posts: 225 ✭✭✭
    #12
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    Re: Miscellaneous questions about breakers...mostly

    BB - What is the formula for copper buss bar size? My maximum draw from the batteries would be about 1500 watts from my inverter. I've found plenty of 1/4 inch thick bus bars online. With insulating mounting hardware included.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #13
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    Re: Miscellaneous questions about breakers...mostly

    I am not sure I can give you a straight forward answer on bus bar design... You have to know what material you are going to use (copper alloy, brasses, etc.). If you purchase the material from a supplier, they should have tables/charts about their products.

    A recommended link from random person on web to a copper industry site (metric):

    http://www.copperinfo.co.uk/busbars/pub22-copper-for-busbars/sec102.htm#Table%2013.%20a.c.%20current%20ratings%20of%20laminated%20bars

    To calculate you maximum current draw--For example a 1,500 watt AC inverter on a 12 volt battery bank:

    1,500 watts * 1/0.85 inverter eff * 1/10.5 volts * 1.25 NEC derating = 210 Amps minimum rating for bus bar/circuit

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #14
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    Re: Miscellaneous questions about breakers...mostly
    Hairfarm wrote: »
    BB - What is the formula for copper buss bar size? My maximum draw from the batteries would be about 1500 watts from my inverter. I've found plenty of 1/4 inch thick bus bars online. With insulating mounting hardware included.
    3/16" x 1" will carry 300 Amps, 1/4 " is harder to deal with and if your going the thru bolt them I'd use it. If you'v ever tried to tap copper you'll know what I mean and I have a power tapper in the shop, drilling it is a pain enough and you better have it clamped down.

    My $.02

    http://www.husseycopper.com/Bar/busbarselector.htm
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #15
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    Re: Miscellaneous questions about breakers...mostly
    Hairfarm wrote: »
    Thanks for the recommendations guys. Those are bit more expensive that I'm prepared to spend. However, the Victron looks like it's more in my price range...

    I'm not sure this was a reference to the Midnite E-Panel or not, but a DC disconnect box might be easier on your pocket and perhaps all you need and a place to mount you Shunt...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Hairfarm
    Hairfarm Solar Expert Posts: 225 ✭✭✭
    #16
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    Re: Miscellaneous questions about breakers...mostly
    Blackcherry04 wrote: »
    3/16" x 1" will carry 300 Amps, 1/4 " is harder to deal with and if your going the thru bolt them I'd use it. If you'v ever tried to tap copper you'll know what I mean and I have a power tapper in the shop, drilling it is a pain enough and you better have it clamped down.

    My $.02

    http://www.husseycopper.com/Bar/busbarselector.htm

    I found some 1/4 inch copper @ 15inches long I may buy. I can cut it in the 5inch pieces and use it for +Pos, -Neg, and ground. I'd bolt them like you said. No need to thread, right?
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #17
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    Re: Miscellaneous questions about breakers...mostly
    Hairfarm wrote: »
    I found some 1/4 inch copper @ 15inches long I may buy. I can cut it in the 5inch pieces and use it for +Pos, -Neg, and ground. I'd bolt them like you said. No need to thread, right?
    Thru bolt is fine, I like to use ny-lock nuts on them just out of habit from another life.
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  • Hairfarm
    Hairfarm Solar Expert Posts: 225 ✭✭✭
    #18
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    Re: Miscellaneous questions about breakers...mostly
    Photowhit wrote: »
    I'm not sure this was a reference to the Midnite E-Panel or not, but a DC disconnect box might be easier on your pocket and perhaps all you need and a place to mount you Shunt...

    Photowit,

    I have a stupid question for you. My 12 volt inverter specifies a 300 amp Class T-FUSE in the positive line between the battery bank and the inverter. But the Midnite E-panel box that you specified seems to max out at 250 amps (with the optional 250 breaker) for the "inverter breaker" part of it. Is it still ok to use a 250amp breaker in line with a 300amp fuse? Or is there a mismatch?

    I'm still learning this stuff?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #19
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    Re: Miscellaneous questions about breakers...mostly

    How much power do you plan on pulling from your inverter? (Maximum continuous).

    300 amps is a lot of current--But not that much power at 12 volts:

    300 amps * 10.5 volts minimum * 0.85 inverter eff * 0.80 NEC derating for continuous power = 2,142 watts max recommended (using NEC)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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