Fuses and Breakers and Wire Sizes for Solar System

Laughing Richard · May 25, 2013

OK I'm getting close to make the order for my solar system and I think that I'm understanding the general overall installation but kind of like Swiss cheese there's a few holes in the brain cells. I hope I can figure out how to get my drawing here so that it's a visual help as well. 1) OK, I'm coming from 3  315 watt panels Vmp 39.8 volts DC and Imp 7.92 amps DC and taking the MC4 connector wires from the panels which are only #10AWG and wish they were 8 or 6 but anyway going into the Combiner box on top of the roof. Out of the combiner box I'm thinking of using a #4AWG wire (or should I go bigger?) to the MidNite Solar Classic 150 MPPT Controller via a breaker in the Baby box. Question is what size breaker is appropriate here. If I'm figuring this correctly I would have 3x7.92amps= 23.76 amps therefore a 30 amp breaker is OK? ( a 30 amp 150VDC DIN rail mount for the Baby box)? Is that correct? 2) OK from the Controller output and going back through the Baby box I would now have a lot more amps as Watts into the Controller = Watts out, and since I have 3x315= 945 watts going in and the other side is going to a 12 Volt battery bank that's 945/12= 78.75 amps going from Controller output to battery bank, right? So if my calculations are correct (please double check me here) then I should have an 80 to 90 amp breaker for the output of the Controller (so like a 90 amp 150 VDC DIN rail mount inside the Baby box for output going to batteries. Correct?) 3) Now from the controller to the battery bank of 6   260 Amp hr Crown Flooded batteries, I'm not sure how big a wire I can go here. I want as large as possible 1/0, 2/0, 3/0 or 4/0 as I'll be using 4/0 cable hooking up between the 6 volt batteries. How big a wire can I use between the controller and the battery bank? And there will be some sort of fuse or breaker on the positve side of the batteries correct? And a 500 amp shunt on the negative side for the Trimetric 2025RV monitor to connect across? But enough questions for now I'll try to attach the drawing I've sketched and will ask more questions later. Hope all this is making sense! Stay tuned....... Richard Well I guess you would have to call me computer illiterate as I don't think I was successful at loading the drawing here sorry need to go back to school!

Laughing Richard · May 25, 2013

One more time of trying to post the drawing this time by taking a photo of it..... I know I know....you're thinking this better be good right? I mean how good can a drawing be? Yeees it worked I think?

blars · May 25, 2013

While it's fine to use a breaker between the panels and the controller, it is not normally done.  (It does make working on the controller easier.)  Breakers are usually sized 50% over the expected current, so I would use a 40 amp on there.  Unless you go from dark to full sun with a dischared battery bank, peak current will be at more like 14v than 12v, so a 100 amp breaker from the controller to the battery bank would be reasonable.  Why use a 500 amp shunt with a 250 amp fuse on your battery bank?  A 250 amp shunt, assuming your monitor can be programmed for it, would be more accurate.

James AKA Lynx · May 25, 2013

Slow down, You did not mention distance and voltage drop and heat. Makes a lot of difference in these voltages. Find the voltage drop tables and measure the distances. Make sure you 2X the distance as you will be making a loop.  You also did not mention wire and shielding. Must be RV/Car rated with good UV and waterproof. Please note that this only applies to the wire coating and not where the wire is exposed.

bee · May 25, 2013

Like already stated use a voltage drop calculator for sizing your wires.  3% drop is considered max recommended.  Always err on the safe side for corrosion and the fact that it always takes more wire length then you expect.  Remember there are 2 kinds of circuit protection used in this kind of wiring.  The first kind is to protect electronic components.  These fuses or circuit breakers will either be built into the electronic device or they will be indicated in the installation manuals.  You don't have to guess or ask us, your components will tell you what they need.  The second kind of protection is catastrophe fusing.  This fusing is to reduce the chance of fire in case a main wire gets shorted to ground, it is designed to protect the wire.  Catastrophe fusing is often not indicated in installation manuals and is placed near large power sources.  Catastrophe fusing is roughly 30-40% higher then your max expected load. Max wire size out of your controller may be dictated by the controller connection, check the manual.  They will probably have various other wiring info in the manual as well.

rokguy · May 25, 2013

Hi Richard, The motorhome/truck solar systems I use is rather simple. From my batteries (the two Century N200 s' connected in parallel using battery cables 400amp bank) I have 4G wiring going upto a 6 switch distribution board it has a battery cut off switch just outside the battery comp. The 6 switch dist has a neg buss bar and a positive feed line, conecting all 6 switches (fused with a 60 amp gold fuse holder/fuse combo). Each lit swtch has its own built in 20amp circuit breaker. From the positive side of each switch I have routed 20amp twin figure 8 wiring to the lights on one cicuit, radio on another, TV another and add on acc another. The panels are two Canon 64watt Unisolars running down approx 9ft of 4G twin cabling into the solar controller halfway down the wall feeding back to the batteries. This sytem is NOT hooked upto the alternator as its sited towards the back of the truck. It is NOT hooked upto a external battery charger. It has nver needed an external charge has the controller will allow it to float, bulk, pulse charge after several days. The other single N200 amp hr bank mounted forward uses a single Unisolar panel, cabling running down through a 20amp sealed solar controller (basic) then back upto  a three switch distribution board (same as above specs) front lights on one circuit, fan another, frig another. This bank is hooked upto the alternator charging sytem aswell. This truck has effectively three battery banks (5 batteries), twin N70s parallel start, one forward mount N200 alt/solar bank and one twin N200 solar bank. Not everyones cup of tea I know but its been working for me for years. Geoff

Laughing Richard · May 26, 2013

blars and James AKA Lynx, and bee, and rokguy Thanks for your help here! OK just to explain to all here I'm a bit new at all of this so if I don't answer things correctly please get after me and slap me around until I get it OK? Thanks. Now the original order estimate that I had Wind and Sun draw up for me had 860 watts of panels and a TriStar MPPT 60 amp charge controller with 870 amp hr battery bank from 4  435AH Trojan L16's. When I placed the order I didn't ask for any cables or fuses or breakers but they were good enough to help me out by putting them in the estimate when they sent them back to me. The Charge Controller was to have a 30amp breaker on the input side and a 63amp breaker on the out put side (both to be mounted inside a Baby box). They don't have Combiner boxes for the roof of the van so I'm to find that elsewhere which I think I found at AM Solar. Now I looked at the 30amp and the 63 amp breaker and again at how many amps might be coming out of the charge controller and it seems to me that I've over powered the TriStar so to speak if it's only a 60 amp controller and I had 860 / 12 volts = 71.67amps or at 14 volts = 61.4 amps, but their first response was With an MPPT controller the output amperage is calculated- watts/batt voltage = amps. (860w / 12v = 72A potential under Ideal Conditions which is rare on an RV where the panels are flat mounted. So the 60A should be okay.   But after giving it some more thought and wanting to have the future option of possibly adding one more panel I decided to go with a bigger Controller a <h1 class="eyTitle">MidNite Solar Classic 150 MPPT Solar Charge Controller  http://www.solar-electric.com/mnclassic.html     a 96amp controller and I saw that the 315 watt panels at a good price were coming in at the end of the month and I changed my batteries to 6  Crown 6V 260AH so will have 780 AH at 12 volts. I haven't replaced the order yet until I get a little more understanding into exactly what all I need for wire and fuses and breakers etc. So blars thank you for the info about using a 40 amp breaker on the input side and a 100 amp breaker on the output side of the controller. It was Wind and Sun's suggestion to go with the breakers and the size of them so I thought that's what I needed as they seem to be really good folks with good information. As for the question of why use the 500 amp shunt as opposed to the 250amp when I'm using a 250amp fuse on the positive side to protect the cable? That is what was recommended by Wind and Sun and after looking at the TriMetric 2025 monitor technical sheet it says there's a choice between using either a 100 amp shunt or a 500 amp shunt but they say that the 100 amp may get too hot.  http://lib.store.yahoo.net/lib/wind-sun/TM-2025-Install-Instructions.pdf  but I may not be understanding the instructions very well. So I couldn't figure out if it can be programmed to go with a 250amp shunt. Sometime it's difficult for me to understand the technical language just reading it without being able to ask them questions such as "what do you mean by what you just wrote?" James AKA Lynx, Sorry you're right I didn't mention the length of wire. From the panels  to the combiner box on the roof should be no more than 12 feet and maybe only 10ft. From the combiner box down to the charge controller should be no more than 4 or 5 feet and from the controller to the batteries should be no more than 4 or 5 ft. I'm mounting the batteries behind the driver's seat in a E350 cargo van inside a box that's ventilated to the outside of the van and will mount the controller, monitor, Baby box, and the 2 inverters ( a 2812 and a 300 watt) on the 3 walls just above the battery box. The cable or wire from the panels to the combiner box are the new code regulated MC4. "All of our MC4 cables are made with #10 AWG stranded UL/NEC approved RHW-2/RHH (USE-2) sunlight resistant wire". So I think I'm ok with them being out in the sun but I've been told that it's better to go with a larger wire for all things in the system in order to cut down on the resistance and heat. But I haven't found anywhere yet that sells the MC4 cable in 8 or 6awg. But maybe that part of the system isn't that critical. bee, Thanks for your help as well, I'm definitely wanting to go with a maximum voltage drop of less than 3% overall. I don't want to skimp on wire size, I'd rather go with much bigger even though it costs a little more in the long run less heat and more power. OK maybe you could help me understand what the technical manual is saying here: <!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:TrackMoves/> <w:TrackFormatting/> <w

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wrcsixeight · May 26, 2013

Look into the differences of wiring the panels in serial vs parallel.  This can effect partial shading output depending to different degrees depending on many factors.  If your charge controller can handle super high voltages, then there are advantages to series, but over 52 volts DC can kill so keep than in mind. The higher voltage panels are less effected by voltage drop to the controller, and the 10awg mc4 cables to a combiner box is fine. Welding wire has a very high strand count and very flexible insulation.  It make routing wires much easier and to get into the charge controller terminals the 500 amp shunt only has resolution to the tenth of an amp where as the 100 amp shunt is able to read hundredths of an amp. If the alternator is feeding the house bank, then the engine grounds must run through the shunt if you want the trimetric/ battery monitor to be accurate. This means the starter current also flows through the shunt.  Way more than 100 amps. Check out Some  wiring type products here:  <a href="http://shop.genuinedealz.com/Marine Electrical Supply/" rel="nofollow" target="_blank">http://shop.genuinedealz.com/Marine Electrical Supply/ </a>Good prices, fast free shipping in my experience. Terminating big battery cables requires skills and tools.  They can make cabling for you after you figure out the lengths and the desired terminations.

Laughing Richard · May 26, 2013

On my drawing I have a 300 watt inverter just siting out in space as I'm not sure how to hook it up. I'm wanting to use this for all the small things that don't need the big inverter to save on the power draw of the larger inverter which I've been told uses power even when it's not needed if it's left on. True? In my tentative order I've got a MorningStar 300 Watt Sine wave inverter. Wind and Sun added a "PV Array Breaker, 30 Amp 150 VDC DIN rail mount for MidNite or Outback Combiners. (For 300 W inverter - Mounts in babybox" So they've given me a hint there that I need a 30 amp breaker for the input side (I'm guessing?) of the small inverter but I'm not sure where I pick the power up from and again not sure of the size wire that I should use here? Richard

Laughing Richard · May 26, 2013

Hi wrcsixeight So what you are saying is if I wire the 315 watt panels in series I could easily get by with the 10 gauge wire correct?  So with the panels having a Vmp of 39.8 volts 3 in series would be just under 120 volts correct? That sounds doable I guess as the Midnite classic 150 can handle 150 volts I think. Otherwise you think the 10 gauge wire is too small?  Those panels have the MC4 connectors right at the panel and it says not to cut the connectors off or it would cancel the warranty so if I didn't go panels in series and just left them in parallel I would be voiding the warranty to add on a larger wire right? Unless of course I bought a couple of MC4 extension cables and used the connectors to tap into the panel connectors then splice into that wire close to the connectors with a larger wire. Is that doable or does that cause a weak connection in the system?  The reason I'm not sure if I want to go with in series is that if one of my panels is shaded but the others are not don't they all lose power because of the shaded one? Oh yeah and thanks for that link to the wiring type products looks good!! Richard

Laughing Richard · May 26, 2013

I just double checked a voltage drop table and it says a 10AWG can take 8amps for 15 feet with a 2% voltage drop so I guess at 12 feet I'd be under a 2% drop. Each panel Imp is 7.92 amps so a little bit less than the 8amps at 2%. That's if I read the table correctly. If so then I'm not gonna worry about the 10AWG panel wire. Also the 12 feet run would  be for only one of the panels from the furthest panel away and the closest panel would only be 2 feet. So I think I was worrying for nothing on the 10 gauge. Richard Edit Using the voltage drop calculator on this site:  http://nooutage.com/vdrop.htm I got 0.7% voltage drop. I entered 36 volts (my panel Vmp is actually 39.8V but the next lowest choice was 36V); I entered 10awg; then 8.5amps (That's the panel Isc which I used instead of the Imp of 7.92amps); then DC; then copper conduit; then 75C (167F); then no conduit; then single set of conductors; then 12 feet (one way distance) then calculate= 0.7% voltage drop. Did I do this calculation correctly? Cheers, Richard

rokguy · May 26, 2013

Hi Richard good info your U.s counterparts are feeding you. The Aust stuff might have different names here, who knows but I buy a heap of 12v stuff of Jaycar Electronics an Aussie company. Coming from a yachting background I might do things a little different from you guys. Figure 8 twin core wiring is just a red + and black - paired automotive wire. Here you can buy it per metre in big 4 gauge, smaller 8 gauge, smaller again 25amp, smaller again 15amp max This is from Jaycar electronics catalogue below. <A href="http://search.jaycar.com.au/search?w=automotive wiring&view=list" rel=nofollow target=_blank>http://search.jaycar.com.au/search?w=automotive wiring&view=list</A> This is the negative buss bar I use, my neg battery bank cable goes to it and I earth the individual neg wiring from each circuit goes back to one of the bolt posts on it. Essentially a movable place to ground earth wires. Widespread use in yachts. <IMG class=bbc_img src="http://a248.e.akamai.net/origin-cdn.volusion.com/efxjc.dkzym/v/vspfiles/photos/4853-1.jpg?1353513360" rel="lightbox"> This is the battery cut off switch, just an on/off switch in the positive cable. <IMG class=bbc_img src="http://a248.e.akamai.net/origin-cdn.volusion.com/efxjc.dkzym/v/vspfiles/photos/2412-1.jpg?1353614080" rel="lightbox"> This is a 6 siwtch distrubution board similar to what I use, when mounted the positive power wire from your bank is individually split six ways (with six circuit breakers or fuses) to where you want them to power this way you can have power only going to one circuit. I like these cause you can have power on only going to say the TV and nothing else. You know the circuit is on cause the light is on (mine ones are LED's) <IMG class=bbc_img src="http://a248.e.akamai.net/origin-cdn.volusion.com/efxjc.dkzym/v/vspfiles/photos/2467-1.jpg?1353513360" rel="lightbox"> Hope this helps Geoff

Laughing Richard · May 26, 2013

Thanks Geoff, Beautiful this makes it a lot clearer especially with the pictures. Was the picture of the 60 amp gold fuses I put up the correct one like you use or is that something different? Richard

rokguy · May 26, 2013

Mine is like what the hoodie in the crib boom box cars use for their high power amps systems. Gold plate fuse and holders. Geoff <IMG class=bbc_img src="http://www.jaycar.com.au/products_uploaded/product_4007.jpg" rel="lightbox"> <IMG class=bbc_img src="http://www.jaycar.com.au/products_uploaded/product_4340.jpg" rel="lightbox"> Jaycar sell these.

James AKA Lynx · May 26, 2013

I do not like breakers. I have had them go bad and not work. Fuses have always worked for me. Go with them and keep spares and a meter to test. Please note that the wires that come with the panels are always the correct ones for the panel. Make sure the ends are well protected from weather. It is best to use fine stranded marine if possible. Painting terminal ends with varnish is also a good idea to keep for loosening. James AKA Lynx

wrcsixeight · May 26, 2013

All inverters give efficiency numbers, but they do not tell you at what load, what % of their max output that number is achieved. On another RV type site, One guy did some testing with different size inverters and different wattage  light bulbs and had results all over the map, and his presumption that 50% of the rated max load was the sweetspot for efficiency was not accurate. I'll see if I can find that thread, but what I took from it was that it was not so easy to say match the inverter for the load rather than just get a huge one which can power everything at once. Some inverters have a feature that they will draw very little power when turned on and powering nothing, called standby load rating or something such.  This is good for powering 120v compressor fridges which cycle on and off. My 800 watt inverter consumes 0.9 amps just turned on, powering nothing.  Nice to have, but I rarely use it instead buying appliances that run on 12 volts.  The inverter is the last resort. The Negative Buss bar is highly recommended.  Next to my Buss bar I have a 12 ATC/ATO gang fuse block, and all my house loads, the wire splits, one to the fuse block, one to the buss bar.  It is not easy to make wiring look organized but this helps greatly.  You do not want many individual wires going to the battery  posts themselves with individual fuses. Gets messy and confusing quick. The Inverters need large fuses, and these cannot go through the ATC/ATO fuse block. I have a manual battery switch whose large terminals on the back serve as Buss studs, like instead of running an individual fused wire from inverter to house battery, I run a wire from inverter to the house battery stud on the battery switch.  From this same stud I also take power for the 10 gang fuse block, and hook my solar to this same stud. You can get an individual buss stud for (+) distribution, or is using a battery cut off switch, you can use the one side of that switch. Note that some devices say to hook directly to battery terminals.  My Danfoss powered compressor fridge says not to share a circuit path with other devices and says to hook right to the battery.  I had to run the (-) to the Shunt, but I ran a wire right to the house battery for the (+) and fused it there. I have a couple electrical product from Absolute.  They do not instill me with confidence. All panels will react differently to partial shading depending on how their internal diodes are arranged, and partial shading takes a huge percentage out of their output.  Saying one way is better than another is not possible without knowing the specifics of the panels. Do not stress the 10awg mc4 cables.  MPPT works best with minimal voltage drop, but it is not as if you are losing a huge percentage of output, especially if you are just running the MC4's to a combiner box.  Just use fat cabling from the combiner box to the controller, and place the controller fairly close to the batteries and use fat wire again between those 2. My one panel uses MC3 connectors, and I bought a 50 foot mc3 10awg cable and cut it in half to run that panel in parallel to my controller.  The wiring is very stiff and was difficult to route.  I bought tinned marine 8awg for my other panel(130watts) from that link in my last post, and this wire was more than twice as flexible. I have a 30 amp circuit breaker in between  solar controller and battery.  This makes it easy to rezero my battery monitor. Much easier than pulling and replacing a fuse, in my electrical cabinet anyway. I am not a fan of regular sized glass fuses.  Mostly their holders are clunky.  I have no experience with those Geoff posted.  I do have some Maxifuse holders which are rated to 100 amps and come with 8 awg, but this is not enough for a large inverter. Car stereo shops are a good place to get cables made up and also the fuses and fuse holders if one does not want to order online, or wait. Usually the word 'Marine' on any product is a clever way of doubling the price, but the products built for the boating world are pretty robust and directly applicable to RV's in most instances. BlueSeas makes excellent wiring type products

Laughing Richard · May 27, 2013

James AKA Lynx, Thanks "Please note that the wires that come with the panels are always the correct ones for the panel. Make sure the ends are well protected from weather". OK Thanks "It is best to use fine stranded marine if possible. Painting terminal ends with varnish is also a good idea to keep for loosening." Do I put an antioxidant on the wires first like Oxguard, before I apply the varnish or forget the Oxguard and just do varnish? rokguy, Thanks for the pictures and info. wrcsixeight, Thanks "I have a manual battery switch whose large terminals on the back serve as Buss studs, like instead of running an individual fused wire from inverter to house battery, I run a wire from inverter to the house battery stud on the battery switch.  From this same stud I also take power for the 10 gang fuse block, and hook my solar to this same stud." So am I understanding correctly that this way the inverter doesn't need a fused wire? Doesn't this leave the inverter vulnerable? And in this case with the manual battery switch you have do you still need a catastrophe fuse or breaker somewhere near the battery+ terminal? Thank you all for your help. I don't understand everything yet but I'll keep reading and trying until I do. Cheers, Richard

Laughing Richard · May 27, 2013

Just a brief note here. I've been having internet connection problems here up in the north east of Thailand and looks like it won't be getting any better for the next few days. I'll be leaving here the morning of the 29th Thai time which is the evening of the 28th there in the US and will be in transit for about 36 hours until landing in Dallas/Fort Worth on the 30th. So if I don't respond right away--- don't think that I'm ignoring you. Who knows the internet may be good until I leave and then I can catch an internet cafe somewhere to check in while traveling. Just saying... Thanks for all your help, Richard

wrcsixeight · May 27, 2013

I am not advocating this, but no, I have no fuse on my inverter, nor catastrophic fuse on the house battery(+).  Just taken extra steps to prevent wire chafing. I lost the instructions to my inverter a long time ago, but I don't recall it saying anything about putting a fuse on the power supply lead.  It came with its  own 6awg leads with ring terminals on the ends. I did replace the fan within it, there are 3 40 amp blade fuses inside of it.

Fuses and Breakers and Wire Sizes for Solar System

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