Help me make wise decisions - First timer

Options
124

Comments

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #92
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    That being said with the first system at 24 volts and under 30 amps, would you buy a true "combiner box" or would you just wire nut the two strings inside a box near the charge controller then one run to the controller? When I see the combiner boxes they all seem to be using fuses rather than breakers, any reason to that?

    You do not NEED a combiner box with only two strings, but I recommend one anyway. And they do come with breakers. Many of the combiners you see with fuses are for high voltage systems (like grid tie). Since you will be running under 150 volts, I would recommend you get a combiner with breakers.

    It is incredibly useful to have breakers in a combiner because they make great switches. If you ever want to work on the system between your panels and your controller, you will want to de-energize the circuit by flipping the breakers. btw, if you pull a fuse out of a combiner box while the sun is shining you can start a fire. No problem flipping an appropriately rated breaker.

    One more thing... Combiner boxes should have lightning arrestors and be located outdoors near the panels. It's good to try and keep the lightning outside your house.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #93
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    That being said with the first system at 24 volts and under 30 amps, would you buy a true "combiner box" or would you just wire nut the two strings inside a box near the charge controller then one run to the controller? When I see the combiner boxes they all seem to be using fuses rather than breakers, any reason to that? Seems like I could even just run both strings through a 40 amp breaker (assuming that sounds correctly sized) then into the charge controller. Do they really need to be individually fused?? I can certainly do it, just seems a bit over the top for a small system like this will start at.

    Again I can buy a box, but it just seems a bit much to spend $150 or so on what two wire nuts could accomplish unless there truly is a 'need', thats half the cost of a new controller in this case.

    I would never wire nut a connection that was anyplace near being in the weather.

    The MidNite boxes can be outfitted with either fuses or breakers. Fuses tend to be 'default' because they are less expensive and you usually do not need to be able to switch panels on/off at all, much less individually.

    The individual fusing is the main point, as it prevents the problem of one shorted panel (string) from being fed the Isc of the others in parallel with it.

    Having a breaker on the combined array is the part that's really not necessary as panels are 'self limiting' in current and therefor if the circuit is wired to accept the maximum potential there is no way the current can go over that amount.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #94
    Options
    Re: Help me make wise decisions - First timer
    vtmaps wrote: »
    You do not NEED a combiner box with only two strings, but I recommend one anyway. And they do come with breakers. Many of the combiners you see with fuses are for high voltage systems (like grid tie). Since you will be running under 150 volts, I would recommend you get a combiner with breakers.

    Except the plan is to expand to four strings of panels in parallel later, so a combiner box is a good idea to start with.
    It is incredibly useful to have breakers in a combiner because they make great switches. If you ever want to work on the system between your panels and your controller, you will want to de-energize the circuit by flipping the breakers. btw, if you pull a fuse out of a combiner box while the sun is shining you can start a fire. No problem flipping an appropriately rated breaker.

    Largely unnecessary.
    One more thing... Combiner boxes should have lightning arrestors and be located outdoors near the panels. It's good to try and keep the lightning outside your house.

    --vtMaps

    You're assuming he's in a lightning-prone area. This may not be the case. Many systems of all types work fine without arrestors for a long, long time.
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #95
    Options
    Re: Help me make wise decisions - First timer

    Well thank you very much for the input, I'll just go ahead and make a combiner box, though I was planning to have it inside with all the other equipment, I suppose it could be outside. As for lightning, does it happen, yes, is it often or very thought about, no.

    Now with 4 panels I'm at just shy of 30 amps total at 24 volts, and just under 15 amps per string. Thats assuming 100% output of the panels which I realize is all but impossible. Would you 'breaker' each string at 15 amps, jump to 20 or is there a 'normal' formula?
    · Share on Twitter
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #96
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Would you 'breaker' each string at 15 amps, jump to 20 or is there a 'normal' formula?

    Most panels have a specification for breaker size. If yours do not, use a breaker that is 150% of your panels Isc.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #97
    Options
    Re: Help me make wise decisions - First timer

    In fact multiplying the Isc by 1.5 is probably better than going with the specified maximum series fuse size. The catch word being "maximum" which means "no bigger than" not "use only this".
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #98
    Options
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    Yes: the breakers or fuses for panel protection remain the same because there is no change in the current carrying ability of a panel string. You're just adding more in parallel.

    This is not true of the wiring from the combiner to the controller which should be sized to handle all four strings to start with (and thus avoid having to change it out at the time of expansion).


    Ok I unfortunately need a quick answer, I already ordered the Kid charge controller and the 1000w 24v Cotek inverter, I am always checking craigslist and today came across a set of (4) Trojan 12 volt "club car" batteries for $200 cash. Seller says they are 4 years old and very lightly used, wants to upgrade the cart to gas and lifted bla bla bla.

    $200 is dirt cheap and almost what I'd pay in core charges for new batteries. I'm not big on buying used but the price is hard to argue. (2) 24v strings at 150ah each gives me 300ah for $200. Assuming they serve me for a year or two I'm in pretty good shape right??

    Thoughts??? What should I check for?? Should I pass them up??
    · Share on Twitter
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #99
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    I am always checking craigslist and today came across a set of (4) Trojan 12 volt "club car" batteries for $200 cash. Seller says they are 4 years old and very lightly used, wants to upgrade the cart to gas and lifted bla bla bla.
    <snip>
    Thoughts??? What should I check for?? Should I pass them up??

    I'm not sure what a 'club car' battery is. Got a model number?

    What to check for? Ideally you would do a load test. The next best thing you can do is check SG on each cell.

    My advice: run away from this 'deal'. These 'lightly used' batteries are probably not a good deal.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #100
    Options
    Re: Help me make wise decisions - First timer

    Agreed. Batterys are more or less consumable,and an 4 year old unknown brand of unknown history is basically worthless.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #101
    Options
    Re: Help me make wise decisions - First timer

    I went with your advice and passed on the batteries. Finally got my Cotek SK-1000 24v 1000w inverter. Looks to be of good quality, thus far I'm impressed, especially cost wise vs others.

    The manual says to use 4awg wire from the batteries to the inverter for my specific model and an 80 amp fuse. It then goes on to list the 48v 2000w and 3000w models also using 4awg wire, just with up to a 100amp fuse. When I actually go to wire the system I'd like to do it once and not waste wire later when I upgrade to 48v, would you all say I'm safe to use 4awg wire? I can certainly go larger, but if there isn't a reason then why waste the money right?

    Best value in line fuse for this??

    Looking around I see people seem to use ANL and Class T, but for this price how do I pass it up???

    http://www.amazon.com/Scoshe-EWFH-Single-Fuse-Holder/dp/B000KIR8M0

    Or is it just completely a bad idea??

    Additionally I'd really like to know what would be the smart choice for wire sizing between batteries, I'm not quite sure what to do there?? Stick with the same 4awg or go larger??
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #102
    Options
    Re: Help me make wise decisions - First timer

    Well 1000 Watts on 24 Volts is about 42 Amps. 4AWG will actually handle about 100 Amps continuous. The 80 Amp fuse rating is based on maximum power at minimum Voltage (probably goes down to 21 Volts before shutdown) times the NEC derating raised to the nearest available or: 51 Amps (1kW /21 Volts) * 1.56 = 79 Amp fuse ^ 80.

    Why use the larger wire size? To reduce V-drop over distance so the inverter doesn't cut out under load.

    2kW on 48 Volt would actually be the same for current, only less V-drop for a given distance. No problem with using 4 AWG there either. 3kW on 48 Volt increases current by about 50%: 62.5 Amps continuous at nominal Voltage. About 71 Amps at minimum 42 Volts so with the NEC derating it would be 111 Amp fuse. They are fudging at 100 Amps. Remember these are maximum fuse ratings; nothing says you can't run undersized fuses/breakers. The important thing is that the wire can handle more current than the circuit protection. With 4 AWG & 100 Amp fuse it's just at the limits (depending on what wire chart you look at).

    So all is good.

    Whereas the ANL fuse holder (doesn't seem to include the fuse) you linked to would probably work, check out the full price and compare it to the Blue Sea terminal fuses if you can find them locally (Marine/RV dealer). In either case keep it as close to the battery as possible to reduce the amount of unprotected wiring.

    Stick with the 4AWG between batteries.
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #103
    Options
    Re: Help me make wise decisions - First timer

    Did a bit more amazoning and found this, under $10 with a fuse, seems stupid cheap! I assume these are for car audio guys, thus 12v, does that become an issue at 24v? Is a 100 amp 12v fuse still a 100 amp fuse at 24v??

    Seems like a dumb question but I figured I should ask!

    http://www.amazon.com/Earthquake-Sound-Fuse-Block-Holder/dp/B00CBB72AM
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #104
    Options
    Re: Help me make wise decisions - First timer

    Scratch that, I looked up the Blue Sea and I like the design more anyways. I'll go that route.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #105
    Options
    Re: Help me make wise decisions - First timer

    No it is not a dumb question at all. It is an important one often overlooked.

    A fuse has both a current and a Voltage rating. That Voltage rating indicates what it can safely interrupt without arcing. If these are "12 Volt" fuses being offered they are possibly good up to 32 Volts which may be usable on a 24 Volt system. Now if that's wrong the fuse can blow the arc can glow and the electronics can fry. I can also tell you that people who have used cheap automotive blade type fuses on their systems have found they don't really stand up to the rated current due to the inherent poor quality which counts on the wiring never being run anywhere close to the limit. This is why circuit protection known to be sufficient for inverter use costs 10X what these things do.

    How much of a gambler are you?
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #106
    Options
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    How much of a gambler are you?

    Well, I live in Reno, sooooo

    Already ordered the dual block Blue Sea terminal fuse and a couple 100 amp fuses. The dual block was only $4 more than the single, no use for the second as of now but who knows in the future.

    Now to find decent priced 4awg wire!

    Inverter showed up along with a phone call about the Kid controller that was supposed to be in the same box... They don't have them in stock. Awesome!

    Also just saw this, and wow what a great idea!

    Attachment not found.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #107
    Options
    Re: Help me make wise decisions - First timer

    Actually you do have a use for the dual battery terminal post fuse holder: one fuse for the inverter, one for the charge controller. All neat and nice in a simple bolt-on package.
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #108
    Options
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    Actually you do have a use for the dual battery terminal post fuse holder: one fuse for the inverter, one for the charge controller. All neat and nice in a simple bolt-on package.

    I was just testing you!

    Ok I lied, but I'm glad I went that route lol! Being that I have a 30 amp charge controller what type of fuse would you use on that side of it? I guess I hadn't thought about fusing the charge controller to battery but I don't see why not?
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #109
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    I was just testing you!

    Ok I lied, but I'm glad I went that route lol! Being that I have a 30 amp charge controller what type of fuse would you use on that side of it? I guess I hadn't thought about fusing the charge controller to battery but I don't see why not?

    Well it's exactly where you want it 'cause the most likely scenario is the battery dumping to the charge controller should that fail. Not likely the controller is suddenly going to dump 100% of the battery's capacity to it.

    You've got a 30 Amp controller so that's minimum 10 AWG. Not sure how big of wire the Kid will take. The Classics take up to 4 AWG and most 60 Amp controllers take 6 AWG so let's guess 8 AWG. Good for about 50 Amps continuous. Try out the NEC formula on 30 Amps and we get 46.8 Amps round up to ... uh, 50 Amps. That seems to work.
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #110
    Options
    Re: Help me make wise decisions - First timer

    Just looked and the Kid has front facing fuses, so maybe I don't need one??

    http://www.midnitesolar.com/productPhoto.php?product_ID=530&productCatName=Charge%20Controllers%20-%20KID&productCat_ID=43&sortOrder=1&act=p

    They even sell a $10 "breaker" you can insert instead of the fuse.

    Would the easily replaceable front facing fuses negate my need for even the combiner box?
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #111
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    Just looked and the Kid has front facing fuses, so maybe I don't need one??

    http://www.midnitesolar.com/productPhoto.php?product_ID=530&productCatName=Charge%20Controllers%20-%20KID&productCat_ID=43&sortOrder=1&act=p

    They even sell a $10 "breaker" you can insert instead of the fuse.

    Would the easily replaceable front facing fuses negate my need for even the combiner box?

    They made negate the need for a battery fuse (although I still prefer having the fuse close to the battery) but not the combiner box & its fuses: remember the circuit protection on the panels is to protect each panel from the other panels in the event of a short. The current in such a case doesn't go to the charge controller at all, but from the good panels to the shorted one.
    · Share on Twitter
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #112
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    I guess I hadn't thought about fusing the charge controller to battery but I don't see why not?

    Never forget: Anything and everything that is connected to the battery must be fused.
    esteban wrote: »
    Just looked and the Kid has front facing fuses, so maybe I don't need one??

    No. Anything and everything that is connected to the battery must be fused. The fuses are to protect the wiring from glowing white hot and burning down the place. A fuse in the controller will not protect the wiring between the battery and the controller.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #113
    Options
    Re: Help me make wise decisions - First timer

    esteban,

    Those built-in fuses on the Kid are for internal functions of The Kid, and NOT for the Input or Output of The Kid.
    EDIT: Here's a link to The Kid Manual, if you do not have it already:
    http://www.midnitesolar.com/pdfs/kidManual.pdf

    Yes, both MinDite's Din DC breakers, and the somewhat more expensive Panel Mount breakers are very good and very inexpensive. Both of these breaker styles will want a metal box for their mounting:
    http://www.solar-electric.com/misobigbabox.html

    The DIN Rail breaker for the above box:
    http://www.solar-electric.com/mnepv.html

    MidNite does make a smaller DIN box, but is it quite small, and if you have the room for the larger box, it is easier to wire and work inside, IMO.

    Your Solar Pergola, Sun Shade, really, is quite nice. Have Fun, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 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.
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #114
    Options
    Re: Help me make wise decisions - First timer

    Looking at ordering the combiner box parts now, and trying to make sure I understand the amperage for the breakers correctly:
    Cariboocoot wrote: »
    In fact multiplying the Isc by 1.5 is probably better than going with the specified maximum series fuse size. The catch word being "maximum" which means "no bigger than" not "use only this".

    My panels have an Isc of 5.4, there are two in series (thus I assume) making it 10.8. Which you end up at 16.2, just above a 15 amp breaker. So would you go to a 20 amp breaker? More or less my combiner box will be an empty steel container with two 20a breakers then a single wire leaving to my controller. I assume I'd also have a negative buss bar where all the panel negatives and battery negative connect.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #115
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    My panels have an Isc of 5.4, there are two in series (thus I assume) making it 10.8.

    Nope. Two panels in series deliver the same current as one but twice the Voltage.
    5.4 Isc * 1.5 = 8.1 = 10 Amp fuse or breaker.
    More or less my combiner box will be an empty steel container with two 20a breakers then a single wire leaving to my controller. I assume I'd also have a negative buss bar where all the panel negatives and battery negative connect.

    All negatives come into the combiner box to a bus bar to be combined. All positives come into the combiner box, go through their individual fuses, then combine. Line from the negative and positive bus bars goes to controller.
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #116
    Options
    Re: Help me make wise decisions - First timer
    Cariboocoot wrote: »
    Nope. Two panels in series deliver the same current as one but twice the Voltage.
    5.4 Isc * 1.5 = 8.1 = 10 Amp fuse or breaker.



    All negatives come into the combiner box to a bus bar to be combined. All positives come into the combiner box, go through their individual fuses, then combine. Line from the negative and positive bus bars goes to controller.

    What's sad about that is that is exactly what I was thinking and how I'd wire it when time came, but I'm working and posting at the same time so I'm about 30% paying attention lol!

    Now that I will end up wiring it correctly (thanks!) will I have a need for a true "ground" of any kind? I imagine I'd want to ground the inverter? Should I run its own ground rod into the ground or would I be ok just connecting into the home's ground wiring? All of that being said I assume many "small" i.e. car inverters don't have a ground to speak of, but at 1000w when my fridge and TV are going I'd like to know they are safe.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #117
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    What's sad about that is that is exactly what I was thinking and how I'd wire it when time came, but I'm working and posting at the same time so I'm about 30% paying attention lol!

    Now that I will end up wiring it correctly (thanks!) will I have a need for a true "ground" of any kind? I imagine I'd want to ground the inverter? Should I run its own ground rod into the ground or would I be ok just connecting into the home's ground wiring? All of that being said I assume many "small" i.e. car inverters don't have a ground to speak of, but at 1000w when my fridge and TV are going I'd like to know they are safe.

    What? Asking questions about grounding? Are you trying to start an argument or something? :D:p

    Well normally the panel frames/mounts would have a ground wire going down the outside of the building to a ground rod. The negative pole of the battery would be connected to that same ground rod (negative is usually 'carried through' on charge controllers so it grounds the panel negatives as well). Then the AC output would have one of its sides connected to, guess what, that same ground rod.

    Now enter the complications.

    First up, if the inverter is like the Cotek/Samlex with built-in sockets then there is usually just a ground lug somewhere on the case to connect to the rod. If there is GFCI output on the inverter you definitely do not want to ground 'after' that part of the output circuitry. And if it is an MSW inverter you probably do not ground the output at all. Same goes for a float AC output application. Translation: consult the inverter manual and pray it wasn't translated wrong.

    Second, if you were to follow the NEC code for DCGFCI then the negative does not get connected to ground, only the ground wire of the DCGFCI breaker(s). Argue all you like about the pros and cons of that section of the code.

    Third, if you've got surge protection installed anywhere it will have one wire (usually green) which needs to go to that ground rod.

    And then there's that ground rod itself. We always think of it as "single point grounding" but by the same token that "point" might need to be comprised of multiple rods tied together the right way or even flat plates. Plus if there's a long distance between, say, the array and everything else there may be a need for a second ground rod and you can have lots of fun arguing with AHJ's about the correct interpretation of code over that.

    You didn't think it would be simple, did you? I've probably left out half the stuff as it is.
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #118
    Options
    Re: Help me make wise decisions - First timer

    That all makes sense, and yes my Cotek has the "chassis ground" which I assumed is literally just a duplicate of the negative wire sitting right next to it. So let me present two scenarios:

    1) Nothing grounded, you hook this all up just like it was in a car. Panels run to combiner, combiner to charger, charger to batteries, batteries to inverter and then an extension cord to whatever 1000w device you decide to run

    My honest guess: Everything works and runs flawlessly.

    Downsides to above, well, all I can TRULY think of would be if your house was hit by lightning then the panels/mounts are not technically grounded thus could cause major issues. But lets be honest here, your house just got hit by lightning... Not much good is going to come of that no matter how you want to look at it. I suppose I'm just not one to believe that a 12 gauge piece of Romex tied to a rod is going to just "suck up" a lightning bolt. I've seen what lightning does to houses that are full of normal wiring with plenty of ways to ground, and guess what there is a giant hole in the roof, everything exploded etc.

    Do I want to use the above setup, no, I think having it grounded is a good idea, but to what extent is my question.

    I've never hooked up any DC device to a true "ground", I've always just hooked to the "ground" of the battery.

    In a real world scenario do I run a piece of romex from my battery ground to a big copper steak in the ground and call it a day??? Maybe this needs to be the same 4 gauge wire etc..

    If I end up with panels on my roof I'll certainly look to ground them correctly, but I'll treat that separately. They very well may be on a metal pole in the ground, thus grounding itself.
    · Share on Twitter
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #119
    Options
    Re: Help me make wise decisions - First timer
    esteban wrote: »
    1) Nothing grounded, you hook this all up just like it was in a car. Panels run to combiner, combiner to charger, charger to batteries, batteries to inverter and then an extension cord to whatever 1000w device you decide to run

    My honest guess: Everything works and runs flawlessly.

    Lightning is not the only reason to ground a system. The panel frames must be grounded to prevent static charge build up.

    If you do a 'floating' ground for the current carrying conductors, you must have fuses or circuit breakers on all positive and negative wiring.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
    · Share on Twitter
  • esteban
    esteban Solar Expert Posts: 66 ✭✭✭✭
    #120
    Options
    Re: Help me make wise decisions - First timer
    vtmaps wrote: »
    Lightning is not the only reason to ground a system. The panel frames must be grounded to prevent static charge build up.

    If you do a 'floating' ground for the current carrying conductors, you must have fuses or circuit breakers on all positive and negative wiring.

    --vtMaps


    Which I would eliminate by tying my battery ground to a ground rod correct?
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #121
    Options
    Re: Help me make wise decisions - First timer

    And now we talk about the difference between ESG (Electrical Safety Ground) and lightning protection.

    First of all, the system doesn't need any kind of ground to function. Ground is for safety reasons. It is not for lightning protection either; that is a whole 'nother kettle of fish.

    The idea of the ESG is two fold: it makes half of the wiring zero Voltage potential in respect to ground (very important on higher Voltages which are generally deemed as >60) and it provides a high current sink should anything short out to an external conductor (such as a metal casing). The former is so that anyone touching something can't become a "lower resistance path" for the Voltage and get a shock; the latter is so that if the 'hot' comes in contact with something that shouldn't be energized the circuit over-current protection will trip and shut down power.

    In most cases DC doesn't have to follow these rules because it is low Voltage and doesn't provide much of a hazard to begin with. The biggest trouble with DC is its ability to sustain an arc if over 15 Volts (this is why most vehicle systems are limited to 12 Volts; more efficient than 6 without presenting the arc problems of 24). But when you put DC in a house it now has to follow the same rules as AC (even though in some cases that makes things worse). So we ground the negative (or not) and make it safer than if we didn't.

    For AC tying one side (or technically the middle for split-phase 240) to Earth ground provides a couple of benefits, the main one being the zero Voltage potential for an alternate path (such as a person) to ground for one side. Then if something shorts you need only trip a single pole breaker to shut off power. When 240 is used you'll notice the breaker is double pole and tied so both side shut down at the same time (that way one wire isn't still 'live' in respect to ground).

    Now about that lightning. Nothing in this world is capable of providing protection against a direct hit. Millions of Volts; it can turn any metal into slag, vaporize trees, and blow rocks into gravel. But there is something that happens in a lightning strike area that can be protected against: the air around the bolt becomes saturated with high Voltage, high frequency power. Any kind of conductor can pick this up and carry it to equipment that is not going to like being introduces to several thousand times the Voltage it was meant to operate at.

    Ground the panel frames and most of that stray Voltage is led away instead of led in (which is why we like the ground wire for this outside the house). Put a surge arrestor on the PV leads and the high Voltage spikes jump across that to ground, nullifying them (up to a limit) before they can hit the charge controller or GTI. Same with the AC wiring, which can present a fairly large 'antenna' for picking it up.

    Even then nothing is perfect. Lightning strikes are unpredictable, and will sometimes hit things you'd never expect them to be attracted to. You can't protect against every eventuality (although some people are obsessed with the idea that you can and keep insisting the "government do something") but you can determine what is most likely to happen and take reasonable measures to reduce the risk/damage.

    BTW the ground lug on the inverter is probably not connected to negative; only to the case.
    · Share on Twitter

Categories