Cable splicing

n1stn1st Solar Expert Posts: 77 ✭✭✭✭
I'm looking to splice into an existing 10g run from solar panels. I think it would be messy & difficult to cut and join with wire nuts. Any guesses if a quick splice like this would do the job (6 amps/600v)? If not, any other ideas?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cable splicing
    n1st wrote: »
    I'm looking to splice into an existing 10g run from solar panels. I think it would be messy & difficult to cut and join with wire nuts. Any guesses if a quick splice like this would do the job (6 amps/600v)? If not, any other ideas?

    Please do not use those things. They are an abomination to electrical wiring. I've had to rebuild many automotive wiring systems where those little nasty splicers were used to mutilate the wiring under the misguided notion they would serve as power taps. They are not only undependable, they are not by any stretch of the imagination weather-tight.

    Nor should you use wire nuts. If this is an exterior splice it needs to be done in a weather-tight box; the wires cut and the additions made with proper terminal blocks. If you're paralleling more than 2 panels you need to add fusing as well.

    One of the big problems with panel wiring is improper outdoor junctions; they allow moisture in which corrodes the wire and increases the resistance resulting in power loss, or even bigger problems.

    If you want to go whole-hog on "simple" splicing, you can break the wire and add MC4 connectors (requires special crimping tool) and then use an MC4 'Y' connector to splice in the additional panel. Same fusing caution as above.

    Don't sentence your system to an early death by using slap-dash wiring methods.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Cable splicing
    n1st wrote: »
    I'm looking to splice into an existing 10g run from solar panels. I think it would be messy & difficult to cut and join with wire nuts. Any guesses if a quick splice like this would do the job (6 amps/600v)? If not, any other ideas?

    Definitely not something I'd ever use in anything but a very low power and definitely non-critical situation that I didn't expect to last anyway. You need good, solid, serious connections, not these. I know some don't like solder, but my preference is definitely a good, solid soldered connection with water-proof, heat shrink insulation to keep out moisture, and protected inside a proper electrical box. The last thing you need is something that will surely develop into a high resistance connection, especially in a DC circuit that could easily result in arcing and a fire. And in a 600 volt, 6 amp DC circuit, arcing and fire is almost a total certainty.
  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Cable splicing

    I used splice blocks somewhat like these

    Splicer-Terminal-Block-1EF57_AS01.JPG
    (but rated for aluminum wire) when I installed my pump system. Solid way to splice.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Cable splicing
    mike90045 wrote: »
    I used splice blocks somewhat like these

    Splicer-Terminal-Block-1EF57_AS01.JPG
    (but rated for aluminum wire) when I installed my pump system. Solid way to splice.

    Have also used similar, and are excellent, inside a proper box of course.
  • n1stn1st Solar Expert Posts: 77 ✭✭✭✭
    Re: Cable splicing

    Thanks, you've talked me out of using those quick locks.

    This is all indoors, so the elements are not a factor. I like the splice blocks but they're pricey and I'd need four of them.

    What about hardware used with stainless steel cable? I've seen 2 channel thingys that you crimp, and I've seen 2 channel thingys that with a screw in the middle that clamps down. Wish I could find pics, but you probably know what I'm talking about. I'm dealing with thnn, so I can keep the wires away from each other easily, and wrap each assembly well with electrical tape. That shold take care of the voltage, no? If the connector is solid, metal, and tight, that should take care of the current/resistance/arcing, no? If this doesn't sound safe, I think my next choice would be to make a small cut in the insullation of each wire, wrap the new wire around it, and solder it well, then tape - how's that sound?
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Cable splicing

    If this is copper wire--Then copper split bolts are commonly used (with lots of tape).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cable splicing

    The existing wires must terminate somewhere; can you not just run the new wires to the same point? Safer than any kind of splice (600 Volts, if that really is the Voltage involved, can be a really big problem with any type of connection).
    Also, whenever you add wiring you add current, and whatever is there already needs to be able to handle that current. Don't forget this will affect the V-drop over the wire too.
  • data_enginedata_engine Registered Users Posts: 8
    Re: Cable splicing

    I like the terminal blocks in an enclosure. My biggest fear of where I am is lightning strikes. Call me chicken little, but use the terminal blocks with some kind of SPD and ground. I would use an enclosure with DIN rail and terminal blocks, with some DIN rail SPD's to drain off static to a really good ground. Even a close strike can turn everything into a raging inferno.
  • n1stn1st Solar Expert Posts: 77 ✭✭✭✭
    Re: Cable splicing
    The existing wires must terminate somewhere; can you not just run the new wires to the same point? Safer than any kind of splice (600 Volts, if that really is the Voltage involved, can be a really big problem with any type of connection).
    Also, whenever you add wiring you add current, and whatever is there already needs to be able to handle that current. Don't forget this will affect the V-drop over the wire too.

    Sorry, let me be more descriptive...

    The situation is that 2 PV strings (2 +, 2 -, and a ground) come into the house and run through a conduit (the ground runs outside of it) to a disconnect that's right next to the GT inverter (SMA). The 2 strings are separate into and out of the disconnect, and are combined at the SMA. ...not sure why the installer did not combine them going into the disconnect. Each string is normally 333v (500 Pov), 5amp. So, I could tap into the strings as they go into the disconnect, or where they come into the house.

    Pros/Cons that I see...

    Tapping into where it comes into the house:
    25 feet away from backup CC - save on wire, save on v drop
    Have to cut through conduit somehow
    Have to tap into the 4 thnn wires somehow

    Tapping into endpoint of existing run at disconnect:
    60 feet away, higher v drop
    easy to tap into (no conduit to cut through, and can use the disconnect as the splice block).
    Maybe takes advantage of some additional lightening/ground protection?

    So looking at the pros/cons above, which seems the better approach?

    If the better approach is to tap into the existing disconnect (Square D Heavy Duty 30a 600v) switch, can I use 1 run of 12/2 wire to the new CC by combing the 2 strings at the top of the switch?
  • data_enginedata_engine Registered Users Posts: 8
    Re: Cable splicing

    I am no expert, not even close. I didn't catch if you had a breaker between the disco and the SMA. Maybe you could add two 2-pole breakers in a small box at the conduit entrance, and make your splice there.
  • ThomThom Solar Expert Posts: 196 ✭✭✭
    Re: Cable splicing

    I use 2 types of tape with split connectors on each splice rubber and scotch brand vinyl .

    Thom
    Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator . Added [email protected] 100w panel with a midnight brat 
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Cable splicing
    Thom wrote: »
    I use 2 types of tape with split connectors on each splice rubber and scotch brand vinyl .

    Thom

    That's what I used to splice the cable going to the submersible pump, 200 feet out in the lake at the cottage, and it worked perfectly under water for many years till I pulled the pump out when the place was sold.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cable splicing

    I have this vague recollection of SMA inverters having multiple string inputs on the inverter itself. This may be why the strings were not combined at the disconnect. If this is the case, you're probably not supposed to unbalance the inputs by increasing the panels on one without a like increase on the other.

    If this is not the case then the question is: does this disconnect box have additional knock-outs that could accommodate a third conduit for input?

    I would expect to find two or three separate arrays coming in to the disconnect box, running through fuses (if breakers are not used) and then combined to the disconnect which is then wired to the inverter. If the SMA has multiple fused array inputs then the disconnect would be a double-pole switch which breaks both strings simultaneously.

    Without knowing exactly how it's wired now (and why it is that way) it's just guesswork on how to change it to add more panels. In theory panel addition to a grid-tie system constitutes a modification requiring re-certification.

    In any case, two or more parallel strings need separate circuit protection per string, the disconnect needs to act on all strings, and the wiring after the combining must be able to handle the full current from the expanded array.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Cable splicing

    Wait, what? Tapping the feed between a PV array and a GT inverter in order to feed a "backup charge controller"?

    So, as I understand it, you are trying to take a PV array feed of two strings - which are not combined - and tap/combine them to feed a battery charge controller as well as feeding your GT inverter?


    I think you'll need to re-rig it to combine the strings at the disconnect, so there is only one pair of wire coming out of the disconnect/combiner (IF the GT inverter can handle that sort of setup) and then run to a transfer switch which can send the PV current EITHER to the GT inverter or the "backup charge controller".

    And - if the disconnect box has 30a breakers, then use #10 and not #12 to the CC.




    EDIT: And technically, split-bolts should have 3 kinds of tape - rubber tape, then PVC tape, then friction tape.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cable splicing
    dwh wrote: »
    Wait, what? Tapping the feed between a PV array and a GT inverter in order to feed a "backup charge controller"?

    dwh, where did you see that? :confused: I know I'm past my "best before" date but I thought he was adding more panel to the GT inverter (which had better match up in terms of array Watts and inverter Watts or else there's no point).

    If he is trying to tap a high Voltage GT array to feed a charge controller this is a major undertaking. For one thing most GT arrays operate in the 250-500 Volt range whereas most charge controllers stop at 150 max in. MidNite Classic 250 is only good for 250 Voc, so it still wouldn't work with most GT arrays. That leaves the Xantrex XW MPPT80-600, which was (I think) designed for such a use. In that case you have to disconnect from the GT inverter before powering the charge controller as having two MPPT devices connected to the same array will confuse one or both of them.

    Not as big a problem as it may seem (although switching potentially 600 VDC isn't easy), providing you use the grid power to maintain batteries when it is available and only cut in the solar controller when the grid goes down (GT inverter would be inactive anyway).

    Note to all: if you want the right answers from everyone, details are important. A good explanation of what end you're trying to achieve will go a long ways towards bringing out the sound advice. The apparent confusion around this question shows just what I mean: there's a big difference between adding more panels to a GT array and tapping the array to power a charge controller.

    And when you're putting in wiring, always think about the future and what may be needed/wanted later. It's easier if you've already got room for more wire in the conduit or put in that larger gauge to begin with than to retrofit after everything is all tightened down and sealed up.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Cable splicing

    Mornin' Coot,

    Post #10

    (under pros/cons)
    25 feet away from backup CC - save on wire, save on v drop

    and

    (last line)
    If the better approach is to tap into the existing disconnect (Square D Heavy Duty 30a 600v) switch, can I use 1 run of 12/2 wire to the new CC by combing the 2 strings at the top of the switch?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cable splicing

    Whoa! Good catch, dwh!

    I plead "information overload". :p (Too early to claim I need a nap already.)

    See why it's important to mention little details like that? Totally different situation!

    So, n1st: What new charge controller?

    SMA inverters run PV strings in the 300-480 Volt range. That will instantly fry any charge controller except the Xantrex XW MPPT80-600.

    See previous post about the difficulties of doing this.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Cable splicing

    Yea, the other major problem I see beside "what charge controller", is that the two strings are not combined right now, but if he taps them both and runs to a CC, then he'll be tying them together...somewhere.

    And even if the CC can handle the high voltage of the array - I don't think it's wise to try to feed both a GT inverter and a CC simultaneously from a single array.

    Better to combine them properly and then use a switch to transfer the output of the combiner to one or the other.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cable splicing

    And we don't know the size of the strings: maybe only one would be needed for the back-up batteries. Which we also don't know the size of.

    Sometimes these threads get to be a bit like a "black box" quiz. ;)
  • n1stn1st Solar Expert Posts: 77 ✭✭✭✭
    Re: Cable splicing
    dwh wrote: »
    Wait, what? Tapping the feed between a PV array and a GT inverter in order to feed a "backup charge controller"?

    Correct, and no intension to feed the GT inverter and backup CC at the same time. It would take a few minutes to disconnect the GT line from the bottom of the 30a disconnect (non-fused), and wire in the line to the backup CC. I'll have the line already run. I think this is the simplest method - no chance of upsetting the GT inverter, and won't require additional disconnects, etc. It's not as easy as flippng a switch (or 3), but it's fine - it's not the only manual step as you'll see below.

    Cariboocoot - I understand your confusion. The way this thread evolved, I didn't make the whole situation clear up front. But, yes, this is really all about getting the PV power to a backup CC. Originally I was thinking about just tapping into the existing line from the PVs, then flipping the Disconnect to the GT when necessary. But with the splicing issues, and especially the conduit cutting (don't have any idea of how I'd do that) I followed your lead to just work at the endpoint (the disconnect). The issue at the endpoint is tapping into the disconnect without upsetting the GT'd SMA (strings are combined there).

    Regarding the panels, yes, I can't use all of them unless I go with the XW 600 . A Classic 250 will allow me to use 5 175w panels from each string without additional copper. The 10 panels (5 in each string) will allow me to charge a 200ah bank at 20ah and I should still should have 500wh+ available for AC loads. I don't think the additional power that the XW would provide, is necessary especially considering the extra cost.

    I have a couple of M/F MC cables that I would snap in place at the arrays to exclude the panels that I can't use.

    So in a backup situation, I'd :
    Wait until night time
    Shut the disconnect off
    Exclude the extra panels
    swap the GT wires for the CC wires at the disconnect
    Turn on the disconnect

    Well I think that's the whole story. Does it all sound reasonable?

    A few questions...
    1) The GT system installer didn't put any breakers between the Panels and the GT inverter, only a disconnect. Why are breakers not needed?

    2) I think 10awg would be better for the MC extensions, but I have 12. Is 12 sufficient at that location even though the runs are 10awg? Each string is 4.8a, so it's well within the capacity of 12awg.
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Cable splicing

    For Solar arrays, typically you do not need any series string fuses/breakers (1 per parallel connection) until you have 3 or more parallel strings. 1 or 2 strings will not over current any of the interconnect cables in the event of a short circuit.

    The number of panels in series does not matter (except for picking the right voltage rated fuse/breaker).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cable splicing

    n1st;

    So when the power goes out you are going to:

    1). Turn off the disconnect for the array to the GT inverter.
    2). Rewire the panels on the roof so the downlead is at 1/2 Voltage.
    3). Rewire the array output at the GT inverter so that it feeds a charge controller.
    4). Turn the disconnect back on so the charge controller is energized.
    5). Switch everything back the way it was when the power comes back on.

    Something about this plan says "great potential for mistakes to be made".

    You are looking to charge 220 Amp hours at 24 Volts, no?
    (I guessed by this: five 175 Watt panels = 875 Watts, 674 after derating / 22 Amps charging = 30 Volts.)

    The panels are 35 Vmp, no?
    (I guessed by this: 10 panels per string * 35 Volts = 350 Volts, a normal operating point for a GT inverter.)

    You could put an MC4 'Y' connector between panel #5 and panel #6 in a string and run a separate "low Voltage" downlead. Either tap the (-) at the disconnect or the GT inverter for the "low Voltage" feed (or you could put another 'Y' in at panel #1 and give the "low Voltage" run its own, entirely separate lines). Run to separate disconnect to charge controller.

    Then when the power goes out:

    1). Turn off "high Voltage" disconnect.
    2). Turn on "low Voltage" disconnect.
    3). When power is restored, reverse process.

    Worst case scenario: both disconnects on at the same time will play havoc with MPPT functions on charge controller and GT inverter.
  • n1stn1st Solar Expert Posts: 77 ✭✭✭✭
    Re: Cable splicing
    n1st;
    So when the power goes out you are going to:

    Yes, those would be the steps when the power goes out. I have added:
    1a: Turn off AC/SMA
    1b: wait 5 minutes for the SMA to discharge.

    I see risk that I could miscalculate which 2 panels in each string to split where I insert the MC cable, but I should be able to test this in advance.

    Its' a 48v battery bank.

    Yes, Vmp is 35v.

    The low voltage idea is nice, but it's a long run and I'd have to pay for all that copper. :D

    The Sunny Boy manual implies that the 2 - and 2+ inputs are just for convenience if you have 2 strings, so there may be nothing more sophisticated to it. If true, I think I could combine the lines at the disconnect. But if someone could confirm this about the SMA, that'd be nice. I have a disconnect at the CC also, so if I can combine the lines at the array input of the GT disconnect, I think I can simply turn the disconnect to the GT off, then the disconnect to the CC on, avoiding rewiring the disconnect (the "-" and ground would be combined as well but aren't effected by the disconnect switch).
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Cable splicing

    i have to inject here as i'm curious as to what is going to maintain the battery bank until this said emergency rewiring of the pvs takes place? batteries don't sit in standby indefinitely without depleting their power so at a minimum you'd have to have a float charge on the batteries until said emergency takes place. might as well put in pvs and controller for that task. if you can during the emergency use a cc that can use the voltage of your gt array downconverted then, fine, you have a means of doing more than a float charge and the guys are addressing this aspect of your dilemma.
  • n1stn1st Solar Expert Posts: 77 ✭✭✭✭
    Re: Cable splicing
    niel wrote: »
    i have to inject here as i'm curious as to what is going to maintain the battery bank until this said emergency rewiring of the pvs takes place? batteries don't sit in standby indefinitely without depleting their power so at a minimum you'd have to have a float charge on the batteries until said emergency takes place. might as well put in pvs and controller for that task. if you can during the emergency use a cc that can use the voltage of your gt array downconverted then, fine, you have a means of doing more than a float charge and the guys are addressing this aspect of your dilemma.

    Niel - I have a couple of 12v Batteryminder desulphating chargers floating the batteries. Each charger handles 2 pairs of a pair of 6v's.
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