Splicing two different types of wiring - Is it ok to do?

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  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Splicing two different types of wiring - Is it ok to do?

    The electrical supply places here carry one kind of heavy guage power cable and one kind of lug. The cable is fine stranded, TPR double insulated 600/1000V 90C in metric sizings. The matching metric lugs are just about always unflared, and the only way to get the strands into the lug is to use a thin peice of string or similar to tigthen the bundle. Even then it takes a good deal of of patience, but if you wrap the thread around twice and grip it and the cable with one hand and hold the lug with the other it will usually go after about three attempts.

    There is no marking on the lug re strand size, but i will ask next time im down there.

    THHN isnt available here. Our common garden ac cable is known as TPS, its a PVC insulation, with PVC jacket.
    BB. wrote: »
    Also, there is more "air gaps" in the fine stranded cables. This means that normal crimp connectors are usually too small to fit the same size cable crimp connector (8 awg course stranded vs 8 awg find stranded) and if you get a larger size, they do not crimp small enough to hold the strands.

    I needed to find very fine stranded heavy cable for -48 VDC power system (very tight space) and it was a pain to find UL listed cable and crimp terminations.

    -Bill
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • BilljustBillBilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Splicing two different types of wiring - Is it ok to do?
    BB. wrote: »
    Tin/Lead solder is, roughly, 1/10th the conductivity (or 10x the resistance) of annealed copper.

    That is why it has been reported that high current/lightning strikes have "blown" the solder out of copper wiring connections (in my humble opinion).

    It is certainly also possible to melt a solder connection (relatively low melting point) vs the copper itself (relatively high melting point).

    A proper crimp connection should be "gas tight" and solder should not flow into the area between the crimp ring and the wire.

    The annealing temperature of pure copper is ~736 Centigrade. Although, it appears that copper wire can start annealing at temperatures as low as ~150-200C. Solders melt around 175 to 220 C (tin/lead to lead free).

    So, there would appear to be a risk of annealing the stresses in a crimp copper connection--Something I would guess that is not a good idea.

    This "high temp" copper crimp connection is rated to 650F or 343C -- So, perhaps the ability to anneal copper at the temperature of solder is not a big issue?

    -Bill

    Hello Bill,

    In the coming days, both 2/0 and 4/0 copper will be used because I found it in the lengths I could use and at a price that was very low.

    Where does "Silver Solder" and a hot Mapp Gas torch fair in this discussion?

    Bill
    Bill
  • BB.BB. Super Moderators, Administrators Posts: 32,235 admin
    Re: Splicing two different types of wiring - Is it ok to do?

    Silver solder is near copper in conductivity and is much stronger than tin/lead.

    However, I would avoid soldering in general. The issue of joint resistance is not really my main issue... It is that soldering is difficult to get right (and silver solder would probably be even more difficult) and the issue of creating a point of "flexure". When cables are flexed, the copper is work hardened right at the point where the solder stops.

    There can also be some issues with corrosion (flux wicks it way up the strands of the cable). Of course, use non-corrosive flux, but still not ideal.

    I have never silver soldered cables--So I don't know how well it would work (or not). It has been 4+ decades since I have done any silver soldering (mechanical sections).

    Looks like Silver solder may run in the range of $30-$40 per Oz in small lots vs something like $30 for 16 Oz for lead free solder (plumbing).

    If you are going to make more than a few battery cable connections, I would highly suggest looking for a proper crimping tool and contacts.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BilljustBillBilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Splicing two different types of wiring - Is it ok to do?
    BB. wrote: »
    Silver solder is near copper in conductivity and is much stronger than tin/lead.

    However, I would avoid soldering in general. The issue of joint resistance is not really my main issue... It is that soldering is difficult to get right (and silver solder would probably be even more difficult) and the issue of creating a point of "flexure". When cables are flexed, the copper is work hardened right at the point where the solder stops.

    There can also be some issues with corrosion (flux wicks it way up the strands of the cable). Of course, use non-corrosive flux, but still not ideal.

    I have never silver soldered cables--So I don't know how well it would work (or not). It has been 4+ decades since I have done any silver soldering (mechanical sections).

    Looks like Silver solder may run in the range of $30-$40 per Oz in small lots vs something like $30 for 16 Oz for lead free solder (plumbing).

    If you are going to make more than a few battery cable connections, I would highly suggest looking for a proper crimping tool and contacts.

    -Bill

    Those 4/0 copper end connectors are not cheap, either, but I'd think that a practice run would be needed for me.

    Yes, the silver solder is up there in price. One cold month at the city's local flea market, I was walking from the car to the flea market grounds when I saw some crumpled-up green paper. Turn out, it was a $10 bill, two $5 dollar bills, and three $1 dollar bills. With this "new wealth", it became a game of trying to see just how far this "free" money could be stretched and used to buy something I'd need and enjoy. I ended up spending $20 of the money on a clear, sealed, long plastic tube filled with 16" long rods of silver solder. Got to love those flea markets and garage sales....

    I bought a dual crimper for the MC3 Kaneka panels and MC4 Kyocera panel string connectors going to the combiner box. I wonder if this much larger type of high pressure crimpers are found at a "Rent-All" type store? In the end, I'll get 30% of the cost back from the solar credit, so renting a big tonnage crimper-version may not be so bad...

    Thanks for the help,
    Bill
    Bill
  • HairfarmHairfarm Solar Expert Posts: 225 ✭✭✭
    Re: Splicing two different types of wiring - Is it ok to do?

    I think everything that can be said about soldering may have been said in this thread ;)

    My take-away is that it's ok to splice two different types of wire if crimped correctly. And that soldering adds benefit if done correctly, which is to say added after proper crimping is achieved and not before.

    Got it! Thanks all.
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    Re: Splicing two different types of wiring - Is it ok to do?

    I have seen wires break with higher temperature solder and brazing at the edge of the heat effective zone.
    The higher temperature stuff might be a lot stronger, but will ultimately weaken the base metal.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • lexingtonlexington Registered Users Posts: 10
    Re: Splicing two different types of wiring - Is it ok to do?

    hi, all.
    please i have 3 questions:
    1.Which gauge of wire will be ok for 96VDC, carrying 75amps maximum over 4m? will it be a AWG 6 or AWG 5?

    2.Cables here are sold in 7-strand, single core and fine strand cables. i will need to maneuver the cables from Inverter and battery into the combiner/breaker box which would be ok?

    3. would you recommend crimping alone or soldering? soldering such large diameter cables would be pretty hard to do in these parts, as soldering machines to handle it are hard to find.
    your inputs and posts are appreciated.

    l
  • BB.BB. Super Moderators, Administrators Posts: 32,235 admin
    Re: Splicing two different types of wiring - Is it ok to do?
    lexington wrote: »
    1.Which gauge of wire will be ok for 96VDC, carrying 75amps maximum over 4m? will it be a AWG 6 or AWG 5?

    In the US, we do not have "odd" gauge wire (1,2,3,4,6,8,10,12,14... etc.) in standard sizes for smaller wire sizes.

    Using the NEC (US national electric code) as a conservative guide, 6 AWG would be the minimum (using high temperature rated wire), and 4 AWG would be better.

    Also note that for "real" NEC rated installations, if your current is 75 amps and you are using a fuse/circuit breaker (usually recommended), then you should multiply by 1.25 for "branch circuit rating":

    75 amps * 1.25 = 93.75 amps

    So, you should be designing the circuit for over ~94 amps, which would put you in the 3, 2, or 1 AWG cable range (depending on insulation and temperature ratings). Fuses and circuit breakers are designed to "blow" at 100% of rated current, and not blow at 80% (1/1.25) of rated current. So sending 75 amps through a 75 amp fuse would be unreliable (your codes may be different).

    Other code (such as marine) could allow you to use lighter gauge wire (over 100 amps for 6 awg wire)--But it is usually a good idea to keep with thicker wire (lower voltage drop, less losses to heating of wire, etc.).

    The voltage drop (generic voltage drop calculator) for a one way run of 14 feet of 6 AWG and 75 amps would be ~0.83 volts.

    We generally design for 3% to 1% voltage drip (2.88 volts to 0.96 volts)--So, voltage drop wise, 6 AWG would be fine. If you are doing this with Metric wire--You should be able to find code and a metric voltage drop calculator so you don't have to work/round to US wiring.
    2.Cables here are sold in 7-strand, single core and fine strand cables. i will need to maneuver the cables from Inverter and battery into the combiner/breaker box which would be ok?

    Most connectors/screw/bolted contacts are designed for solid or coarse strand wire.

    Fine strand wire (such as welding and some battery cables) are actually quite difficult to properly bolt/crimp down. The fine stranded cable has "more air" between the wires (larger physical diameter) and may not easily fit the designed hole (i.e., a 6 awg coarse cable will fit a 6 AWG connector but a 6 AWG fine stranded cable may not).

    If the cable is not being moved after being installed, then the coarse stranded (and solid) is OK. If the cable moves (say equipment mounted on a door), then you may need a more flexible cable. Copper "work hardens" and constant bending will cause the wire to eventually harden and break.
    3. would you recommend crimping alone or soldering? soldering such large diameter cables would be pretty hard to do in these parts, as soldering machines to handle it are hard to find.
    your inputs and posts are appreciated.

    Solder melts at a lower temperature--So crimping (or clamping) that physically holds the wire in place, even if it gets hot in a short circuit is usually required by code.

    There has been some arguments over which is better; soldering, soldering+crimping, crimping only.

    Code and design requires clamping or crimping. Solder is OK if wire is physically held somehow that the connection will not come apart if the solder melts.

    Good with soldering is it keeps out water/corrosion. Easier to make connections than crimping (cannot find tools/crimp connectors). Must use "electrical grade" flux (typically rosin or newer fluxes for electronics). If you use "plumbing" fluxes, many are corrosive and will ruin the cable over time.

    Problems with solder is that the solder wicks up the cable strands and stops. This forms a "fulcrum" which focuses the bending force right where the solder stops. If there is bending on the cable, the copper will work harden right where the solder stops and break much faster than a crimp/clamped connection. If you solder, make sure the connection is not subject to flexing (i.e., where flexing is expected, clamp down the cable past the solder joint).

    For soldering large gauge wiring/cable, one person here has used a solder pot as a very nice way to quickly and fully heat large cable connections. Works better than an iron and more controllable than a torch (as posted earlier in this thread).
    2manytoyz wrote: »
    I work in the aerospace industry. Per our regs, we can either solder, or crimp, but we can't crimp and solder. FWIW, either are acceptable methods for flight hardware.

    Part of the issue is trying to crimp a soldered connection. The solder doesn't compress as well as unsoldered copper wires. Ends up failing a pull test. Also, if the connector gets hot, the solder can melt, and things can get "interesting" as the wire starts to slide out of the connector. This is why big power cables use compression fittings, not solder.

    Some of the industrial crimpers for large wire compress the termination so hard that the wire is almost fused together. I've seen pics of these cut apart after crimping, nothing short of impressive. I don't expect YOUR crimper to have these results.

    I have soldered connectors after crimping. It probably made no real difference, but it looked better having the ends of the wire tinned, and a nice solder fillet to the lug. That said, this was only on small conductor cables (~10 ga).

    Once I started moving up in wire size, soldering became much more difficult. Takes a lot of heat to get solder to flow in the ends of fat wire. Even with 6 ga wire, I ended up using a solder pot to tin the wire, then pre-tinning the inside of the lug, and finally heating up the wire and lug just prior to cramming them together.

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    We are also required to have the insulation back about the thickness of the conductor for a visual inspection, prior to covering it with heatshrink. This wasn't a work project, but old habits...

    I must say, soldering 6ga wire was PITA! No way I'd attempt that on 4/0 cable. I use an anvil type crimper instead. Makes decent crimps in a fraction of the time.

    If you have crimp connectors available--Here are a couple of options if you cannot get a good crimping tool... One is to get a hammer crimper.

    Hammer Crimp Tool for Large Terminal Lugs

    A second method somebody posted here--Get a large set of bolt cutters and heat the jaws red with a torch and then let them slowly cool (to soften the steel). Drill the cutter with several different sizes of drills. Then reheat and quench in oil or water to re-harden. Now you have a home made crimper.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: Splicing two different types of wiring - Is it ok to do?

    I actually used the hammer crimp tool listed. I just beat the hell out of it, (one hit might of been enough, but I usually gave it more hits), the tool held up and the crimps seemed good.. I used it for wire as small as 6 awg to as big as 4/0.
    gww
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    Re: Splicing two different types of wiring - Is it ok to do?

    Use 6 gauge THHN wire for 75 amps so long as your ambient temperature the wire is exposed to doesn't go about 30'C.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • BB.BB. Super Moderators, Administrators Posts: 32,235 admin
    Re: Splicing two different types of wiring - Is it ok to do?

    He is in Africa (I think)--So he may have European or other standard wire available.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    Re: Splicing two different types of wiring - Is it ok to do?

    Euro has a wire standard pretty much identical to THHN but I don't remember what they call it.
    Its going to be the type of wire with the insulation that is rated for 90'C.

    Wait if he is in Africa, then you can bet on ambient temperatures higher than 30'C, so might want to move up to 4 or 5 gauge.

    I was in north Africa for a time a couple years ago, and you will find a mix of pretty much anything there. Most places there run 220 volt L to N power.
    Where I was in north africa they favored British standard receptacles, plugs and code, but had US spec romex and TH wire ran in buildings.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • cosmicraycosmicray Registered Users Posts: 24 ✭✭
    Re: Splicing two different types of wiring - Is it ok to do?

    I want to add one more thought to this thread. No matter how good your crimp/solder might be, always walk around the finished installation with a DMM, looking for unusual voltage drops. Particularly during higher current flows, which will expose non-obvious problems.

    A few nights ago I found a 0.25V drop between the crimped/soldered wire connector, and the battery lug (where it entered the battery case). This was with a 25-30 amp charge flow in progress. Shut everything down, examined it carefully, and found no obvious issue. On a hunch, I added a star washer between the wire lug and the top of the battery post. retightened and powered back up. Drop now looked more like 0.01V (typical). My guess is there was some corrosion or solder flux between the lug and the post.
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