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

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.











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