What makes the best electrical join?

[Danny Jo]

I have spent many, many hours ripping out dodgy-looking chocolate box connectors and replacing them with soldered joints protected by heat-shrink tubing. And I felt very smug about my work. Until today, when a marine electronics service expert told me "You shouldn't use soldered joints on a boat - the wires move, the joints don't, and the solder cracks. Use waterproof junction boxes or crimp connectors instead."

I was so gobsmacked that I forgot to ask whether he would recommend tinning the wires before crimping. What does the panel think?

 

[Lakesailor]

F1 teams don't solder joints for the same reasons.
I don't know if they tin the end, but suspect not. You would still have a soild/flexible interface on each cable.

 

[Salty John]

When I rewired my last boat I used the American Boat and Yacht Council (ABYC) standards and practice.
On the subject of connections the ABYC says that solder should not be the sole means of mechanical connection except in the case of battery lugs where the solder contact length is not less than 1.5 times the wire diameter. On smaller wire gauges they express concerns about the solder causing rigidity which can lead to breakage just like a solid conductor.
The ABYC approves crimp connectors with the proviso that on friction connectors - the blade type and the bullet type - they must resist the tensile force set down in their table; for example a 12AWG wire must stand a 35 lb force for 1 minute. They recommend adhesive shrink tubing and the use of a ratchet crimper.
The ABYC recommends pretinned, stranded wire. In fact they have two grades of stranding, - Type 2 and type 3. (Unstranded wire is forbidden on boats). As an example of the difference between the two grades, AWG12 wire type 2 would have 19 strands and type 3 would have 65 strands. Type 3 is recommended where frequent flexing will occur such as on an engine.
There are many other ABYC dc standards and practices that are extremely helpful. There must be a UK version, I'm sure.
I use Charlie Wing's excellent book Boatowner's Illustrated Handbook of Wiring when doing wiring jobs.

 

[Salty John]

Lakie,

In tinned wire each individual strand is tinned so the strands remain separate, thus flexible.

 

[Piddy]

I try and use multi-strand tinned copper wire with good quality choc blocks.

My first job was with a marine radar manufacturer and all wiring was done using what I knew then as equipment wire (eg. 7/0.2 tcw). Now it's harder as you have to buy 100m (or use Ebay) and I usually want much heavier wire making it so much more expensive.

The choc blocks were made by Belling Lee http://uk.farnell.com/belling-lee/l1325-ni/terminal-block-12way/dp/9427066 and made of brass with plated brass screws that don't rust. However, they are expensive!

Cheers

 

[NeilT]

I have always soldered the join and used heat shrink BUT its a type of heatshrink with a "hot glue" inside.
The solder makes the electrical joint and the glue the physical one, the glue also flows and seals the whole thing from moisture.
The cheap heat shrink aint worth a light!
N

 

[Danny Jo]

I should add that my soldered joints are made by laying the stripped ends of the wire together, in line, then twisting them together in an opposing spiral before soldering.

I find it difficult to believe that the solder could fail along the full length of the spiral. I am however concerned about the effect of flux on the neighbouring untinned strands.

 

[Scotty_Tradewind]

I have spent many, many hours ripping out dodgy-looking chocolate box connectors and replacing them with soldered joints protected by heat-shrink tubing. And I felt very smug about my work. Until today, when a marine electronics service expert told me "You shouldn't use soldered joints on a boat - the wires move, the joints don't, and the solder cracks. Use waterproof junction boxes or crimp connectors instead."

I was so gobsmacked that I forgot to ask whether he would recommend tinning the wires before crimping. What does the panel think?

How often have you had a soldered joint fail or fracture due to vibration/movenet?
I've had reason to solder crimped joints which have failed, several times in the past 5 years since owning my boat.

 

[Danny Jo]

How often have you had a soldered joint fail or fracture due to vibration/movenet?
I've had reason to solder crimped joints which have failed, several times in the past 5 years since owning my boat.

Once, possibly, if it is indeed the soldered joint in my Navtex antenna that has failed. (I've yet to check it.)

Lakey's comment about F1 and considerations of crack propagation in metals make me think that vibration may well be an issue with soldered joints. So I take the point: don't use solder for electrical connections on vibrating engines. But a blanket ban on solder in boats? I remain unconvinced. Danny Jo is not one of your slamming, juddering, tooth-socket-loosening lumps of vibrating plastic; she's a stiff wood-epoxy 8.5 ton cut-through-the-water-rather-than-bounce-about-on-top-of-it sort of boat, and when the engine's running, you can barely hear it, let alone feel any vibration.

 

[gunman]

Yes, a solder joint is rigid, but then so are connector blocks and crimp connectors. If it were that much of an issue the wire would flex and break at the joint. I have never had a solder joint fail.

 

[Coaster]

There is no one optimal method. In each case the right choice will depend on location, size and type of wire, size and type of boat, required durability and other factors.

For example joints in permanent external lighting cabling on a 30' seagoing cruising sailing boat will be best dealt with differently to a temporary CD player connection inside a 60' inland waterways boat.

I find it hard to understand the rationale for tinning the ends of copper wire before making a crimped or other mechanical connection. Presumably the intention is to deter corrosion. But the tinning only protects the part of the wire from which insulation sheathing has been stripped. Moisture and oxygen will still cause the copper to corrode in the unstripped part of the cable adjacent to the joint. That's why I use tinned cable for most of my wiring.

Of course, adhesive heat shrink can be used to protect the joint, using different sizes as necessary to step up or down to ensure proper sealing where there is large variation in diameter. But if heat shrink is used properly there seems to be no good reason for tinning the end of otherwise untinned wire.

 

[Scotty_Tradewind]

When an apprentice in the 60's, we were encouraged to wire anything that may vibrate with a single coil/loop of wire just after the connection and before any loom. This I suppose was an attempt to get the loop to absorb some of the vibration.
I must admit that in some of my recent soldered connections I've failed to do that.

Quote/Coaster....But if heat shrink is used properly there seems to be no good reason for tinning the end of otherwise untinned wire. ....end Quote
Doesnt a solder tinned end 'grip' better in a connection and prevent some of the cabling from fracturing when tightened in certaian connectors?

Danny Jo.....sounds a dream boat?

 

[Spyro]

I voted soldered joint but I would say it depends on whether you would need to undo the connection again if so I would solder the ends and use a choc box. Great for future testing and easily replaced if need be, though I've never had to.

 

[Coaster]

Doesnt a solder tinned end 'grip' better in a connection and prevent some of the cabling from fracturing when tightened in certaian connectors?

Good point.

When putting very small wires into screw-type connectors I twist the exposed strands then bend the end over to double the cross section. That arrangement seems to hold better. Is there a downside to that arrangement?

 

[Danny Jo]

I find it hard to understand the rationale for tinning the ends of copper wire before making a crimped or other mechanical connection. Presumably the intention is to deter corrosion. But the tinning only protects the part of the wire from which insulation sheathing has been stripped. Moisture and oxygen will still cause the copper to corrode in the unstripped part of the cable adjacent to the joint. That's why I use tinned cable for most of my wiring.

The intention is partly to deter corrosion, but I wouldn't expect it to be particularly effective in conditions severe enough to corrode right through the adjacent unprotected copper wire. Rather, I am concerned about an increase in resistance due to build-up of an oxide layer between the contact surfaces. The second reason for tinning the ends with solder before making a chocolate box joint is to increase the rigidity of the wire in the terminal - then, when you screw the connector up tight it creates a dimple and makes it much harder to pull out. On the other hand, solder-tinning the ends before crimping on a connector may cause more problems than it cures, because perhaps (and I speculate here) crimping may work better if the substrate conforms to the shape of the crimp.

I agree that pre-tinned wire is the best option. Pre-tinned wire and the sort of chocolate box connector that uses tinned brass (or similar) with a plate between the screw and the contact point takes a lot of beating. But this thread is about the best way to join copper cable that is not pre-tinned. There is a place for non-pre-tinned wire on boats, I think, unless you want to spend loads of money when running 12v supply cables around the boat - to the masthead light, the fridge, the hydraulic pump for the autopilot, etc.

 

[markdj]

Soldering the ends before crimping heats the outer plastic sheath which in turn melts slightly causing a better seal to the untinned copper and crimping with a ratchet crimper is a very strong joint. Preferable to use tinned cable of course which is cheap from furneaux riddall.

 

[Danny Jo]

Soldering the ends before crimping heats the outer plastic sheath which in turn melts slightly causing a better seal to the untinned copper and crimping with a ratchet crimper is a very strong joint. Preferable to use tinned cable of course which is cheap from furneaux riddall.

Thanks for the name - Furneaux Riddall - now bookmarked.

It's interesting that their price for tinned cable is only approximately 10% more than for untinned. When I think of the time I have spent tinning ends, I am forced to conclude that using untinned cable may be a false economy.

 

[Trundlebug]

The most important things to me , after the integrity of the initial joint are to keep it sealed to prevent oxidation and water / moisture ingress, and to be able to re-make or at least inspect the joint at some time in the future. All joints are high on the suspect list when fault finding, so if it's totally sealed in resin or something you just don't know what's going on underneath.

So whether I've crimped or chocolate boxed it, I always tape it up tight with insulating tape afterwards. I reckon heat shrink would be equally as good or better. The other advantage is that it provides additional support to the joint and prevents movement or fatiguing, hence improving reliability that way too.

 

[Danny Jo]

So whether I've crimped or chocolate boxed it, I always tape it up tight with insulating tape afterwards. I reckon heat shrink would be equally as good or better.

I have two issues with insulating tape. Firstly it's messy and a pig to remove. Secondly it's ugly (and might make a future potential buyer/surveyor surmise, albeit correctly, that an amateur had been at work).

The main limitation with heat shrink tubing is that it will only reduce it's diameter by about 60-70%. So if it's big enough to go over the choc box, it'll be too big to make a good seal on the cable.

I quite like butt splice crimp connectors incorporating heat shrink insulators, but they are quite pricey.

 

[Ubergeekian]

Soldering the ends before crimping heats the outer plastic sheath which in turn melts slightly causing a better seal to the untinned copper and crimping with a ratchet crimper is a very strong joint. Preferable to use tinned cable of course which is cheap from furneaux riddall.

Aluminium crimps to copper wire, if properly done, form a cold welded intermetallic bond between the two metals. In other words they aren't just touching, but form a continuous metallic structure.

Does this happen when there's tin in the way? I dunno.