Connecting Stranded Wire; A Better Way

RJSakowski

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Wiring up projects is much easier with stranded wire than solid. But there is a drawback when making connections with screw terminals. The strands tend to splay out giving rise to possible shorts. An answer to this problem is the use of wiring ferrules. A ferrule is a thin tube that the stranded wire is inserted into. The ferrule is the crimped to secure the wire and make a solid electrical connection. I have also tinned and soldered the wires in the ferrule. The ferrule is seated in the screw connector and the clamping screw tightened, making a secure connection. They are available to accommodate different wire gauges and strip lengths and with or without insulating bushings. They are available from McMaster Carr and major electronic supply houses.
 
Ferrules are really nice, but often depends on the terminal and application. I use crimps with spades for larger screw connectors, usually crimp and solder. High voltage screw terminals, crimp ring terminals are a bit more secure. The ferrules work well for smaller wires with push in or small screw terminals that push down/compress the wires, like VFD input terminals. With the ferrules, I like to strip the wires so they extend slightly past the tip of the ferrule when slipped on vertically. Solder under low heat or small iron at the tip so the solder runs down inside the tube, then snip the excess wire. You can also use shrink tube for added support behind the crimp if needed. They do work great and provide additional wire support.
 
I recently used some from HD to rewire a motor and the worked very nicely. The serrations inside the bit you poke the wire into grip extremely well - no pulling the wire out halfway through crimping it :) Only downside that I can see is that there may not be enough space around the posts to fit the ferrules. Much better connection than before though, I think the lathe the motor came with may have been thrown out as one of the start winding wires had come loose in the drum switch.
 
i have ben told that soldering or tinning a stranded wire will leave you with high stress section right where the heated / soldered area stops. and wires do vibrate with current running thru them, I'm told. . .
 
Crimp or solder on terminals/ferrules are the best. But if you'e in a jam and don't have any, you can you can improvise one. Strip the wire extra long, make a loop by wrapping the end of the wire around the point where it protrudes from the insulation. Tin the whole loop with solder, then flatten it out with a hammer. this makes a good ring terminal. You can convert it into a spade, by cutting off the top of the loop. In leu of a ferrule. I bend the stripped portion into a tight u bend so that the tip is touching the point where it protrudes from the insulation and parallel to itself then tin with solder. A boot of heat-shrink tubing can be added if needed.
 
i have ben told that soldering or tinning a stranded wire will leave you with high stress section right where the heated / soldered area stops. and wires do vibrate with current running thru them, I'm told. . .
I have heard that too, Dave. However, in more than fifty years of making soldered connections, I could probably count on my fingers and toes the ones which failed due to breaking immediately adjacent to the soldered connection. This includes numerous connections in harsh environments ( automotive, marine, heavy machines, etc.). For a century, the electronics industry used solder as a means of connecting wires in a circuit. On the other hand, I have had many connections fail because of wires pulling out of a crimp, corrosion in the crimped connection, or individual strands being sheared because of the crimping action. This is less likely to happen with a professional crimping tool but unfortunately, I have only the hardware store version.

My personal best practices consists of soldering all crimp connectors. I pull off the insulated sleeve prior to soldering and slide some heat shrink on the wire. After soldering, he heat shrink is slid over the connector. A properly soldered connection wicks solder up the wire past the joint which moves the stress point away from the connection. If flexing wires is a concern, I use an additional layer of heat shrink to move the stress point further up the wire.
 
I've worked on quite a few machine tools and various industrial equipment and really have come to appreciate ferrules. That especially in densely populated terminal strips or devices on DIN rails. I too have heard that at the point the solder bond stops, vibration and movement causes failures. I believe that it may be so in some cases, since you are giving up some of the integrity of the tightly woven strands when the wire is stripped, and especially if it is splayed out. I have seen a few questionable connections where this is quite credible, although I have not seen a total failure attributed to that alone. Most of the installations where I have seen stranded wire soldered and inserted under a screw head or square washer also make good use of loom wrapping, which minimizes movement, at least until someone comes in and "works" on it and snips the string.

On larger wire (#8 and up) I have used short pieces of copper tubing to couple and splice by crimping AND soldering. A little shrink tubing and it looks decent. Probably not to strict code, but I always felt comfortable with the safety of it. I use the tubing simply because I do so little of that kind of work that I won't buy the factory ferrules. Been known to flatten the end and drill a hole and make a custom ring terminal too.

I stumbled across an interesting white paper for those of you who may want to read a little about the subject. Be aware that it is written by a manufacturer of ferrules, but I am not so sure they could get away with too much bias.

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCcQFjAA&url=http://www.weidmuller.com/bausteine.net/f/7862/Weidmuller_Ferrules_White_Paper.pdf?fd=3&ei=Vo7wVI7UB4KHyQTk0IDgBw&usg=AFQjCNH5vx1BllllAGmZgAtSo09-GWzgkg&bvm=bv.87269000,d.aWw
 
I've started using double crimps for just about all my connections, the crimp tools are expensive and several are required but once they are done they do not come loose.
I have three Packard crimp tools that I use depending on wire gauge, there are ratcheting crimpers that will crimp the core and wings at the same time but they only work on smaller gauge wire.
I originally bought the crimpers for doing Packard 56 and 59 terminals on my 67 chevy so any o the wiring I replaced would match the factory crimps
 
Manufacturers of compression-type terminal blocks and connectors recommend against tinning any stranded wire that comes under direct compression, for the reason that over time the solder can deform and cause a loose connection.

If you use a ferrule, this deformation should not take place, so it will do no harm to solder the wire in the ferrule, but I believe it is unnecessary, as crimped connections have been shown to be the most reliable,
 
What do machine manufacturers do? I worked in a shop that made specialized machinery. I think they used closed eyelet crimped connectors, its been a long time ago. One man did about all their wiring.
 
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