The perennial discussion of solid vs stranded, Romex, Boat wire etc. has recently presented itself again.
What has not been discussed much is the actual termination method used, particularly with binding screws typically found on convenience outlets.
12 ga stranded type THHN or similar is typically run in commercial wiring. The only reason it is chosen over solid is that it is easier to pull through conduit. When connecting this wire, the electrician will twist the stripped end and form it into a hook, and put it under the binding screw just like a solid conductor. This does require a little extra care to insure that all the strands are under the screw head.
The question comes when using the much finer stranded boat wire. Just putting it under the screw is difficult as some strands will inevitably squirm out from under the screw head.
That leave two methods. The first is to crimp a spade lug on the wire, the second to twist and form the wire, then tin it to effectively make it a solid conductor. Forming and tinning were common practice years ago in electronics where binding screw were often found.
One of the problems I see with using lugs is that they would stick straight out of the rear of the device, perhaps reaching the back of a shallow box (as might be used in an bus conversion wall) forcing the conductor to make a hard bend at the end of the crimp lug. Good practice dictates that the conductor should come straight out of the crimp lug before making a turn.
If the wire is bent right at the lug, different strands will bend at different radii, causing some to either stretch or pull out of the crimp. If you MUST have a hard bend at a lug, it is better to bend the wire before crimping the lug.
Since finely stranded wire is not usually used for general wiring, this question would not often come up. The solutions must be garnered from other electrical disciplines than general wiring.
I would choose some of the newer outlets that have a compression connection rather than a binding screw and just insert the stripped wire, no lug, no solder.
Comments?
Putting stranded wire under a screw is asking for trouble - regardless if the rules allow it or not it is poor practice.
I solder the end of stranded wire before I put it under a screw.
At work, we use a sleeve/ thimble we crimp on the end of the wire that goes under the screw in the terminal strip.
Any wire needs to be properly supported. If you solder a stranded wire, the soldered end needs to be treated as a solid wire & supported as such. . . . duhhhh
Any wire will break if not properly supported.
Any will break if supported if the movement is excessive.
I used commercial grade outlets to try to get around this issue. There is a hole to stick the stripped wire into. The screw is then tightened which secures the wire. This is NOT the cheesy spring lock mechanism used in residential grade outlets.
I have designed my outlet placement so they all have standard depth boxes. I have no switches right now except low voltage.
Quote from: belfert on September 17, 2009, 07:42:54 AM
I used commercial grade outlets to try to get around this issue. There is a hole to stick the stripped wire into. The screw is then tightened which secures the wire. This is NOT the cheesy spring lock mechanism used in residential grade outlets.
I have designed my outlet placement so they all have standard depth boxes. I have no switches right now except low voltage.
That's what I meant by compression type connections, good choice. The "cheesy' connections will no longer accept anything larger than 14 ga. Still junk to my way of thinking.
I agree with 100% on that method Kyle I use it even for butt splices on the 12 volt system with a little never seize of course LOL just kidding.Every coach I worked on with wire nut splices 90% of the time the nuts are the problem by vibrating loose
good luck
;D
All of my outlets are on seperate circuits except one circuit with a GFCI and a outlet downstream. I used the second set of connections on the GFCI for the second outlet (as required anyhow). No wire nuts although eventually I need to add more outlets so I need to figure out how to add more outlets without wire nuts.
I used stranded wire (mostly 12 gauge) pulled through flex plastic conduit. On the was used double walled crimp fittings, and haven't had any wiring issues in the 14 years since installing the electrical system. Good Luck, TomC
And once again, my personal take on crimps and wire termination:
http://www.heartmagic.com/crimps.html (http://www.heartmagic.com/crimps.html)
Remember, this is the way I do it after having been the head wookie in an electronics manufacturing biz (mine) for 35 years. This doesn't mean it's right, it doesn't mean it's to code, and it doesn't mean there's no room for improvement. It's simply what I've found to be reliable...
Cheers
boogie
I worked for United Air Lines for many years and all aircraft wiring is done with tools specifically designed to properly crimp specific supplies that are used. As for parts the previous sugestion to use commercial style units is the best way to go . Stranded wire is best for hadling vibration and canbe used with the commercial type units. Jerry
Boogie,
That isi the best info on crimping ever. Thank you for taking the time to put it together.
I was first taught to strip wires using Dikes in 1957 in Voc training. They had the dikes upside down then and I have done it "wrong" for the past 52 years. In their defense they were using electricians dikes and they have no "flat side" but I have done it wrong using "electronics grade" dikes, just the same.
John "ever learning or ever stupid, one".
Guys,
I have to strongly disagree with some of the comments here. Diagonal cutters (dikes) are for cutting not stripping. Strippers are for stripping and must be the proper size for the wire being stripped. Anyone who has ever worked in a telephone central office or mil spec manufacturing knows that and would be severely reprimanded if not fired for using cutters to strip wire. It is nearly impossible not to nick the wire when stripping that way. A microscopic nick would be rejected by an inspector.
Now, I'm more used to working with smaller gauges, 24-26 ga wire where a small nick is more critical, but the theory remains the same for any size wire.
Do what you want, but so many here talk about wanting to do the best, most professional job possible out their bus. Use the proper tool for wire stripping.
Gary, thanks for posting your link...you have some good information there, backed up by years of personal and practical application.
After dealing with stranded wire soldered connections in aircraft and old cars, truck and tractors for years I decided against ever doing it again.
This also applies to soldered heavy battery cables. These heavy cables seem to corroded back a long distance from the soldered joint, much more so than smaller wires.
The number one electrical problem I had with all these was corroded solder or brittle wire breaking at the solder ending in the wire, not to mention burned and brittle insulation.
I don't mean that I am an expert or that this is the final word, all I'm saying is that this has been my experience.
I thought I would throw in my two cents, take it for what it's worth.
I worked in the concrete block industry for over 25 years, which is the second worst environment for equipment, followed by mining. They were subjected to cement dust, bursting hydraulic hoses covering them in oil, extreme heat in the summer, you name it. These concrete block machines make the block under severe hydraulic pressure along with pneumatics, a vibrator driven by an electric motor to produce movement to the mold, using eccentrics and bearings. We are talking about extreme vibration here, nothing I have seen to compare it with. All the wiring in these machines range from 12 ga to 16 ga stranded suppling electricity to power valves and such. These babies rock back and forth as they go through the process every 6-8 seconds, 6-7 days a week, 16-24 hours a day. I have seen machines that were 25 years old and still producing, all with original wiring and termination strips. Most of the problems I encountered was not the failure of the wire, unless it was not secured properly, it was due to loose or missing termination screws. Nothing was ever soldered. Some problems were due to the age of the wire, insulation becoming brittle and breaking off. The copper wire itself was never the issue, it may have turned a brownish color over time, but it still did it's intended job.
The point I'm trying to make here is this, our coaches sit most of the time, they are never under such extreme conditions unless you roll it. Check and tighten your terminations yearly on all connections, will help to keep the smoke in.
As someone famous once said "Do it your way", but do it properly. ;)
Paul
Thanks for the article and pictures Gary. I, like others, have done it wrong for many years. Even when I was doing it wrong, I was wondering, "ok, what's the right way".
Now I know.
Thanks again for the time you put into putting the article together.
Chris