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In most cases, I am splicing a power cable because it has seen rough service. My repair must be at least as strong and safe as the original. Here is how I do it.
If you are interested, please, click here.
Your comments are welcome. All of us are smarter than any one of us.
Thanks,
Rick
-Thanks for the tips Rick, and AFAIK your splice will be at least as strong as the original.
Depending on your local code & applicable regulations,
I'd think the heat shrink & -sheath should be of proper thickness and grade for the applied voltage.
One caveat though when it comes to fatigue strength of soldered joints thru bending forces*.
Personally, I always do staggered splices (even for lo-voltage duty), and use the thickest possible heatshrink for the wires,
build up the missing sheath thickness over the spliced & shrunk wires with self-amalgamating rubber tape,
and finally slipping the heatshrink sheath over, with 2 extra inches of shrink overlap added on each side.
*Thus each wire steadies the others in the tight bundle, and the cable is more prone to bend in the supple cable,
rather than at the relatively much stiffer splice: hopefully offering less risk of fatigue breaks.
But then again - that's just my two precautious cents.
Cheers
Johan
-Yup - even after some 35 years it does happen at times that I forget to put the heatshrink on before soldering...
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ditto, I use similar methods for all cable splicing (ELV, LV) but once over 4mm2 I use crimped butt splices instead of soldered joints. I picked up a hydraulic crimper off ebay for a decent sum, and it's good from 10mm2 up to 135mm2. 4 and 6mm2 crimps are done with standard electrical pliers (mine have a notch designed in for that purpose.
Hi Johan, glad I am not the only one that forgets.
Thanks for this Rick
The method you show is the prescribed way used by NASA, in house and by their contractors.
One thing they also specify is using clear or translucent shrink tubing on the connections to allow inspection without disrupting the splices in the event there is a question later. This allows visual confirmation to check in event of leakage into splice area that could cause joint corrosion.
This may be helpful in situations where multiple people work on an assembly. (or where we are getting old and leakage from our little gray cells inside is going out gray and our follicular strands are getting silvered. We are looking at opaque tubing thinking, "I did solder that one, didn't I?")
To Johan's reference on strength, testing has shown these joints to exceed the tensile strength of the unsoldered wire.
Thanks! I have updated the article with the added credibility. It is now linked to a video demonstrating the Western Union plus pointing to the NASA regulations.
Rick
I suggest that you de-oxidize the copper before twisting and soldering it.
I always use flux. Is that what you mean?Quote:
Originally Posted by katy
Rick
The oxidation of the copper prevents the solder from bonding to the copper, if the flux that you're using removes the oxidation, you're good. Most fluxes only prevent the base metal from oxidizing due to the heat. The copper should be clean before soldering, either chemically, sanding, or scraping.
https://www.instructables.com/How-to...es-in-minutes/
With flux the problem is most chemicals that clean the copper are also corrosive and then need to be washed out, which is pretty much a No-No with an electrical repair.
Since my solder flows nicely around the copper, I must not have this problem.Quote:
Originally Posted by katy
Rick
It's been a while since I looked, but I thought NASA required the splice be wrapped with bus-wire before soldering for stability. Regardless of NASA, if these cables handle mains power or decent amount of current, they should be mechanically reinforced before soldering. Crimp is the preferred method, but wrapping with solid wire is acceptable. I have seen, on more than one occasion, over-current melting the solder joint before the circuit breaker could trip. Should the live end of the wire detach and touch something, it can be hazardous.Quote:
Originally Posted by techcollect
While I am at it, tinning wire before crimping, or using in screw clamp connectors is a bad idea, since the solder relaxes and migrates overtime and the joint becomes loose (solder does not spring back and push against the screw, leading to loosening over time).
However, on low voltage and low current circuits, I do the same thing.
I now see that I caused some confusion when I talked about "power cables". I have changed the title to "extension cords".Quote:
Originally Posted by FEM2008
I'm not sure what you mean by "low voltage" and "low current" but my intent was to splice extension cords used in 120V circuits which carry under 10 amps.
I completely agree about the dangers of tinning wires before crimping or using screw clamps.
I had not thought about faults causing the solder to melt before the breaker trips. It does surprise me given the large resistance of the extension cord and the low resistance of the splice. Wouldn't the extension cord start to burn first?
I have never been able to apply heat to a Western Union splice and have it detach unless it is also under a lot of tension. In this case, the wire usually breaks next to the splice. Now, if it was a simple lap joint, it is not to be trusted.
Rick
In our new house I was surprised the electrician could bury junction boxes behind the plaster in the walls. Then he showed a closeup of how the wires were connected...
Attachment 38925
After brazing they're wrapped with two independent layers of insulation, the lid is put on the junction box and it's covered with "plaster" (more like stucco).
Quote:
Originally Posted by rgsparber
BY the way, if anyone is looking for the NASA link on workmanship, here it is:
https://nepp.nasa.gov/files/27631/NSTD87394A.pdf
Soldered splices start at page 68.
Other standards can be found here: https://nepp.nasa.gov/index.cfm/5511
I believe Jon posted a link to NASA standards in one file a while back. HERE IS ONE:https://archive.org/details/nasa-wor...ge/n3/mode/2up
What I meant regarding low voltage and low current are battery powered type projects, such as an Arduino circuit. Mains circuits have the capacity to supply hundreds, even thousands of amps very quickly during a short circuit. That's why circuit breakers are rated for 10,000A short circuit capacity for home panels and much higher for industrial applications and building distribution panels. Also, conductors experience tremendous forces during a short-circuits due to generated magnetic forces and capable of whipping cables around, hence the requirements for fastening cables at regular intervals and at junction boxes. Solder is much less conductive than copper (by a factor of ~10 if I recall correctly) and in an event of an overload, the temperature of the solder will rise very quickly and can melt. By the way, eutectic solder is used in thermal circuit breaker and melts during an overload, which then allows a ratchet mechanism to rotate and trip the breaker.
I am not saying that your method will result in a the wires separating, but I would not trust it from burning down my house.
What is applicable here is not NASA, but NEC code. I am not sure that NEC code allows electrical splices outside of a junction box or without an approved splice device that completely encloses the splice and mechanically secures the cables. There are products like these below that can be used for solid wire in certain situations (such as fished wire in existing building): https://www.homedepot.com/p/NSi-Indu...MS-3/307358485. Perhaps some electricians can shed some light on the NEC code requirements. I worked with industrial equipment twisting wire and soldering to splice is a no no.
While the western union splice is accepted by NASA, it is used with solid wires. Twisted soldered stranded wires fail quicker than untwisted wires. If you dig in the NASA case files and others, you'll find examples.
By the way, I love your posts and ideas you publish and always learn something new.
I am surprised as well. Your area must have a different codes that supersedes NEC regarding hidden junction boxes.Quote:
Originally Posted by jdurand
Quote:
Originally Posted by FEM2008
You really got me thinking about this. After a few false starts, I came up with this argument. If I'm "blowing smoke", please let me know. All of us are smarter than any one of us:
The worst case scenario would be a fault in the extension cord that is just below the breaker's trip current. A UL approved cord must not cause a fire. My guess is that the heat from the conductors will cause the plastic to melt and cause the conductors to short. This would greatly increase the current and the breaker should trip. In thinking about the heat needed to melt plastic versus the heat needed to melt solder, I expect that the splice will remain sound during this fault.
As to burning a house down, I recently almost had a front row seat. My neighbor came over and asked me to check out a problem. In the kitchen was a blackened outlet pulled about 6 inches from the wall. All of the plastic around one of the screws was gone. All that was left was the screw and the conductor. A few MONTHS before, she had heard crackling so turned off power and pulled the outlet out. Then she reapplied power because it was essential to the lives of some very expensive tropical fish. Eventually the crackling got worse and she could see a tiny but bright light in this area. The insulation on the attached wire fell off. Hmmm. Maybe something is amiss...
After removing power and letting it all cool, I gently moved the wire. It was only attached to the screw because it was formed around it. I think the installer forgot to tighten the screw in the first place. That was over 15 years ago.
I was able to cut off the damaged wire and replace the outlet. I then checked that the current being drawn through this wire was safely below the breaker's trip current. I left after suggesting to her that she hire an electrician to check that all screws are tight so this doesn't happen again.
Rick
I once was asked to look at someone's kitchen outlet for the microwave, it kept having problems cooking.
I unscrewed the cover plate for a look-see before bothering to turn off the power and ZAP...darkness as the breaker tripped. Getting a flashlight, the outlet wasn't in a box. Just a hole in the wall with outlet hanging off the cover plate. Ok, that explained the larger plate than a normal USA one.
Fished the outlet out of the wall and on the back was the crumbling remains of brown zip-cord going straight into the wall and to a box on the other side. Opened THAT box and the two wire cord was just tucked under the screws that held the original building wires in.
I added a box, real 3 conductor building wire and put the wall back together. MUCH better.
Some wiring jobs are scary, others are worse.
That is a mind blowing story!Quote:
Originally Posted by jdurand
Rick
We can agree, no matter the scope and bulletproof practices of NASA, NNSA, AN, MilStd, and such, those cover environments no where near concerns of NEC and local codes.
On the skin, it would be convenient for an umbrella-like code, but physical differences make it impractical.
First exposure to Western Union splice would be earliest of the 70's, Peterson Publishing shop manuals, and edition concerning auto wiring. Made sense then, done so ever since. Same for terminals, crimp - solder - sleeve.
