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wire termination for screw terminals

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MarkF:
Crimp terminals are recommended.



tooki:

--- Quote from: Vovk_Z on June 05, 2020, 03:58:02 pm ---
--- Quote from: Ian.M on June 05, 2020, 11:15:35 am ---*NEVER* tin stranded wire for direct connection to a screw terminal (of any sort).  Solder cold-flows under the typical clamping pressure of a screw terminal and the connection *will* loosen and become unreliable. 
--- End quote ---
Solder itself cold-flows of cause, but solder with copper wire cold-flows about an order less, so with a minimal amount of solder it may work quite good very long (with up to several amperes current).
I can agree that *NEVER* screw untinned stranded wires (without tin/solder), because stranded copper wires "cold-flow" and loosen very much.

--- End quote ---
It’s more likely vibration causing stranded wire to loosen.

Either way, tinning stranded wire is a big no-no, since it’ll loosen even without vibration.

The correct answer is “ferrules”.

Vovk_Z:

--- Quote from: tooki on June 05, 2020, 04:31:12 pm ---It’s more likely vibration causing stranded wire to loosen.
--- End quote ---
- No, stranded wire loosen without any vibration. I've seen it many times.

calzap:
Building wiring in conduit in the U.S. usually involves stranded wire.  Termination at bus bars and breakers usually means inserting the wire in a metal surround and tightening a set screw.  I've noticed that in a few months/years, the set screw needs additional tightening.  Not sure if this is "flow" or the strands being pushed into a more geometrically compact arrangement or the screw backing out a bit or a combo.

When wiring a receptacle or switch that only has screw terminals, most electricians don't use a crimp-on terminal.  The usual trick is to cut the insulation about 35 mm from the end, and slide the insulation so as to create about a 15 mm gap.  This keeps the strands from splaying.  Then wrap the exposed section around the screw shaft, tighten the screw and snip the excess wire.

Often though some or even most of the strands will be squeezed out from under the screw as it's tightened.  Sometimes there are only a few strands are making contact.   Then a conscientious electrician will redo it ... not all of them are conscientious ... whatever the boss and inspector allow is good enough.  And eventually, the screw will need retightening no matter how good the initial installation.  I always use a crimp-on terminal to connect stranded wire to a screw terminal.  It's just as quick, maybe quicker, and more secure.

Mike in California

wizard69:
The correct answer is depends. 

There are a number or different terminals Strips  designs   Which is the best solution depends upon those designs.   

Setscrew type terminal strips and stranded wire are best assembled with wire ferrules. 

Clamp type blocks need ring or fork terminal for the termination of stranded wire and specifically not wire ferrules.   In case you are wondering clamp type screws have (usually) a captured square washer under the screw head.  These types of terminals work best when the load on each side of the screw is even.    Thus I prefer ring or fork terminals but they may not be required.  A variation of these terminals are designed to terminate bare wire copper or stranded and can be seen in home wiring devices like sockets and light switches are designed for bare copper wire. 

Another type of terminal block just has a pan head screw.  These absolutely need a ring terminal or fork terminal.  In some cases you can wrap solid copper wire around the screw but this isn’t optimal and you need to do it the right way. 

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