Thoughts (?) about tinning "tip" of stranded #12 awg wire.

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K1GMB

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Telecommunications Engineer (Master Electrician)
Hi Folks, got a construction/installation question. This is my individual home wiring project, so I have plenty of time to think and try to do my electrical work safely and neatly. I am installing a 100-amp sub-panel with 20-amp Square D QO CAFI breakers. What are your thoughts about "tinning" the tip of the stranded #12 awg neutral wire, that will attach to the neutral buss bar in the panel. Traditionally when tightening down, the strains tend to spread out under the torque of the screw. Lots of articles about not tinning the wire completely because mechanically it "softens" the connection over time. Electrically this works, but yea I'm being very picky. Thoughts and field experience feedback is greatly appreciated. Thanks!!
 
The instructions for the terminals say what sort of wire they are suitable for. If the terminals are listed for stranded wire then I'd just use it.

For things such as the screw terminals on receptacles, properly twisting stranded wire is key to a neat and secure connection. This means twisting the wire snugly in the 'reverse' direction, so that under the screw head the 'rope' tightens rather than loosens. My guess is that similar twisting will make a difference in the neutral bar, but I've never seen a problem with the strands just splayed a bit by the screw.

If I were to go 'off the marked trail' in my own home, then I'd crimp wire ferrules over the ends of the stranded wire.

Jon
 
The neutral bar is designed for stranded or solid conductors. IMO anything beyond striping the end, inserting the wire, and properly tightening is a waste of time.
 
OK folks thanks for the feedback. Yes, thanks the torque screwdriver is a must. I'll ponder the feedback, and plan to finish the install this weekend. Part of me wants to cut the neutral pigtail on the CAFI to length for the specific breaker but I think that I will just fold back any excess, in case I need to move things around in the future. Thanks for the comments.
 
winnie said:
The instructions for the terminals say what sort of wire they are suitable for. If the terminals are listed for stranded wire then I'd just use it.

For things such as the screw terminals on receptacles, properly twisting stranded wire is key to a neat and secure connection. This means twisting the wire snugly in the 'reverse' direction, so that under the screw head the 'rope' tightens rather than loosens. My guess is that similar twisting will make a difference in the neutral bar, but I've never seen a problem with the strands just splayed a bit by the screw.

If I were to go 'off the marked trail' in my own home, then I'd crimp wire ferrules over the ends of the stranded wire.

Jon
Click to expand...
Don't think you'll be able to tin just the end of the wire. The flux and heat will always draw the solder up the strands. As the OP stated, screw terminals on tinned wire is a bad idea. The solder is soft and will cold flow over time, leading to a bad connection.

If you decide to use wire ferrules, buy a good crimper. There are some really terrible crimpers available, and good ones are $$ but worth it.

I've owned this one for almost 7 years. Probably 50k+ crimps and no issues.


SceneryDriver
 
SceneryDriver said:
Don't think you'll be able to tin just the end of the wire. The flux and heat will always draw the solder up the strands. As the OP stated, screw terminals on tinned wire is a bad idea. The solder is soft and will cold flow over time, leading to a bad connection.

If you decide to use wire ferrules, buy a good crimper. There are some really terrible crimpers available, and good ones are $$ but worth it.

I've owned this one for almost 7 years. Probably 50k+ crimps and no issues.


SceneryDriver
Click to expand...
Thanks, I thought that I could clean the tip and quickly touch it with solder, but you're right about the heat drawing it up. Thanks for the suggestion, I'll order that. Yea I have read stories about tinned wires becoming loose under terminals, (causing a high resistance), and any amount of current thru this causes heat generation and possibly a fire condition. It's amazing that a small amount of resistance with high amperage flow can create such heat generation. Makes me think about this when people run high wattage electric strip heaters in older houses where the wiring can be sub-standard. Good post, I enjoyed reading it.
 
I am not suggesting doing this, but the key to soldering only a portion of the wire is to heat it up very quickly so that the solder flows to the desired location without having time to flow further. Think 'solder pot' in the way old school knob and tube wiring was done.

Another approach is to use ultrasonic welding to fuse the strands of wire together into a section of solid wire, with no solder applied.

Your occupation lists master electrician, but this is a project in your own home. Don't let perfect become the enemy of the good; it is easy to laser focus on one perceived deficit of standard installation, and put so much effort into fixing it that you actually create problems with other aspects of the installation. Just a caution from an engineer who DIYs in his own home.

-Jon
 
winnie said:
I am not suggesting doing this, but the key to soldering only a portion of the wire is to heat it up very quickly so that the solder flows to the desired location without having time to flow further. Think 'solder pot' in the way old school knob and tube wiring was done.

Another approach is to use ultrasonic welding to fuse the strands of wire together into a section of solid wire, with no solder applied.

Your occupation lists master electrician, but this is a project in your own home. Don't let perfect become the enemy of the good; it is easy to laser focus on one perceived deficit of standard installation, and put so much effort into fixing it that you actually create problems with other aspects of the installation. Just a caution from an engineer who DIYs in his own home.

-Jon
Click to expand...
Thanks!!! Ain’t that the truth, good grounding techniques another issue
 
Before I would even consider tinning the ends I would focus on proper termination and just look at the data. There's ten billion (Okay I made that number up) stranded wires terminated on neutral bars with a flawless track record when properly torqued.
 
K1GMB said:
Hi Folks, got a construction/installation question. This is my individual home wiring project, so I have plenty of time to think and try to do my electrical work safely and neatly. I am installing a 100-amp sub-panel with 20-amp Square D QO CAFI breakers. What are your thoughts about "tinning" the tip of the stranded #12 awg neutral wire, that will attach to the neutral buss bar in the panel. Traditionally when tightening down, the strains tend to spread out under the torque of the screw. Lots of articles about not tinning the wire completely because mechanically it "softens" the connection over time. Electrically this works, but yea I'm being very picky. Thoughts and field experience feedback is greatly appreciated. Thanks!!
Click to expand...
2 things.................
1) As Infinity mentioned, great number of stranded connections done every day with no problems
2) If installing a new panel, why not get one with plug-on neutral and you won't have to worry about the stranded pigtail on the AFCI

My input............
It's your own house, you're doing the install, leave off the AFCI and your worries go away about the stranded wire!
 
To answer the question, as much soldering in electronics as I have done over the years, I rarely use soldering for power wiring. I prefer appropriate connections for stranded wire than to try to convert it into solid wire.
 
Square D says to put that stranded white wire into the screw terminal hole of the neutral bar and tighten the screw. If they thought it would not work, they would have designed it differently over the 35+ years they have been selling them!

BTW. new Square D (and many other manufacturers) stuff uses screws that accept a #2 Roberson (Square Drive) bit. Use that instead of Phillips or Slotted. Makes tightening easier.

In NASA type connector/solder training it is verbotten to tin the stranded leads before using crimp connections. Crimp connections are for bare wire, not tinned. Same problem with screw connections, initial torque does not hold as solder moves with time/heat.
 
LarryFine said:
To answer the question, as much soldering in electronics as I have done over the years, I rarely use soldering for power wiring. I prefer appropriate connections for stranded wire than to try to convert it into solid wire.
Click to expand...
Hey Larry, same here with lots of soldering in electronics. I hate solid wire cause it remembers bends and movements, and eventually breaks.
 
Frank DuVal said:
Square D says to put that stranded white wire into the screw terminal hole of the neutral bar and tighten the screw. If they thought it would not work, they would have designed it differently over the 35+ years they have been selling them!

BTW. new Square D (and many other manufacturers) stuff uses screws that accept a #2 Roberson (Square Drive) bit. Use that instead of Phillips or Slotted. Makes tightening easier.

In NASA type connector/solder training it is verbotten to tin the stranded leads before using crimp connections. Crimp connections are for bare wire, not tinned. Same problem with screw connections, initial torque does not hold as solder moves with time/heat.
Click to expand...
Good info Frank, thanks, I have a part number for the square drive, thank you! I know that even bare copper wires loosen up over time but soldering or tinning them escalates the failure time. Thanks!!
 
Little Bill said:
2 things.................
1) As Infinity mentioned, great number of stranded connections done every day with no problems
2) If installing a new panel, why not get one with plug-on neutral and you won't have to worry about the stranded pigtail on the AFCI

My input............
It's your own house, you're doing the install, leave off the AFCI and your worries go away about the stranded wire!
Click to expand...
These are new old panels before the neutral buss. Definitely a neater installation, but I'm kinda nervous about how good the connection is, and the standard answer is it's as good as the clips for the hot side of the breaker. Yea, I'm concerned about usings these CAFI's, but I'm trying to do things right, and maybe it's a plus when we go to sell the house. It will be very interesting to see how these CAFI's operate in the presence of a high-power ham radio station. I've spoken to many, who say that should not be a problem, but 1 kW of RF is a lot to be induced into something that has computer I.C.'s in it. I've exceeded the grounding size from #6 to #2 and have installed multiple 8-foot 5/8" ground rods, (correctly spaced apart). We will see??? With potential RFI issues, you never know until you fire things up. Thanks, good points to consider
 
One issue with "tinning" the ends of stranded wire is that it creates a mechanical stress riser (a point where stress can potentially be concentrated) right where the solder begins on the wire. And so bending can cause more stress at that point. I have only seen failures due to this issue on fine stranded wires and in cases where bending could occur after installation. With terminations on the neutral bar in a panel it would not likely be an issue.
 
K1GMB said:
Hey Larry, same here with lots of soldering in electronics. I hate solid wire cause it remembers bends and movements, and eventually breaks.
Click to expand...
I started in electronics building crystal radios when I was six years old.

One advantage of solid wire is it makes dressing panels a little easier.
 
synchro said:
One issue with "tinning" the ends of stranded wire is that it creates a mechanical stress riser (a point where stress can potentially be concentrated) right where the solder begins on the wire. And so bending can cause more stress at that point. I have only seen failures due to this issue on fine stranded wires and in cases where bending could occur after installation. With terminations on the neutral bar in a panel it would not likely be an issue.
Click to expand...
In the motorcycle forums I frequent, soldering is strongly recommended against for this reason.
 
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