Landing stranded wire on screw terminals

mgookin

Senior Member
Location
Fort Myers, FL
I read some older threads on this forum about landing stranded wire on screw terminals such as receptacles and switches. It appears to be allowed and there were some good tips mentioned:
1. Twist the wire CCW so it pulls together vs. pushing apart as the screw is tightened.
2. Tinning the wire. We already do that anyway even if landing in a wirenut to a solid conductor; it just makes better looking work. We tell our people to expect that every unit has the same chance of landing in a testing lab and if it's not good enough for that, it doesn't go out.

The discussion thread on this subject was from 2011. Does anyone have any information to indicate whether there have been any changes with respect to this being allowed?

I just did some experimenting after reading the thread. On one I left it with the factory CW twist and the other I twisted CCW. I found that the CCW twist became a larger diameter because I am unable to twist it as tightly and neatly as is done in the wire factory.

On both of them I formed the lead by wrapping around a rod, then tinned the lead.

As you can see, the CCW is a poorer job with wire protruding from under the screw. Not only was it harder to get under the screw head because of larger diameter, it was also hard to keep it from being pushed out as I tightened the screw. With a smaller diameter wire the results would probably be different but for now I'm sticking with CW twist.

Here's what I got:

Landing stranded wire on screw terminal with notes.jpg
 

infinity

Moderator
Staff member
Location
New Jersey
I don't think that the average installed would tin a stranded conductor for termination did you do this soley for demonstration purposes? BTW both look fine to me from the photo.
 
I don't think that the average installed would tin a stranded conductor for termination did you do this soley for demonstration purposes? BTW both look fine to me from the photo.
I have seen tinning cause problems. The connection gets hot and the solder reaches a plastic state and relieves the tension from the screw, causing a bad connection. And bad connection means more heat, more heat means more solder being deformed and so on.
 

mgookin

Senior Member
Location
Fort Myers, FL
I don't think that the average installed would tin a stranded conductor for termination did you do this soley for demonstration purposes? BTW both look fine to me from the photo.
It was done to establish the manufacturing process for a requested product which is cord & plug connected controlled receptacle. The landscape lighting industry uses them and some people use them for holiday lighting. Supply houses have been asking for them because they have a very high failure rate with the brand they are using.

The reason for tinning is to keep the strands together. Nothing is nastier than seeing a bunch of strands falling out from under a screw.

I have seen tinning cause problems. The connection gets hot and the solder reaches a plastic state and relieves the tension from the screw, causing a bad connection. And bad connection means more heat, more heat means more solder being deformed and so on.
That's very interesting. I just looked it up and found some history on it. I'll do some environmental chamber testing with a torque driver. Our rating goes to 176F (80C) and solder is liquid at around 370F. Somewhere between those numbers it's going to be malleable.

I was trying to avoid pigtailing to solid but maybe that's what we'll do. We have lead forming operations and they can crank out pigtails preformed in a jiffy.

Thanks for the heads up!
 
It was done to establish the manufacturing process for a requested product which is cord & plug connected controlled receptacle. The landscape lighting industry uses them and some people use them for holiday lighting. Supply houses have been asking for them because they have a very high failure rate with the brand they are using.

The reason for tinning is to keep the strands together. Nothing is nastier than seeing a bunch of strands falling out from under a screw.



That's very interesting. I just looked it up and found some history on it. I'll do some environmental chamber testing with a torque driver. Our rating goes to 176F (80C) and solder is liquid at around 370F. Somewhere between those numbers it's going to be malleable.

I was trying to avoid pigtailing to solid but maybe that's what we'll do. We have lead forming operations and they can crank out pigtails preformed in a jiffy.

Thanks for the heads up!
I have been soldering for half a decade. First, if you are worried about something looking nasty, why don't you notice the poor tinning, lack of removal of flux, melted insulation and part of the insulation under the screw?

When you do your environmental tests, don't forget to include dynamic testing. Vibration can cause the solder to crack and smush, causing a weakened termination.

The flux that is there can now promote degradation of the terminals over time, especially if subject to heat.

If you want the best connection, use a terminal and crimp it properly. And don't scrimp on the connectors or the crimper unless you are really good at making near perfect crimps with your Sta-kons.
 

mgookin

Senior Member
Location
Fort Myers, FL
I have been soldering for half a decade. First, if you are worried about something looking nasty, why don't you notice the poor tinning, lack of removal of flux, melted insulation and part of the insulation under the screw?

When you do your environmental tests, don't forget to include dynamic testing. Vibration can cause the solder to crack and smush, causing a weakened termination.

The flux that is there can now promote degradation of the terminals over time, especially if subject to heat.

If you want the best connection, use a terminal and crimp it properly. And don't scrimp on the connectors or the crimper unless you are really good at making near perfect crimps with your Sta-kons.
I think you meant half a century.

The only thing being tested was whether the strands would deform and they did not. But it looks like we're not going with tinning anyway.

Thank you.
 

macmikeman

Senior Member
Tinning stranded wire is what Mr. Lewis the electrical instructor at Lee County Vocational Tech (Fort Myers Florida) always pushed us to do. I don't bother with that......................
 

mgookin

Senior Member
Location
Fort Myers, FL
Tinning stranded wire is what Mr. Lewis the electrical instructor at Lee County Vocational Tech (Fort Myers Florida) always pushed us to do. I don't bother with that......................
Why did I think you were in Hawaii?
Or was it Washington state?
I must have your handle confused with someone else.

Are you in Lee County?
 

MD84

Senior Member
Location
Stow, Ohio, USA
I try to avoid using stranded wires on screw terminals. When I do it I like to leave a small section of the stripped insulation on the end of the wire. This keeps the strands from coming apart.
 

macmikeman

Senior Member
Why did I think you were in Hawaii?
Or was it Washington state?
I must have your handle confused with someone else.

Are you in Lee County?
Beach Elementary, Villas Elementary, Cypress Lake Jr. and Sr High School, Edison Community College , Lee County Voc. Tech.

Moved to Hawaii in 1976 and stayed.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
I try to avoid using stranded wires on screw terminals. When I do it I like to leave a small section of the stripped insulation on the end of the wire. This keeps the strands from coming apart.
That is the best way -- make the connection then pull the strip piece off or leave it on. Otherwise crimps are the other choice short of a pigtail with solid.
 

iwire

Moderator
Staff member
Location
Massachusetts
Are screw terminals on devices listed for use with tinned stranded?

Before anyone goes ballistic ;). keep in mind they are already having to include fork terninals in the listing for folks that like to go that route.
 

mgookin

Senior Member
Location
Fort Myers, FL
I try to avoid using stranded wires on screw terminals. When I do it I like to leave a small section of the stripped insulation on the end of the wire. This keeps the strands from coming apart.

+1
You're the man!

That works wonderfully. Thank you very much. It's a high quality, quick, consistent, durable method. Everything we were looking for.

No solder pot to deal with, no flux washing, etc. We are going with this method.

Thank you.
 
Top