Stranded wire .... Bare, soldered, Ferrule.....which?

[klaatu]

I assume he means mechanical lug type.

They are typically wire size dependent. Sounds like it's pushing the limits on size or has the incorrect size even.

I was trying to be non specific. Any termination where stranded wire is captured and connected. This could be the grounding strip, a breaker, a 240+V outlet, at the equipment end, etc.

 

[klaatu]

It is still not clear (to me) if you are addressing small conductors (`14-10) and screw terminals or larger conductors and pressure terminals.

Anything stranded. But I was specifically interested in anything10AWG or larger in diameter.

 

[Dennis Alwon]

Anything stranded. But I was specifically interested in anything10AWG or larger in diameter.

There is no choice on wires larger than 10 for choosing between bare or stranded. All wires, barring a few for ground rods and grounding electrode conductor, are stranded. Breaker terminals and lug terminals are mostly rated for stranded wire but yes it will compress the wire. This is not an issue unless you inserting conductors under lugs that are too small for the conductor.

 

[4-20mA]

Seemed fairly specific when you mentioned...

"Several examples recently where the lug was torqued down, but many of the strands were not captured. Other instances where after torqueing and later removing, the wire was deformed and could not be reinserted, and had to be cut off."

I guess I misinterpreted your several examples and other instances as "examples and/or instances." My bad.

 

[klaatu]

I noticed inside an 7600W inverter, where they are using 8AWG stranded copper, they are using ferrules everywhere. Any place where a stranded wire is inserted and a torque applied to a screw, has a ferrule.

 

[jim dungar]

I noticed inside an 7600W inverter, where they are using 8AWG stranded copper, they are using ferrules everywhere. Any place where a stranded wire is inserted and a torque applied to a screw, has a ferrule.

But there they are probably using fine stranded flexible conductors not the standard '7strand' construction as found in THHN and other building wire.

 

[letgomywago]

But there they are probably using fine stranded flexible conductors not the standard '7strand' construction as found in THHN and other building wire.

When it is up to a manufacturers ability to get a product listed they have more leeway than we do with mechanical choices. When we need to joint 2 22awg wires we go for button crimps usually but a manufacturer could use a breadboard and soldered connection no problem or some other plug in connector. We don't get the freedom with this but we don't have to destructive test every splice we make so we can make a few more identical ones.

 

[klaatu]

Let me be more direct....does NEC forbid the use of Ferrules or soldered wire ends?

 

[letgomywago]

Let me be more direct....does NEC forbid the use of Ferrules or soldered wire ends?

It doesn't forbid much. Its the product listing doesn't allow this connection method and the NEC requires you follow the product instructions which are part of the listing.

 

[jim dungar]

Let me be more direct....does NEC forbid the use of Ferrules or soldered wire ends?

Distortion is often part of the clamping process such that a poor connection may occur if the conductor 'stays round'.

Very few connectors rated for building wire are also rated for the fine stranding found in flexible cables.

I have seen some standard lug instructions that suggest wrapping a thin copper foil around fine stranded conductors or to use ferrules. I have not seen any that suggest soldering the conductor.

 

[winnie]

I think we might be bumping into confusion over different stranding types found in wires, and possibly lugs being used outside of their proper listing.

As already mentioned, there are different classes of stranding. You can have the minimal stranding used to make large conductors flexible enough to be installed without using bending machines, and you can have the fine stranding used to make conductors intended to be continuously flexed such as welding cables.

Very often lugs intended for minimally stranded conductors are not suitable for fine stranding. Ideally the instructions would specify the permitted stranding, but this is probably buried in the listing requirements.

Lugs for fine stranded wire are usually compression type, not set screw type.

I've specifically seen copper foil or ferrules required for mechanical connections to fine stranded wire on some connectors, mostly 'cam-lock' type connectors. Not on lugs that I recall.

But I have encountered lugs where I've used normal stranded wire, at the small size of the allowed wire range for the lug, tightened the screw, and found that the screw splays the strands apart and several strands end up between the screw and the body of the lug.

Jon

 

[Speedskater]

Never solder tin the end of a stranded wire for a screw terminal. With time the solder-tinning will cold flow and the screw will loosen.

 

[klaatu]

 

[letgomywago]

"I declare (electrician) I didn't say it I declared it"