Using stranded wire with screw terminals

[iwire]

I can't tell you about code.
I just think that a crimped fork terminal has to be a better and more reliable method.
In my field, industrial, it would be a minimum standard acceptable to the customer.

It has always baffled me why people think doubling the number of connections makes things more reliable.

Personally I think people are putting a higher value on how it looks vs how it works.

 

[Besoeker]

It has always baffled me why people think doubling the number of connections makes things more reliable.

Personally I think people are putting a higher value on how it looks vs how it works.

I assume that you mean the crimped terminal adds another connection?
A valid point, I suppose.
Our crimping tools are routinely calibrated to ensure correct operating pressure. We have a testing machine that checks how much force it takes to pull a crimped wire out of a joint.
It is a simple pass/fail test. If the tool fails, it is discarded.

The merit of crimped terminals is that there are no loose strands to cause problems and the connection, if required, can be opened or made as often as required for test purposes without degradation.

 

[delectric123]

It has always baffled me why people think doubling the number of connections makes things more reliable.

Personally I think people are putting a higher value on how it looks vs how it works.

Probably the same reason I've seen on factory wiring in control panels, where they crimped ferrules on all the ends of the wires connecting to terminal blocks, contactors... etc... I've often wondered what the reasoning is behind it.

 

[GoldDigger]

Probably the same reason I've seen on factory wiring in control panels, where they crimped ferrules on all the ends of the wires connecting to terminal blocks, contactors... etc... I've often wondered what the reasoning is behind it.

Not having designed or built such control panels, I can only speculate, but:

1. Appearance, as you suggest.
2. To make a reliable connection with terminals that are not designed for stranded (or fine stranded) wire in the first place.
3. To make sure that there are no loose strands sticking out on the hidden side of the wire. You can get a 360 degree view of the ferrule in place on the end of the wire while you cannot always look at the back side of the terminal.
4. To accommodate wire sizes larger than the terminal was designed for (reducing ferrule)
5. To allow the connection to be removed and reconnected multiple times without cumulative damage to individual strands which could lead to eventual failure.
6. Strain relief if the ferrule has a section that is crimped on over the insulation.

 

[don_resqcapt19]

I assume that you mean the crimped terminal adds another connection?
A valid point, I suppose.
Our crimping tools are routinely calibrated to ensure correct operating pressure. We have a testing machine that checks how much force it takes to pull a crimped wire out of a joint.
It is a simple pass/fail test. If the tool fails, it is discarded.

The merit of crimped terminals is that there are no loose strands to cause problems and the connection, if required, can be opened or made as often as required for test purposes without degradation.

The typical crimp tool that would be used for the crimping of a connector for a switch or receptacle is not a controlled crimp tool, and it has probably never been tested, other than the original manufacturing prototype for that tool.

 

[kwired]

And if you really want to impress them also quote WJQR which states (for standard snap (wall) switches:
"Terminals of the wire-binding screw, setscrew, or screw-actuated back-wired clamping types are suitable for use with solid building wires unless otherwise indicated either on the device or in the installation instructions.
Terminals of a flush snap switch are permitted for use with Listed field-installed crimped-on wire connectors or an assembly, if so identified by the manufacturer."

Which prohibits the use of stranded conductors and allows the use of fork crimps.

but according to what you said, the fork crimps need to be ones that are identified by the manufacturer, not just any ol' fork crimp. Take that a step further and you need to use a crimp tool identified by the fork terminal manufacturer, and if the tool has any crimp pressure setting that is field adjustable it must be correct as well, or you have violated the listing instructions.

 

[PetrosA]

The typical crimp tool that would be used for the crimping of a connector for a switch or receptacle is not a controlled crimp tool, and it has probably never been tested, other than the original manufacturing prototype for that tool.

True, my Panduit CT-1551 is totally out of control

Actually, I think you're right. Most of the times I've seen guys use crimp tools, they've used the pliers style ones and usually they used the wrong die for the terminals they were crimping. It would be like using a HSS bit in a rotary hammer, which they'd never do. But they're stubborn for some reason.

 

[kwired]

It would be like using a HSS bit in a rotary hammer, which they'd never do.

You underestimate the intelligence of some people I have had the opportunity to work with/around.:happyyes:

Or maybe I really meant overestimate?

 

[Besoeker]

The typical crimp tool that would be used for the crimping of a connector for a switch or receptacle is not a controlled crimp tool, and it has probably never been tested, other than the original manufacturing prototype for that tool.

Yes, I can understand that. Different fields I would imagine.

We manufacture electrical control panes that are normally used in industrial applications and, quite often, petrochem.
Absolutely everything has to be documented and that includes calibration certificates for all the test instruments and includes those for ratchet type crimp tools. Failure to produce such certificates results in a failure of the factory acceptance test (FAT), delays in shipping, delays in payment, and liquidated damages for late delivery - none of which sits well with the bean counters, of course.

But I accept that it isn't appropriate for all applications - if it had to be implemented, the costs in doing so would just kill the job off financially in many cases.

 

[Aleman]

Probably the same reason I've seen on factory wiring in control panels, where they crimped ferrules on all the ends of the wires connecting to terminal blocks, contactors... etc... I've often wondered what the reasoning is behind it.

I use ferrules on 18awg and smaller. I believe ferrules make a better connection in terminal blocks and field wirable connectors. Definitely makes for easier insertion and rework,
but then the ferrule is an added step. European equipment manufacturers use lots of these. Ferrules are best for inserting in the spring style terminal blocks, the ones
without a screw. The idea is that stranded wire is better for panel construction for a variety of reasons, but solid makes a better connection. So the ferrule will 'adapt' stranded wire to a
solid at the connection.