Solid vs Stranded MTW

[fifty60]

I always use stranded 14 and 16 AWG for my control panels.

I am tired of messing with the stranded wire, inserting it into terminals and having the stray strands sticking out. Plus, I lose strands sometimes when crimping. So instead of 14AWG, I have 16AWG by the time I accidentally cut off some of the strands.

I know stranded gives you the benefit of being able to bend better. But is there any other benefit to stranded wire? It seems like solid wire would be better in every way except that it is not as easy to bend...

 

[jumper]

I have always used stranded in control panels since my specs always call for it. Just used to it I guess.

 

[fifty60]

So it would be pretty strange to use solid wire on a control panel. But why? Is solid wire that hard to work with in 14 and 16AWG?

 

[K8MHZ]

Solid wire doesn't play well with crimp on connectors. Stranded may be a bit tedious, but at least it will stay in the connector.

 

[bei]

A fellow electrician once changed out a relay using solid conductors. I don't recall what the relay controlled, but it was located in a 12"x12" junction box in the common hallway of a condo building. I was sent back within two days to change his solid to stranded as the solid caused the coil to hum loudly (or maybe it was the contacts chattering - I can't remember clearly). It had to do with the coil needing to be free to move a bit and the solid copper was too rigid to allow that.

 

[fifty60]

That is one of the problems i was hoping to alleviate by going to solid. I am having trouble with pull tests. The panel gets constructed, then somebody comes and tugs on the wires and some of the wires pull out.

I was thinking that strands were falling off when the wire was stripped, as something contributing to this. But you think solid wire would be worse?

I have a mixture of cage/clamp and screw terminal connectors. Seems like the screw terminals are the worst. Any suggestions on how to keep them in the terminals better?

 

[GoldDigger]

That is one of the problems i was hoping to alleviate by going to solid. I am having trouble with pull tests. The panel gets constructed, then somebody comes and tugs on the wires and some of the wires pull out.

Are you using dedicated full-cycle crimping devices which match the terminals you are using?
Have you looked at changing the brand of terminals you use?

 

[jim dungar]

So it would be pretty strange to use solid wire on a control panel. But why? Is solid wire that hard to work with in 14 and 16AWG?

I have seen many CNC type machines, from Japan, with solid wiring. Those 90 degree bends sure looked pretty.

 

[Jraef]

Some terminals on control devices typically found in control panels will ONLY be rated for use with stranded wire. Crimp lugs (fork or ring tongue for example) will be the same; stranded only. You COULD use solid where permissible, but you will need to use stranded where not, so you will end up with two types of wire in your panels.

Get better strippers, ones that don't damage the conductors like the self-adjusting type. The stripper mechanism is a series of spring loaded sharp plates that conform to whatever diameter you put into it automatically and cut ONLY the insulation, never the conductors.

http://www.greenlee.com/products/STRIPPER%40FCUTTER-%40d-STRIPAX-PRO-6.html?product_id=17696

Then before you try to put them in the terminals, either dip them in a solder pot (old fashioned way), crimp on a sleeve, or just give the strands a twist first.

 

[fifty60]

Very useful information everyone. Thanks!

 

[SceneryDriver]

Some terminals on control devices typically found in control panels will ONLY be rated for use with stranded wire. Crimp lugs (fork or ring tongue for example) will be the same; stranded only. You COULD use solid where permissible, but you will need to use stranded where not, so you will end up with two types of wire in your panels.

Get better strippers, ones that don't damage the conductors like the self-adjusting type. The stripper mechanism is a series of spring loaded sharp plates that conform to whatever diameter you put into it automatically and cut ONLY the insulation, never the conductors.

http://www.greenlee.com/products/STRIPPER%40FCUTTER-%40d-STRIPAX-PRO-6.html?product_id=17696

Then before you try to put them in the terminals, either dip them in a solder pot (old fashioned way), crimp on a sleeve, or just give the strands a twist first.

DO NOT tin the leads of your wires! We had a run of trouble with some of our panels getting loose connections recently, and we narrowed it down to the power supplies (Meanwell LED power supplies) we use coming with their tails pre-tinned. Our techs were putting the tinned tails in screw clamp terminals. Those connections were failing 6-12 months later. We now cut off the tinned section and crimp ferrules onto the wire and land in the terminals. No more problems.

The solder was cold flowing / creeping under the pressure of the screw terminal, and loosening the connection over time. This was more of a problem on high current (+15A) connections. The NEC forbids tinned ends under screw connections in fire alarm circuits for precisely this reason.

Buy a good wire strippers, and learn how to use it so you don't damage the individual wire strands. Invest in a good ferrule crimper and use it.

https://www.amazon.com/KNIPEX-97-53...487200&sr=8-4&keywords=knipex+ferrule+crimper

With few exceptions, we ferrule every connection in our panels, and we have few if any loose connections. If you're failing the tug test, you're not tightening the terminals properly. Solid wire will not solve that problem, and will make building the panel more difficult. It also will make things a pain to troubleshoot in the future.



SceneryDriver

 

[junkhound]

..any other benefit to stranded wire...

the vibration of machine tools can cause solid wire to break due to metal fatigue over time if not properly tied down.

Have see 'fast-on' terminal come loose also.

 

[GoldDigger]

the vibration of machine tools can cause solid wire to break due to metal fatigue over time if not properly tied down.

Have see 'fast-on' terminal come loose also.

But if you tin the stranded wire you end up with the same metal fatigue problem or worse at the point where the tinning stops.

 

[junkhound]

But if you tin the stranded wire you end up with the same metal fatigue problem or worse at the point where the tinning stops.

Correct: No tinning, crimp on terminals only.

No solid wire on aircraft except items such as jumpers on circuit boards. Some connector pin terminations are tinned before being soldered into the pins, but the wires are clamped within millimeters to prevent movement (and pullout)

 

[tkb]

I too recommend ferules on the stranded control wire.

 

[just the cowboy]

NFPA 79 machine control

NFPA 79 machine control

I don't have a 79 manual anymore but I belive it says no solid on machines.