CONDUCTOR -- stranded vs solid

I have my own thoughts on this question
BUT
I want to hear yours.

I see lots of discussion (mentions) of overcoming difficulties using stranded wire. Some methods include tinning the end or using a crimp on end to stick in the terminal.

Seems to me that tinning or crimping on a solid sleeve takes you right back to a solid conductor.

I wonder if it would be easier in the long run to use solid??
Admittedly drawbacks of solid include harder to pull in conduit and a little harder to "lay in" in a control panel or in Panduit and vibration.

Dan Bentler

Solid wire? For control wiring?

Not a good idea in control wiring or industrial wiring in general. You know all the reasons that you should use stranded wire. Solid conductor wire is fine for office lights and outlets or in a commercial/residential building for the same purpose if you use something like ROMEX. Others here will doubtless have other reasons for stranded over the ones you have already listed.

I forgot ,,,,,,,,,

Randy

What I forgot (and reminded of with your post) was that in past what I have done is use stranded in the conduit. Then in the panel for "intra panel" connections and jumpers etc etc used solid.

Seemed to work OK and saved a few bucks and a fair amount of time by subsituting solid wire for ring or spade terminals.

Dan Bentler

some of the larger manufacturing plants have in-house wiring standards that don't allow bare wire to be terminated. the place i work is one of them. we have to use pin terminals on the end of the wire, or, if there's room, spade terminals. all grounds use either pins or rings. we also use Brady sleeve labels on all wires, slid over the crimped portion of the terminal. we also have to use ratchet-type crimpers. and i don't think there's any solid wire in the plant, other than lighting, or our "earth" grounds.

Back to electron theory basics...
It's called the "skin effect" of a conductor. I am just quoting Lord Kelvin! (yup the temperature guy!)

www.mos.org/sln/toe/skineffect.html



:site:

ROB beerchug

ps. nope ROB is NOT my name, people in the know are familiar with the ROB

It's called the "skin effect" of a conductor. I am just quoting Lord Kelvin! (yup the temperature guy!)

Click to expand...

To elaborate on Bitmore's statement:

Theory says that most of the current in any conductor flows near the outside diameter, or on the "skin". Stranded conductors have many times the skin area than a solid conductor. That's why welding cable (many, many very small strands) is rated to carry so much more current than a THHN of the same size--and why THHN will carry more than solid.

I once had a contractor substitute solid conductor telephone type cable in place of specified stranded belden cable for proportional valve signals with disastrous results. This attempt at cost reduction cost all involved.

To add a little more

Stranded wire is made like rope so the many strands reinforce each other and make it stronger therefore less likely to break. If a break does occur in stranded wire it may have less effect than a break with solid core.

Personal opinion: Solid wire is not easy to work with in a panel. I prefer using stranded with terminals or tinning.

Solid conductors in industrial/control applications is a bad idea. Simply put, it breaks.

Solid conductors are in fact easier to pull through conduit. Reason being is that you can pull and push the conductors at the same time through the conduit.

The reason welding cable has so many fine strands is because it makes the conductor more flexible and less likely to break over time. Welding cable is generally used to carry more current than a THHN conductor because of the applications they are generally used in. Welding cable is generally used as a Free Air conductor while most THHN conductors get derated because they are generally installed in conduit.

A conductors ampacity is based on it’s ability to dissipate heat. Conductors are rated the way that they are to prevent the destruction of the conductors insulation.

THHN denotes the insulation used on the conductor, not whether the conductor is solid or stranded.

Some things you might find interesting –

Did you know – If you have a bunch of conductors inside wire duct and you cable tie them together (to make it look nice and neat) and the bundle is longer than 24” you must derate those conductors. NEC 310-15(b)(2)(a)

Did you know - It is possible (in some cases) to use a conductor at a higher ampacity than what is shown in NEC Table 310-16. See NEC 310-15(c)

And one last note – Check the temperature rating of the device to which you are terminating the conductor to. Lets say you need a conductor rated at 55 amps and you are going to use a THHN conductor. You look at the NEC Table 310-16 and see that a #8 THHN is rated at 55 amps at 90C. But you are connecting the conductor to a starter that has terminals rated at 75C, can you use the #8 THHN? No. The #8 conductor must be derated to 75C in which case it can only handle 50 amps. This is important if you work with/on older equipment as most older electrical equipment was rated at 75C.

our machines have a lot of vibration, and the solid conductors tend to vibrate loose from the terminal strips. and on those strips where you have 2 or 3 wires on one lug, we always make sure they are all stranded because the solid may not allow the lug to close all the way up on a stranded wire.

The only times yours truly have seen and have used solid wires for controls were the times of the good old Soviet Union. And the reasons were very simple: it was impossible "to get", not mentioning "to buy", anything but the very basic stuff. Socialism at work, you know.

And by the way: that was mostly aluminum wire.

Liv n Lern / refresh memory

Not too sure it is really "fair" to compare THHN to weld cable. Two completely different applications. I sure would not try nor put up with agravation of using THHN for welding lead. You'd break your neck in the concertina caused by THHN.

Skin effect -- knew about it but forgot about it with referance to this. That is one of probably many they use aluminum tubing for conductors in switchyards. On high amp circuits skin effect is for sure there - but is it realistic to worry about it on low current applications ie 20 amp or less??

Flexibility and less prone to breakage -- no argument at all.

I use ratchet crimpers (Greenlee) whenever I can.

If I am only terminating into clamp type terminals I always twist stranded with pliers to avoid the jagggers - either getting in contact with neighboring terminal or something else or sticking one in my finger - how come they feel like a phone pole but when you want to pull it out you need a microscope to find it??

Thanks for the feedback.

Dan Bentler

in a large panel, with several bundles of power, control, and signal wires terminating there, i might spent days labeling and terminating. but it sure looks good when its done, if you use a wiring standard similiar to what we have, with the sleeve labels, crimped terminals, and standardized color-coding. makes it so much easier to troubleshoot later, too.

grouch

Make it easy ??

Most of my work has been trouble shooting.

Minutes taken to properly ID the wires, use color code etc etc save
HOURS tracing wire.

EVEN just labeling the J boxes makes life a bunch easier.

Dan

Stranded wire because of machine vibration.

Stripping solid wire improperly (cutting around the insulation) can result in a score mark that says "Break Here".

Skin effect? Yes for ampacity, moot here. I heard that the cabling between high tension towers are made of concentric tubing.

I cannot recommend putting more than two wires to a lug UNLESS they have spade or ring terminals, and I HATE ring terminals!
I love having to completely back out the screw to fumble finger it and drop it or the washer. It ALWAYS falls into a power supply or drive.
My wire nippers convert rings to pinch-spades very quickly - Japanese machine builders do love those rings.

Rod (The CNC dude)