Solid vs stranded wire

Co-worker is trying to tell me that solid wire carries current better than stranded. I asked him why you didn't find solid wire on tractors and automotive things. I know industry uses almost all stranded wire and houses are wired with solid. Is it a d.c.vs a.c. thing? How about it some of you like John T. and Buick&Deere and other electrical know how to guys.

Stranded carries more current, electrons travel on the surface of the wire, stranded had more surface area.

I have always been told that the current goes around the outside of the wire,not 'through' it.Thus a stranded wire will have less resistance.A stranded wire will stand movement and vibration,where a solid wire will fatigue and break.OK experts,am I correct,or mistaken?

In makes very little difference with AC or DC electrical wiring. Household wiring is NOT just solid-core. If conduit is used, it's going to have stranded wire, e.g. THNN. Not solid.

Solid wire has a slightly smaller OD then same gauge stranded. As to all the power carried on just the outer shell? That's true for certain applications, especially with certain wavelength video and radio signals.

I think my old 78 caddy may have used solid wire for the lights and it may have been aluminum. Not totally sure, it was a very long time ago. I do remember I saw solid wire used in a car and I had to repair a broken wire. Thought at the time it was very strange.

Stranded is for vehicle use because it is flexible enough to avoid fatigue breakage when moved and vibrated. Not the case in house wiring. There is an effect, but at high frequencies, not enough to even consider at 60 Hz in AC house wires. Jim

The following is from Argon National Laboratory:

DC current will use the wire's whole cross-section evenly.

Imagine a single solid wire divided by invisibly-thin barriers into parallel strands of equal thickness and shape. Only at the ends are they joined together, metal-to-metal. In this picture, each strand has equal resistance, and equal voltage from end-to-end, so the current in each is equal.

Only AC has a preference for a particular depth. It prefers to be shallow, staying towards the outside. This is a consequence of changing magnetic fields caused by the changing current.

If it is DC, it is not changing, so the magnetic field is steady, and has no effect on the DC current density. DC current only cares about resistance, not inductance or magnetism.

Weird but moot minor point: The steady field around a wire with DC current may cause a small voltage difference between the outside and the inside. However the difference at one end cancels out the difference at the other.

Due to electromagnetism, parallel currents attract. So if the metal conducts electrons, then they are squeezed inwards, and the interior would be slightly more negative than the outside. Contact at the starting end is made to the wire's outside. So is contact at the finishing end. So an electron going travelling the wire-center route may go up a small potential step at the start, then go down the same amount at the end. These two steps cancel each other out. The end-to-end voltage in the wire interior is the same as the wire exterior, so the current densities are the same too.

Nobody even thinks about those last two paragraphs. They do not need to. Except maybe physicists doing plasma hi-power sparks with Z-pinch. Z-pinch is when the glow of the current in the ionized gas spontaneously squeezes itself into a very intense sharp narrow strand, even though it started out wide and diffuse. It only does that if the current is very high, and because a gas can be compressed. In a solid metal the mobile electrons (charge -1) are forced to keep a constant density by the need to keep charge neutrality with the hard-packed metal-ions (charge +1) they wander amidst.

Jim Swenson

We lert that the strantbded bens easier

The "skin effect" is negligible at 60 hertz, although it is a factor when you're talking about transmission lines. There is no skin effect at all with DC, while at UHF it becomes very pronounced.

The main reason for stranded wiring is flexibility.

I saw a solid wire running to rear of 80 Chevy once that was original to the car.

Yes, I helped an uncle add the latest feature, the third brake light to his new 85 Buick.
When we tapped into the wiring harness to the brake lights, we discovered a flat strip with solid, single strand aluminum wire in it.

It was a bit of ugly stuff to splice into reliably with standard stranded copper wires.

What makes you think you can only run stranded wire in conduit? You can get THNN in solid wire also. Lots of solid wire has been used in conduit in the 12 and 10 gauge sizes.

Jon,
Thanks for your post. I was thinking my memory may have been playing tricks on me and there are some people here that generate great pleasure telling me I'm wrong. Good to know I haven't lost all my brain cells, and it was solid aluminum wire. Must have been cheaper than stranded copper.
George

Bubba the Grad, How are classes at Redneck Teck going? Still seeing BUBBIE?
George

Don't overthink it. Solid makes a better connection on standard switches and receps in a house setting. Many engineers spec. stranded wire in many /most buildings. Stranded will take the bending /vibration where solid will break. Both will cary the same current, by the National Electrical Code. You will need a meter costing much more than you can afford to prove otherwise. Joe

I don"t think that is what he is saying. Now days with the availability of stranded wire it"d be stupid to run solid in conduit. Stranded is so much easier to work with and pull through a conduit.

In a comparision of ampacity of large condutors [which are all stranded] a 500 kcmil cable can carry 430 amps yet a welding cable 500 kcmil can carry 695 amps. Cost is way higher but when you need the flexibilty for something like tapping conductors into an old box stuffed with wires the flexibility becomes a factor .Welding cable can be layed into the box where 500s of normal cable would not allow the cover to go back on . For a trough pull box etc. sometimes you have to get the expensive welding cable to close things up. You will have bloody knuckles trying to work with normal cable forget about solid.For something like generator lead to temp power up a building welding cable is the only way you can wrap them up like a small cord and place them back in the generator . For pools solid #8 must be used to equalize the potential of any metal part larger than 4 square inches. But does not have to be run back to the panel.Stranded will fail inspection. Solid conductors are usually only going to be 10s and 12 awg sizes[excepting swimming pool 8awg s]. Years ago solid was speced out more but I have not seen that for a good while. Solid has more chance of being nicked on any sharp edge when pulling a bunch through pipe. Like I said all large conductors are stranded.
Unless you order solid the supply house is sending stranded. I have not seen solid larger than #8 that I can remmeber offhand. To use anything but stranded on a vehicle is probably bad practice.

Bingo.

Solid wire is less expensive to manufacture thus it is universally used in building construction where flexibility is not an issue.

Dean

"solid wire carries current better than stranded"

BUT isnt stranded wire just a bunch of smaller SOLID wires all bundled together????

Stranded wire is used for its flexibility and vibration resistance properties.

At DC or low frequency AC the so called "skin affect" isn't a consideration like at high frequencies where current tends to flow more in the outer perimeter of a wire.

The cross sectional area or sum of all the cross sectional areas is what determines a wires rating to carry x amount of current.

John T

In my experience stranded is easier to pull in conduit but solid is better for putting under wire nuts and on devices. Like was mentioned usually autos are stranded for vibration. If you ever have to pull wires back out of a conduit hope they are solid, stranded will look like a bad slinky.

Dean got it right, price verses usability .
Walt

It has been mentioned that high frequency AC moves near the surface of the conductor. Because of this, almost all coaxial cables for high power utilize a hollow conductor. The large coax cables you see on broadcast and cell towers utilize a hollow center conductor made of copper. Looks just like soft copper tubing for plumbing. For RF, the surface area determines current carrying capacity.

Just another note in this good discussion.

Electronics and electricity are fun! (diodes are like check valves except when they are voltage regulators or capacitors) Fun stuff!

Josh

If you want the best battery cables or booster cables, you use welding cable that it is made up of many more individual smaller solid wires. Similar to wire rope where more strands is stronger.

Different wire for different purposes so what point is the real question the wire used is the best for that job thats why they use it.

Bubbie is going to increase the size of her famlley. She is skered that it is not realley hers

I can't imagine what kind of pups will come out of that litter.

The ampacity of stranded wire of any given gauge is lower than solid as the cross section is partly air. It is more flexible and less prone to vibration cracking.

On my wire striper the stranded strip hole is one size bigger than the solid. Solid wire is much easier to hook to switches and receptacles. Stranded wire is much easier to pull threw conduit in most cases. Depends on what I am doing as to my preference.
industry explanation

That is also what is used to come out of large battery back up cabinets to go over to main gear. It is much easier to lay in a cable tray and land than the stiff normal wire. Then there is lightning protection cable which is braided way differently.Must be a theory about lightning traveling down it.

Only exception I can think of is solid bare #4 for grounding purposes. Somebody else can probably think of more

I love this website. An old redneck country boy can learn anything here. Best site on the net.

It appears the ampacity difference is not for all stranded. I ran into it sizing some big SOW flexible cords for a sawmill that have very fine stranding. We had to go up from 6 to 4 for the run to keep the voltage drop ok.

Ask him if he has ever pulled solid wire in conduit....lol. There is a time and place for solid wire.....but.....IT SUCKS to work with compared to stranded.

"ampacity" Sounds like a word I should be able to use at the Friday night fishfry.