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Old 07-31-2017, 02:05 AM   #1
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Stranded wire vs. Solid on AC

I know the debate will always continue, and it really gets us nowhere closer to anything but the true root of all evil; personal choice. I really just want to keep seeing the arguments for each side. I see points made for both and I know my choice and reasons (they'll be following this poetic opening statement), but I know that a lot of people out there have absolutely no experience with the electrical world and any information that can be backed with validity, is good information from which to form your own ideals.

Now on to the fun part.

I personally have great faith in my stranded wire. It has, in my experience, a better tolerance to both vibration and shock. I've read the arguments that if you are anchoring your wire appropriately you should have no issue with vibration and even less of one if using conduit. These are true statements, I agree, when working with the usual home/office/garage type scenarios. I base my stranded wiring use off of my experience working with automobiles, motorcycles, and actual shop environments, where the normal day to day stress these wires undergo is something quite different.

The primary argument you I would think of for automobiles and motorcycles is moving parts vs the rigidity of solid wire. The main harnesses on both of those aren't exposed to moving parts though. Most your in-cabin wiring is securely fastened to the main chassis on a car along with most of your light circuit wiring on unibody setups, up to the actual pigtail that plugs in. Same for motorcycles. The primary harness is secured to your backbone and usually has pigtails running to the other sections, with the only real moving components being the ones for lighting, moving at the stem/neck assembly, and for drivetrain on rubber mounted models. So why not save some cash and run the Solid? My best guess, and to what me seemed like a duh moment when I saw it, was because of shock. Unlike a house, a traveling vehicle is exposedd to things like body twist in high winds, opposing forces moving in who knows what directions on heavily bumpy roads, and the shock of accidents.

I ran into this problem the first time on my shop shortly after I had installed an upgraded, stationary air compressor. Up until that point, the original solid wiring, that was up to code for all of those detail guys reading this, had never given me any sort of issue. However, a while after I hard lined the air compressor to quick connect drop points throughout my shop with steel tubing, I began having a whole slew of small, thorn in side electrical issues. After many many temporary fixes that had to be redone over and over, I just so happened to be looking up one day when the air compressor cycled on. As the air hit the steel lines it caused a small, unnoticeable little wave through them, and from there into the walls where all of my electrical conduit was also run. I began taking down sections at a time to notice that rose little shocks where just enough to be causing small flexes at my conduit junctions and elbows even with the straps at one foot increments. It cost a small fortune in lost time and materials but I replaced it all stranded and haven't had an issue for 10 years.

The second time is when I caught on to what it was though. My house I was living in atf the time was late 1800's with wiring that had been brought up to code some time after ground spikes but before square D breakers. We were hit by a tornado one January that somehow didn't destroy the house but managed to get enough shift in it to flex the walls and floors to the extent that the water lines began giving out from the aftermath of the stress. We immediately began having electric nightmares pop up and after pulling wire after wire I saw the same thing as I had before. When the walls had flexed it bent and broke a large portion of the houses wiring in the attic. It wasn't the vibration, but that instantaneous stress applied to it.

When I apply that to a conversion, I think about how many times a year I slam on my brakes because some idiot pulls out; or how many times I've picked up a little too much speed coming down that curvy steep grade; or even how many times I've caught a girlfriend or idiot family member pulling stuff out of the plug ins by their cord instead of at the plug. Then I think of the instant stress that puts on the wire and say too myself, good thing I ran stranded.

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Old 07-31-2017, 05:21 AM   #2
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welcome to the forum.
So what sort of bus you running?
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Old 07-31-2017, 06:04 AM   #3
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Right now I'm still in the plan phase. I had an 80's vw bus I did with the pop up years back and just decided this time I want bigger.

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Old 07-31-2017, 06:10 AM   #4
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I whet my teeth on VW's as well. Although my first one was so old it was 6 volt!
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Old 07-31-2017, 06:15 AM   #5
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Worked on a lot of 6v bikes, never a car. I got lucky and had a lot of chances to work on a lot of different stuff as a kid. Now I consider myself lucky because despite have 2 bad back surgeries and a third mostly unsuccessful one; I get a chance to just be free at a young age, 30. So, I'm taking what I've been given, building a bus with a small single bike workshop in the rear, and a living quarters in the front, selling everything but my books and tools, and driving off the edge of the world, haha.

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Old 07-31-2017, 09:33 AM   #6
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Ill throw my 2 cents worth in here. As an electrician for 43 years and running a service truck for most of those years, you learn to do things by yourself. I always liked solid wire when having to pull wire by yourself. If you planned right, you could usually push the wire in from j-box to j-box. The solid wire would not tend to unwind on you. Knowing how much movement is happening on the bus, I will have to lean more on the stranded wire and sta-con lugs and terminal blocks where I can use them. It also lets me keep the wires in a nice little organized bundle to troubleshoot later.
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Old 07-31-2017, 10:57 AM   #7
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I see where most newer campers and motorhomes use solid romex copper wire , just like a house. If its good enough for the factories then its good enough for me.
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Old 07-31-2017, 11:06 AM   #8
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I'm more of a believer in the motto, if it's good enough for the factory it needs to be upgraded, hahaha. Like phantom said, the solid is easier for a cat to do on their own and romex means one push you have a whole junction laid out. The factory wants to pay that temp worker as little as possible, have as few of them as possible, and get them I the next one and out of the electrician's way as quickly as possible. That's how they make a buck or two million. They don't care as long as it gets past warranty date which is what likme 3 years. So for most people that buy campers or rv's, 1 trip. It's all numbers to them.

By the way Phantom; thanks for being one of the crazies brave enough to do it that long. My great grandfather was a long term electrician before the days of breakers and ground posts, he'd probably be swearing on the solid wire, but that's because his breaker boxes had to be like someone used a square to line the wires up. Overly organized. Mine are clean, but his were like show poodles, haha.

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Old 07-31-2017, 02:45 PM   #9
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For all of 100 to 150 feet that I'll be needing.. I've been converted to using marine wire for my AC system. It's stranded, but not all stranded is equal.

The common building wire THHN has 7 strands (Southwire brand 14, 12, and 1 gauge), is rated for 90C dry or 75C when exposed to oil or coolant, and has a tough PVC insulation with nylon over-coat.

Type SO cable is much finer with 65 strands of type K (30 gauge strands) (Southwire ROYAL brand, 12/3 gauge), is rated for 90C, and has soft but thick EPDM rubber insulation and CPE (chlorinated polyethylene) jacket.

Marine cable is very similar to the SO with the same type K/30 gauge strands. I didn't find a strand count published but having the same size strands as SO cable I'd guess the strand count is comparable too. (Ancor Products 12/3 gauge) This one is rated for 105C dry/75C wet and "resists salt water, battery acid, oil, gasoline, heat, abrasion and ultra-violet radiation."

Definitely agree with the motto "if it's good enough for Jayco and Forest River, there's probably something better available."
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Old 07-31-2017, 04:10 PM   #10
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you always use stranded wire on a vehicle.. and the right type of it. as well as putting in some type of conduit... is not rocket science.
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Old 07-31-2017, 04:32 PM   #11
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Originally Posted by family wagon View Post
For all of 100 to 150 feet that I'll be needing.. I've been converted to using marine wire for my AC system. It's stranded, but not all stranded is equal.

The common building wire THHN has 7 strands (Southwire brand 14, 12, and 1 gauge), is rated for 90C dry or 75C when exposed to oil or coolant, and has a tough PVC insulation with nylon over-coat.

Type SO cable is much finer with 65 strands of type K (30 gauge strands) (Southwire ROYAL brand, 12/3 gauge), is rated for 90C, and has soft but thick EPDM rubber insulation and CPE (chlorinated polyethylene) jacket.

Marine cable is very similar to the SO with the same type K/30 gauge strands. I didn't find a strand count published but having the same size strands as SO cable I'd guess the strand count is comparable too. (Ancor Products 12/3 gauge) This one is rated for 105C dry/75C wet and "resists salt water, battery acid, oil, gasoline, heat, abrasion and ultra-violet radiation."

Definitely agree with the motto "if it's good enough for Jayco and Forest River, there's probably something better available."
If I understand wire sizing correctly, it's a logarithmic thing. You double the cross section, you drop 2 numbers in wire size. So 64 strands of 30 gauge maths out to be 18 gauge not 12 gauge? 2^6 = 64; 6x2=12; 30-12=18. Am I thinking this out right?
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Old 07-31-2017, 07:03 PM   #12
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Interesting question. I hadn't ever taken time to study a gauge chart that much. Here are some additional resources that might be of interest.
  • The 65 strands of 30 gauge figure cited earlier came from the table in this product data sheet (PDF) for Southwire's ROYAL SOOW line.
  • There's an answer on electronics.stackexchange.com with an image showing how the circular mil size of solid and stranded wires is determined. Note that circular mils are not mils squared; it isn't a true measure of area. In any case I noted that the 12 gauge combinations from solid up to 65x30ga and 165x0.0063" stranded are all about 6500 circular mils.
  • This Wire Gauge Conductor Size Table from Platt Electric Supply has a footnote that says "every 3 gauge decrease doubles the cross sectional area." It leaves me wondering whether that's the square inches area or the circular mils area.. Also as an extra bonus, this table lists the 100% skin depth frequency for conductors from 40 to 4/0 gauge. It's in the low kHz range for gauges we're usually interested in.
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Old 07-31-2017, 08:52 PM   #13
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Interesting question. I hadn't ever taken time to study a gauge chart that much. Here are some additional resources that might be of interest.
  • The 65 strands of 30 gauge figure cited earlier came from the table in this product data sheet (PDF) for Southwire's ROYAL SOOW line.
  • There's an answer on electronics.stackexchange.com with an image showing how the circular mil size of solid and stranded wires is determined. Note that circular mils are not mils squared; it isn't a true measure of area. In any case I noted that the 12 gauge combinations from solid up to 65x30ga and 165x0.0063" stranded are all about 6500 circular mils.
  • This Wire Gauge Conductor Size Table from Platt Electric Supply has a footnote that says "every 3 gauge decrease doubles the cross sectional area." It leaves me wondering whether that's the square inches area or the circular mils area.. Also as an extra bonus, this table lists the 100% skin depth frequency for conductors from 40 to 4/0 gauge. It's in the low kHz range for gauges we're usually interested in.
DANG!!!!! I need a beer after all that.

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Old 08-01-2017, 07:18 AM   #14
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I like that KnottyDevil. Where did you find that one?
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Old 08-01-2017, 07:22 AM   #15
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I'm more of a believer in the motto, if it's good enough for the factory it needs to be upgraded, hahaha. Like phantom said, the solid is easier for a cat to do on their own and romex means one push you have a whole junction laid out. The factory wants to pay that temp worker as little as possible, have as few of them as possible, and get them I the next one and out of the electrician's way as quickly as possible. That's how they make a buck or two million. They don't care as long as it gets past warranty date which is what likme 3 years. So for most people that buy campers or rv's, 1 trip. It's all numbers to them.

By the way Phantom; thanks for being one of the crazies brave enough to do it that long. My great grandfather was a long term electrician before the days of breakers and ground posts, he'd probably be swearing on the solid wire, but that's because his breaker boxes had to be like someone used a square to line the wires up. Overly organized. Mine are clean, but his were like show poodles, haha.

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Yeah Jacobdduncan you are correct. One of the crazies !!!! Never got rich but made a decent living from it. "I thought I wanted a career. Turns out all I wanted was a paycheck." So I could do the things that required me spending money. LOL.
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Old 08-01-2017, 08:47 AM   #16
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I thought the thing about the stranded stuff was interesting, too. And that's a great bottle opener! Would've been especially amusing if it were sized for bending a nice J-hook into the end of wire to fit around a screw terminal.
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Old 08-03-2017, 06:20 AM   #17
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I like that KnottyDevil. Where did you find that one?
Saw it on Facebook. I googled it and bought a couple. $10 each. Several places have them. Very well made and heavy duty. Its pretty cool

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Old 08-03-2017, 09:44 AM   #18
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Stranded vs solid

There might actually be a reason every vehicle on Earth uses stranded only. Jus' sayin'.
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Old 08-03-2017, 12:39 PM   #19
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Saw it on Facebook. I googled it and bought a couple. $10 each. Several places have them. Very well made and heavy duty. Its pretty cool

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Thanks KnottyDevil
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Old 08-04-2017, 11:02 PM   #20
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Thanks KnottyDevil


Stranded wire is necessary for DC because electrons traveling along wires in DC current, travel on the surface of the wire - not the sub-surface or the core. This makes a single strand of wire turn into lightbulb filament if too much DC is applied. Stranded wire provides a bunch of wire surfaces for the electrons to choose from avoiding the filament scenario.

AC electrons don't care where they travel in a conductor. So stranded or solid core should make no difference to them. If you like stranded for one reason or many, then there's no technical reason to dissuade you IMHO.


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