stranded vs. solid wire

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dominic42

Member
hi I'm new to the forum, iv been a electrician for 20 years in the Detroit area. currently I'm working on a 800 sq foot hospital wing and I'm in charge of purchasing tools and material for this project. the job is a mix of pipe and wire and HFC (Healthcare Facility Cable) here in the Detroit area we use all stranded wire. last week i was invited out to Massachusetts to visit the plant where this cable is made to witness the process. i was surprised to hear that Michigan is the largest user of stranded wire and the rest of the country uses solid. how do you justify this, solid wire is much more labor intensive then stranded. id like some input on this from those around the country.
 

Nick

Senior Member
Re: stranded vs. solid wire

I am on the second project in two years that has in the specs #10 and smaller to be solid. I asked this engineer why and his reasoning was that it is a long standing engineering practice due to human error at the terminations. Some of the strands on the solid wire can break or fray out at the termination if the installer is not careful reducing the ampacity of the conductor. He also said when following conduit fill maximums and 360 degree maximum bends that the #10 solid is not any more difficult to pull.
Well, this guy has obviously never pulled any wire in his life! #10 Solid is a bear to pull. I don't buy the termination excuse either. How many problems can be traced to a stranded termination where a couple of strands were inadvertently cut? I bet zero.
We had two 3/4" conduit runs side by side. Same footage (about 500') same bends same pull box locations. One contained 4 #10 (solid) the other contained 3 #6 and 1 #8 (obviously stranded). The number 6 run went in in half the time and half the frustration.
With #12 wire I don't really have a preference but with #10, stranded is defiantly the way to go.
 

dominic42

Member
Re: stranded vs. solid wire

well what prompted me to start this post was that because the HFC was a special order cause it had to be steel jacketed by spec and i wanted stranded. they told me stranded was a special order "i said what are you talking about" they being AFC said solid is the norm for armored cable and once again i say "your kidding right" who in there right mind would choose solid over stranded. well im in my own little world here and now that iv seen the manufacturing process of this cable i have a better understanding of it but it still boggles my mind why the rest of the country is so solid minded. iv wired a few houses in my time and have had to use nmb which is all solid and always thought what a pain in the rear it is compared to stranded wire as far as the terminating is concerned.
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: stranded vs. solid wire

I live in MA and am quite familiar with AFC cable.

This may surprise you but until I saw some on this forum I had never seen stranded AC or MC cable in 20 years in the trade.

If I was given the choice I would stick with solid, I am used to it and I do not see much more labor with it. IMO it terminates better and easer.

Putting wire in a raceway my choice is stranded, but I do not get to choose to often. :p

Most of our job specs require solid for 10 awg and smaller.
 

bennie

Esteemed Member
Re: stranded vs. solid wire

When I was in New Zealand, on the way to the South Pole, I bought some non-metallic sheathed cable. It was mostly 2 conductor with ground. There was no white wire. Only red, black, and green. It was stranded, very pliable. I took about 10 thousand feet of it with me on the Air Force C-141.

The wire was nice to work with in the freezing environment of Antarctica.

The size was between #14 and #12. When I was asked "what is the ampacity 15 or 20 Amp?" I always answered "yes".
 

dominic42

Member
Re: stranded vs. solid wire

Originally posted by iwire:

Most of our job specs require solid for 10 awg and smaller.
so its in the job specs more then its a choice, wonder why the engineers are so different. unless its just a standard spec and they dont change it or it doesnt get questioned.
 
G

Guest

Guest
Re: stranded vs. solid wire

Some pros of stranded:

Stranded has more surface area. The electricity moves on surface area.

Stranded is less likely to break from a small nick.

Stranded is less likely to suffer from metal fatigue if exercised.

Stranded costs more (more P&O for the EC).

It pulls easier.

====
Some cons of stranded:

Stranded costs more for the client.

Stranded can be harder to terminate on screws.

Stranded cannot be backstabbed (wait, that's a good thing!).

Stranded has a larger diameter.

Stranded fills up the wire nuts faster.

Stranded is hard to self-fish. You can't unlock your car door with stranded.

Stranded must be run off spools (well usually anyway). Otherwise you end with a hairball.

And so forth :)
 

pierre

Senior Member
Re: stranded vs. solid wire

The two main reasons for the use of solid vs stranded are COST and the termination situation.
Remember termination failures are much higher than most would want to believe.

Pierre
 

jrdsg

Senior Member
Re: stranded vs. solid wire

wayne,

i could be mistaken, but i thought that high-frequency signals such as catv or fm were transmitted on the skin [hence the prevalence of copper-coated steel center conductor in catv rg6, while lower-frequencies [60Hz has got to be considered low-frequency by comparison] travelled through the core of the conductor.

am i nuts?

jr
 
G

Guest

Guest
Re: stranded vs. solid wire

When you are moving RF or data stranded wire has a greater attenuation than solid wire. RF & data only move on the outer surface of a conductor. As the signal moves along the surface, it has to hop to another conductor as the conductor heads into the center of the wire. This causes any excessive attenuation on stranded data or RF wires.

To this end, data cables (say CAT-5/CAT-5e/CAT-6) are run with solid wire if for long runs (in excess of 15-feet). Stranded cables are only suitable as patch cables. Stranded is usually the preferred patch cable only because of its flexibility. Solid CAT-x wire is typically run in maximum of 100-meter runs. A diehard will make-up his/her own solid patch cables too.

Maybe an EE can jump in here and confirm or deny that stranded is any better than solid for carrying line voltage. It was my understanding that stranded does a better job of moving the electrons for line voltage. After doing some online research I will likely be retracting that belief.

It's interesting to me that when data moves faster on different classes of wire the gauge remains the same. The increased data transfer happens because of increased twists, and because of better & more consistent insulation (say for CAT-3 vs. CAT-5). As EC's to move more electricity we mostly have to provide bigger gauge wire. In data we just need better wire.

../Wayne C.

[ October 20, 2003, 12:04 PM: Message edited by: awwt ]
 

Ed MacLaren

Senior Member
Re: stranded vs. solid wire

Most high speed data signals are a stream of voltage pulses, representing digital 1s and 0s.
The current is very low, so resistance is not too critical.
The propagation time of these high speed voltage pulses is affected more by the capacitance of the cable than any other factor.

(Quote from cable manufacturer's literature)
"Capacitance in cable is usually measured as picofarads per foot (pf/ft). It indicates how much charge the cable can store within itself. If a voltage signal is being transmitted by a twisted pair, the insulation of the individual wires becomes charged by the voltage within the circuit. Since it takes a certain amount of time for the cable to reach its charged level, this slows down and interferes with the signal being transmitted. Digital data pulses are a string of voltage variations that are represented by square waves. A cable with a high capacitance slows down these signals so that they come out of the cable looking more like "saw-teeth", rather than square waves. The lower the capacitance of the cable, the better it performs at higher frequencies.

At low frequencies the impedance is largely a function of the conductor size, but at high frequencies, conductor size, insulation material and insulation thickness all affect the cable's impedance.

Matching the cable impedance to the transmitting and receiving devices is very important. If the system is designed to be 100 Ohms, the cable should match that impedance, otherwise error-producing reflections are created."

Ed

[ October 20, 2003, 12:47 PM: Message edited by: Ed MacLaren ]
 

dominic42

Member
Re: stranded vs. solid wire

Originally posted by pierre:
The two main reasons for the use of solid vs stranded are COST and the termination situation.
Remember termination failures are much higher than most would want to believe.

Pierre
you know pierre i thought the same thing but i checked with several suppliers today and #12 thhn stranded is 36 dollars a thousand and solid is 45 so that isnt it. as for the termination i dont buy that either since solid requires pretwisting the wires but with stranded that isnt so. from what i can tell is that solid is a granfather spec and no one challanges it. it was in our specs also till about 15 years ago but we fought it and now its changed. i guess till you work with both you dont relize the difference. yes ill agree the terminations are easier at the device but thats all thats easier, you still have to fight folding them sold wires back into the box and i sure wouldnt want to be the one doing that all day. geeezz i dont even want to think about #10's.

[ October 21, 2003, 10:12 PM: Message edited by: dominic42 ]
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: stranded vs. solid wire

I do work with both solid and stranded and I have no problem with either one.

I just recently got to choose what type to use for some outside under ground branch circuits for landscape lights and I chose solid 10 awg as IMO it stands up better in wet locations, the water seems to wick through the spaces in stranded and lead to faster deterioration.

Also a few years ago I read an article in EC&M that claimed solid wire runs cooler and saves the customer money in electric bills over time.

I am sorry I do not have time to look that up right now, and as far as I know it may have been written by a member of "The Solid Wire Manufactures Association" :D

[ October 22, 2003, 06:45 AM: Message edited by: iwire ]
 
G

Guest

Guest
Re: stranded vs. solid wire

From the research I've done in the meantime stranded wire does have slightly more resistance. Resistance=Heat
Heat="Lost" energy to the consumer.
 

hurk27

Senior Member
Re: stranded vs. solid wire

I think the biggest difference is stranded is more flexible and there for it is the wire of choice for wiring machinery (vibrations) and where flexibility is needed. the current carrying capability of ether is the same as #12 stranded. is rated 20 amps as well as #12 solid. there has been old story's about skin effect and others but they are unfounded for the Hz that we use. If this was the case then stranded would carry more current as there is more skin on stranded wire as each strand has surface (skin) and would have to be counted in calculating it. now many of the High power coax cable that I use in transmitters including hard-line will have a stranded core. even for the common C/B's the better grade of RG/58 u will have stranded core but at very low freq's it doesn't come in to play.
 

charlie tuna

Senior Member
Location
Florida
Re: stranded vs. solid wire

twentytwo years ago i was forced to use solid wire due to some large building's specifications. their reasoning was stranded wire can be reduced in diameter while pulling without the installer knowing it. after you get used to working with it --- you find it more advantagous than stranded in many ways. every once in a while we get some stranded by mistake and it never gets used - the guys stay with the solid. terminating - and splicing is easier - and if you do maintainance -consider opening an existing spliced neutral feeding more than one circuit with stranded - with solid and twisted - no problem.....
 

dia480

Member
Re: stranded vs. solid wire

It has to do with government spec as well. When I lived in Connecticut we used almost always stranded, in fact my Father-in law sold wire for 39 years and when he visited me in Montana were I now work he could not belive we used solid. All of Montana uses solid.
 
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