stranded vs. solid wire

[dominic42]

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]

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]

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]

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.

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

[bennie]

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]

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.

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]

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]

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

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 ]