Solid verses stranded wire in conduit

[smalltown]

I'm almost ready to buy wire for my garage project. Everything is in conduit. The max distance between pulls would be ~12 feet. I was planning on solid wire as I like the way it gets secured to switch and receptacles terminals.
Any thoughts?

 

[rlitman]

For 12', there's not much advantage to stranded. Have fun!

 

[pattenp]

Use the solid and save a few pennies.

 

[vonhef]

I used solid 12 gauge. Most of my conduit runs I was able to feed/push the wire through. Would have probably required a fish tape to pull the circuits if I had used stranded wire.


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[dfiler2]

I used solid and one thing I learned from someone here was to not tape the ends together and to put an inch or two difference in length of the individual wires, especially if you are going around corners. Doing that made it a piece of cake.

 

[checkthisout]

I can't see stranded provided any benefits, only increased costs and more hassle hooking it up outlets and switches.

 

[katmat]

In theory, stranded will carry more current than solid wire because electricity travels on the outside of the wire. So with stranded wire you have more wires for the electricity to travel on.

 

[rlitman]

In theory, stranded will carry more current than solid wire because electricity travels on the outside of the wire. So with stranded wire you have more wires for the electricity to travel on.

It doesn't work the way you think it works. And the skin effect is hardly there at 60hz in 12 gauge wire.

 

[Slowgsr]

I would pull solid wire because I'm not sure what devices it's going to be connected to but it's a lot easier to terminate properly on a setscrew then stranded wire which technically isn't supposed to be terminated by wrapping around I setscrew

 

[Alchymist]

In theory, stranded will carry more current than solid wire because electricity travels on the outside of the wire. So with stranded wire you have more wires for the electricity to travel on.

Rlitman pegged it - no skin effect to speak of at 60 Hz.
Skin depth is defined as the distance below the surface where the current density has fallen to 1/e or 37% of its value at the surface.

For copper at 70C:

S= 2837/sqrt(f)

Where f is frequency in Hertz, and S is the Skin depth in mils.
At 60 hz, the skin depth is 366 mills, AWG 12 wire is 80 mills in dia, if I calculated correctly.

 

[exmaxima1]

Rlitman pegged it - no skin effect to speak of at 60 Hz.
Skin depth is defined as the distance below the surface where the current density has fallen to 1/e or 37% of its value at the surface.

For copper at 70C:

S= 2837/sqrt(f)

Where f is frequency in Hertz, and S is the Skin depth in mils.
At 60 hz, the skin depth is 366 mills, AWG 12 wire is 80 mills in dia, if I calculated correctly.

+1
And people also mistakenly assume that current flows on the skins of the individual strands. Unless those strands are insulated from each other, the "skin" is the outer surface of the bundle, and stranded does no better than solid.

 

[w1im]

+1
And people also mistakenly assume that current flows on the skins of the individual strands. Unless those strands are insulated from each other, the "skin" is the outer surface of the bundle, and stranded does no better than solid.

Yup, that's what Litz wire is for.

https://en.wikipedia.org/wiki/Litz_wire

 

[hotdogstand]

It doesn't work the way you think it works. And the skin effect is hardly there at 60hz in 12 gauge wire.

Beat me to it. Really don't need to worry about skin effect with the kind of power a consumer would be using.

 

[gregtwojeeps]

I have heard this argument for years from well respected sparky's that stranded wire will carry more current. The "skin" effect sounds interesting to me, for sure. But I have to question this theory as it puzzles me somewhat....

If the wire fabricating industry KNEW that only the outside wrapped conductors carry the most current, then why would they invest all that money in making say a 350 MCM copper conductor.... FULL of twisted conductors. Why not just put a plastic filler cording in the middle of the 350, reduce the amount of strands.... and then just let the outside strands do the work for the same price, and make a LOT more money ?

 

[dfiler2]

Saturday morning and I'm already learning "stuff". Great info, thanks guys.

 

[k-os]

I used solid 12-gauge when I re-did my electrical with conduit. My longest pull was ~36 feet. I contemplated using stranded, but for the same reasons others mentioned I chose solid for a more solid termination, and I thought it would be easier to push/pull due to the added stiffness.

 

[rlitman]

+1
And people also mistakenly assume that current flows on the skins of the individual strands. Unless those strands are insulated from each other, the "skin" is the outer surface of the bundle, and stranded does no better than solid.

Well, technically insulation isn't required, and the outer surface area of stranded is higher than solid, but again, at 60hz, with 12 gauge wire, it just isn't a factor that comes into play.

Beat me to it. Really don't need to worry about skin effect with the kind of power a consumer would be using.

Exactly. Some of the bigger devices at my office have multiple wires feeding them, but we're talking about copper that's as thick as your thumb.

I have heard this argument for years from well respected sparky's that stranded wire will carry more current. The "skin" effect sounds interesting to me, for sure. But I have to question this theory as it puzzles me somewhat....

If the wire fabricating industry KNEW that only the outside wrapped conductors carry the most current, then why would they invest all that money in making say a 350 MCM copper conductor.... FULL of twisted conductors. Why not just put a plastic filler cording in the middle of the 350, reduce the amount of strands.... and then just let the outside strands do the work for the same price, and make a LOT more money ?

Funny you mention that. For lightening protection, they do make a hollow braided cable that uses this effect to its advantage.

 

[Cmreschke]

It's really no better or worse. It's all personal opinion. I personally like stranded wire. As far as terminating in devices, I use good spec grade compression plate devices, or sta kons to terminate.
Though not legal but, 2 #12 thhn will fit under 1 yellow sta kon eliminating the need for splicing as well.

 

[Norcal]

I would pull solid wire because I'm not sure what devices it's going to be connected to but it's a lot easier to terminate properly on a setscrew then stranded wire which technically isn't supposed to be terminated by wrapping around I setscrew

Show me where it's not supposed to terminated around the device screw. BTW, I used to believe the same thing, & still prefer the better devices that stranded can be terminated with ease.

 

[ddawg16]

At 60 HZ, the skin effect 'depth is 8.5mm.....or about .3". 12g wire is not nearly that thick.

https://en.wikipedia.org/wiki/Skin_effect

You will never find any solid wire that thick. You wouldn't be able to bend it.

Hence, skin effect is NOT a factor with residential or commercial 60Hz systems and has no reason to be in any discussions.

 

[ddawg16]

Getting back on topic. I'd use stranded.....a hell of a lot easier to pull through conduit.

Your not going to tie those wires to the outlet directly anyway. The proper method is to use a pigtail, that way your bundle stays at the back of the box.

So....make up your pigtail using short pieces of solid and wire nut them to the stranded wire.

 

[rlitman]

Getting back on topic. I'd use stranded.....a hell of a lot easier to pull through conduit.

Through a long pull, absolutely yes. But the OP said his longest run would be 12'. On a 12' run, solid is easier to push than stranded is to pull.

 

[gregtwojeeps]

In my experience working with hospital electrical systems, stranded was by far the most popular conductor.... used in the two hospitals that I worked in at least.

Saying this.... I found more small ampacity circuit problems with stranded wire, than solid. Why ? Improper wiring practices by the electrician/maintenance worker. I would find lighting /receptacle circuits dead or flickering, open neutrals throwing wild voltages. .

Problem most times ? Improper joining of the spliced stranded conductors in J-boxes. The stranded conductors from what I could tell, were stripped, then laid side by side and then a red Scotchlok wire connector was twisted on to them..

As the wire nut was twisted on, the stranded conductors "loaded" up like a big spring inside the wire nut and then unwound and relaxed later, allowing the conductor strands to de-compress and the compressed wire joint to loosen, heat /cool and started arcing from the intermittent loads...

 

[Cmreschke]

You get same issues frequently enough with solid wire as well. Both are caused by the same thing. Improper installation methods.

 

[zmaxmotorsports]

I used solid and one thing I learned from someone here was to not tape the ends together and to put an inch or two difference in length of the individual wires, especially if you are going around corners. Doing that made it a piece of cake.

 

[zmaxmotorsports]

I have heard this argument for years from well respected sparky's that stranded wire will carry more current. The "skin" effect sounds interesting to me, for sure. But I have to question this theory as it puzzles me somewhat....

If the wire fabricating industry KNEW that only the outside wrapped conductors carry the most current, then why would they invest all that money in making say a 350 MCM copper conductor.... FULL of twisted conductors. Why not just put a plastic filler cording in the middle of the 350, reduce the amount of strands.... and then just let the outside strands do the work for the same price, and make a LOT more money ?

Id say stranded wire has less resistance.
Run a battery cable with thick course wires and see how far you can run the battery down before it wont start,then try it with a cable made of fine stranded welding lead cable and see the differance.

 

[zmaxmotorsports]

Show me where it's not supposed to terminated around the device screw. BTW, I used to believe the same thing, & still prefer the better devices that stranded can be terminated with ease.

I usually just pull an extra 1/2" of insulation up to the end of the wire leaving a 3/4" or so of bare stranded copper behind it and wrap that around the screw.
The insulation on the end keeps it from unraveling.

 

[wyliesdiesels]

I usually just pull an extra 1/2" of insulation up to the end of the wire leaving a 3/4" or so of bare stranded copper behind it and wrap that around the screw.
The insulation on the end keeps it from unraveling.

 

[Alchymist]

Id say stranded wire has less resistance.
Run a battery cable with thick course wires and see how far you can run the battery down before it wont start,then try it with a cable made of fine stranded welding lead cable and see the differance.

A solid wire of a given gauge and a stranded wire OF THE SAME GAUGE will have the same resistance per foot at DC and 60 Hz. The battery cable comparison is apples to oranges, as the cable with the finer wire will have a greater cross sectional area than one with larger wires, for a given diameter.

 

[soj]

I changed out some outlets once (long ago and far away) that were wired with spade terminals crimped on stranded wire. The outlets were bad (loose connection to the plug, one had smoke stains around the openings), but the terminal crimps were tight, (passed the pull test and showed no signs of heating up), so I reused them. Are crimp on terminals OK to use like that? Do they meet code?
jp

 

[sberry]

In my experience working with hospital electrical systems, stranded was by far the most popular conductor.... used in the two hospitals that I worked in at least.

Saying this.... I found more small ampacity circuit problems with stranded wire, than solid. Why ? Improper wiring practices by the electrician/maintenance worker. I would find lighting /receptacle circuits dead or flickering, open neutrals throwing wild voltages. .

Problem most times ? Improper joining of the spliced stranded conductors in J-boxes. The stranded conductors from what I could tell, were stripped, then laid side by side and then a red Scotchlok wire connector was twisted on to them..

As the wire nut was twisted on, the stranded conductors "loaded" up like a big spring inside the wire nut and then unwound and relaxed later, allowing the conductor strands to de-compress and the compressed wire joint to loosen, heat /cool and started arcing from the intermittent loads...

I found issues with red Scotch on solid too especially where the installer wasnt real strong and careful and those pos didn't help. I actually tossed the remains of a few boxes of those in the junk. The wing nut type allow for so much more power a guy can twist them right to a near welded condition.

 

[rlitman]

I found issues with red Scotch on solid too especially where the installer wasnt real strong and careful and those pos didn't help. I actually tossed the remains of a few boxes of those in the junk. The wing nut type allow for so much more power a guy can twist them right to a near welded condition.

I'm with you, and only buy the wingnut type. I've seen Ideal screwdrivers with a recess in the back that fits the teeth on the wingless wire nuts, but never used one.
Yes, you've got to put some effort into the tightening.

I changed out some outlets once (long ago and far away) that were wired with spade terminals crimped on stranded wire. The outlets were bad (loose connection to the plug, one had smoke stains around the openings), but the terminal crimps were tight, (passed the pull test and showed no signs of heating up), so I reused them. Are crimp on terminals OK to use like that? Do they meet code?
jp

So long as the terminals themselves are rated (most of what you find at HD is, but most of what you find at HF is not), then yeah.

 

[sberry]

I am an either or guy, I really don't like mixing them for some reason, prolly just me.

 

[exmaxima1]

Well, technically insulation isn't required, and the outer surface area of stranded is higher than solid, but again, at 60hz, with 12 gauge wire, it just isn't a factor that comes into play.

Insulation is required to make high-frequency Litz wire. I only noted the insulation because so many don't appreciate that plain stranded wire behaves electrically just like solid wire, except it is more flexible. Agreed, at 60 hz it is all moot.

 

[exmaxima1]

Id say stranded wire has less resistance.
Run a battery cable with thick course wires and see how far you can run the battery down before it wont start,then try it with a cable made of fine stranded welding lead cable and see the differance.

Solid AWG (American Wire Gauge) = Stranded AWG. No difference in resistance per foot.

Your analogy of "thick coarse wire" vs Welding cable has too many variables. What is the actual AWG of the cables. Are the "coarse wires" actually cheap jumper cables made of copper plated aluminum, or even STEEL wire? What were the connections made of---spring clamps vs bolted clamps, etc??

 

[gregtwojeeps]

[..............................................................

 

[600SL]

Getting back on topic. I'd use stranded.....a hell of a lot easier to pull through conduit.

Your not going to tie those wires to the outlet directly anyway. The proper method is to use a pigtail, that way your bundle stays at the back of the box.

So....make up your pigtail using short pieces of solid and wire nut them to the stranded wire.

I use pigtails but prefer stranded pigtails. I just use good quality devices that have a captive washer. I prefer the stranded for reduced wire stress during any kind of maintenance.

 

[nsula_country]

Stranded. Hands down. OP can PUSH stranded if only 12'... If OP needs to pull a longer run, it will also be easier.

CT

 

[simpler=better]

Solid, it's easier to terminate. 12' is nothing.

 

[rlitman]

Stranded. Hands down...

Solid, it's easier...

LOL. Don't you like it when the internet comes to a consensus?