I'm still learning so pardon the dumb question. In wiring a new addition for 110v and 220v electrical outlets, switches and lights is there a certain time when you would want to use stranded core THHN wire vs solid core THHN wire? I guess in particular I'm referring to when you would use something in the 12 or 14 gauge size.

I'm running counduit throughout in my new addition and when looking for the feed wires on spools the store carried both stranded THHN and solid THHN in both 12 and 14 gauge. Pricewise they both seem very comparable.

Thanks,
Royce M

Hey Royce,

First of all, my preference would be to use the solid copper AWG 12 wire.

Here's my thinking, I can install a 15 amp breaker on the AWG 12 wire but I cannot install a 20 amp breaker on AWG 14. So as I look down the road, there may become a reason to replace the 15 Amp load in favor of a 20 Amp load.

When that happens, if that happens, the 14 AWG will have to be pulled and replaced by 12 AWG along with the R&R of the breaker.

Also, please consider this, if all wiring is going to be encased in metal conduit, then it will not be necessary to pull a ground wire. The conduit will serve as the ground for the circuit.

If the stranded is about the same, use it. It is easier to pull. I would pull a green too.

Labman,

I'm curious as to why you would pull a Green (ground) wire. Would you be kind enough to elaborate?

While solid has a lower resistance per 1000 foot, #14 solid is 3.07 ohms/1000 ft, and #14 stranded is 3.14 ohms/1000 foot, as you can see the difference is negligible, and not an issue with normal distances.

Solid had been traditionally less expensive than stranded. Large wiring jobs would use solid simply to save money. Nowadays with copper prices so out of wack, there is probably not much difference.

Stranded wire is much more flexible and is widely used for pulling through conduit.

If you chose to use solid, you will see a huge difference in labor effort to pull it.And the ore effort to pulling wire will stress the wire and insulation, which can contribute to early failure.

As far as pulling an equipment ground, while metallic conduit is allowed to act as the equipment ground, pulling a separate equipment ground conductor is widely done by all professionals, in all metallic conduit.

Conduit must remain perfectly intact to function as a valid, low impedance, path for fault currents. Once the continuity of conduit is broken, due to damage, or a loose set screw connector, or a loose or poorly tightened locknut, the equipment ground is lost.

If the conduit is PVC, or any other non-metallic raceway, a separate equipment grounding conductor is mandatory.

For the purpose of this forum, and providing advice to Do It Yourselfer's, I suggest that all advice given is to always provide a separate equipment ground conductor in all conduit, raceway, etc.

Let the pros decide what they want to do as they know the code, what they are allowed or not allowed to do, and judge the specific installation and the pros and cons of their decision.

As far as the issue between a 15 or 20 amp circuit, 15 amp circuits using #14 wire are perfectly allowed by national and local codes. One may suggest to use #12, for the obvious reasons, but there is no reason to use #14 wire on 15 amp circuits.

I'd like to add that solid makes a much more neater appearance in the load center. Whne I was doing some control wireing with 18 AWG, I used stranded, but I chose a smaller number of strands which made it less flexable. I also ordered the wire direct from a manufacturer which means that in order to get the lower price, I might have to wait for the order.

I agree, if there is no need for flexing, solid should be used. It's also easier to terminate because with stranded if your not careful when stripping you can cut strands. It's also easier to pull.

Stranded should be used for AC connections to the disconnect because of the vibrations and flexing that inherently happens in that application.

Pulling a separate green and for sensitive equipment and using orange outlets which use an independent ground may also be worthwhile. By sensitive equipment, I mean computers, servers, FIOS locations and structured wiring panels. In this case green with yellow stripe is preferred. A separate ground for each orange outlet all the way back to the load center.

When it's protective ground use green.

Remember to leave a pull string in place.

Getting off topic.

Isolated Equipment Ground (Orange Outlets) is poorly understood, rarely installed properly, and is only for sensitive equipment that requires a signal reference to operate or noise on the equipment ground would cause issues.

I have a 20,000 square foot data center that is for a large financial institution, with dual redundant 1200 amp 480/277 volt services, and not one IG outlet in the facility is used.

Isolated Ground is beyond the scope of this forum, and should not be recommended to DIY'ers.


As far as choosing between a neat panelboard and less stress from pulling wire, I chose the latter. Neatness can be taken care of with wire ties.

My View?
Stranded is more Expensive, I use it and like it, It is less Stressfull on devices, Panels Can
Be tough, You have to train the wire straight, What I did like about Solid wire was Making up the Main Panel. Twist strands tight, before tightening on Screw.
As Far as Pulling a Ground in Metal Conduit, Pull a Ground. Separated conduits, with a Shorted Condition, could Kill. The wire will maintain ground on both sides of the conduit
Should the Conduit separate. No matter the Code. Always Pull a Ground.

OK, I understand the reasons for the equipment ground lead, however, I don't recall ever seeing the metal conduit fail in the ways described. I do recall trouble shooting a failing "Mini computer" in Suffolk, VA at a General Electric Television plant.

When ever a rain storm with lightning moved in, three minis would always go "toes up". We did every thing we could do including hanging a Dranetz meter on the 110 vac.

Eventually, we brought a specialist in from Richmond, VA to aid us. What we finally discovered, was that the building ground was flaky because some misguided genius ran copper water pipes internally in the building, but when the water main left the building to service an adjacent building they used PVC for the run to that building.

What a bizarre bug to find. Equally obvious is that had a equipment ground been pulled and tied to a decent ground we would never have had the problem.

At our data center, we apparently had an issue under the same conditions where the ground potential was apparently different from one end of the building to the other and it poped some crucial switches. They ran fiber from one end of the room to the other, so it would not happen again. Somebody eventually has to pay, whether it be the electrical guys or the data guys or someone else all together.

My favorite was a low end, about $3K, multi-channel analyzer kept failing and I looked at the schematic (remember these) and found that there was not a single component used for protection. The manufacturer said, "We specify that the equipment operates on 120V, 60 Hz" and evidently your not supplying this. So, it was another $1K repair.

Similarly, we had a themocouple scanner that would quit scanning. I obtained the schematic and found that the board layout and schematic both showed a regulated power supply, but none of these components were fitted in all of the 4 units we had. They were CMOS logic based and therefore they popped easy with overvoltages. I added a few cheaper parts and all was well.

Maybe my years of managing a factory and needing to beat OSHA to problems calibrated my eyeballs, but in different public places I have spotted thin wall conduit pulled out of its fittings and hanging by its wires. I think I have even seen rigid conduit broken off. Nothing is forklift proof, or idiot proof.

One more comment. All too often the beancounters have the last word on things.

Thanks everyone for all the info. As usual a wealth of info. I really appreciate it.

On separated conduits.
Old Attics that have had numerous Service People working for Decades, From AC Techs, Electricians, Alarm Companies, Plumbers, Stereo speakers/wiring, Satellite, Cameras, Remodeling, etc.
Conduits get bent, pulled, Abused, Seeing a separated conduit does not Shock me.
No Pun intended.

When I was an apprentice my employer always told me you can only use stranded wire in conduit. I was curious of this so I checked the NEC and you can use either. I would recommend using stranded wire, only because it is much easier to pull, since it is more flexible. Also, it doesn't matter whether it is metal conduit or not, you must always put in a ground wire. If it is steel, it is not as conductive as copper, therefore it won't ground a ground fault as well. There could also be a bad bond on a coupling or something that wouldn't allow continuity. Also a fitting for enering a box could be improperly bonded, having the same continuity effect. A bonding jumper and a grounding (green) wire can prevent this.

Stranded wire is limited in how the receptacles are connected... you can't back stab. (which you shouldn't do anyway) Stranded wire is great if you decide to change the wiring configuration, it holds much less memory than solid. (pulls out of the conduit more easily) Solid wire twists together tighter than stranded, but I have never have had a stranded connection come apart. In a vibration installation, actually stranded wires ability to flex tends to keep the wire nut on, where a solid wire will shake with the equipment and possibly loosen the wire nut. Longer pulls will most definitely be eased by stranded wire. To answer your question, use whatever you want... both are fine for all applications.

Don't mean to be offensive, but I think you need to hit the books again, as this statement is incorrect:


Also, it doesn't matter whether it is metal conduit or not, you must always put in a ground wire.

Review 2008 Edition NEC Section 250.118, you will find that EMT, rigid conduit, IMC, etc, are allowed to act as the equipment grounding conductor, and a "ground wire" is not required.


As I explained in a previous post, adding a EGC in all raceway is a common practice, very wise I might add, to prevent any problems from loose or broken conduit fittings, esp with EMT ,and the practice is done by any good electrician, specifier, design engineer, etc.

There is not 1 inch of conduit I install, (or should I say watch get installed) that does not have an EGC. However, it will be wise to know the actual Code requirements.

I agree with TK on always pulling a ground. I will always pull a ground, weather it is code or not.
Tk, I noticed a mistake, You didn't write what I know you wanted to say in the last sentence of your Oct. 18th/ 4:34 P.M. where you said:
"but there is no reason to use #14 wire on 15 amp circuits".
Take Care.
If you have 12 why not put it on a 20 unless certain cercumstances or voltage drop.

I think "not" is missing as in " no reason not to use #14".

Ahhh.