When to Use Bare Stranded Conductor？

Hey All,
I may be overthinking this one, but one of our interns asked about the application of bare ground wire vs insulated ground wire, and I can't stop second-guessing my answer.

My gut response was that bare copper wire allows the user to connect to earth or other grid materials (thinking ground grids, rebar and the like), and the reason we use insulated is to prevent unintentional grounding to objects not intended for that use.

Could someone please confirm or school me on other differentiating applications?

All the Best,
--Nate If you are going to "school" him, the 1st step would probably be to teach him the NEC tern "Ground" refers to EARTH, so if he qants to talk conductors he needs to learn "groundED" and "grouindING".
But I think you answer is likely a good one. Applying the above, a groundING condcutor can often be insulated or bare but the groundED conductor needs to be insulated as you say to prevent an unintentional and non-compliant connection to grounding.

My gut response was that bare copper wire allows the user to connect to earth or other grid materials (thinking ground grids, rebar and the like), and the reason we use insulated is to prevent unintentional grounding to objects not intended for that use.

What possible unintentional objects would you be grounding by using a bare EGC? For the most part bare or insulated can be used interchangeably in most applications.

Hey All,
I may be overthinking this one, but one of our interns asked about the application of bare ground wire vs insulated ground wire, and I can't stop second-guessing my answer.

My gut response was that bare copper wire allows the user to connect to earth or other grid materials (thinking ground grids, rebar and the like), and the reason we use insulated is to prevent unintentional grounding to objects not intended for that use.

Could someone please confirm or school me on other differentiating applications?

All the Best,
--Nate

Bare conductor laying in the earth or in concrete can't increase overall resistance when dealing with grounding electrode conductors, but nothing in code states you must use a bare conductor either. I typically only keep #6 and #4 bare on hand and if a GEC needs to be larger typically just use an insulated conductor for it. It can have insulation stripped where you make connections:happyyes:

There are some places where NEC does require an insulated EGC. I believe EGC for swimming pool equipment and the feeder to a mobile home both need to be insulated, not really certain why. Might be some other places, otherwise general rule ordinarily allows bare, insulated or covered. Aluminum conductor has more requirement to be insulated or covered - especially if installed in wet/damp or other more corrosive locations. My thoughts. Depending on where your gec is terminating to it sometimes might be better to use one over the other. For instance: when bonding to the rebar in the footing for an offer ground electrode, should we be looking at the listing of an insulated wire as to it's ability to be encased in concrete? This is something an electrical inspector has asked me in the past when I used a stranded #4 thwn copper insulated wire to my bonding clamp. I think he was concerned with the stranding of the wire due to it's size rather than the covering on the outside. Now bare solid #4 cu wire has no outer covering and it in itself as a twenty foot of footing concrete encasement is an acceptable electrode even without rebar bonding. Will it corrode given time due to the nature of the concrete itself? How about when either is exposed to direct burial in dirt/soil? Which one is more subject to possible corrosion? I think probably the insulated one would outlast the bare one in that situation, but again is the thwn wire listed for direct burial? (NOTE: bent up rebar exposed above slab is typically rejected here, we must bond to the rebar at the bottom of the footing) Other than for isolated ground, I think the only reason anybody uses insulated EGCs or GECs is to reduce physical damage to the wire. And because it's available, or they had it on the truck, or they've seen others do it and haven't thought about the reasoning. It's not the greatest idea to pull bare stranded wire with other conductors in a wire pull, and solid conductors larger than 8awg, IIRC, are not allowed to be pulled in raceways. Smooth outer insulation of THHN probably makes for an easier pull in many cases. For GECs run outside raceways the insulation provides a bit of extra protection from damage.

Other than for isolated ground, I think the only reason anybody uses insulated EGCs or GECs is to reduce physical damage to the wire. And because it's available, or they had it on the truck, or they've seen others do it and haven't thought about the reasoning. It's not the greatest idea to pull bare stranded wire with other conductors in a wire pull, and solid conductors larger than 8awg, IIRC, are not allowed to be pulled in raceways. Smooth outer insulation of THHN probably makes for an easier pull in many cases. For GECs run outside raceways the insulation provides a bit of extra protection from damage.

Damage from what? The insulation is physically weaker then the conductor it envelops. Corrosion - has to be pretty severe for copper to really matter much - aluminum is a different story. So what if the copper turns green - that is what copper does but just on the surface.

Damage from what? The insulation is physically weaker then the conductor it envelops. Corrosion - has to be pretty severe for copper to really matter much - aluminum is a different story. So what if the copper turns green - that is what copper does but just on the surface.

Physical damage (e.g. severing of strands). Not corrosion. The insulation doesn't have to be stronger than the copper to take the brunt of abrasion.

With that said, now I'm wondering why I shouldn't look into just using bare stranded. Anybody tried it? Almost all of our long pulls are 3-5 #10s in 3/4" conduit.

Physical damage (e.g. severing of strands). Not corrosion. The insulation doesn't have to be stronger than the copper to take the brunt of abrasion.

With that said, now I'm wondering why I shouldn't look into just using bare stranded. Anybody tried it? Almost all of our long pulls are 3-5 #10s in 3/4" conduit.

Ok maybe some point there with finer stranded conductors. I was thinking mostly of grounding electrode conductors that are 6 AWG and larger in most instances. I don't know that many suppliers even stock bare conductor smaller then 8 AWG. All I can usually get is solid and in 8, 6 and 4 AWG, but that must just mean nobody is demanding much of anything else so they don't stock it.

Physical damage (e.g. severing of strands). Not corrosion. The insulation doesn't have to be stronger than the copper to take the brunt of abrasion.

With that said, now I'm wondering why I shouldn't look into just using bare stranded. Anybody tried it? Almost all of our long pulls are 3-5 #10s in 3/4" conduit.

I tried it once. I'll never do it again. The #12 we tried pulling kinked and bird-caged with little more than a strong glance. It's just not worth it. We also had several instances of the bare #12 stranded pushing up against the back of receptacles. It caused several GFCI trips and breaker trips when we began to power things up. I'm not a huge fan of the solid bare EGC in Romex either, but at least it stays where you put it.


SceneryDriver For EGCs and GECs, the NEC allows ground wire to be either insulated or bare in most applications. I'm not aware of any case where insulation is explicitly required by the NEC for grounding conductors. It is an engineer's/installer's discretion to specify insulated grounding wire.

One reason to specify it, is mechanical, as insulation reduces the abrasion to other wires in the conduit during a pull. Insulated wires are also available in finer stranding patterns (which improve pull mechanics) than their bare counterparts, such as 19-strand instead of 7-strand in size 6. Another reason is chemical, as insulation avoids corrosion conflicts if the wire is routed among dissimilar metals (such as copper in contact with aluminum, zinc galvanizing, or concrete).

For EGCs and GECs, the NEC allows ground wire to be either insulated or bare in most applications. I'm not aware of any case where insulation is explicitly required by the NEC for grounding conductors. It is an engineer's/installer's discretion to specify insulated grounding wire.

One reason to specify it, is mechanical, as insulation reduces the abrasion to other wires in the conduit during a pull. Insulated wires are also available in finer stranding patterns (which improve pull mechanics) than their bare counterparts, such as 19-strand instead of 7-strand in size 6. Another reason is chemical, as insulation avoids corrosion conflicts if the wire is routed among dissimilar metals (such as copper in contact with aluminum, zinc galvanizing, or concrete).

There are some places where it is required. A few I am aware of are in 517.13, 550.33, 680.25.

I have a question regarding bare wire in a conduit as an EGC, maybe someone could answer this for me. Would a bare conductor pulled through conduit not give potential for the “choke” effect? Same as the age old debate for the GEC going into your meter/disconnect without a bushing of some kind.


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Insulated or bare isn't the issue here, it is magnetic fields around the conductor when it carries current. If the other conductor(s) of the circuit are inside the same ferrous tubing, those fields cancel on another. A single conductor (grounded or not) carrying current and inside a ferrous tube is basically a one turn core and coil.

Insulated or bare isn't the issue here, it is magnetic fields around the conductor when it carries current. If the other conductor(s) of the circuit are inside the same ferrous tubing, those fields cancel on another. A single conductor (grounded or not) carrying current and inside a ferrous tube is basically a one turn core and coil.

Maybe I misread the OPs statement. I thought he was talking about using bare vs insulated to prevent unintentional grounding(I.e. the choke effect). I was just thinking a bare copper wire inside a ferrous metal tube could cause unintentional grounding.

But if you could elaborate a little more on the fields canceling one another. I would like to understand that a little more.

Thanks


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Maybe I misread the OPs statement. I thought he was talking about using bare vs insulated to prevent unintentional grounding(I.e. the choke effect). I was just thinking a bare copper wire inside a ferrous metal tube could cause unintentional grounding.

But if you could elaborate a little more on the fields canceling one another. I would like to understand that a little more.

Thanks


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If the ferrous metal tube is bonded at some point anyway does it matter if it touches the grounding conductor inside? They should be at same potential.

Clamp on ammeter measures magnetic field caused by current flowing in conductor. Clamp on to just one conductor and you read whatever current it has flowing in it. Clamp on to two conductors with same load on them but one goes out to a load and the other returns from that load - then current is flowing opposite direction at any instant in time on each of those conductors. Clamp your meter on both and it should read zero, because of opposing magnetic fields canceling one another. Same effect would be apply to how it effects a ferrous tube surrounding the conductor(s), in fact the clamp on meter does have ferrous component in the clamp to pick up the magnetic fields in the conductors you are measuring.

Both shielded and unshielded twisted-pair copper cable comes in either stranded or solid wire versions. There are plenty of considerations when it comes to choosing one or the other, including standards, environment, application, and cost. Let’s take a look at the differences and considerations, so you can decide whether stranded copper wire or solid copper wire cable is right for your specific installation.

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Differences Between Stranded and Solid Wire Cable

Stranded and solid wire cable differ in key ways, including construction, flexibility, and performance.

What Is Stranded Wire Cable?

In a stranded cable, each of the eight copper conductors are made up of multiple “strands” of small-gauge wires that are wound together concentrically in a helix, much like a rope. Stranded wire is typically specified as two numbers, with the first number representing the quantity of strands and the second representing the gauge. For example, a 7X32 (sometimes written as 7/32) indicates that there are 7 strands of 32 AWG wire that make up the conductor.

What Is Solid Wire Cable?

In a solid cable, each of the eight conductors are made up of a single larger-gauge wire. Solid wire is specified by just one gauge number to indicate the size of the conductor, such as 24 AWG. Whether it’s a one-, two-, or four-pair cable, the gauge of the solid conductor is the specification for the cable.

Stranded Wire Cables Are More Flexible than Solid Wire Cables

Beyond the way they're made, another key difference between stranded and solid wire cable is flexibility.

• • Stranded wire cables are much more flexible and can withstand more bending. In terminations, however, those flexible strands can break or become loose over time.
• • Solid wire cables are more rigid and can break if flexed too far or too frequently. However, solid conductors will hold their shape over time and seat properly within insulation displacement connectors (IDCs) on jacks, patch panels, and connecting blocks.

Solid Wire Cables Are Better Conductors

A less-obvious difference between stranded and solid wire cable is performance.

• • In general, solid wire cables are better electrical conductors than stranded wire cables, and they provide superior, stable electrical characteristics over a wider range of frequencies. They’re also considered more rugged and less likely to be affected by vibration or susceptible to corrosion, since they have less surface area than stranded conductors.
• • Solid wire can also carry more current than stranded wire. Higher-gauge (thinner) conductors have more insertion loss than lower-gauge (thicker) conductors; stranded cables exhibit 20 to 50 percent more attenuation than solid copper conductors (20 percent for 24 AWG and 50 percent for 26 AWG). Because the cross section of a stranded conductor is not all copper (there’s some air in there), they also have higher DC resistance than solid cables.

Now that you understand the differences between stranded and solid wire cable, let’s cover what you need to consider when making a choice.

Is Stranded Wire Better Than Solid Wire?

Which type of wire is the best choice depends on the installation's requirements.

When to Use Solid Wire Cable

When it comes to 90-meter horizontal permanent links, there’s no choice: whether it's shielded or unshielded twisted pair, both TIA and ISO/IEC standards require solid wire cable. Stranded cable (24 and 26 AWG) is limited to patch cords and 10-meter lengths within a 100-meter channel.

When to Use Stranded Wire Cable

Because stranded cables are more flexible and can withstand bending, they make excellent patch cords for equipment connections and cross-connects where cables are frequently bent and manipulated; at just 10 meters of the channel, the increased insertion loss and resistance aren’t a factor in the overall channel performance. However, smaller 28 AWG stranded patch cords that have even more insertion loss and resistance due to their smaller gauge do have some limitations — get the Skinny on 28 AWG Patch Cords to learn more.

Goto zhuhaicable to know more.

Open office environments, however, are special situations; they’re faced with regular reconfigurations and may require a more flexible cabling system. In those installations, the standards allow stranded patch cords to take up more than 10 meters of the channel. However, if you’re using more than 10 meters of stranded cable in a channel, industry standards require de-rating the overall channel length to accommodate for the greater insertion loss and DC resistance.

When it comes to de-rating stranded cable per industry standards, the overall gauge is a factor: higher-gauge (thinner) cables have a higher de-rating factor. The de-rating for 26 AWG stranded cable is 0.5, while 24 AWG is only 0.2, and 22 AWG stranded cables require no de-rating at all.

Here are the calculations to determine overall channel length, where H=horizontal cable length, D=de-rating factor, C= total stranded cable length and T=total channel length.

For example, if you’re using 60 meters of horizontal solid category 6A cable and 40 meters of stranded 24 AWG category 6A patch cable with a 0.2 de-rating factor, the total length of the channel must be reduced to 97.5 meters. (If you prefer the actual math: total stranded cable length = [105-60]/[1 + 0.2], or 37.5, and total channel length = 60+37.5, or 97.5 meters.)  If you’re using 26 AWG stranded cable with a 0.5 de-rating, the channel length needs to be reduced to 90 meters.

PoE Makes Greater Demands on Stranded Cable Patch Cords

While stranded cable is the norm for patch cords at patching areas in the telecommunications room (TR) and at the work area (perhaps longer than 10 meters in open offices), a primary application to consider in today’s LANs warrants the use of solid patch cords: Power over Ethernet (PoE). When PoE is delivered over twisted-pair copper cable, some of the power dissipates as heat. When power dissipates as heat, the cable temperature increases. With higher insertion loss and DC resistance, stranded patch cords are more likely to exhibit degraded transmission performance at elevated temperatures.

While not typically a concern in environmentally controlled spaces like the TR, stranded patch cords could become an issue once you start connecting devices in the ceiling — think wireless access points, security cameras, LED lights, and more. In best practice, if the environment isn’t temperature controlled and the cable doesn’t have to bend much, solid cable patch cords should be used. If you do use stranded patch cords in uncontrolled environments, it’s better to keep them short (about 5 meters or less). And when it comes to higher-temperature environments, industry standards require de-rating channel length for that, too; more cables in a bundle, each generating more heat, can require even more length de-rating (though there can be An Exception to Every Rule).

Balancing the Cost Difference Between Stranded and Solid Wire

While more strands in a conductor mean greater flexibility, a higher strand count also means a higher price. To keep costs down, stranded category 6 and category 6A cable are designed to strike a balance: enough strands to maintain proper flexibility, but not so many that it creates a dramatic price difference. You don’t have to compromise performance (or standards compliance) by selecting stranded wire cable instead of solid for environments and applications for which it’s not suited. Keep your stranded cables in environmentally controlled areas that require greater flexibility, and use solid wire cable where rugged performance (and little bending) is required.

Whether it’s patch cords, permanent links, or channels, you can configure a Fluke Networks Versiv™ tool to certify the cable's performance.

View the Versiv Configurator

If you want to learn more, please visit our website Bare Stranded Conductor.