Insulated vs. Bare Ground Wire Application

Status
Not open for further replies.
B

BlaineXD

Member
Location
Rockville, MD
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.
 
BlaineXD said:
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.
Click to expand...

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.
 
BlaineXD said:
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
Click to expand...
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.
 
Last edited:
jaggedben said:
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.
Click to expand...
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.
 
kwired said:
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.
Click to expand...

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.
 
jaggedben said:
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.
Click to expand...
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.
 
One recommendation for an insulated EGC was in either the IEEE green book or Soares, namely use an insulated EGC so in the event of a ground fault the insulation would help from damaging the adjacent conductors from the heat generated in the EGC.
Small sized bare EGC, IE 14-12-10 are fine stranded, easy to damage, kink when pulling and harder to pull.
 
jaggedben said:
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.
Click to expand...

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).
 
Carultch said:
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).
Click to expand...
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.


Sent from my iPhone using Tapatalk
 
ElectricMatt said:
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.


Sent from my iPhone using Tapatalk
Click to expand...
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.
 
kwired said:
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.
Click to expand...

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


Sent from my iPhone using Tapatalk
 
ElectricMatt said:
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


Sent from my iPhone using Tapatalk
Click to expand...
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.
 
kwired said:
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.
Click to expand...

Thanks for going into a little more detail. I completely understand what you are saying now. I appreciate you taking the time to explain it further.


Sent from my iPhone using Tapatalk
 
Status
Not open for further replies.
Top