# Purpose of "semi-conductive layer" in wire?



## kaboler

Today I got to work on some higher voltage conductors. We pulled in a conductor that goes from a big transformer to a neutral-ground resistor transformer-looking thing. I believe it goes from the big transformer (changing the voltage from c. 67k to c. 10k) and we took a neutral off that and went to said neutral-ground resistor thing.

I don't really know what that's all about. Surges and lightning strikes? Don't know.

Anyway, the cable we pulled in had a copper core, followed by a thin insulator, and then a relatively thick chunk of rubbery-looking stuff, then another thin insulator (which was covered by writing that said "semi-conductive layer remove only for splicing" something like that) then some copper winding for grounding, followed by the outer sheath.

Explain why would anyone want a semi-conductive layer in a wire please.

I'm thinking that if voltage starts leaking out (can it leak?) it'll disperse over a wider area with that semi-conductive layer instead of arcing and exploding if it's a thin area.

What do you think of my thoughts?

TY!!!

BTW excellent day today. I threaded pipe today, for the first time (aluminum, not rigid, good for me!) and tapped a drill hole for the first time too. Lots of fun!!!! A really good day. I even fixed an idling problem on the customer's car hahaha. Vacuum issue.)


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## backstay

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## guest

backstay said:


> It takes the voltage produced by the HV and takes it to ground.


BZZZZZTZTTTT...sorry, wrong answer. :no:

The purpose of a semi-conductive layer in HV cables is to even out the voltage stresses on the insulation layers and reduce or eliminate corona induced breakdown of the insulation. 

Our POCO here has found out firsthand what happens when the semi-conductive layer is damaged/missing on the 16kV cable they have locally. We have had several outages and cable blow-ups of late. 


Here's a link on cable construction:

http://www.wireworld.com/proton/contents/products/images/CVlineenglishV2.pdf

And from page 25 of that pdf:


> Semi Conductive Materials
> •Semi conductive materials are used to control electrical field on both conductor
> and insulation outer surface.
> •Material is copolymer, highly hygroscopic, containing 30 to40 % carbon black.
> Therefore it has to be maintained dry and usually dried before use.
> •Border between the semicon and insulation layer must be smooth as ever to
> avoid electric field concentration


The next page (pg.26) has a great graphic representation of how the semicon layer affects electrical field distribution within the cable. 


Google "HV Cable Semiconductive layer" for a lot more info. :thumbup:


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## backstay

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## Zog

mxslick nailed it, mostly, there are generally 2 semi con layers, the inner one is between the conductors and insulation, which is the one that evens out the flux distribution. Without the semicon layer the insulation would need to be much thicker to insulate the high density flux pockets produced by the strands. The semi conductor evens these pockets out so electrically the conductors act more like a single condcutor. 

The 2nd semi con layer is between the insulation and shield, this layer is where the capacitive charge is produced and safely discharged to ground so the outer jacket does not become charged from the capacitive effect produced by typical MV cable construction.


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## RIVETER

kaboler said:


> Today I got to work on some higher voltage conductors. We pulled in a conductor that goes from a big transformer to a neutral-ground resistor transformer-looking thing. I believe it goes from the big transformer (changing the voltage from c. 67k to c. 10k) and we took a neutral off that and went to said neutral-ground resistor thing.
> 
> I don't really know what that's all about. Surges and lightning strikes? Don't know.
> 
> Anyway, the cable we pulled in had a copper core, followed by a thin insulator, and then a relatively thick chunk of rubbery-looking stuff, then another thin insulator (which was covered by writing that said "semi-conductive layer remove only for splicing" something like that) then some copper winding for grounding, followed by the outer sheath.
> 
> Explain why would anyone want a semi-conductive layer in a wire please.
> 
> I'm thinking that if voltage starts leaking out (can it leak?) it'll disperse over a wider area with that semi-conductive layer instead of arcing and exploding if it's a thin area.
> 
> What do you think of my thoughts?
> 
> TY!!!
> 
> BTW excellent day today. I threaded pipe today, for the first time (aluminum, not rigid, good for me!) and tapped a drill hole for the first time too. Lots of fun!!!! A really good day. I even fixed an idling problem on the customer's car hahaha. Vacuum issue.)


Could the resistor...transformer looking thing have been an impedance grounding transformer?


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## tkb

kaboler said:


> Today I got to work on some higher voltage conductors. We pulled in a conductor that goes from a big transformer to a neutral-ground resistor transformer-looking thing. I believe it goes from the big transformer (changing the voltage from c. 67k to c. 10k) and we took a neutral off that and went to said neutral-ground resistor thing.
> 
> I don't really know what that's all about. Surges and lightning strikes? Don't know.
> 
> Anyway, the cable we pulled in had a copper core, followed by a thin insulator, and then a relatively thick chunk of rubbery-looking stuff, then another thin insulator (which was covered by writing that said "semi-conductive layer remove only for splicing" something like that) then some copper winding for grounding, followed by the outer sheath.
> 
> Explain why would anyone want a semi-conductive layer in a wire please.
> 
> I'm thinking that if voltage starts leaking out (can it leak?) it'll disperse over a wider area with that semi-conductive layer instead of arcing and exploding if it's a thin area.
> 
> What do you think of my thoughts?
> 
> TY!!!
> 
> BTW excellent day today. I threaded pipe today, for the first time (aluminum, not rigid, good for me!) and tapped a drill hole for the first time too. Lots of fun!!!! A really good day. I even fixed an idling problem on the customer's car hahaha. Vacuum issue.)


I thought you were an expert in all things electrical.


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## Lone Crapshooter

Sounds to me like a grounding resistor. It limits the phase to ground fault current. It is on the secondary side of the transformer and there is a jumper wire between the XO bushing and the resistor and the other side of the resistor is tied to ground . The XO bushing is the center point of a wye wound secondary transformer.


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## RIVETER

Lone Crapshooter said:


> Sounds to me like a grounding resistor. It limits the phase to ground fault current. It is on the secondary side of the transformer and there is a jumper wire between the XO bushing and the resistor and the other side of the resistor is tied to ground . The XO bushing is the center point of a wye wound secondary transformer.


It could very well be from his description. I have heard of transformers being used as the medium to ground in order to attempt to eliminate the I2R loss of a resistance grounded system.


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## kaboler

I wanted to take a picture of it today, but I spent all day inside grounding cable tray. Mind-numbing but it's work!!!!

I'll try to remember to take pictures tomorrow, I'll be working a half day there and hopefully doing other stuff. I'm suspecting that industral electrical work is kinda mind-numbing.

Except of course that crazy cable stuff. I don't think I'll be around to attempt something called a "stress cone", and I doubt he'd let me do it because it's serious hardware. Then I pointed out that "everyone has a first time" and "we all gotta start somewhere". It sounds like it's a skill thing not too many people have, so you know me! I want it!!!!


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## Big John

Cable splicers go to school for many weeks performing, testing, and reworking medium-voltage splices to be sure they know what they're doing. The problem with MV splicing is that failures often don't show up instantly, but instead occur as a sudden fault weeks or even months down the road.

Anyone that lets an apprentice get his hands dirty "practicing" a MV stress cone needs to be fired immediately.

-John


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## kaboler

Like I said, I doubt he'd let me do it. I doubt it even more now, so I'm not even going to ask. Ask to watch of course


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## kaboler

Lone Crapshooter said:


> Sounds to me like a grounding resistor. It limits the phase to ground fault current. It is on the secondary side of the transformer and there is a jumper wire between the XO bushing and the resistor and the other side of the resistor is tied to ground . The XO bushing is the center point of a wye wound secondary transformer.


that's the setup!


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## piperunner

kaboler said:


> Like I said, I doubt he'd let me do it. I doubt it even more now, so I'm not even going to ask. Ask to watch of course


Well Kaboler dont be in a hurry to learn everything a once it will come in time . Splicing HV cables is not as hard as some folks make it out to be .

Been splicing on and off for many years now mostly we sub it out now less worries .

But before our company grew we did it and learned on the job .As far as training we were splicing cables before our company had training .

Today its a 4 day course General Electric HV splicing 2 days of class and 2 days of splicing .

Also Kerite cable company has a 2 day course .

They teach you cable theory and you do hands on splicing and testing good class its fast and you need to be a cable splicer before you go or a electrician that has seen it or has done it a few times.

But if you ever watch the power company splice there cables youll pick up new ways.
Remember 
Keep it clean dont use a metal ruler sand it wipe towards the cut end only ! The cleaner it is thats the key to a good splice using the correct tape in the correct spot lots of different tapes used .

We were splicing before kits were on the market .

If you get a chance watch a good cable splicer with no kit then watch a splice with a kit done youll see its all the same process just more tape the old way .

You have to learn by doing it bottom line you can read all the books in the world but hands on splicing is it .


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## kaboler

Piperunner, I'm pretty sure he has some kind of kit like you say, because the company seems to be anal as anal can be.

I've never seen anyone phase tape with shrink wrap instead of tape all the way to where the wire comes in. Looks great! But takes a lot of time.

He might be generous and show me how it's done because I fixed his car (idle problem) and he's a nice guy. I don't know at what stage they'll be doing that as well. I'm really curious because it looks like he'll need 2 parallel runs of probably 2/0. I think that's what the crimps are rated for.

It's subbed out now? Makes sense. I'd rather hire a guy who does it all day than say, a guy who does it twice a year. Or, it's a rather simple process, you just have to be a perfectionist? Don't know! Want to find out hahaha.


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## sparky970

Big John said:


> Cable splicers go to school for many weeks performing, testing, and reworking medium-voltage splices to be sure they know what they're doing. The problem with MV splicing is that failures often don't show up instantly, but instead occur as a sudden fault weeks or even months down the road.
> 
> Anyone that lets an apprentice get his hands dirty "practicing" a MV stress cone needs to be fired immediately.
> 
> -John


So, don't teach the apprentices anything? Let them get their hand dirty after they top out.


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## piperunner

kaboler said:


> Piperunner, I'm pretty sure he has some kind of kit like you say, because the company seems to be anal as anal can be.
> 
> I've never seen anyone phase tape with shrink wrap instead of tape all the way to where the wire comes in. Looks great! But takes a lot of time.
> 
> He might be generous and show me how it's done because I fixed his car (idle problem) and he's a nice guy. I don't know at what stage they'll be doing that as well. I'm really curious because it looks like he'll need 2 parallel runs of probably 2/0. I think that's what the crimps are rated for.
> 
> It's subbed out now? Makes sense. I'd rather hire a guy who does it all day than say, a guy who does it twice a year. Or, it's a rather simple process, you just have to be a perfectionist? Don't know! Want to find out hahaha.


Well what iam saying is its not all fun days lots of tuff days like this and its a boring job at times iam glad when we hire a sub to splice






















Sometimes i wish i didnt learn how nasty work this is downtown Orlando they share the HV and the fiber in the same manholes its not fun you cant move to work . Old brick wet damp lots of black spiders it smells scum its just lots of fun splicing cable on these jobs and its hot inside when you suit up .

Its funny but the power company doesnt suit up just our company they work inside hot with no suit just gloves .

Yes even what you said about just using shrink tubing they still put on tape around the air gaps of the lug insulation and semi con and there is still taping done under that shrink tube .

Prep and cleaning the cable is fun sanding the insulation when theres no room to move inside a manhole .


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## Big John

sparky970 said:


> So, don't teach the apprentices anything? Let them get their hand dirty after they top out.


So, if you go in for surgery, you're perfectly fine with it being preformed by an untrained med student just so they can get the experience and get their hands dirty?

Same concept applies to some functions of electrical work; some things absolutely need to be done right the first time.

-John


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## sparky970

Big John said:


> So, if you go in for surgery, you're perfectly fine with it being preformed by an untrained med student just so they can get the experience and get their hands dirty?
> 
> Same concept applies to some functions of electrical work; some things absolutely need to be done right the first time.
> 
> -John


When I was an apprentice, my journeyman and I went through the directions and highlighted strip out dimensions, and discussed MV cables. I watched him make a couple of cones as he explained what and why. Then I started helping. After helping for several cones, he watched me make one up. After that we worked side by side prepping cables. I'm not saying hand an apprentice some kits and directions say "Go". I'd rather have an untrained med student helping versus a Dr. with no hands on experience.


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## Big John

sparky970 said:


> ...I'd rather have an untrained med student helping versus a Dr. with no hands on experience.


 I'd rather have neither: I'd want a doctor who was experienced in his craft, and that's what I expect from guys making MV splices.

I don't think green guys should have their hands in a customer's MV splices, ever. There's too slim a margin for error where the negative consequences of a screw-up far outweigh the positive benefits of success. 

Train them first in a controlled environment and then they can practice the craft in the field. 

-John


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## Zog

Big John said:


> I'd rather have neither: I'd want a doctor who was experienced in his craft, and that's what I expect from guys making MV splices.
> 
> I don't think green guys should have their hands in a customer's MV splices, ever. There's too slim a margin for error where the negative consequences of a screw-up far outweigh the positive benefits of success.
> 
> Train them first in a controlled environment and then they can practice the craft in the field.
> 
> -John


I don't think anyone should do MV splices unless they are certified splicers.


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## Big John

Zog said:


> I don't think anyone should do MV splices unless they are certified splicers.


 Basically what I'm trying to say, I just can't shut up.

-John


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## piperunner

Well i really think we are taking this way to far splicing cables is pretty basic stuff not rocket science .

You get faster after time but a green helper with common sense could learn the splicing craft in one week i would not let him splice alone the first day or week .

Now would we let a green electrician do it alone never but would i let him do a splice yes i would with me hands on any day .


Most splicing is a two man job anyway. So after a few jobs its time to see what the kid can do under supervision that is .

I started splicing and learned from my foremen hands on nothing wrong about learning in the field .

But now we get certified each year if and when we splice its not everyday but it does happen from job to job .

I think most folks think its harder then it is .

You have to learn sometime to me its better to do it in the field school is not everything but today it seems like it is and its not heart surgery by no means .

Its hard work nasty boring and its always at night .


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## kaboler

They're not really disagreeing with you piperunner, as much as hating me for thinking I could give it a try hahahahaha. They believe firmly that I should know my place. My place is behind a shovel, because that's all these guys think I'm capable of hahahaha.

They don't even have the splice kits on site yet, and I don't know if I'm working there anymore because of all the other jobs on the go. They need me in a lot of places, and I never get to choose.


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## Big John

kaboler said:


> ...They believe firmly that I should know my place....


 Has nothing to do with knowing your place, and everything to do with knowing your present limitations. 

-John


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## piperunner

kaboler said:


> They're not really disagreeing with you piperunner, as much as hating me for thinking I could give it a try hahahahaha. They believe firmly that I should know my place. My place is behind a shovel, because that's all these guys think I'm capable of hahahaha.
> 
> They don't even have the splice kits on site yet, and I don't know if I'm working there anymore because of all the other jobs on the go. They need me in a lot of places, and I never get to choose.



Well Kaboler iam not real popular here myself that said i dont really care ! But i do work with my crew everyday and if someone wants to jump in and show me what they can do ill watch.


I think school is good but its not everything and splicing should be in the field not in some class room with some runny nose college boy factory cable manufacturing rep who never had to make a splice in a wet dark nasty hole in the ground .
Its nice on a table in school but thats not the case when your out in the field with water in the hole .

Well just so ya know we still use a shovel which is not that often anymore .

listen to me dont try and learn it all in one day just take it one day at a time .


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## Shockdoc

Is your avatar the star of Brokeback mountain ?


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## Wireman191

kaboler said:


> They're not really disagreeing with you piperunner, as much as hating me for thinking I could give it a try hahahahaha. They believe firmly that I should know my place. My place is behind a shovel, because that's all these guys think I'm capable of hahahaha.
> 
> They don't even have the splice kits on site yet, and I don't know if I'm working there anymore because of all the other jobs on the go. They need me in a lot of places, and I never get to choose.


 No dude, if the shovel needs to be pulled out that is your job, I what you need is to be in there watching the splicing. Learning. Now we know you can hook up PCs. You need to be doing stuff you haven't seen yet. Your CHEAP labor! The company you work for is ******** for sending you out on your own. It will do you no good in the long run.


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## Zog

You guys kill me, some homeowner shows up here with a question and he gets insulted, stomped on, ridiculed and banned because he is not a licensed electrician. 

But it seems to be just fine for anyone to splice a 15,000V cable that is usually a critical point in a system and if it fails cause cause some serious damage or injuries. Get certified or don't do it. http://www.njatc.org/cert/ncscb/index.aspx

Gotta give props to the unions here, at least they support certifications and offer training though the hall. I am not a big union backer but this part hey have right. :thumbup:


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## piperunner

Well were non union and we work for a company who trains us daily weekly & yearly . 

Our budget on safety is more than most electrical contractors make in commercial over a years net worth .


We are a certified cable splicer with a card they give us a paper for the wall which means nothing its like a masters card it really doesnt make the electrician sorry i disagree .

Also seen sub contractors who do splicing screw up and testing outfits that can not make dates or do shotty work so theres a two way street .

We test our own cables and have been to class on testing at our shop and GE & Kerite give the classes .

Some times we sub it out testing and splicing . GE & Kerite have a good course they come to the shop in our training building once a year .

Its not free my company pays for the course and the hours of the workers to attend this week class .


Yes MV cable can cost dollars if its done incorrectly but were non union and in 30 plus years of making up cables ive yet to have one blow.

And i didnt learn this in a class room i learned it out in the field .

The class is all theory which is good but its not good enough you need to do it hands on .

And i dont mean in a perfect air condition class room under perfect conditions . To me it should be a Manhole at night about 100 degs with some water about one foot high in the bottom .

What does union have to do with this post or training its who you work for and your company not union or non union .

If you work for a small EC outfit they dont have dollars for each worker to go to a course like sorry no training .

So what do you do close up your company because your not trained .


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## knowledge29

Sounds like you might of been working on an N.G.R.(neutral ground resistor)


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## ojouhar

Do you have any idea how much does a linear foot of concrete for a 4 way and a 6 way duct bank cost? And where we can find this information!


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## Pbhome

As a 30 year cable splicing instructor I suggest you take a course that will teach all types of terminations and splices. The manufacturers that put on the 2 - 4 day classes teach students just enough to get into trouble. Most programs take many days of classroom and hands on applications. While running the one at our utility it was a 6 week program followed up with 6 months to a year in the field working with a cable splicer.


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## walkerj

It's hard to believe kablower has been gone for so long


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## The_Modifier

walkerj said:


> It's hard to believe kablower has been gone for so long


Please don't tell me you miss him.:laughing:

I thought he was back when I saw this on the new posts list.


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