# Resi electrician attempts 4160.



## backstay (Feb 3, 2011)

Medium voltage is not something to learn by trial and error.


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## macmikeman (Jan 23, 2007)

Do you know for sure he was a "resi' electrician, or are you just guessing?


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## nrp3 (Jan 24, 2009)

I know I’m licensed to do it, but have no experience with it. So I pick up the phone and find someone who does. Not that hard. Suppose I could watch YouTube videos…. Maybe some good ones, too lazy to look.


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## Slay301 (Apr 23, 2018)

That’s how I learned hahahahah . Jk if you can follow instructions on a 3m kit a monkey can do it


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## SWDweller (Dec 9, 2020)

4160 can be shielded or non shielded wire depending on the situation. 
Depending on the materials used and termination required you may or may not need a stress cone.

As you stated the mix of cables will cause problems. I have never seen anyone mix cables in conduit before. I would never run medium voltage in conduit with out a ground wire.


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## paulengr (Oct 8, 2017)

Slay301 said:


> That’s how I learned hahahahah . Jk if you can follow instructions on a 3m kit a monkey can do it


I disagree. That’s if you know what you are doing. You can make a huge mess of the semicon especially. Those instructions tell you what to do, not why or how.


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## micromind (Aug 11, 2007)

I'm surprised it didn't blow up when energized the first time.


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## 99cents (Aug 20, 2012)

You have bigger ballz than me.


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## kb1jb1 (Nov 11, 2017)

What gave out? Was it defective materials, wrong choice of materials, poor workmanship? It's been 30 years since I worked with medium voltage and to me it looks like a 480 - 120/208 one except for the marking.


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## Southeast Power (Jan 18, 2009)

kb1jb1 said:


> What gave out? Was it defective materials, wrong choice of materials, poor workmanship? It's been 30 years since I worked with medium voltage and to me it looks like a 480 - 120/208 one except for the marking.


Me too. I thought it looked like 483 phase.


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## kb1jb1 (Nov 11, 2017)

From what I remember about medium voltage, the primary and secondary were in separate compartments.


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## micromind (Aug 11, 2007)

I've connected dry-type transformers that had 4160 and low voltage in the same compartment though a lot of them have 4160 in the back and low voltage in the front. 

If the 5KV wire is terminated as shown in the pics, then the shield, which is supposed to be grounded, is at the same potential as the wire. With 4160, it's 2400 to ground. So the only thing holding the voltage in is the outer covering. 

The reason for the cable burning up at the ends is because of corona. This is a blue ball of plasma that is present at sharp edges. It's not much of an issue at 4160 but higher voltages can be a problem if it's not mitigated. 

Since the edge of shield tape is quite sharp (honed to a knife-edge at the factory with the intent of slicing up the hands of the poor schmuck that installs it......lol) there will be a small amount of corona present. Over time, it will oxidize the copper. 

The other bad thing about corona is if it's present in a medium-voltage switchgear and you open the door and flood the compartment with oxygen......BOOM!!!!


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## joe-nwt (Mar 28, 2019)

That's what happens when you don't remove the semi-con.


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## SWDweller (Dec 9, 2020)

I had forgotten about corona, did some terms at 12k above sea level. Had to put both ends of the cable in plastic bags to get it to test. Had the coolest aurora going in the bags for a time.


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## macmikeman (Jan 23, 2007)

I never touch that voltage , because one time I wired a house for somebody. After doing that I knew I was ruined forever. Such a sad ending to what could have been a career at being an electrician.


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## joe-nwt (Mar 28, 2019)

Corona is not a big deal at 4160.


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## macmikeman (Jan 23, 2007)

Tell that to the people stuck in the elevator.


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## kb1jb1 (Nov 11, 2017)

I like Corona with a lime. Not the lite one.


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## Wirenuting (Sep 12, 2010)

kb1jb1 said:


> I like Corona with a lime. Not the lite one.


I got vaccinated with no lime


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## canbug (Dec 31, 2015)

First 4160 splice I helped with as a call out, 2am and a blizzard. It held up for 15 yrs before it was hit again at the same spot. Don't tell me there are no coincidences.

Tim.


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## Wirenuting (Sep 12, 2010)

I’ve watched but never tried to terminate 4160. 
I’ll leave it to those who know what they are doing.


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## joe-nwt (Mar 28, 2019)

Wirenuting said:


> I’ve watched but never tried to terminate 4160.
> I’ll leave it to those who know what they are doing.


You should ask to participate next time. It wouldn't take much to show you a few tips and tricks to help you learn a new skill.


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## paulengr (Oct 8, 2017)

micromind said:


> I'm surprised it didn't blow up when energized the first time.


Seen this before. It will work for a while. A couple months.


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## paulengr (Oct 8, 2017)

joe-nwt said:


> Corona is not a big deal at 4160.


This is partly true. It gets worse as voltage increases. It starts at around 2500 V. So with 4160 it’s only 2400 V phase to ground so you won’t see corona damage there. It’s only phase to phase and even then unshielded 5 kV cables seem to be right on the ragged edge…some do fine for 10+ years, some not so good. But at say 7200 V the 15 kV stuff is destroyed over time without some air gaps between phases.


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## paulengr (Oct 8, 2017)

micromind said:


> I've connected dry-type transformers that had 4160 and low voltage in the same compartment though a lot of them have 4160 in the back and low voltage in the front.
> 
> If the 5KV wire is terminated as shown in the pics, then the shield, which is supposed to be grounded, is at the same potential as the wire. With 4160, it's 2400 to ground. So the only thing holding the voltage in is the outer covering.
> 
> ...


Corona is just that. If oxygen was so bad insulators on poles would explode in humid weather.

The simple explanation is this. Can you just use a hose clamp on a hydraulic line? No. Why not? Because it’s high pressure and so you need high pressure fittings. Voltage is a measure of electron pressure. So we need high electron pressure fittings.

So the basic problem is voltage flux, the rate the the voltage must change through the insulation. At medium voltage we can put too much of a voltage delta across a part of the insulation. When this happens instead of insulating the electrons jump the gap. They arc. Now at first it might not be a full on power arc. Just a little light discharge or corona where it tears up insulation at a microscopic level. We call this a voltage tree because when you look at a cross section of the insulation it’s like a tree. The damaged void has a lower dielectric than the good insulation, increasing the stress around that point and increasing the rate of failure. At first it might only happen from surges every time the motor stops but eventually as the minimum voltage to arc drops it gets catastrophically worse.

So if we have a solid core cable surrounded by air it sees very even stress. But if we bring another conductor nearby, even laying it on a grounded housing, the voltage is attracted (opposites attract) where they are close. This increases the rate that the voltage changes on that side because now it’s not an even voltage gradient anymore. So if our insulation is borderline in withstanding the change in voltage over a local spot (voltage flux), this can put it over the edge and we get discharges and insulation damage. At first it looks like whitish powder but eventually it gets to black.

So the solution is shielding. We wrap the insulation in another conductor like a coaxial cable. It doesn’t need 100% coverage…concentric neutral cable has gaps. It can be foil or braid but foil is easier to manufacture. It does not need to be a full conductor. In fact that’s bad because it increases losses excessively. So if we have a charge in the conductor it creates a mirror charge in the shield making the outer surface zero Volts but more importantly since the shield is perfectly symmetrical the voltage flux is very even so it minimizes stress on the insulation and since the outer surface is unaffected by the inner voltage, we can lay cables right next to each other or grounded metal like in a tray or conduit,

Second problem is that we don’t want solid conductors. So we use stranded but now the area around the strands isn’t even enough. So we wrap it in a semi-conductive tape that evens this out, again reducing voltage flux on the insulation. One issue with semicon is it is tape saturated with carbon black. There is so much even touching it gets it all over everything so we have to wipe everything down with alcohol to remove every last bit of it.

This is great within the cables but at the ends except with elbow connectors we have to remove the shield and semicon. So at that point the flux is not even. In fact the stress goes WAY up right where the shield stops. So to prevent this thd old trick was a stress cone. We would add insulation and flare out the shield in a cone shape until the gap was so wide it did not matter any more then stop shielding. The new method is this magic green putty that does it within the putty by creating a capacitive effect. It is much easier to wrap an even layer of putty than build a special hyperbolic curve shaped curve out of tape and the putty tolerates surges and mistakes better. So we might call it a stress cone but it’s just an old term.

Now what this guy did is basically connect the shield to the phase conductor. So the jacket becomes the insulation (not!) So we are capacitively conducting to zero far from the shield but then have a big current flow and a big voltage flux stress at the end which quickly burns up the insulation and this eats slowly down the cable burning away the insulation as it goes until it reaches a spot where the jacket finally gives out.

If you don’t hook up drains the shield just kind of floats like any ungrounded circuit. It still mostly works but not as well since there is nothing to maintain zero Volts on the outer surface. It just capacitively couples to the conduit, tray, or other cables. Again far enough away this happens anyway but at the ends where all the action is it needs a drain. Over a few feet one drain is enough but longer than that you need both ends grounded. I’ve heard arguments for mid span grounds but never seen evidence that this is necessary.


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## glen1971 (Oct 10, 2012)

I think I've only worked on 5 kv shielded cables maybe twice. Otherwise it's been unshielded and numerous times with no issues. Always got in the habit of pencilling the insulation at the terminations, even on larger 480 volt and above conductors. Just took the time, and it wasn't a lot more time either.


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## Kevin (Feb 14, 2017)

joe-nwt said:


> You should ask to participate next time. It wouldn't take much to show you a few tips and tricks to help you learn a new skill.


I'm down to fly out and learn next time if I can arrange it into my schedule...


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## Slay301 (Apr 23, 2018)

paulengr said:


> I disagree. That’s if you know what you are doing. You can make a huge mess of the semicon especially. Those instructions tell you what to do, not why or how.


True once you no how to remove the simi con without nicking the insulation it’s easy. Something else that helps with the tape sheiks removal is to put a zip tie where the removal point is and score it with a razor and it comes off cleanly at that spot.


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## Wirenuting (Sep 12, 2010)

joe-nwt said:


> You should ask to participate next time. It wouldn't take much to show you a few tips and tricks to help you learn a new skill.


I did many years ago, but I’m not exposed to it very often. 
I know a little and that’s enough. By the time I would work with it again, something new to do it would be available.


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## joe-nwt (Mar 28, 2019)

Wirenuting said:


> I did many years ago, but I’m not exposed to it very often.
> I know a little and that’s enough. By the time I would work with it again, something new to do it would be available.


I don't know about that. The last big change was when they went from heat shrink terms to cold shrink and that was eons ago. The cable prep, which is the important part. hasn't really changed at all ever since I've been doing it.


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## Wirenuting (Sep 12, 2010)

joe-nwt said:


> I don't know about that. The last big change was when they went from heat shrink terms to cold shrink and that was eons ago. The cable prep, which is the important part. hasn't really changed at all ever since I've been doing it.


Heat shrink? Cold shrink?
What friction tape went out the window?


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## paulengr (Oct 8, 2017)

Wirenuting said:


> Heat shrink? Cold shrink?
> What friction tape went out the window?


Today there are roughly 3 methods. In the K-tape method it’s roughly like taping a motor. You cut back the jacket, shield, semicon, and insulation. Attach a lug, secure the shield and connect with a drain wire. Then lay on some kind of water proofing sealant, and the capacitive grading. Then it’s pretty much like taping a motor except at 15 kV+ one of the layers is silicone tape and semicon. Layers of 130C insulation then 88 or 33 outer covering to hold it all. Friction tape is supposed to be replaced with varnish cambric but I still see it used and I’ve seen some glass tape and just using sticky side out 88 or 33 on unshielded stuff but none of this is used in the kits.

Cold shrink is very similar except instead of 130C and vinyl you squeeze on a silicone sleeve with the QT II kits. With QT III the capacitive grading is inside the sleeve. With hot shrink you hear it on instead of just pulling it off a tube.

Regardless of what method you use the results are all very similar. The biggest difference is you only get sheds with the cold shrink stuff. Not that it’s truly necessary even outdoors.


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## five.five-six (Apr 9, 2013)

backstay said:


> Medium voltage is not something to learn by trial and error.


There’s a lot of things I’m licensed to do that I’m not qualified to do. I stick to things I’m qualified to do.


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## OldWiggy (Jan 4, 2020)

Reminds me of when I was TNG at the ammo plant. They had just spliced a phase of 4160 in a vault not far from the shop. (70% of the plant distribution was underground.) When they turned it on there was an immediate bang coming from the vault. Not one to miss an opportunity I went down there for a peak. The lead and another lineman had just cut out the new, and now destroyed splice trying to figure out what went wrong. I picked up the splice and gave it a twist exposing the braided grounding conductor. IIRC they penciled it but neglected to 'gather' the grounding braid to bridge the splice.
Wish'd I'd had pictures to post from that lesson...


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## Tonedeaf (Nov 26, 2012)

wow the dumb ass should of at least pulled the cooper tape shield back from the terminations...4160 is pretty forgiving for bad terminations....this guy was way above the I don't know what i am doing bar.


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