# Medium voltage cable



## SELECTRICIAN (Apr 23, 2017)

Is it safe to handle a medium voltage armored cable while it is in service? I have never done so but have been asked too do so by a customer. Have consulted with other contractors and one engineer and all have said they would not.


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## Bird dog (Oct 27, 2015)

What voltage is this cable exactly? 5kv?


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## SELECTRICIAN (Apr 23, 2017)

Its 13.8


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## Big John (May 23, 2010)

Why do they want you to?

I'd want to avoid it: You run a risk of a fault by moving around any cable while energized.

70E says "examining" MV cables is at least HRC 2 and maybe 4 depending on the conditions, so at a bare minimum you would need to be suited up.


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## frenchelectrican (Mar 15, 2007)

I am on the same page as other guys posted.,,

Try not to move that medium voltage cable at all.. espcally that much voltage in there. there is a risk of fault if you try to move it for any reason.

Big John did make a good point on suiting up but I would go at least HRC 6 maybe 8 depending on the location you are at.


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## MechanicalDVR (Dec 29, 2007)

@SELECTRICIAN are you an electrical contractor or what kind of contractor?


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## JRaef (Mar 23, 2009)

No. It is totally unsafe. Even a very slight corona discharge that makes it through the shielding could go through you to ground and could be lethal. 

On a couple of occasions I have had to observe 15kV cable in switchgear while energized, there is an eerie moving blue spider web of electrical corona discharge crawling over the surfaces looking for a ground point to discharge to. It looks like it is alive. In daylight you don't see it, but in the dark it stands out.


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## MechanicalDVR (Dec 29, 2007)

JRaef said:


> No. It is totally unsafe. Even a very slight corona discharge that makes it through the shielding could go through you to ground and could be lethal.
> 
> On a couple of occasions I have had to observe 15kV cable in switchgear while energized, there is an eerie moving blue spider web of electrical corona discharge crawling over the surfaces looking for a ground point to discharge to. It looks like it is alive. In daylight you don't see it, but in the dark it stands out.


Truly one of the times you have to be smarter than what you are working with.


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## glen1971 (Oct 10, 2012)

FWIW.. Any place I've worked, anything over 600 vac is not to be moved energized, including teck (armoured) cable.. Client specifics may vary on what you can and can't do, but most have drawn the line at 600 volts..


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## Big John (May 23, 2010)

JRaef said:


> No. It is totally unsafe. Even a very slight corona discharge that makes it through the shielding could go through you to ground and could be lethal.
> 
> On a couple of occasions I have had to observe 15kV cable in switchgear while energized, there is an eerie moving blue spider web of electrical corona discharge crawling over the surfaces looking for a ground point to discharge to. It looks like it is alive. In daylight you don't see it, but in the dark it stands out.


 To be clear, though, the exterior of shielded cable is at ground potential.

I'm not saying there's no risk, nor am I saying it's a good idea to play with it while energized, but unshielded cable has a far higher contact hazard than sheilded precisely because of the corona: That is not a problem on correctly terminated cable shielding.

I agree, there is still the risk that by moving it, they cause insulation failure, and it blows up in their hands.


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## Signal1 (Feb 10, 2016)

Shutdown. <<< (that's a period)


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## JRaef (Mar 23, 2009)

Big John said:


> To be clear, though, the exterior of shielded cable is at ground potential.
> 
> I'm not saying there's no risk, nor am I saying it's a good idea to play with it while energized, but unshielded cable has a far higher contact hazard than sheilded precisely because of the corona: That is not a problem on correctly terminated cable shielding.
> 
> I agree, there is still the risk that by moving it, they cause insulation failure, and it blows up in their hands.


True, but the operative issue is _*CORRECTLY *_terminated cable shielding. When touching live 15kV cables, you are putting your life into the hands of the previous installer and his work ethic, not to mention any possible ravages of time on all the components and connections and/or what disturbing it might cause.


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## Bird dog (Oct 27, 2015)

Something is fishy here. Where is the customers' usual HV EC? You don't just call Mr Sparky.


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## MechanicalDVR (Dec 29, 2007)

Bird dog said:


> Something is fishy here. Where is the customers' usual HV EC? You don't just call Mr Sparky.


Yeah you're right. 

I've never had a customer ask about any HV work like out of the blue.


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## micromind (Aug 11, 2007)

If you've ever seen a MV cable that has blown up, I'd bet that you won't get very close to it, let alone actually handle it. 

Also, when opening the doors of an energized MV switchgear, if there is corona discharge inside the cabinet and the door is opened as you normally would, you'll flood the compartment with oxygen and there's a fair chance that the pretty little blue arc dancing show will get really ugly really fast.......


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## Southeast Power (Jan 18, 2009)

I recall seeing a window in the 13.8 substations. This might be for inquiring minds.
It make me wonder why we went into freshly pumped out manholes with those old paper lead splices racked up the sides.

I remember getting yelled at as an apprentice for stepping on one. 
This was before safety was invented outside of the industrial sites.


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## frenchelectrican (Mar 15, 2007)

Suncoast Power said:


> I recall seeing a window in the 13.8 substations. This might be for inquiring minds.
> It make me wonder why we went into freshly pumped out manholes with those old paper lead splices racked up the sides.
> 
> I remember getting yelled at as an apprentice for stepping on one.
> This was before safety was invented outside of the industrial sites.


I have see that couple time before and what I call them snake widow maker or blue blaster one of two will get in the head fast.

I got hit with indriect blast from 12.8 KV spices but good thing no one was that close to that splice due myself and one other guy spotted pretty good sized blue cornia pattern all we just high balled fast. it blew apart few seconds later so we did kinda cover from that but let me tell ya that sonvagunner is LOUD it more louder than standard shotgun is.

Oh yuh no one was hurt at all but short ear rinning that was it.


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## MechanicalDVR (Dec 29, 2007)

Suncoast Power said:


> I recall seeing a window in the 13.8 substations. This might be for inquiring minds.
> It make me wonder why we went into freshly pumped out manholes with those old paper lead splices racked up the sides.
> 
> I remember getting yelled at as an apprentice for stepping on one.
> *This was before safety was invented outside of the industrial sites.*




 Dinosaur!


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