ECN Forum Forums General Topics of the Trade General Discussion Area SHOCKED

Above 600 volts, the ‘rules’ change drastically. With contact accidents at this level, the amount of current and path through the human body can readily cause live tissue to be “cooked” from the inside out.

Medium- {and high-}voltage circuits demand a much higher level of care and “respect” and are much less forgiving of accidents.

There is a universal rule dealing with medium {and high} voltage — NOT Grounded: NOT Dead. The seriousness of this issue for routine operations is evidenced in: http://www.hubbellpowersystems.com/powertest/tips_news/pdfs_best/09-9501clamp.pdf




[This message has been edited by Bjarney (edited 01-30-2004).]

Easy answer:

Watch a Medium Voltage Primary Feeder Conductor when it falls off an Insulator and finally reaches the Earth Ground.
It will dance around like crazy - blowing sparks, creating plasma arcs, making all kinds of noise - until something gives out (like Breaker, Fuse, fried wire, etc.).
Then it becomes still - but by no means is it "Dead"!

Of course, Automatic Reclose will occur - resulting in the same crazy-bouncy dance sessions again (and if someone with a death wish grabs the wire, the same will happen to that person!).
But even if the circuit does not get re-energized, there will be discharging from Coupled Reactances, along with the circuit's initial Line / Circuit Charging plus any other stored Reactive Power - all of which, if drawn through a load connection with an Impedance similar to that of living people, will result in a similar crazy dance on that person!

So the answer is:
Yes, you can get shocked very easilly in almost any circumstance.

I know you are only asking this to know, and do not plan on attempting this ever!

If you want to know more about this, let us know!

Just ask the Linepersons here about L-G flows! Things take a drammatic change above 2KV, a really drammatic change above 35KV;... and a mind boggling change above 200KV!

Scott35

Don't even go close to a downed HV or MV line. Step potential!

Just because it's not making sparks on the ground, there is no guarantee the line is dead and even if it is dead, there is no guarantee that it will remain so.

As I understand the original question, you are thinking of an ungrounded system. At first sight, it seems you could get away without getting shocked. But to detect a fault there has to be a current. The utility may to have a resistance ground which allows a small current to flow back to "sound the alarm". You don't want to be part of this circuit. In addition, there are unintentionally grounds along the line. I'm sure Bjarney, Trumpy and Scott35 know more about these things.

sorry for the confusion,i mean a power transmission line that carrys the power from customer to customer(ex:27.6kv).
now if one of these lines comes down and is still alive it being fed from a delta source where there is no potential to ground,then why is it that if you were to grab this that it would kill you,remember that there is only potential phase to phase.

with voltage present, there is potential. whether by design or not. I don't know about HV stuff, but it's like the bird on the wire. bird is at same potential as wire no shock. bird puts one leg on pole, thanksgiving dinner, pre cooked!!

So if somebody grabs the insulated portion of a downed wire, he'll get fried no matter what? Please explain why this occurs.

Another example of operating under different rules than us <600V guys...

Many HV lines are designed with "semi-conductive" insulation. I have no idea how/why, but I've seen it in the product descriptions for the big stuff.

Depending on the voltage of the line you could get nailed and good from a few feet away, without even touching it at all. I'm sure some of the other members could get really technical on it. But voltage will break down the die-electric strengh of most insulating material easily once the path is made. Even the air it self! The average rubber soled shoe, and leather glove is useless above 120/240. Otherwise you should be wearing proper PPE for the voltage.
http://www.corvib-int.com/catalog/index.php?cPath=29_30

And the conductive properties of a dry 2x4 may as well be a copper pipe at +10KV. I'm sure there will be some corrections to what I said, but can not stress enough to stay clear of downed lines of any kind!

 
DougW has a good point about higher-voltage cables. At 2-35kV, the cable dielectric layer is typcially ethylene-propylene rubber or cross-linked polyethylene. [Typcially, 15kV-class, 133% insulation-level cable has a dielectric thickness just under ¼ inch.] Inside (under) the dielectric layer in imitate contact with the center conductor, and over the outside of the dielectric are are two semiconducting layers to even out electric stresses in the dielectric. Over the outer semicon is helically-wrapped copper tape or copper wires that must be solidly grounded as part of limiting electric stress in the dielectric layer. A generic term for this material is shielded polymeric cable.

In the last ~80 years, cable manufacturers have found that the dielectric material has to be of extremely high purity with antiseptic conditions during the extrusion process. Also, field preparations during installation of cable terminations and splices must be performed by a skilled and experienced person in a clean area to limit premature failure. Before energization of the cable, it is routine to apply DC-overpotential testing to reasonably assure that the circuit will have acceptable reliability over expected life of the installation. Workmanship on installation can be proven by good {or rejected} by poor} overpotential-test results.



An MV-cable splice illustration energy.tycoelectronics.com/rrg/raychem_rrg/59.pdf

On the North American continent, the practical upper limit of routinely manufactured extruded-dielectric shielded cable is presently 138kV.

P.S.: Never forget that In all but limited cases, overhead spans are BARE.




[This message has been edited by Bjarney (edited 09-12-2004).]

I e-mailed Joe Tedesco, and said,
'Hey Joe, I think this thread could us a scary video link..."

No video, but sent this poor sole.
(Too greusom to show!) Blown off fingers! Or that video of the guy on angle dust climbing a pole. Ot this one: Ryan posted a while back. http://www.mikeholt.com/documents/mojofiles/BoomTruckinPowerLines.wmv