# what voltage is safe to handle through insulation

You handle power cords of 120 or 240 volts all the time with no worry. There is insulation, so there's no risk of getting shocked, unless
there is some failure such as it drying out and cracking.
But just how high a voltage can we go and keep it safe to handle, even if the insulation is thicker?
I see lots of insulation rated 600 volts (presumably RMS so it could probably handle 900 volt peaks or more). I suppose then, it is safe to handle a power cord when the voltage goes as high as 600 volts.
But what about beyond that when you beef up the insulation?
I'm guessing thee is a (fuzzy) point where it is just no longer practical to beef up the insulation. Maybe it gets to thick or too stiff to work with.
But is there a voltage level beyond which you simply cannot make wire safe for humans to handle? Would you handle (with no further protection) wire carrying 12000 volts if the insulation is rated for at least twice that?
How does corona play into this? Can corona ever be blocked by a sufficient amount of insulation?
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
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snipped-for-privacy@ipal.net wrote:

If the wire has an outer earthed screen the user won't even know that voltage is present - as long as the insulation between core and screen holds up. (note that the insulation doesn't have to be "perfect" - any leakage current will flow to the screen and not the human.). A screened wire produces no corona and is safe to handle, even at the rated voltage.
"Stiff and difficult to work with" is just as much a problem with low voltage cables carrying very high currents. For any particular power transfer needed in kW or MW, there will be a voltage at which transfer costs are lowest - a lower voltage needing more conductor or having higher heating losses and a higher voltage needing more elaborate insulation.
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Sue

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wrote:
| If the wire has an outer earthed screen the user won't even | know that voltage is present - as long as the insulation | between core and screen holds up. (note that the insulation | doesn't have to be "perfect" - any leakage current will flow | to the screen and not the human.). A screened wire produces | no corona and is safe to handle, even at the rated voltage.
For cable having no such screen or shield or metal cladding of any kind, but is rated for breakdown at well beyond the voltage in use, and the cable has not been abused, what voltage would you consider the maximum that is safe for people to handle, assuming the people have no further insulation (e.g. no gloves, no special shoes, wet ground, etc).
| "Stiff and difficult to work with" is just as much a problem | with low voltage cables carrying very high currents. For any | particular power transfer needed in kW or MW, there will be | a voltage at which transfer costs are lowest - a lower | voltage needing more conductor or having higher heating | losses and a higher voltage needing more elaborate insulation.
I'm just trying to determine if the issue can simply be mitigated with "enough insulation" regardless of voltage. Can insulation alone be made enough to prevent corona effects on humans handling the cable at any voltage? Or is there a voltage cutoff where it just can't be done anymore because the corona caused currents are starting to affect humans regardless of the insulation level?
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
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snipped-for-privacy@ipal.net wrote:

It is the "handling" aspect that I am having difficulty with. Very high voltages on cables being man-handled, to me indicate very high power levels and those cables would be armoured(ie screened). Very high voltages at low power levels are mostly in test equipment and internally within some electronic equipment (eg transmitters, TVs) - where they aren't usually handled with the power on.
The insulation of an unscreened very high voltage cable will act as a dielectric and anyone grabbing the exterior will become the other plate of a capacitor. Enough charge will transfer to make your hair stand on end and maybe get some sparks from your fingertips - you can play these games with Van de Graff generators but I wouldn't want to do it with the National Grid..
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|> I'm just trying to determine if the issue can simply be mitigated |> with "enough insulation" regardless of voltage. Can insulation |> alone be made enough to prevent corona effects on humans handling |> the cable at any voltage? Or is there a voltage cutoff where it |> just can't be done anymore because the corona caused currents are |> starting to affect humans regardless of the insulation level? |> | | It is the "handling" aspect that I am having difficulty | with. Very high voltages on cables being man-handled, to me | indicate very high power levels and those cables would be | armoured(ie screened). Very high voltages at low power | levels are mostly in test equipment and internally within | some electronic equipment (eg transmitters, TVs) - where | they aren't usually handled with the power on.
Going downward in voltage, at what point would you no longer need to have the screen or shield in there?
| The insulation of an unscreened very high voltage cable will | act as a dielectric and anyone grabbing the exterior will | become the other plate of a capacitor. Enough charge will | transfer to make your hair stand on end and maybe get some | sparks from your fingertips - you can play these games with | Van de Graff generators but I wouldn't want to do it with | the National Grid..
I'm not thinking of handing that much power. What I want to know is aside from the risks of direct conductor contact, what limits the voltage for power conductors with respect to human safety.
Would you feel OK handling an electrical cord plugged into a 2400 volt power source if the insulation was rated for 6000 volts (this being 10 times what might commonly be found in a home), when there is no screen/shield layer in the cord?
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
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snipped-for-privacy@ipal.net wrote:

I have a clamp ammeter/voltmeter with dc voltage ranges to 6kV (ac to 5kV) - without special probes or screened leads. I have used it at 1200V dc without adverse efects, effects, effects, effects :). The manual simply says that it should not be used at voltages > than 6kV and that the "ground" lead should be connected first and disconnected last.
I am never happy working on anything "live" - unless it is essential - the voltage is a bit secondary; ask anyone who has seen what happens when a spanner is dropped across the battery bus in a telephone exchange..In the case you describe, I would take advice from the cable manufacturer.
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Sue

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At work we have 250 feet of 15KV extension cord. It is about 3.5 inches in diameter and the cannon connectors that we use to connect the pieces take at least to men to connect. The cable can be picked up when energized and moved. We even had an salt truck drive over it (loaded with 30 tons) and nothing happened. Salt company got to pay for new cable and the labor to replace the section they screwed up.
The mining industry has lots of cables that are commonly called surface cable. Meaning that you can lay them on the ground with out much danger. The cable can carry from 1kv to 35kv. I have seen surface cable laid on the ground and they take an end loader and dump dirt over it and smooth it out to make an drive over the cable. 5-6 inches is all.
I have worked up to 35 kv and have not seen but a couple of underground applications of voltages greater than 35 KV. The insulation gets to be pretty big and awfully expensive compared with bare conductors in the air.
Your wrong about the 600 volt rating. It is 600 not any more. Could you in an emergency go higher? Sure. In standard practice no sensible person exceeds the voltage rating of an cable or wire.
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| Your wrong about the 600 volt rating. It is 600 not any more. Could you in | an emergency go higher? Sure. In standard practice no sensible person | exceeds the voltage rating of an cable or wire.
Then is that rating for the peak voltage? If so, that would make it not usable at 480 volts, since the peak is 679 volts.
But maybe the rating for phase to phase is higher since it goes through two layers of insulation, one on each wire. The peak for 277 is 392.
What insulation rating would be used on 480 volt corner grounded delta?
What insulation rating would be used on 600Y/347?
What insulation rating would be used on 600 volt corner grounded delta?
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
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snipped-for-privacy@ipal.net wrote:

I've been to equipment tests where there were cords on the floor with 13.8 KV in them. We were walking over them. I was a little hesitant at first, but the people there that did this day in and day out had no problems. Yes there was high available fault current. It was 7 MW equipment being tested which was pretty small for this facility.
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