I am from a city of overhead cable chaos like this.

I often come across news of people including children being electrocuted by touching overhead transmission lines while playing in the rooftop, while picking up a ball from a tin roof etc.

I feel both sorry and confused when I read these news. I have always known that electrical wires have rubber insulations around their whole body. If that is the case in general, how can people die merely from touching a live wire? Aren't there supposed to be insulation? Do the accidents take place due to uninsulated cables or worn-out insulations?

 

In my back yard there's a pole with a transformer on it. The 240VAC coming from it has a center tapped transformer. That center tap forms a neutral, which is also grounded at the pole and at the transformer. The three wires going to my house carry 120VAC (L1) - 0VAC (Neutral/Gnd) - 120VAC (L2). Those lines go directly to the house and are insulated. I can touch any or all of those insulated wires without harm. The two wires going TO the transformer are not insulated. One carries 7KVAC, the other is ground. They are the highest wires on the pole. Locally, the rule is that no one should be able to get closer than 10 feet (3.048M). To insulate all that distribution wire would cost more than I can imagine.

In poorly regulated and enforced localities people steel power. To do that they make unauthorized connections to the grid. Not knowing what they are doing they run the risk of electrocution. I've seen this video before:

Since he wasn't killed it's likely he touched an uninsulated 120 volt line. Different localities have different rules. And some say rules are made to be broken.

 

I have always known that electrical wires have rubber insulations around their whole body.

Only those that are in buildings or run underground.
Generally the high-voltage, outside power transmission lines don't have any insulation, since they are high off the ground where no one is supposed to get near them.
Unfortunately, in some areas of the world the wires are apparently close enough to roofs where they can be touched.

The lack of insulation is why the are suspended from the power poles by insulators.
The length of the insulator is generally proportional to the voltage on the line.

 

Since he wasn't killed it's likely he touched an uninsulated 120 volt line.

Depends upon the conductivity of whatever he was standing on and the pole (wooden broom?) that touched the wire.

 

Oh how many times I contacted 120VAC from hand to hand. Those times when I thought I could change an electrical outlet without killing the breaker and my fingers slipped down onto the metal shaft of the screwdriver.

They say every village has an idiot. Well, mine didn't. Either that or I was that idiot.

Have I learned my lesson? If learning it means shutting off the breaker then - no, I haven't. I still work on live lines. I just try to remember not to make contact with both live and ground or neutral lines at the same time.

In the end an insulated wire is typically of no danger. Unless the insulation is cracked and the line is wet; especially with salt water. Then there's a real risk of shock. But honestly, if the roof he was standing on was made of a rubber membrane then, unless wet, he wouldn't have gotten shocked. Touching a live line while the rest of you is insulated is not dangerous. Birds land on high power lines all the time and with no consequences. Not unless they make contact at the same time with something grounded.

 

Certainly many of the power wires on the poles ate not insulated, although some of them are coated to reduce corrosion and also to reduce corona discharge RFI generation. One time there was a storm while we were traveling, and when I returned home days later there was a wire from the top of the poles group down in my back yard. Since the storm had been several days earlier, I presumed that the wire must not be live. But being cautious, I kept well away from it , and tossed the hook on my polyproplene rope across it from about 20 feet away, so that if it suddenly whipped, I would be out of reach. I gave it a gentle pull and it started arcing to the dry ground. My ropes hook had not caught it, so I retrieved my rope, and called the power company. I very politely requested that they remove the hot wire on the ground from my garden. They did remove it and thanked me for letting them know. They could tell that a wire was down, but there was no outage and so they had no clue as to where.
That wire was about 1700 volts above ground. It was insulated, but not for that high a voltage.

 

Thank you everyone for answering. From your answers, I came to know that overhead power cables are not insulated. I'd like to know one thing. Are these cables left uninsulated because the manufacturers by default think that no one will reach them or is there any technical reason for that? If these overhead cables are always insulated, will there be any problem in power transmission? Will these be any significant power loss?

 

It's actually mostly engineering and physics, not just cost.

If you tried to put full dielectric insulation on high-voltage overhead lines (11kV, 33kV, 110kV+), you run into serious technical walls:

• Heat dissipation (Ampacity): Bare aluminum (ACSR) is cooled directly by ambient air and wind. Thick polymer insulation acts like a thermal blanket — trapped heat means you'd have to severely derate the line or use massively thicker conductors to carry the same current without melting.
• Weight and mechanical load: High-voltage insulation is thick and heavy. Adding that weight across kilometer-long spans means conductors sag heavily, catch way more wind/ice load, and require massive, closely spaced steel towers instead of standard poles.
• Capacitance & reactive losses: Surrounding high-voltage conductors with solid dielectric creates a giant capacitor with ground. Over long AC transmission distances, this charging current generates huge reactive power losses (which is the main reason why long-distance underground HV cables need expensive reactor compensation).
• UV & weather degradation: Bare aluminum oxidizes and then happily sits in the sun and rain for 50+ years. High-voltage insulation breaks down from UV, ozone, and thermal cycling, turning maintenance into a nightmare.

 

It's actually mostly engineering and physics

Now I've learned something. Thanks.

 

Surrounding high-voltage conductors with solid dielectric creates a giant capacitor with ground.

I don't think the capacitance to ground of a high wire would be much affected by whether the conductor has a dielectric insulator or not.
It would only have a significant effect if the ground plane is close to the wire, such as an underground cable.

 

It's actually mostly engineering and physics, not just cost.

If you tried to put full dielectric insulation on high-voltage overhead lines (11kV, 33kV, 110kV+), you run into serious technical walls:

• Heat dissipation (Ampacity): Bare aluminum (ACSR) is cooled directly by ambient air and wind. Thick polymer insulation acts like a thermal blanket — trapped heat means you'd have to severely derate the line or use massively thicker conductors to carry the same current without melting.
• Weight and mechanical load: High-voltage insulation is thick and heavy. Adding that weight across kilometer-long spans means conductors sag heavily, catch way more wind/ice load, and require massive, closely spaced steel towers instead of standard poles.
• Capacitance & reactive losses: Surrounding high-voltage conductors with solid dielectric creates a giant capacitor with ground. Over long AC transmission distances, this charging current generates huge reactive power losses (which is the main reason why long-distance underground HV cables need expensive reactor compensation).
• UV & weather degradation: Bare aluminum oxidizes and then happily sits in the sun and rain for 50+ years. High-voltage insulation breaks down from UV, ozone, and thermal cycling, turning maintenance into a nightmare.
• AND It would be much more complex to splice an insulated wire, or to connect it to a terminal. Consider that every length of wire used must connect to something at each end.

The effect of capacitance to the ground is not affected by any insulation on a wire many feet above the ground. BUT corrosion does affect the conductors, rather slowly, but it is persistant. And in areas with a corrosive ambient atmosphere it progresses more rapidly.

 

Moisture, as in rain, can create a path to surroundings. Tin roofs could have capacitance, charging to line voltage.

 

Everybody knows to ground a metal roof!! A "not-grounded" metal roof is subject to static build-up, with sparks that can start a fire. Even from nearby lightning.

AND, insulation on a wire slows the corrosion, just like the paint on a metal roof slows the rust.. But the insulation is probably longer lasting.

 

Everybody knows to ground a metal roof!!

Surprisingly, the NEC does not require metal roofs to be grounded except under specific circumstances. Primarily "Risk of accidental energization" i.e. coming in contact with feeder wires crossing the roof. It is also required by the NFPA (and not their NEC) when utilizing a lightning protection system. NFPA claims that a metal roof is no more prone to lightning than "other" roofing materials. Mine is grounded as per NFPA but not bonded to the electrical system ground that NEC requires for "special conditions" as it initially had a lightning suppression system which was not reinstalled upon reroofing due to leakage due to the initial installation method being defective. The grounding was not removed, however.

 

Since a metal roof would not be part of the electrical system, there is no "electrical system" rules applicable. That makes sense.
BUT so does grounding the roof to avoid a possible fire-starting hazard.

 

I am from a city of overhead cable chaos like this.
View attachment 370342
I often come across news of people including children being electrocuted by touching overhead transmission lines while playing in the rooftop, while picking up a ball from a tin roof etc.

I feel both sorry and confused when I read these news. I have always known that electrical wires have rubber insulations around their whole body. If that is the case in general, how can people die merely from touching a live wire? Aren't there supposed to be insulation? Do the accidents take place due to uninsulated cables or worn-out insulations?

I have seen photos of those wire installations, and they are "a bit scary." Safely tapping onto a bare live wire would certainly require skill and caution, and some adequate insulation. For a 120 volt mains tap in that would not be a serious challenge. To access the 1700 volt line higher up above would be rather more demanding.

 

I am aware that safety standards differ around the world. BUT ONLY IN THE USA was there a lawsuit from one who got shocked and injured while attempting to steal electricity from a power line.