down power lines

[mbrooke]

When I was a kid in Philadelphia I saw a live wire on the ground melt insulation and leave burn marks in the concrete. It also jumped up and down when they would reclose the switch, so even if it is off, it may come back on with a automatic reclosure.

Very true, even worse with automatic loop schemes.

 

[cowboyjwc]

That's funny, I just received this from our utility.

Power lines are not covered with an insulating material. Most overhead power lines are made of highly conductive aluminum with a steel core or copper and they are NOT covered with an insulating material. All downed wires should be considered energized and dangerous.

Don't be fooled by the covering. The covering on the service drop wires that go from utility poles to homes. This coating is designed to protect the service drop from the elements and will not prevent injury to people. This covering will NOT protect you from electrical shock

 

[Rampage_Rick]

The thing that I always remember from childhood was a downed 14kV line that cut through a fire hydrant. Well, burned through a hydrant.

 

[meternerd]

That's funny, I just received this from our utility.

Power lines are not covered with an insulating material. Most overhead power lines are made of highly conductive aluminum with a steel core or copper and they are NOT covered with an insulating material. All downed wires should be considered energized and dangerous.

Don't be fooled by the covering. The covering on the service drop wires that go from utility poles to homes. This coating is designed to protect the service drop from the elements and will not prevent injury to people. This covering will NOT protect you from electrical shock

Well....not quite true. The "covering" on secondary service drops is in fact insulation, rated for the voltage of the supply. Minimum is usually 600V. Since most overhead service drops include two insulated "hot" leads and one bare neutral, if there were no insulation you would have an immediate phase to ground fault to the bare neutral. What is true, though, is that you should never count on the insulation to protect you. Never work on energized services unless you are wearing appropriate PPE.

 

[meternerd]

The videos are crazy scary


If you have any links or comments about the subject Id be very interested!


To some degree the jumpers might help if the line became energized. In theory if the lineman was in contact with the MGN near the jumper a voltage potential would exist, but it would be reduced since the MGN would also rise in potential.

If the fault was 3 phases coming on at the same time the fault current would actually choose the other phases over the ground so the potential rise here wouldn't be as great?


Not fail safe, but in theory you are reducing potential should the line reenergize?

Here's one of many videos....http://www.youtube.com/watch?v=6GuR5nF7VGY

Just search for "Equi-potential grounding" or "single point grounding" and you should find lots of info.

As far as grounding power lines, we normally jumper all three phases and then run a jumper to neutral. That way, if the line were to come hot, there would be a phase to phase and a phase to ground fault. Line clearing would be pretty quick, but not nearly fast enough to prevent injury or death to a lineman in parallel with any phase and ground. That's why Equi-potential Grounding" was developed. No parallel path through the worker, since he is in the "Zone of Protection" and any fault current will flow around the worker to the ground connection.

 

[cowboyjwc]

Well....not quite true. The "covering" on secondary service drops is in fact insulation, rated for the voltage of the supply. Minimum is usually 600V. Since most overhead service drops include two insulated "hot" leads and one bare neutral, if there were no insulation you would have an immediate phase to ground fault to the bare neutral. What is true, though, is that you should never count on the insulation to protect you. Never work on energized services unless you are wearing appropriate PPE.

That came straight from Southern California Edison, so I can only assume that they know what they are talking about. Now as to your point, I can't tell you how many services I have hooked up and have never had a problem with the insulation, of course I was always wearing gloves too.

So how are things up in Truckee? My dad was raised in Sierraville and I've lived in Reno and Sacramento, so we spent a lot of time up in that area camping either around Sierraville or at Boca.

 

[meternerd]

[That came straight from Southern California Edison, so I can only assume that they know what they are talking about.]

Hmmm....I have my own opinions about SCE, so we won't go there.

Truckee is as beautiful as always. Even better now that every day is Saturday. I love retirement!

 

[cowboyjwc]

[That came straight from Southern California Edison, so I can only assume that they know what they are talking about.]

Hmmm....I have my own opinions about SCE, so we won't go there.

Truckee is as beautiful as always. Even better now that every day is Saturday. I love retirement!

You dog.:happyyes: Lot's of stuff to do up that way if you're retired. So many great day trips you can do.

 

[growler]

Don't be fooled by the covering. The covering on the service drop wires that go from utility poles to homes. This coating is designed to protect the service drop from the elements and will not prevent injury to people. This covering will NOT protect you from electrical shock

That's what I was taught many many years ago.

That there is a big difference between covered and insulated.

I suspect it has a lot to do with liability, many screw drivers have a plastic handle and you probably can use them on a 120V circuit and not get shocked but they are still not considered insulated because they haven't been tested and listed as insulated so you must use at your own risk.

I think the same goes for covered cable, it may protect you but it's not listed as insulated so it's up to you to be safe and wear protective equipment.

 

[GoldDigger]

I wonder whether POCOs once used the service drop equivalent of knob and tube with two or three spaced wires that therefore did not need to be insulated from each other?

Tapatalk!

 

[ActionDave]

I wonder whether POCOs once used the service drop equivalent of knob and tube with two or three spaced wires that therefore did not need to be insulated from each other?

Tapatalk!

Based on some old, abandoned services I have seen I would say yes.

 

[just the cowboy]

I wonder whether POCOs once used the service drop equivalent of knob and tube with two or three spaced wires that therefore did not need to be insulated from each other?

Tapatalk!

In Philadelphia they ran them like that down the back of the rowhomes, then tapped into them with service cable. Odd thing was they would run something like a #1 or so and feed the whole block

 

[meternerd]

Yup...it's called "open secondary." Pretty common back in the day. We redid some of the old commercial services in downtown Truckee a few years ago and we found several open secondary services with lighting circuits, heating loads, etc. tapped directly off of the bare wires ahead of any protection. The only protection was the transformer fuse...not likely to blow until the building is burned to the ground. Not good!

 

[K8MHZ]

I wonder whether POCOs once used the service drop equivalent of knob and tube with two or three spaced wires that therefore did not need to be insulated from each other?

Tapatalk!

There are still lines like that here. It's actually quite common to see. Lot's of them have what used to be insulation just hanging off of them in little chunks and pieces.

Here is a pic from the web. Look close and you can see the bare wire where the insulation no longer exists.

View attachment 10291

 

[GoldDigger]

There are still lines like that here. It's actually quite common to see. Lot's of them have what used to be insulation just hanging off of them in little chunks and pieces.

Here is a pic from the web. Look close and you can see the bare wire where the insulation no longer exists.

Nice picture! I wonder whether we see insulation missing or just covering missing?

I was thinking more about using open wires for the service drop to the building, with each wire strain relieved at a separate insulator, and then splicing to insulated wires to allow them to come together in the weatherhead. That would fit in better with the SCE warning.

 

[kwired]

I wonder whether POCOs once used the service drop equivalent of knob and tube with two or three spaced wires that therefore did not need to be insulated from each other?

Tapatalk!

Based on some old, abandoned services I have seen I would say yes.

There are still some in use out there, but they are getting harder to find, if the load hasn't really changed otherwise mother nature usually eventually gives a good reason to change them. Most of the time you saw hard drawn copper used, I have run into an occasional solid aluminum conductor - makes you wonder how those ever lasted as long as they did whenever you do find one.

There are still lines like that here. It's actually quite common to see. Lot's of them have what used to be insulation just hanging off of them in little chunks and pieces.

Here is a pic from the web. Look close and you can see the bare wire where the insulation no longer exists.

View attachment 10291

that is also common around here in cities and villages - but is generally older construction still in place. Multiplexed conductors on a messenger is about all you will find for anything newer. I am assuming we are seeing maybe service drops to final customer supported from the "span" of another distribution conductor here. I see that occasionally when I venture away from home, but is nothing you ever see at all around here. Service drops here (doesn't seem to matter which POCO you are dealing with either) are always attached to a pole or other structure and not to the middle of a span of other conductor. With the kind of wind we see at times I don't think is a good idea to attach to another conductor either, that is just asking for more to repair when it does fail.

Nice picture! I wonder whether we see insulation missing or just covering missing?

I was thinking more about using open wires for the service drop to the building, with each wire strain relieved at a separate insulator, and then splicing to insulated wires to allow them to come together in the weatherhead. That would fit in better with the SCE warning.

 

[K8MHZ]

Nice picture! I wonder whether we see insulation missing or just covering missing?

I was thinking more about using open wires for the service drop to the building, with each wire strain relieved at a separate insulator, and then splicing to insulated wires to allow them to come together in the weatherhead. That would fit in better with the SCE warning.

Whatever is missing, it's bare wire that's exposed.

What we have around here is worse. If I get a chance, I will get some pics.

All the new stuff is AL triplex and the like. But there is as much old stuff as new stuff around here.

 

[mbrooke]

That's funny, I just received this from our utility.

Power lines are not covered with an insulating material. Most overhead power lines are made of highly conductive aluminum with a steel core or copper and they are NOT covered with an insulating material. All downed wires should be considered energized and dangerous.

Don't be fooled by the covering. The covering on the service drop wires that go from utility poles to homes. This coating is designed to protect the service drop from the elements and will not prevent injury to people. This covering will NOT protect you from electrical shock

If that applies to twisted service drops that is untrue. Open wires on spools maybe. However, when dealing with cables above 1kv that often holds true. A good example is tree wire. Its not meant to be insulation.

Here's one of many videos....http://www.youtube.com/watch?v=6GuR5nF7VGY

Just search for "Equi-potential grounding" or "single point grounding" and you should find lots of info.

As far as grounding power lines, we normally jumper all three phases and then run a jumper to neutral. That way, if the line were to come hot, there would be a phase to phase and a phase to ground fault. Line clearing would be pretty quick, but not nearly fast enough to prevent injury or death to a lineman in parallel with any phase and ground. That's why Equi-potential Grounding" was developed. No parallel path through the worker, since he is in the "Zone of Protection" and any fault current will flow around the worker to the ground connection.

Thanks! I appreciate it! I actually see that all the time. Unfortunately around here they often leave the pole and earth ground out of it:happysad: But then again Gloves are policy.

That's what I was taught many many years ago.

That there is a big difference between covered and insulated.

I suspect it has a lot to do with liability, many screw drivers have a plastic handle and you probably can use them on a 120V circuit and not get shocked but they are still not considered insulated because they haven't been tested and listed as insulated so you must use at your own risk.

I think the same goes for covered cable, it may protect you but it's not listed as insulated so it's up to you to be safe and wear protective equipment.

Most cables that are below 1kv that are covered are insulated as well. Only issue is that over time a chunk might get damaged from say a falling pole or tree leaving a bare spot. Very, very old cable may start to crack and loose insulation.


HV cable is another story. It comes in covered, protected, tree wire, spacer cable, spacer cable for treed areas, "insulated" (basically URD without the concentric shield) and ariel bundle/underground insulated cable with a concentric ground.

Other than concentric ground shielded cables (even then its a god idea) must be treated as bare.

Covered wire is only covered to protect against the elements. It will pass some current, often lethal. Good tree wire and Spacer cable is often "half way insulated" meaning it wont short circuit nor pass major currents, however, the covering at higher voltages can have a capacitive charge that can cause a nasty shock. At higher voltages and with enough surface contact it may even be lethal. This is assuming the spacer cable has a full functional covering. Repeated contact with trees that last for months or longer will cause the wire to track and encounter dielectric breakdown. Basically the insulation develops pin holes or just burns through all together since its not intended to be continually in contact with something off opposite potential. The end result is a cable that can pass lethal currents even though it appears fully covered. First thing linemen are told is that tree wire and spacer cable should always be treated as live since you never know where the covering is compromised.

 

[meternerd]

[Thanks! I appreciate it! I actually see that all the time. Unfortunately around here they often leave the pole and earth ground out of it:happysad: But then again Gloves are policy. ]

Unfortunately, most deaths from incidental contact are not from hands. It's usually arms, shoulders, or other parts you may not be paying attention to. Expect the unexpected....plan for the worst and hope for the best....never assume ANYTHING! Lots of cute sayings to say one thing. Keep your mind on the job. If EPG is a company policy, it will be followed. If not, it will sometimes be ignored because it takes special equipment and more time. Besides...."that's the way we always used to do it!":happysad:

 

[Rampage_Rick]

HV cable is another story. It comes in covered, protected, tree wire, spacer cable, spacer cable for treed areas, "insulated" (basically URD without the concentric shield) and ariel bundle/underground insulated cable with a concentric ground.

Thanks, learned something new today. I've seen spacer cable around here but never knew what it's called. In all my travels throughout BC I think I've seen it in maybe four places.