down power lines

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pegggu

Member
Location
Los Angeles
if a utility power line goes down, so long as it doesn't land on a car or some other object, if instead it makes contact with the road, ground, dirt, earth. Would it not then be considered a phase to ground fault? Would it not be dead at that point? If somewhere to grab it would it not be safe (not saying some one should) but would it not be technically safe? Would the current not go through a system ground somewhere back along the circuit?

If this isn't the case, what would happen? would the line still be energized and just see the ground as a low resistance path to ground?
 

kwired

Electron manager
Location
NE Nebraska
if a utility power line goes down, so long as it doesn't land on a car or some other object, if instead it makes contact with the road, ground, dirt, earth. Would it not then be considered a phase to ground fault? Would it not be dead at that point? If somewhere to grab it would it not be safe (not saying some one should) but would it not be technically safe? Would the current not go through a system ground somewhere back along the circuit?

If this isn't the case, what would happen? would the line still be energized and just see the ground as a low resistance path to ground?

It really depends on the conditions at the time of the event, and is why you must always assume a downed line is live. Even if it is live and you are in the nearby vicinity, you may not be electrocuted, but there are voltage zones in the earth and surrounding materials. All you need to do is contact two points or enough difference in potential and you are in big trouble. As long as you stay in contact with one potential you are safe, doesn't matter if it is true earth ground or 10,000 volts, you need to touch two different points of potential to get shocked.

They usually recommend if you are in a vehicle and it comes in contact with a downed line that you should stay in the vehicle until help arrives - this lessens the chance of you contacting something with a big enough difference in potential to harm you. If the situation dictates you need to get out of the vehicle then they suggest you jump out and not step out as there may be too much potential between the vehicle and the ground and you do not want to touch both at the same time. Even after hitting the ground they do not recommend running, as that may allow you to span across voltage zones in the ground but instead you should "shuffle your feet" as you move away to prevent yourself from crossing too high of any voltage gradients in the earth below you.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Treat as energized. When utilities do work on a line without HV gloves they will first open all switches and/or disable all reclosers and breakers from closing (hot line tag), jumper the lines to ground and then test, retest and test everything is de energized.




One of the biggest dangers believe it or not are back feeding generators. I have known line men after storms to ground down a line that they know is disconnected and locked out only to find a generator back feeding it on a side street.
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Two unbreakable rules for linemen:

If it isn't grounded, it isn't dead.

Identify, isolate, test and ground.

Been keeping us power guys alive for a LONG time.

Power lines are de-energized due to ground faults by either blowing fuses (cutouts) or tripping breakers. Both rely on fault current of a high enough level to clear the device. Not always guaranteed. Resistance to ground varies a lot. Snow, rocky soil or anything else that might reduce current can cause lines to remain energized. Current to ground is what trips the protection. Actually, on most electronic line breakers (reclosers), it's current imbalance between phases that trips the device, but that's a whole other discussion.
 
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mbrooke

Batteries Included
Location
United States
Occupation
Technician
Two unbreakable rules for linemen:

If it isn't grounded, it isn't dead.

Identify, isolate, test and ground.

Been keeping us power guys alive for a LONG time.

Power lines are de-energized due to ground faults by either blowing fuses (cutouts) or tripping breakers. Both rely on fault current of a high enough level to clear the device. Not always guaranteed. Resistance to ground varies a lot. Snow, rocky soil or anything else that might reduce current can cause lines to remain energized. Current to ground is what trips the protection. Actually, on most electronic line breakers (reclosers), it's current imbalance between phases that trips the device, but that's a whole other discussion.


100% true. Unless its tested, isolated, grounded and tested again its not safe to touch. Some pocos will glove up despite that if say the circuit they are working is next to a live one or a circuit of a higher voltage is present. as overbuild. Ie 12.47kv circuit is de-energized for work but above that is a live 34.5kv sub transmission circuit.



Adding to what you already said, a downed wires doesn't always clear. Its entirely dependent on soil resistance and the amp rating of breakers/fuses. Most of the time the idea is more to protect the system from overload and short circuit stress (thousands of amps) rather than people (a few milliamps).

When reclosers are involved its the most dangerous since they may temporarily de-energize a circuit making it look dead only to close back into the fault at a latter time.


I will post some videos of how to and how not to treat a down wire situation.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician

iwire

Moderator
Staff member
Location
Massachusetts
Two unbreakable rules for linemen:

If it isn't grounded, it isn't dead.

And to make things perfectly clear you do not mean laying on the ground, or simply resting on something grounded. You mean someone has physically tied the conductor directly to a grounded conductor.
 

bob

Senior Member
Location
Alabama
If this isn't the case, what would happen? would the line still be energized and just see the ground as a low resistance path to ground?

That's where you are making a mistake. The earth is not a low resistance path. Usually there is not enough current flow to trip the breaker. I saw a 7200 volt line fall in a pool of rain water and there were bubbles from the water boiling from heat generated and the breaker never tripped.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
And the grounding jumpers and their connectors are rated for the available fault current.

yep. they call them "personal shorts and grounds" for a good reason.
they save your personal butt.

before you can touch anything, you test it "hot, dead, hot" with your
squealer, and then apply shorts and grounds to both ends of your
clearance.

the voltage will follow ALL paths to ground, not just the best one.
current flow will be based on combination circuit calculations.

something they teach when in switchracks, is that if you have a
major fault to ground, and you are standing at right angles to
the dissipating energy, there can be enough difference of potential
between your feet that you can be your very own "ground loop" and
get nailed just standing on the ground. 2' of separation of your feet
can be enough.

my thought was that if i was that close to a major fault, there is
no way both my feet would be on the ground at the same time, until
i'd made it all the way to my car in the parking lot.
 

kwired

Electron manager
Location
NE Nebraska
Ok, these videos are worth their weight in gold. Some are good examples some are down right scary but all are worth studying and learning from:


How not to tackle a down wire:eek::jawdrop::

https://www.youtube.com/watch?v=dUjo4FAJmuA


POCO power kill, the right way:

https://www.youtube.com/watch?v=ovp6mbl1uCI


To close to a fence for comfort. Very cool to watch though:

https://www.youtube.com/watch?v=28Xq3JulV1o


Wire on tree call:

https://www.youtube.com/watch?v=cFe8eyZJnfY
Read all the comments lower on those pages written by all the "experts":(

At least a few are smart enough to know you need to leave it alone until qualified people show up. I did see some risky activity from some firemen at different points in the videos. The one with the car on fire - they shouln't have done anything with that car before the downed line was deemed safe, in fact they shouldn't have even walked as close as they did a few times. The downed line on the swing set - first frame of the video those guys were way too close to the chain link fence - the downed line was far enough away, but was only like 10 feet or less from that same fence - and they later got to see that it was energized, and IMO they still did not move far enough away after that warning from the fence itself happened.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Read all the comments lower on those pages written by all the "experts":(

At least a few are smart enough to know you need to leave it alone until qualified people show up. I did see some risky activity from some firemen at different points in the videos. The one with the car on fire - they shouln't have done anything with that car before the downed line was deemed safe, in fact they shouldn't have even walked as close as they did a few times. The downed line on the swing set - first frame of the video those guys were way too close to the chain link fence - the downed line was far enough away, but was only like 10 feet or less from that same fence - and they later got to see that it was energized, and IMO they still did not move far enough away after that warning from the fence itself happened.



I don't expect any truthful or valid remarks on You Tube. Nearly every video Ive ever watched is followed with comments by people who don't have a clue yet claim they are somehow "experts".:roll: Same goes for most News sights in the comments section.


I ended up being chewed out once by a group of people after I remarked on a guy who thought it was safe to handle downed wires after a storm by just wearing some rubber cleaning gloves. Guys reasoning was "rubber doesn't conduct electricity" "had I paid attention in science class I would have known that" :happyno:


The car video was one of the worst Ive seen. They not only got close but were spraying water directly on the fire underneath the car. If there were people trapped in the car Id give them some credit but that was just reckless. The fence is a good example of keep your distance. One of the guys was a actually resting his elbow on the wooden fence across from the metal one.:eek:

I think the issues behind a lot of this are many of the misconceptions that still exist even among first responders ie, electricity takes the quickest path to ground, wood and rubber don't conduct electricity, if it isn't sparking its de-enegized ect ect.
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Been a while since I looked at this thread. Lots of good comments. Yes, grounded means connected to the neutral (if available), which is the best available ground in the field. Jumpers are special. Have very low impedance connectors and wire size is much larger than regular jumpers. Even then, you always test the line after it's grounded. The main thing is "isolate". That means getting a visible open on both sides of the work area, since a backfeed can be just as deadly as a normal feed. Grounds are not there to protect the workers. They are there to trip any protective devices in case the line comes hot. Any lineman in parallel with a ground will still receive full voltage until the line trips. "Kirchoffs Voltage Law on parallel circuits." The only safe grounding system for personal protection is EPG (or EPZ), meaning Equi-Potential Grounding (or Zone). Also known as single point grounding. Whole other subject, probably not appropriate here.

Thanks for the links to the videos. Now that I'm retired, I wonder why I ever got into the electric utility business in the first place. That stuff is SCARY!
 
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mbrooke

Batteries Included
Location
United States
Occupation
Technician
Been a while since I looked at this thread. Lots of good comments. Yes, grounded means connected to the neutral (if available), which is the best available ground in the field. Jumpers are special. Have very low impedance connectors and wire size is much larger than regular jumpers. Even then, you always test the line after it's grounded. The main thing is "isolate". That means getting a visible open on both sides of the work area, since a backfeed can be just as deadly as a normal feed. Grounds are not there to protect the workers. They are there to trip any protective devices in case the line comes hot. Any lineman in parallel with a ground will still receive full voltage until the line trips. "Kirchoffs Voltage Law on parallel circuits." The only safe grounding system for personal protection is EPG (or EPZ), meaning Equi-Potential Grounding (or Zone). Also known as single point grounding. Whole other subject, probably not appropriate here.

Thanks for the links to the videos. Now that I'm retired, I wonder why I ever got into the electric utility business in the first place. That stuff is SCARY!


The videos are crazy scary:eek:


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?
 

kwired

Electron manager
Location
NE Nebraska
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?

I would think that would depend on each phase having identical impedance, reality is there probably will be some differences and the neutral will carry the imbalance.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
I would think that would depend on each phase having identical impedance, reality is there probably will be some differences and the neutral will carry the imbalance.

Id say so. But in theory the voltage rise would be smaller (say 1000 volts instead of 10,000) assuming the lines are within 10% of each other. But it does break the age old clich? that electricity prefers ground. In reality if it had a chance it prefers the other phase (split phase) or the other 2 phases (3phase)! :p:p
 

just the cowboy

Inactive, Email Never Verified
Location
newburgh,ny
saw one on ground burn the concrete

saw one on ground burn the concrete

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.
 
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