No worries, I guess this thread was destined to go this direction no matter what.

BTW, good tip about the cut off switch. I'll have to keep an eye out or them.

Thanks,

-john

John,

I don't think anyone is intentionally being difficult on this topic, just advocating the surest strategy and tactics for dealing with a very high risk scenario. High energy systems of any type should be approached with utmost paranoia. High pressure steam, high energy turbines, even lightning are things to be very very careful around.

Tools and techniques do exist for working with live high voltage power systems. As pointed out in another post the training is expensive, extensive and I'll add not a guarantee that you will survive the job. The tools are also expensive and require regular inspection/certification to be "trusted". Several sensors are available for EMS and trained Line workers. Try looking up "lineman tools" or "Hot Sticks" or "non contact voltage detector" in your favorite search engine. I think that name brands and certification to applicable standards would be critical things to consider. Keep in mind, these are tools for trained experts, not a DIY project.

My understanding (limited) is that there are relatively reliable non-contact voltage detectors that can be used by electrical workers. The challenges with these are that they are subject to interference from various sources (including automotive ignition systems) and while they are non-contact they need to be in relatively close (within a few inches or feet) to the voltage source. This is usually closer than you would want to approach a downed line. For professionals this is less of a problem because they have the other tools/equipment/procedures for getting the sensor in close without undue risk. These sensors are also usually considered backup systems, not primary.

With most high power systems (electrical, RF, mechanical) the best safety assurances for those involved is iron clad processes and procedures, including two person checks on everything. In the scenario being discussed that is not an option so nearly all of the safety "margin" has been eliminated. At this point most trained lineworkers will stay away unless they are part of a team working together to manage the problem.

The step voltage differential that both Martin and I mention is one of many things to be aware of and I brought it up to make a point. I'll emphasize the point here - If you have on "typical" footwear near a distribution line that is shorting to ground your foot/shoe could be the best path to ground (or at least a lower potential level). In the example I provided the surface voltage difference from your toes to your heel would be over 300VAC and essentially unlimited Amps. At that potential level, arcs through your foot are not just possible but likely. The example also assumed a solid grounding into soil (not an arcing, jumping line) so other parts of you may become part of the circuit (via air/plasma arcs) if the line is not actually grounded into the soil. Shuffling only really helps at lower potential gradients (i.e. farther away from the ground contact point or a lower voltage source).

I will keep trying to answer / research questions that are brought up in this discussion but I sincerely hope the information I provide brings anyone reading this thread to the recognition that Stay Away is the only survivable alternative for those of us who do not have the proper training.

For reference I have a degree in Electrical Engineering and I do not work in the electrical power industry.

If I did offend (and I hope i didn't) then I am sorry. Please remember that when some of us answer we are also answering it with the thoughts that SOMEONE out there (usually a nonregistered guest just 'peeking' at things) will take what we say as ABSOLUTE FACT even if we clearly state it is our OPINION! Please remember that as is in this case....I am CERTAIN there are ways to check the line.... BUT I know I don't know specifically so I will advocate the SAFEST way to approach the situation (don't even think of checking) so that the most causual observer will think---I'd be insane for even thinking it! Personally I do think it is an excellent topic. I am interested in the answers. Don't know if I'd try any unless I had ABSOLUTELY NO OTHER WAY....I've seen the damage done by them first hand.

Aside from all the problems of determining if the lines are powered now, there is the fact that they may become powered in an instant with no notice.

Scenario: you need to cross the downed line. You check and are sure the line is dead. You take a couple of steps and are near the line when somewhere someone throws a switch or something else happens and the lines are now instantly powered and deadly.

Please, treat all downed lines as live at all times just like you treat all guns as loaded.

There are lots of self resetting circuit breakers out there for critical circuits, where the line can go dead and come back on after a set delay.

You can buy the testing tools at any electrical supply house if you really want to. I've seen them in use, just point the stick toward the line in question and it lights up if its powered (inductive amplifier). Those tools are not cheap since a false readng will carry a high price so they are quality made and the companies making them have high insurance.

<sarcasm>I suppose that means we shouldn't learn anything about firearms, either.</sarcasm>

-john

To answer the original question of "How can I tell?". The answer is, you can't, and that is precisely why everyone tells everyone to treat them as live, and to stay back.

See this video: http://www.youtube.com/watch?v=kVXi_0H_ZzM

This video shows a tree being blown into power lines, and it illustrates a couple of things:

1. The lines remain energized long enough to burn the tree. A current is being applied between two points, and no effect on power transmission. This is probably happening between the two sets of power lines (the high and medium ones shown in the video). In other words: The system does not detect the problem.

2. Once the line shorts (about the 4:00 mark), automatic breakers trip shutting off power. This is what you would expect, right? Then, what you would not expect (but has been mentioned here) is the additional shorting. That is the system attempting to clear the obstruction and returning the system to normal. Useful for clearing squirrels and other small animals. This is an AUTOMATED response to the transient power issue and is NOT initiated by a human.

Rules of thumb (yes, already mentioned):
- Treat all WIRES as live (regardless if they are telephone, cable, or insulated)
- Stay back at least 3 poles away from a downed pole. Tension in the lines could cause a cascading failure of the poles down from the broken pole.

Please watch the following electrical system safety video: http://www.youtube.com/watch?v=7VXEb3_apOc ( ~20 minutes long - geared towards construction workers below supervisor level. Does contain good information on emergency info.)

This video shows the conductive nature of a steel-belted radial tire:

http://www.youtube.com/watch?v=UqcK2t6eWrs

The design of modern electrical systems and liability issues, no one will tell you how to really tell a line is dead. Pretty much comes down to a human telling another human "I shut off the power to that line by a physical mean".

I have a feeling that the people who keep trying to figure out how to get close to live power lines are not looking at the videos. Please see the explosion at 4:01. Then, imagine the tree is you. That's what happens if you get electrocuted with that amount current.

So, here's another answer to the original question. From a safe distance, find some macho dude in the area who knows everything and has a need to impress people. Inform him that he absolutely should NOT go near the downed power lines because they're a great risk to his life. Being the type of guy he is, he'll figure out somehow if the line is live or not...

OMG! My head is hurting. It looks like we're going to be planning a couple of memorials, gang.