6 ms·
It's a bit disingenuous to suggest that accidents like this don't also happen in the U.S. (or other "first-world" countries). In the mid-to-late '90s I was wor
by smoyer 13y ago
It's a bit disingenuous to suggest that accidents like this don't also happen in the U.S. (or other "first-world" countries). In the mid-to-late '90s I was working on a project that had a fatal accident in the Omaha NE area (fortunately I wasn't present to witness it).
Another contractor was lacing new fiber-optic cable to the existing coaxial cable and realized they'd run the fiber over a safety ground about 7 poles back. Rather than unlace that much cable, they opted to lift the safety ground, move it outside the fiber and reconnect the ground. These ground wires are not supposed to be carrying current when things are working correctly - this one was an it electrocuted those working on it.
Regulations are pretty explicit about how to add cable and telephone wires to a power pole ... and only the power company is supposed to mess with the power. The SCTE and NCTA both have training regimens that obsess over safety, especially when you're working around power (since none of us are actually power experts).
So why did this accident happen? The workers were contractors of contractors of contractors who got paid by the mile. The more fiber they laced up in a day, the more they got paid. They knew there was a slight risk the ground wire would be hot once disconnected but they chose to ignore it for financial reasons.
I've seen tall scaffolding on wheels being moved around in the U.S. and I'm hoping the workers were well versed in the perils of letting their metal structure touch power lines, but what you can't tell from this video is how well these workers were trained and whether they realized the wire they hit was active.
I'm not disagreeing with your article's main points ... that we need to value human life and protect the environment. But I also don't think this video is particularly good at promoting those values.
- jcrites 13y ago> They knew there was a slight risk the ground wire would be hot once disconnected Is there some way you could measure that before touching it or messing with it? And then call in the power company if its properties are not what they are expected to be?
- cnvogel 13y agoYou could measure a lot of things when messing with power lines, but ultimately someone has to be responsible that circus that are powered of or safe for any reason stay safe. You measurements cannot give that guarantee, but installations have procedures that ensure this. Everything deviating from that procedure, which normally includes setting a switch with a safety pin and attached note about the work carried out, will lead to accidental powering up at some point or another. Again: when dealing with high voltage circuits make absolutely certain that the person or machine controlling the circuit is informed (or it's you personally who shut off the power and no one else can turn it on). If you are trained to work on live circuits, please ignore my advice. You'll know better :-)
- snowwindwaves 13y agoOnly in a perfect world would there be zero current on a ground wire. The current can be measured by measuring the field around the wire. There are many manufacturers of clip on ammeters which make a loop around the wire and then measure The current or potential induced in the loop by the field resulting from the current in the ground wire. That video was truly horrible. Was that metal scaffolding? I am surprised that fault carried on for 3 Minutes. A fuse should have blown or other protection operated. Maybe if it was wooden scaffolding it was a high impedance fault undiscernable from high loads.
- smoyer 13y agoA clip on ammeter is is a good recommendation. I don't know how sensitive they were and the nature of the stray voltage. The video was indeed terrible. I'm guessing the scaffolding was metal but that the wheels were rubber (it seemed as though the current was only going though the workers).
- smoyer 13y agoWhen the cable is properly connected into the ground stake, any stray current is diverted to the ground. If the cable had resistance, you could (in theory) measure voltage drop over it but a heavy copper cable has a very low resistance. You can't measure current without interrupting the circuit, so it's really hard to know which grounds are actually being used. And in power systems, the ground is the sum of the grounds throughout the system. If you look near where the power goes into your meter, there should be a 1/2" (or more) copper rod driven 8-10' into the ground and the ground for your house is connected directly to it. Disclaimer: I'm not a power engineer (optics, RF, embedded systems and software) but I understand the basic principles. Someone else can probably talk about how the earth ground is actually established (after every transformer I believe) with a lot more detail.