4 ms·

> 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

by 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 ago
You 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 ago
Only 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 ago
  A 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 ago
When 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.

by jcrites 13y ago

cnvogel 13y ago

You 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 ago

Only 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 ago
A 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 ago

When 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.