- #1
Scott Pratz
- 10
- 0
Touching live wires is inherently dangerous and should not be attempted. This thread is ONLY about the physics behind why it is dangerous, and not about how to do it safely. Do not touch live wires.
I'm looking at an ungounded 3-phase system here for starters. In a perfectly ungrounded system, grabbing a phase seems safe in theory, but in practice (because perfect ungrounded doesn't exist), this is a bad idea. I'm trying to determine exactly WHY.
If I have a perfect ungrounded system (zero potential between any phase and earth), and I measure the voltage of a wire, have I not begun to move the Earth into the same potential reference at the phase that I have connected to it? I guess it is easier to explain if we are looking at a shipboard system. I'm going to assume that we are looking at this ship at a single instant. If I have a phase and connect it to the ship, then the ship will "polarize" and become equivalent of the phase connected to it. What is physically happening here? Is there initially current flow, in order to polarize the object to bring it into the same reference? I'm trying to understand the difference in voltages (i understand they are all relative to a point)... However, I don't see how physically a difference can exist between a ship touching a branch, and that same ship touching another branch at that same instant. What changes? can I measure a potential difference? If I have a honda generator sitting in the bed of a pickup truck, and I measure the potential difference to the warehouse floor, why do I get a voltage reading? Is this only temporary as the warehouse is undergoes constant "hysteresis"? Is that word even allowed to be said in this conversation?
I have conducted this test before and it has given me a voltage reading on the meter at the potential difference of the generator's terminals.
Also, I ended up measuring the potential voltage difference between one branch of a 440V 3-phase terminal and literally 10 feet of wire in a coil sitting on a rubber matted table, and I measured 30 volts... how does this make any sense? I would get current flow through the terminal to the wire as well... this makes no sense to me. I initially measure a low current and it slowly goes up until reaching a maximum.
Can anyone clarify all these crazy current flow questions? I have a formal education in circuit analysis, however these things aren't exactly covered in class. I see these all as open circuits and my brain tells me zero current... or connecting anything to a terminal of an open circuit just transfers the voltage across the resistor/object, and gets
If I have a perfect ungrounded system (zero potential between any phase and earth), and I measure the voltage of a wire, have I not begun to move the Earth into the same potential reference at the phase that I have connected to it? I guess it is easier to explain if we are looking at a shipboard system. I'm going to assume that we are looking at this ship at a single instant. If I have a phase and connect it to the ship, then the ship will "polarize" and become equivalent of the phase connected to it. What is physically happening here? Is there initially current flow, in order to polarize the object to bring it into the same reference? I'm trying to understand the difference in voltages (i understand they are all relative to a point)... However, I don't see how physically a difference can exist between a ship touching a branch, and that same ship touching another branch at that same instant. What changes? can I measure a potential difference? If I have a honda generator sitting in the bed of a pickup truck, and I measure the potential difference to the warehouse floor, why do I get a voltage reading? Is this only temporary as the warehouse is undergoes constant "hysteresis"? Is that word even allowed to be said in this conversation?
I have conducted this test before and it has given me a voltage reading on the meter at the potential difference of the generator's terminals.
Also, I ended up measuring the potential voltage difference between one branch of a 440V 3-phase terminal and literally 10 feet of wire in a coil sitting on a rubber matted table, and I measured 30 volts... how does this make any sense? I would get current flow through the terminal to the wire as well... this makes no sense to me. I initially measure a low current and it slowly goes up until reaching a maximum.
Can anyone clarify all these crazy current flow questions? I have a formal education in circuit analysis, however these things aren't exactly covered in class. I see these all as open circuits and my brain tells me zero current... or connecting anything to a terminal of an open circuit just transfers the voltage across the resistor/object, and gets
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