In hindsight I'd have worded it differently. Either can kill you, so neither is really notably safer, and I've never seen any stats that compare the outcomes of incidences of AC vs DC. AC events are certainly much more common due to the much greater number of potential exposure points. Thanks for keeping me straight.
When you think about it, what is more interesting is the systemic differences. AC presents the phase to ground danger that makes approaching an energized component more dangerous. With DC its harder to become part of the circuit, but if you do its more likely from touching two points with opposite hands or arms, sending the current across your upper body. With AC its likely a path from an arm down through your legs. Then, of course, you may get some help from resistivity of your shoes. In a DC circuit, you have the internal resistance of the battery itself that can limit current. The good thing about AC ground faults is they can be easily detected to open a breaker. If you become part of a DC circuit, it may not be detected as a overcurrent, as current is expected through that path. It is only cleared if it is excessive. On the other hand, lower voltage DC breakers sometimes clear faster when triggered as they don't hold for a zero current break.
Also, arcing: to bridge 1 cm of air with an arc you need 30KV. At that point, the arc is the least of your worries be it AC or DC.
That is to initiate an arc in an open circuit. That will vary of course with air humidity, particluates, etc. But when interrupting a circuit, arcing continues for a much greater distance before it is extinquished. That distance is significantly higher in a DC circuit.
I agree that my use of peak voltage was confusing, it was an attempt to oversimplify as with AC sources the re are a number of things that influence the severity of a fault, such as phase to phase vs phase to nuetral or ground, available short circuit contribution, system grounding, etc.
Reaction is not relevent to me because I dont assume a person will react and release theirself in either case.
You are right, when stating voltage in terms of RMS values rather than peak. Yes, that is the standard why to express for system ratings and such, but from a physics perspective it is helpful to explain in terms of peak voltage. I never said anything about removing a person from the circuit, however, the act of interruption of an AC circuit creates less arcing and dissipates at a smaller distance than an equivalent DC circuit.
That's a myth, and one that is perpetuated every time this topic comes up. Let's leave aside that your muscles wouldn't be able to react fast enough to make use of the AC current going through zero at 50 or 60 Hz.
No, it is a fact. That is why you have an RMS current value with AC vs DC. And as far as reacting, is not about reaction speed, not sure why you brought that up. So, as I said, there will be more current, and therefore more energy dissipated in the DC case. I said the firefighter would fry faster with DC, that is the case.
I never said anything about gripping or letting go. Again, not sure why you brought that up. However, if the person did break the circuit, there would be less arcing in the AC case, and the arc would extinguish at a smaller opening distance than with DC.
But the idea that AC or DC are more dangerous at these voltages and currents doesn't make sense.
Actually, DC can be much more deadly at lower voltages than AC. The main reason is that AC current goes to zero twice per second, while DC is full current at a constant rate. So a resistive load (a firefighter in the circuit) will fry faster under 600VDC that 600VAC. For this same reason, it is also easier to interrupt an AC current vs a DC current, and why high voltage DC interrupting and switching devices are much more expensive and elaborate than same voltage AC equipment.
How did they know he wasn't just unconscious or in a coma from the crash?
I think firefighters are probably some of the most qualified persons to make that call. Sometimes its quite obvious when a person is dead. You can assume this was not one of those situations, but there is no information available to support that assumption.
It actually could have been an interesting article that talked about the procedures firefighters use in these situations. Maybe some people could have been educated on little things they are trained on, such as 'if you see something that doesn't look safe, don't take chances if there is no need to." In other words, people might learn it is not such a bad thing for firefighters stop and think when facing situations that have even a remote chance of being dangerous.
Oh quit being rational and thinking. A good Slashdotter will over-react, blame the firemen for being stupid, and make assumptions about training and such based on the tone of an article writer's misleading headline. No matter that the firemen had no reason to hurry, they should have rushed in there and started doing something to the car immediately. Surely their training didn't say anything about stopping and thinking if you see something unusual. Firemen hate Tesla's and now we have proof.
I was taking apart an old failed tablet, was going to use the battery for a fun project with mw daughter. When trying to cut away some adhesive I accidentally sliced the battery which immediately sparked and smoked. I was aware of that possibility but it was surprisingly easy to cause.
It's more "ready" than human beings are, in many different driving scenarios.
How many scenarios? The thing is that humans can deal with a much larger range of scenarios, so maybe there is a subset that the existing system handles as good or better, but nobody at this point can pinpoint an overall safety improvement. The system itself has only been exposed to limited scenarios thus far.
What we've seen is that even this advanced system still has its limits, and there are dangers related to partial autonomous systems and the human factors elements that need to be worked on. People that use the feature and experience no issues gain confidence in its capabilities, sometimes possibly to the point of not paying proper attention, then all it takes is one scenario that they system simply cannot read correctly or is not configured to respond to correctly and something bad can happen. The solutions only come with many miles and years of driving and improving.
Further, this argument that claims that it was the fault of the drone pilot for being "on private property" can be used to support the shooting death of any person who happens to wander onto your private property, for any reason. "If only they hadn't been there, my discharge of a lethal weapon wouldn't have killed them..."
Someone might make such an argument if they did not realize that there are a very different set of laws when it comes to injuring or killing people than there are for property damage. Fortunately, folks here are smarter than that.
Here's a novel idea. How about a drone operator inform a property owner that he or she would like to fly the drone over the property, and explain why in advance?
When it gets cheap enough, somebody please send up a bunch of VR cameras on rovers to the moon, mars, and wherever else, and have them map as many different areas in high res VR as possible, then we here on earth could all take a walk on those worlds. It would be a cool educational tool as well as entertainment. It might also be useful for planning future landings and activities.
Is there simple a plug & play solution for installing a NAS/server (encrypted) at a family member's home, and using that as an offsite backup? That way two family members could keep each other offsite backup, but not be able to access the files. For a while I was hoping BTSync would serve this purpose, but as I recall it never quite had the right functionality.
It seems that someone would have created such an animal.
Slashdot Mirror
In hindsight I'd have worded it differently. Either can kill you, so neither is really notably safer, and I've never seen any stats that compare the outcomes of incidences of AC vs DC. AC events are certainly much more common due to the much greater number of potential exposure points. Thanks for keeping me straight.
When you think about it, what is more interesting is the systemic differences. AC presents the phase to ground danger that makes approaching an energized component more dangerous. With DC its harder to become part of the circuit, but if you do its more likely from touching two points with opposite hands or arms, sending the current across your upper body. With AC its likely a path from an arm down through your legs. Then, of course, you may get some help from resistivity of your shoes. In a DC circuit, you have the internal resistance of the battery itself that can limit current. The good thing about AC ground faults is they can be easily detected to open a breaker. If you become part of a DC circuit, it may not be detected as a overcurrent, as current is expected through that path. It is only cleared if it is excessive. On the other hand, lower voltage DC breakers sometimes clear faster when triggered as they don't hold for a zero current break.
Also, arcing: to bridge 1 cm of air with an arc you need 30KV. At that point, the arc is the least of your worries be it AC or DC.
That is to initiate an arc in an open circuit. That will vary of course with air humidity, particluates, etc. But when interrupting a circuit, arcing continues for a much greater distance before it is extinquished. That distance is significantly higher in a DC circuit.
I agree that my use of peak voltage was confusing, it was an attempt to oversimplify as with AC sources the re are a number of things that influence the severity of a fault, such as phase to phase vs phase to nuetral or ground, available short circuit contribution, system grounding, etc.
Reaction is not relevent to me because I dont assume a person will react and release theirself in either case.
You are right, when stating voltage in terms of RMS values rather than peak. Yes, that is the standard why to express for system ratings and such, but from a physics perspective it is helpful to explain in terms of peak voltage. I never said anything about removing a person from the circuit, however, the act of interruption of an AC circuit creates less arcing and dissipates at a smaller distance than an equivalent DC circuit.
That's a myth, and one that is perpetuated every time this topic comes up. Let's leave aside that your muscles wouldn't be able to react fast enough to make use of the AC current going through zero at 50 or 60 Hz.
No, it is a fact. That is why you have an RMS current value with AC vs DC. And as far as reacting, is not about reaction speed, not sure why you brought that up. So, as I said, there will be more current, and therefore more energy dissipated in the DC case. I said the firefighter would fry faster with DC, that is the case.
I never said anything about gripping or letting go. Again, not sure why you brought that up. However, if the person did break the circuit, there would be less arcing in the AC case, and the arc would extinguish at a smaller opening distance than with DC.
But the idea that AC or DC are more dangerous at these voltages and currents doesn't make sense.
Actually, DC can be much more deadly at lower voltages than AC. The main reason is that AC current goes to zero twice per second, while DC is full current at a constant rate. So a resistive load (a firefighter in the circuit) will fry faster under 600VDC that 600VAC. For this same reason, it is also easier to interrupt an AC current vs a DC current, and why high voltage DC interrupting and switching devices are much more expensive and elaborate than same voltage AC equipment.
How did they know he wasn't just unconscious or in a coma from the crash?
I think firefighters are probably some of the most qualified persons to make that call. Sometimes its quite obvious when a person is dead. You can assume this was not one of those situations, but there is no information available to support that assumption.
It actually could have been an interesting article that talked about the procedures firefighters use in these situations. Maybe some people could have been educated on little things they are trained on, such as 'if you see something that doesn't look safe, don't take chances if there is no need to." In other words, people might learn it is not such a bad thing for firefighters stop and think when facing situations that have even a remote chance of being dangerous.
Oh quit being rational and thinking. A good Slashdotter will over-react, blame the firemen for being stupid, and make assumptions about training and such based on the tone of an article writer's misleading headline. No matter that the firemen had no reason to hurry, they should have rushed in there and started doing something to the car immediately. Surely their training didn't say anything about stopping and thinking if you see something unusual. Firemen hate Tesla's and now we have proof.
I was taking apart an old failed tablet, was going to use the battery for a fun project with mw daughter. When trying to cut away some adhesive I accidentally sliced the battery which immediately sparked and smoked. I was aware of that possibility but it was surprisingly easy to cause.
It's more "ready" than human beings are, in many different driving scenarios.
How many scenarios? The thing is that humans can deal with a much larger range of scenarios, so maybe there is a subset that the existing system handles as good or better, but nobody at this point can pinpoint an overall safety improvement. The system itself has only been exposed to limited scenarios thus far.
What we've seen is that even this advanced system still has its limits, and there are dangers related to partial autonomous systems and the human factors elements that need to be worked on. People that use the feature and experience no issues gain confidence in its capabilities, sometimes possibly to the point of not paying proper attention, then all it takes is one scenario that they system simply cannot read correctly or is not configured to respond to correctly and something bad can happen. The solutions only come with many miles and years of driving and improving.
Not sure, but if one drifts from shooting drones to make some point about shooting people, I have to wonder.
these regulatory people have an exaggerated notion of their power in real world.
Maybe they just need a reason to exist,... or expand.
We call em "targets".
Further, this argument that claims that it was the fault of the drone pilot for being "on private property" can be used to support the shooting death of any person who happens to wander onto your private property, for any reason. "If only they hadn't been there, my discharge of a lethal weapon wouldn't have killed them ..."
Someone might make such an argument if they did not realize that there are a very different set of laws when it comes to injuring or killing people than there are for property damage. Fortunately, folks here are smarter than that.
Here's a novel idea. How about a drone operator inform a property owner that he or she would like to fly the drone over the property, and explain why in advance?
An abandoned stroller could be a bomb. Better blow it up, just to be safe.
If it is in my yard, and I was certain there was no baby in it ( as I am with a drone), it would probably be perfectly OK.
So, you cannot distinguish any differences at all between an airliner passing overhead and a drone, with a camera, hovering low over your back yard?
Maybe your property right extends further upward than you think it does.
Great info. Thanks
Crashplan has this. I'm not a shill. I'm a customer though.
I checked it out, it might be a solution. Thanks. From reading their info, I can't tell if the remote backup is stored as encrypted data.
When it gets cheap enough, somebody please send up a bunch of VR cameras on rovers to the moon, mars, and wherever else, and have them map as many different areas in high res VR as possible, then we here on earth could all take a walk on those worlds. It would be a cool educational tool as well as entertainment. It might also be useful for planning future landings and activities.
Is there simple a plug & play solution for installing a NAS/server (encrypted) at a family member's home, and using that as an offsite backup? That way two family members could keep each other offsite backup, but not be able to access the files. For a while I was hoping BTSync would serve this purpose, but as I recall it never quite had the right functionality.
It seems that someone would have created such an animal.
The only use I see is something that might make a better desalinizer for lifeboat emergency kits. Maybe a food steamer for boaters?
Professor John Goodenough demonstrated the first Lithium Ion battery at the age of 57, and continued to lead battery development efforts for decades.