If you look at it as a system along with the fuse and also the circuit breaker, even at 220v, the fuse or circuit breaker will operate long before there would be any chance of thermister failure. Pass Labs uses one per leg in some of their 220V power amps for soft start, they are very robust. I also use them in my class A amps for soft start and haven't experienced any problems at all. My stereo Aleph 5 has been running for years with just one on the primary side.
I never felt the need to test with fault current but it would be easy to do, just hook one up between hot and chassis ground and flip the switch.
I never felt the need to test with fault current but it would be easy to do, just hook one up between hot and chassis ground and flip the switch.
IMHO, whatever scheme is used it should pass a ground bond test at 15-20A. That means between *any* exposed metal including RCA shells, and the ground pin of the mains plug. At the same time the voltage between those two points is monitored to give the resistance. I can't remember the exact fail level, but I think it's around 0.1 ohms. Probably more info on the Quadtech site.
Professor Smith
If you think of the return path (GND) as inductive as well as resistive, you can start to see how a large bass transient will cause a current surge down a PCB trace (or wire), this will cause an voltage to apear (V=dI/dt), this would swamp a low level signal who's return was following the same path, its level would be decreased by the induced voltage.
As to mains, Babowana's picture of how mains works missed only one thing, the LINE (live) terminal is a direct link back to the generator, it is hardwired through the transformers etc to the power plant, these things have huge mechanical inertia (and electrical) as they supply large areas and have to handle localised surges, so swapping the live and neatral would connect your wiring directly to this supply.
I wouldn't be having a bath
If you think of the return path (GND) as inductive as well as resistive, you can start to see how a large bass transient will cause a current surge down a PCB trace (or wire), this will cause an voltage to apear (V=dI/dt), this would swamp a low level signal who's return was following the same path, its level would be decreased by the induced voltage.
As to mains, Babowana's picture of how mains works missed only one thing, the LINE (live) terminal is a direct link back to the generator, it is hardwired through the transformers etc to the power plant, these things have huge mechanical inertia (and electrical) as they supply large areas and have to handle localised surges, so swapping the live and neatral would connect your wiring directly to this supply.
I wouldn't be having a bath
AndrewT said:
I've been wondering then, in the case where I've got normal, non-double-insulated device, that is intended to be grounded for safety, but I have no earth wiring in the room or house. This is a common case with old buildings here and I have no ability or authority to provide safety earth connections. Isn't an RCD enough for connecting any such device? It will trip the live and neutral connectors at the moment the current in them differs by 30mA. That is current that leaked out trough ANY other connection, including my unfortunate body. I know that the earth connection will trip the RCD or blow the fuse (or both) before I touch anything, while without it me or another device will have to act conductor for 1/16th of the second. Safety-wise though, the RCD looks like it should be mandatory no matter what (they are, in fact, mandatory in all new installations here, but with buildings dated back to 1920, *new* is a very small percentage)
Again, here I'm talking about a situation that leaves me without choice. Like plugging in my computer, where the SMPS is to be grounded. or the DIY amp, for which I can't get the double-insulation tag - no matter how safe you try to make it, it'll still need to be grounded.
Essentially, the safety practices here are at best ambiguous, at worst inadequate. At least I am not aware of any regulation that mandates all equipment to be double-insulated, which would be the only way to protect people and property from damage in a non-PE system.
I seriously need to look up what those people have as regulations, since it seems a little .. awkward. No wonder so many places end up in fires....
Point aside, just how much of a buzz will 30mA for 1/16th of a second be?
I seriously need to look up what those people have as regulations, since it seems a little .. awkward. No wonder so many places end up in fires....
Point aside, just how much of a buzz will 30mA for 1/16th of a second be?
Well it's kind of like dropping an electrical device in the bathtub. There grounding doesn't help you, because it may very well be the case that current will flow trough you down to the metal pipes and trough them to ground.
Of course, we're considering here that you haven't stabbed yourself with the electrodes and there's some resistance of your body available, so you don't literally evaporate.
The RCD will trip as fast as it could, trying not to get the 40-50 mA or so trough your heart or something as important, that can get you into the deep trouble. So, theoretically it's a quick buzz, a lot of adrenaline, a lot of swear words and hopefully nothing else.
I'm not exactly sure how much and for how long is really bad, but as far as Rod Elliot's article on earthing goes, a few mA over the RCD trip value trough the heart is enough to get you down.
BTW, as far as pop-science goes, there's an episode of Mythbusters that deals with that. Apparently, RCDs, or however you call them in different places, could save you if you play with toasters in the bathtub. Nothing can save you from stupidity though
Of course, we're considering here that you haven't stabbed yourself with the electrodes and there's some resistance of your body available, so you don't literally evaporate.
The RCD will trip as fast as it could, trying not to get the 40-50 mA or so trough your heart or something as important, that can get you into the deep trouble. So, theoretically it's a quick buzz, a lot of adrenaline, a lot of swear words and hopefully nothing else.
I'm not exactly sure how much and for how long is really bad, but as far as Rod Elliot's article on earthing goes, a few mA over the RCD trip value trough the heart is enough to get you down.
BTW, as far as pop-science goes, there's an episode of Mythbusters that deals with that. Apparently, RCDs, or however you call them in different places, could save you if you play with toasters in the bathtub. Nothing can save you from stupidity though
I saw my 6 foot 2 inch and 16 stone mate poking about in a washing machine that was still live. He was thrown out through his open kitchen door landing in a crumpled heap in the back yard.
He was a martial arts type of many years fighting but said it hurt him more than any beating ever had. If it can hurt someone that fit it is something to be careful with in my opinion.
Funniest thing I have ever seen mindst.
John
He was a martial arts type of many years fighting but said it hurt him more than any beating ever had. If it can hurt someone that fit it is something to be careful with in my opinion.
Funniest thing I have ever seen mindst.
John
**interesting topic**
This really is an interesting topic. To make it even more complex, I would like to add the following:
When we considder a star ground and return all signal lines to this single star, we should have perfect accuracy according to Kirchoff's law's. However what about the paracitic capacitance of the wires picking up signals and hum?
When we leave the star topology and use a distributed ground system, what about the common routes of different signals from the different parts of the electronics causing feedback and cross-over of signals?
Typically designers are building different prototypes and experimenting with ground schemes in order to optimize the performance. This is exactly what we should be doing when we build a DIY circuit.
We can ask ourselves: Where is this signal going to? Is it carrying a large current? What signals have a common section of trace and to what node impedance is it routed? What is the CMMR of the signalpoint I am grounding?
I have done various experiments with spice simulations for various topologies. When using Montecarlo analisys one can get a look and feel for the sensetivity of the different circuit sections for interactions with other ground connections and work out a proper scheme.
It sounds like vodo (sometimes it is...) but there is a book out there called Analog Design Seminar (Analog Devices) that describes the grounding challenge in detail. I would very much advice to read it when you serious about proper diy-ing
This really is an interesting topic. To make it even more complex, I would like to add the following:
When we considder a star ground and return all signal lines to this single star, we should have perfect accuracy according to Kirchoff's law's. However what about the paracitic capacitance of the wires picking up signals and hum?
When we leave the star topology and use a distributed ground system, what about the common routes of different signals from the different parts of the electronics causing feedback and cross-over of signals?
Typically designers are building different prototypes and experimenting with ground schemes in order to optimize the performance. This is exactly what we should be doing when we build a DIY circuit.
We can ask ourselves: Where is this signal going to? Is it carrying a large current? What signals have a common section of trace and to what node impedance is it routed? What is the CMMR of the signalpoint I am grounding?
I have done various experiments with spice simulations for various topologies. When using Montecarlo analisys one can get a look and feel for the sensetivity of the different circuit sections for interactions with other ground connections and work out a proper scheme.
It sounds like vodo (sometimes it is...) but there is a book out there called Analog Design Seminar (Analog Devices) that describes the grounding challenge in detail. I would very much advice to read it when you serious about proper diy-ing
john blackburn said:
Your muscles are run off of electric current. His muscles were more developed, so they were probably more powerful than, say, someone who sits at a computer constantly. It probably hurts you more the stronger you are.
From my point of view, the reason Professor doesn't understand what is being said is because it's all using terminology and I'm sorry, the two-sentence explanations given at the beginning of the thread simply don't cut it. If he doesn't understand grounding surely it is best that we explain it in terms that don't only make sense to someone who's been in college for 4 years of EE
Tomorrow, if I remember, I will try and explain all this in a way that should make sense and does not resort to terminology and complex grammar simply to keep it short for the writer.
Honestly, I think I could be an electronics genius by now IF ONLY there were guys who wrote about complex topics in a way that doesn't require 4 years of college EE (I can infer many things just based off of one piece of information). It can be done, yes it can be done. I hope to be living proof of that one day. I don't need terminology, I just need to know how it works. Tell me once and I remember it forever. There are almost no materials for people who are like this. The only reason to learn terminology is so that you can communicate with others clearly.
I don't aim to offend anyone, I'm just throwing this out there. This is the frustration for me with almost any topic. They teach the terminology before the concepts are even properly understood. I think that's bass-ackwards.
- keantoken
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