Nearholmer Posted January 2, 2019 Share Posted January 2, 2019 Phil As a mild caveat, I think that in a real track circuit arrangement, rather than the simplification that i’ve sketched, there will he trimming/balancing resistors close to the source, adjusted when ‘setting up’ the circuit, which you need to factor-in when analysing the circuit, but the principles hold. Kevin Link to post Share on other sites More sharing options...
RMweb Premium phil-b259 Posted January 2, 2019 RMweb Premium Share Posted January 2, 2019 A late friend of mine used to live in Paris pre-WW2 and he 'learnt' about electricity from the 100? Volts DC circuits back then. He maintained that the problem people have, is that they are 'afraid' of electricity. He never did understand that 230 Volts is significantly more dangerous than 100 Volts. Tried to explain to him that electricity needs treating with respect, which is completely different to fear. We (and indeed all other living mammals only exist due to electricity - its what makes or muscles contract and relax, what keeps the heart going and what powers our brains. Therefore it is rather illogical to be 'afraid' of electricity any more than it is to be 'afraid' of fire or bacteria. Context is everything..... Also technically a high voltage figure in itself does not necessarily always indicate a grater risk to life - its why we allow low level electric cattle fences or let children be fascinated by a Van de Graaff generator. It takes just 50ma to stop a human heart I believe - and it doesn't matter whether the potential difference is 1V or 1000V (accepting that voltage dies have a role to play in other respects like 1VAC is unlikely to 'jump' to you where as 25KV will if you get too close), the key criteria is whether that 50ma passes across your heart muscles. Link to post Share on other sites More sharing options...
RMweb Premium phil-b259 Posted January 2, 2019 RMweb Premium Share Posted January 2, 2019 Phil As a mild caveat, I think that in a real track circuit arrangement, rather than the simplification that i’ve sketched, there will he trimming/balancing resistors close to the source, adjusted when ‘setting up’ the circuit, which you need to factor-in when analysing the circuit, but the principles hold. Kevin The most common track circuits I am involved with are of the 50HZ AC type or Audio frequency based tracks, so yes, the real thing is considerably more convoluted than the basic resistive network with reactance, capacitance, inductance and frequency all playing a role. However the basic principle of what you explained is still sound and still useful when comparing a track circuit to other electrical setups such as a campsite full of RVs. If only others had been more willing to try and help me work things through than point scoring. Link to post Share on other sites More sharing options...
RMweb Gold Colin_McLeod Posted January 2, 2019 RMweb Gold Share Posted January 2, 2019 Did I imagine that I made a post to this thread this morning about television? I'm sure I did but can't find it now? Link to post Share on other sites More sharing options...
royaloak Posted January 2, 2019 Share Posted January 2, 2019 Did I imagine that I made a post to this thread this morning about television? I'm sure I did but can't find it now? It has probably been deleted as being nearly on topic, unlike the last 5 pages of arguing over something which doesnt really matter as it was sorted out within the first 10 posts but people just had to continue making their point over and over and over again. 2 Link to post Share on other sites More sharing options...
Crosland Posted January 2, 2019 Share Posted January 2, 2019 This equation quite clearly sates power is a function of voltage multiplied by current, and that if the power figure is to be maintained when voltage lowers then the current must increase. So now we have gone full circle. The whole point is that the type pf heater that set of this thread CANNOT MAINTAIN A FIXED POWER OUTPUT whne the supply voltage is out of spec. PLEASE, stop digging. The sides of the hole will soon fall in on top of you Link to post Share on other sites More sharing options...
Crosland Posted January 2, 2019 Share Posted January 2, 2019 BTW Amazon.com lists dozens of 110v electric kettles, so they can hardly be rare. And US houses can and often do have 220V supplies by connecting across both sides of the transformer that delivers the 110V. Often used for laundry equipment, just a big kettle really Link to post Share on other sites More sharing options...
Crosland Posted January 2, 2019 Share Posted January 2, 2019 Where I worked (admittedly now more than 20 years ago) moulded plugs were outlawed as the local safety regulations deemed them dangerous, so immediately any equipment arrived with a moulded plug it was cut off and replaced by a Crabtree, MK or other quality wire-on plug. SImilar experience. As an engineer I was even allowed to fit the plug myself Not even officially allowed to change a fuse now. Link to post Share on other sites More sharing options...
raymw Posted January 2, 2019 Share Posted January 2, 2019 Therefore it is rather illogical to be 'afraid' of electricity any more than it is to be 'afraid' of fire or bacteria. It is possibly safest for people to be afraid and therefore avoid what they do not understand. More so they should be afraid of things they think they understand. Be afraid, very afraid, is my advice to you and many others. Link to post Share on other sites More sharing options...
Crosland Posted January 2, 2019 Share Posted January 2, 2019 (edited) It takes just 50ma to stop a human heart I believe - and it doesn't matter whether the potential difference is 1V or 1000V (accepting that voltage dies have a role to play in other respects like 1VAC is unlikely to 'jump' to you where as 25KV will if you get too close), the key criteria is whether that 50ma passes across your heart muscles. You will not electrocute someone with 1V. Think ohms law again. See https://en.wikipedia.org/wiki/Extra-low_voltage for what is generally considered to be a safe voltage below which a lethal current cannot be established. Building sites used to use 110V power tools, but these were actually powered from a 55-0-55 V transformer so were safe as no part was ever more than 55 V above Earth potential. I seem to recall this has been relaxed to accomodate EU wrokers with 230V tools. Edited January 2, 2019 by Crosland Link to post Share on other sites More sharing options...
Nearholmer Posted January 2, 2019 Share Posted January 2, 2019 (edited) Crosland The flaw with applying Ohm’s Law to animals, us included, is that we aren’t nice, neat linear resistors. We are grubby, sweaty, bags of stuff saturated in salty water, so are prone to surface tracking, sudden change of bulk resistance at threshold voltages etc etc. This grisly topic was discussed in detail in another thread, where I think I might have cited the disturbing literature. Kevin Edited January 2, 2019 by Nearholmer Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted January 2, 2019 RMweb Premium Share Posted January 2, 2019 (edited) We (and indeed all other living mammals only exist due to electricity - its what makes or muscles contract and relax, what keeps the heart going and what powers our brains. Therefore it is rather illogical to be 'afraid' of electricity any more than it is to be 'afraid' of fire or bacteria. Context is everything..... Also technically a high voltage figure in itself does not necessarily always indicate a grater risk to life - its why we allow low level electric cattle fences or let children be fascinated by a Van de Graaff generator. It takes just 50ma to stop a human heart I believe - and it doesn't matter whether the potential difference is 1V or 1000V (accepting that voltage dies have a role to play in other respects like 1VAC is unlikely to 'jump' to you where as 25KV will if you get too close), the key criteria is whether that 50ma passes across your heart muscles. Just as well batteries don't put out AC then. At least none I've come across! All those billions of 1.5V batteries out there. As for the 9 volt ones (shudder)! I didn't say 'fear' in relation to electricity, my friend did. I did refer to respect! I think you're getting carried away, by bringing muscle control into the discussion. Maybe clutching at straws, because almost no one is agreeing with you. But on the subject of muscle control, this is very relevant - even if it does come from Wikipedia! A shock caused by low current that would normally be harmless could startle an individual and cause injury due to suddenly jerking away from the source of electricity, resulting in one striking a stationary object, dropping an object being held or falling. So yes, electricity can be dangerous, without actually being the direct cause of the injury or even death. https://en.wikipedia.org/wiki/Electrical_injury#Voltage-current_characteristic_of_skin Edited January 2, 2019 by kevinlms Link to post Share on other sites More sharing options...
raymw Posted January 2, 2019 Share Posted January 2, 2019 The snag, with this sort of topic, is that someone tries to give a quick answer, to a question that does not give enough detailed information. Others interpret the question in a different way, and criticize the the answer given. Others, who think they can answer, of course join in. Then the folk who can give an answer, realise the detail of the background, the ifs and buts, and find they need to write a fifteen page diatribe, at least, to cover all the aspects raised, and don't do so, they just mention the bits they think are most important. Then, something similar gets raised,,which in fact is entirely different, and so it goes. fwiw, ohm's law applies to all resistors. Link to post Share on other sites More sharing options...
raymw Posted January 2, 2019 Share Posted January 2, 2019 and, 1.5 volt button cells will kill a young human/animal, if swallowed. Not necessarily by causing direct heart defibrillation, though, afaik. Link to post Share on other sites More sharing options...
sharris Posted January 2, 2019 Share Posted January 2, 2019 So yes, electricity can be dangerous, without actually being the direct cause of the injury or even death. Without electricity nobody would be able to text and drive at the same time, so we could put those accidents down to electricity, or am I just confusing electricity with stupidity? Link to post Share on other sites More sharing options...
ejstubbs Posted January 2, 2019 Share Posted January 2, 2019 Our hobby involves a more sophisticated use of electricity than most so we do need to be properly aware of its dangers. I remember being quite shocked to discover from those refurbishing their layouts that both Peter Denny and Frank Dyer had mains voltage wiring mixed freely with the low voltage wiring under their respective layouts. I believe Frank Dyer was a professional electrician/electrical engineer but it's often the strongest swimmers who drown. I've seen similar things on exhibition layouts with integral 240V lighting. I still struggle a bit with the fact that submersible pond pumps and UV filter lamps commonly run off 230V mains supplies. We've just had a new pond put in, complete with a buried armoured cable that has two RCDs: one where the tap comes off the incoming mains, and one in the summerhouse next to the new pond. I did the final connection of the pump and the UV to the terminations provided by the sparky, and went through at least three cycles of checking what I'd done before committing any of it to the water and then switching everything on... You can get 12V pond pumps but they don't seem to be what's supplied as standard these days. I guess they do have a drawback of needing chunky cabling to support the high currents they draw for the same pump power. And modern RCDs do seem to be extremely effective so perhaps that explains why the balance has shifted. Plus, as you suggested, running mixed mains and low voltage circuits in close proximity could lead to mistaken assumptions about what voltage a particular circuit is being supplied at, with potential unfortunate consequences. Link to post Share on other sites More sharing options...
Nearholmer Posted January 2, 2019 Share Posted January 2, 2019 Ray Most do, but there are several varieties of sneaky ones, and a lot of natural, as opposed to man-made substances/objects have non-linear behaviours https://www.tutorialspoint.com/basic_electronics/basic_electronics_nonlinear_resistors.htm Kevin Link to post Share on other sites More sharing options...
RMweb Premium phil-b259 Posted January 2, 2019 RMweb Premium Share Posted January 2, 2019 and, 1.5 volt button cells will kill a young human/animal, if swallowed. Not necessarily by causing direct heart defibrillation, though, afaik. This is quite true - but somewhat irelent as a small Lego brick can also kill a young human / animal if swollowed. There is also the mater that some batteries contain pretty toxic chemicals and if these leak out (maybe because the child or animal chewed the battery before swolowing it) the. Death by poisoning is a possibility. Link to post Share on other sites More sharing options...
RMweb Premium phil-b259 Posted January 2, 2019 RMweb Premium Share Posted January 2, 2019 Without electricity nobody would be able to text and drive at the same time, so we could put those accidents down to electricity, or am I just confusing electricity with stupidity? No, but an individual is only able to drive or operate a mobile phone due to the electrical impulses being sent from the brain to the muscles. As with all such questions it depends on how pedantic or through you want to be. Link to post Share on other sites More sharing options...
RMweb Premium dhjgreen Posted January 2, 2019 RMweb Premium Share Posted January 2, 2019 This is quite true - but somewhat irelent as a small Lego brick can also kill a young human / animal if swollowed. There is also the mater that some batteries contain pretty toxic chemicals and if these leak out (maybe because the child or animal chewed the battery before swolowing it) the. Death by poisoning is a possibility. Much nastier than that. The child is killed by the electrolytic action of the cell eating through their stomach or other digestive organs; I will not post a picture, if you want to see it there are pictures if you search "swallow button cell". Link to post Share on other sites More sharing options...
AndyID Posted January 2, 2019 Share Posted January 2, 2019 Where did you find 120v in Spain? I first went in the '60s and it's always been 220v. Keith Balearics! Ibiza probably. Link to post Share on other sites More sharing options...
AndyID Posted January 2, 2019 Share Posted January 2, 2019 As with all such questions it depends on how pedantic or through you want to be. At the risk of being pedantic, don't you mean "thorough"? 1 1 Link to post Share on other sites More sharing options...
RMweb Premium jjb1970 Posted January 2, 2019 RMweb Premium Share Posted January 2, 2019 Without wanting to add to the debate on Ohms law (which others have already addressed more thoroughly than I would) I think the moulded plug issue is one that I've seen arise more than once, generally to raise question marks about their safety. Now for sure there is nothing at all wrong with a properly fitted non-moulded plug, the problem is that quite a lot do not appear to have been properly fitted. Yes I'm sure that there are badly made moulded plugs but I suspect that a statistical analysis would probably indicate that there was a greater chance of a badly fitted traditional plug than of getting an unsafe moulded one. All the ones I've had have been fine, and generally the stress relief on the cable inlet is more than adequate. Link to post Share on other sites More sharing options...
raymw Posted January 2, 2019 Share Posted January 2, 2019 At any instant for any resistor, ohm's law applies. Nothing to do with non-linear behavior of the resistor. It's easy enough to make a resistor that appears to be different, but you will find that at any time, the resistance, current and voltage comply with ohm's law. Obviously, if one was to measure the voltage today, and the current tomorrow, you would be unlikely to get the same resistance value cf measuring both at the same time. In the same way, a non linear resistor, e.g. a diode, will by definition within ohm's law, have a resistance based on the voltage applied and the resultant current. Of course the resistance can/will vary if the voltage and/or current varies, but at any instant ohm's law applies. Link to post Share on other sites More sharing options...
Nearholmer Posted January 2, 2019 Share Posted January 2, 2019 (edited) Yes, I've seen varied and exotic ways of mucking-up the fitting of a "proper" plug. My brother, generally a pretty clever chap, and a headmaster by trade, having produced one of the "best"; he had stripped the cores of insulation waaaay too far back, which eventually led to a rather spectacular blowing-apart of the plug, the incident being materially aided by the ancient fuses still in use in his house at the time. Years ago, when I lived in a flat, the woman opposite called me across in a terrible fluster, the plug on her hoover having just done something similar; her husband had fitted it, and it was hard to tell from the blackened remnants exactly what had gone wrong, but something had, because it created a major scorch-mark above the socket. On balance? Factories probably do a better job than amateurs, but even they screw it up sometimes. Ray - yes, true, at any instant, but not understanding that something is non-linear will truly thwart circuit analysis/calculation. Edited January 2, 2019 by Nearholmer 2 Link to post Share on other sites More sharing options...
Recommended Posts