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Bridge Failures ...
When a diode power bridge - discrete devices or four-legged package - fails,
it's almost invariably one diode in the 'negative' arm which goes short circuit. Any thoughts on why this should be, rather than any one of the four failing at random ? Arfa |
Bridge Failures ...
Arfa Daily wrote: When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. No it isn't. Any thoughts on why this should be, rather than any one of the four failing at random ? Your observation is obviously flawed. All the diodes pass the same current. By chance you've simply experienced a statistically anomalous percentage of such failures. Graahm |
Bridge Failures ...
"Eeyore" wrote in message ... Arfa Daily wrote: When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. No it isn't. Any thoughts on why this should be, rather than any one of the four failing at random ? Your observation is obviously flawed. All the diodes pass the same current. By chance you've simply experienced a statistically anomalous percentage of such failures. Graahm Oh, sorry. I must be more stupid than I thought then. Do you honestly think that if I had not genuinely observed this, that I would be taking the trouble to post the question ? Sometimes, Graham (how long have you not been able to spell your own name BTW ? ) you can be a real contentious prat. Arfa |
Bridge Failures ...
Arfa Daily wrote: "Eeyore" wrote Arfa Daily wrote: When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. No it isn't. Any thoughts on why this should be, rather than any one of the four failing at random ? Your observation is obviously flawed. All the diodes pass the same current. By chance you've simply experienced a statistically anomalous percentage of such failures. Oh, sorry. I must be more stupid than I thought then. Do you honestly think that if I had not genuinely observed this, that I would be taking the trouble to post the question ? Sometimes, Graham (how long have you not been able to spell your own name BTW ? ) you can be a real contentious prat. And what makes you so sure you haven't just experienced a statistical anomaly ? I mean, you'd have to believe in black magic or voodoo / whatever otherwise. There's certainly no possible scientific explanation. What amazes me as much as anything is that you'd keep a record of this ! Graham |
Bridge Failures ...
On Sep 18, 6:47 am, Eeyore
wrote: Arfa Daily wrote: "Eeyore" wrote Arfa Daily wrote: When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. No it isn't. Any thoughts on why this should be, rather than any one of the four failing at random ? Your observation is obviously flawed. All the diodes pass the same current. By chance you've simply experienced a statistically anomalous percentage of such failures. Oh, sorry. I must be more stupid than I thought then. Do you honestly think that if I had not genuinely observed this, that I would be taking the trouble to post the question ? Sometimes, Graham (how long have you not been able to spell your own name BTW ? ) you can be a real contentious prat. And what makes you so sure you haven't just experienced a statistical anomaly ? I mean, you'd have to believe in black magic or voodoo / whatever otherwise. There's certainly no possible scientific explanation. What amazes me as much as anything is that you'd keep a record of this ! Graham- Hide quoted text - - Show quoted text - Graham: You obviously don't know very nmuch about electronic componentgs and circuits. It is very possible that there are components that are associated with the bridge, either on the input or output side, that are not completely symmetrical and that might lead to Arfa's observations. I can think of several components, such as small value bypass capacitors, bleed resistors, that are not cymmetrical, and that could have an effect, especially during surge events. Look at any TV schematic and you should be able to find these components. Don't dismiss someone else's observations with such disdain when you don't have firm evidence that you are 100% correct. I have been doing electronics servicing for 50 years, from vacuum tubes to IC's, and there are many strange things that I have seen, but closer investigation has usually allowed me to figure out what the likely cause was, sometimes not at all what things seemed to be at first glance. H. R. Hofmann |
Bridge Failures ...
"Eeyore" wrote in message ... Arfa Daily wrote: "Eeyore" wrote Arfa Daily wrote: When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. No it isn't. Any thoughts on why this should be, rather than any one of the four failing at random ? Your observation is obviously flawed. All the diodes pass the same current. By chance you've simply experienced a statistically anomalous percentage of such failures. Oh, sorry. I must be more stupid than I thought then. Do you honestly think that if I had not genuinely observed this, that I would be taking the trouble to post the question ? Sometimes, Graham (how long have you not been able to spell your own name BTW ? ) you can be a real contentious prat. And what makes you so sure you haven't just experienced a statistical anomaly ? I mean, you'd have to believe in black magic or voodoo / whatever otherwise. There's certainly no possible scientific explanation. What amazes me as much as anything is that you'd keep a record of this ! Graham Well, all right then. Just *what* qualifies *you* to tell *me* that I'm wrong ? I have probably changed more bridge rectifiers in the 35 years that I've been repairing stuff for a living, than you have ever even seen. Do you think that you are teaching me something by coming out with 'big' words like "statistical" and "anomaly" ? And what qualifies *you* to be so certain that there is "no possible scientific explanation" ? Explain why it's always the neutral terminal screw that comes loose in a plugtop, for instance. Same current flows in both pins. I don't "keep a record" of this. If you knew the first thing about the practical world of service, instead of just pretending that you do all the time, you would know that this is just the sort of thing that sticks in a proper service engineer's head. As it happens, the reason that I brought it up was that a colleague of mine, just last week, made the comment to me, and I agreed with him. Then, this morning, the very first job on the bench, had a faulty bridge in it, and what d'ya know - it's one of the diodes in the negative arm again that's short circuit. Whilst the magnitude of the current in all diodes is theoretically the same - and even that might not be quite true if there is any residual DC magnetism in the core of the transformer - the current which flows in the diodes in the negative arm, flows in the opposite direction to that in the positive arm. Also, the arse end of the diodes in the negative arm, typically go to the chassis mass, which may well be tied to power ground (mains earth) so I think that there might very well be a "possible scientific explanation". Anyone with a better understanding of the real world than Graham care to comment ? Arfa |
Bridge Failures ...
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Bridge Failures ...
Arfa Daily wrote: Explain why it's always the neutral terminal screw that comes loose in a plugtop, for instance. Is it ? Is this a 'well known fact' or something ? Are you actually serious ? Graham |
Bridge Failures ...
Arfa Daily wrote: Whilst the magnitude of the current in all diodes is theoretically the same It IS the same. - and even that might not be quite true if there is any residual DC magnetism in the core of the transformer Any residual magnetism won't affect the load current one tiny bit. - the current which flows in the diodes in the negative arm, flows in the opposite direction to that in the positive arm. So what ? Also, the arse end of the diodes in the negative arm, typically go to the chassis mass, which may well be tied to power ground (mains earth) so I think that there might very well be a "possible scientific explanation". No, that would be voodoo thinking. Check out Kirchoff's Laws. Graham |
Bridge Failures ...
Arfa Daily wrote:
When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. Any thoughts on why this should be, rather than any one of the four failing at random ? An interesting observation; some thoughtful speculation and perhaps a few experiments may be useful. 1. perhaps the dominant failure mode in some equipment happens on the negative half cycle of input power, especially in switching applications. 2. perhaps in some areas, power line glitches occur more often on the negative half cycle. 3. perhaps the devices are manufactured with a deviation of thermal characteristics in the region of the negative arm making them more prone to failure there. It would make an interesting science project for a student to accumulate a number of encapsulated bridge rectifiers (I'll leave it to others to outline the statistics) and build a shorting fixture that randomly shorts the device (in a symmetrical fashion, making sure that it is not synchronized with the power line) and run the experiment. If the anomaly is verified, then deeper investigation is in order such as microscopic examination of intact good devices and post mortems on bad ones. What with the _vast_ amount of trashed electronics these days, it shouldn't be difficult to accumulate hundreds of rectifiers for the endeavor. Also a 'net search on "bridge rectifier" "failure modes" may turn up something. Regards, Michael |
Bridge Failures ...
Arfa Daily wrote:
Explain why it's always the neutral terminal screw that comes loose in a plugtop, for instance. Same current flows in both pins. I'd say the reason is mechanical. The neutral pin shakes about by the action of the (UK) plug being placed in / removed from the socket. This pin probably shakes about more than the earth pin, as the user is more careful to locate that pin first before slamming the rest in. The Live connection is at the other side of the fuseholder which takes up some of the movement energy. -- Adrian C |
Bridge Failures ...
"Eeyore" wrote in message ... Arfa Daily wrote: Explain why it's always the neutral terminal screw that comes loose in a plugtop, for instance. Is it ? Is this a 'well known fact' or something ? Are you actually serious ? Graham Deadly. I check the mains plug on every bit of kit that comes across my bench, and in at least 50% of cases, one terminal screw will be loose, and that is *almost* invariably the neutral one. There has been discussion about this in trade magazines, so amongst proper service engineers, it would seem to be well known. Arfa |
Bridge Failures ...
Arfa Daily wrote in message
... "Eeyore" wrote in message ... Arfa Daily wrote: Explain why it's always the neutral terminal screw that comes loose in a plugtop, for instance. Is it ? Is this a 'well known fact' or something ? Are you actually serious ? Graham Deadly. I check the mains plug on every bit of kit that comes across my bench, and in at least 50% of cases, one terminal screw will be loose, and that is *almost* invariably the neutral one. There has been discussion about this in trade magazines, so amongst proper service engineers, it would seem to be well known. Arfa There's a simple explanation for that one. The neutral retaining screw is connected to the prong that goes in and out of socket each time and vibrated each time. The live one is decoupled from a lot of that vibration by the fuse. But why do christmas tree lights always fail to light when reused the next year but were fine before packing away, at least one bulb is always loosened over that 11 months. ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
Bridge Failures ...
Arfa Daily wrote: "Eeyore" wrote Arfa Daily wrote: Explain why it's always the neutral terminal screw that comes loose in a plugtop, for instance. Is it ? Is this a 'well known fact' or something ? Are you actually serious ? Deadly. I check the mains plug on every bit of kit that comes across my bench, and in at least 50% of cases, one terminal screw will be loose, and that is *almost* invariably the neutral one. There has been discussion about this in trade magazines, so amongst proper service engineers, it would seem to be well known. Adrian C's explanation sounds quite convincing. Graham |
Bridge Failures ...
Arfa Daily wrote: Ah, so "statistical anomalies" *are* a scientific reason now then. I thought you said 5 minutes ago that "There's certainly no possible scientific explanation". Make your mind up. Statistical anomalies are simply a fact of life. It's why if you toss a coin 100 times, it's no freak if it comes up heads 75 times and tails 25 times for sake of argument.. Graham |
Bridge Failures ...
N Cook wrote:
But why do christmas tree lights always fail to light when reused the next year but were fine before packing away, at least one bulb is always loosened over that 11 months. ? Vibration.... It is a sad ;-( moment when the feast of Christmas has finished, so the lights are gently, carefully and slowly placed into the original wrapping (cardboard cutouts to hold each lamp are a bit fiddly to do in a rush). When the time comes to have them out again - bash, crash, wallop, ping.... -- Adrian C |
Bridge Failures ...
Arfa Daily wrote:
When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. Any thoughts on why this should be, rather than any one of the four failing at random ? Arfa Maybe the same reason that it`s always the negative wire from a battery pack that corrodes away? Ron(UK) |
Bridge Failures ...
Arfa Daily wrote:
When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. Any thoughts on why this should be, rather than any one of the four failing at random ? Arfa Ok Arfa, I think now that I have posted physical theories to the last two (plugtop; xmas light) I might have a similar *physical* answer to the diode anomaly. Sinking away heat from the diode PN junction is more efficient with a large amount of ground plane to connect to which is the case with the negative half of the bridge. These diodes will run with a higher Vf and hence a higher power dissipation than the remaining diodes on the bridge given that both positive and negative halves will be conducting the same current. Where fault conditions exist on the DC side of the circuit, these harder running diodes may be the first to fail? Dunno. On the other hand, I tried looking for conditions for thermal runaway in bridge rectifier diodes and came up with the following link http://www.freepatentsonline.com/6731030.html but can't say from that which half of the bridge would be suceptable to shorted failure. -- Adrian C |
Bridge Failures ...
"Eeyore" wrote in message ... Arfa Daily wrote: "Eeyore" wrote Arfa Daily wrote: Explain why it's always the neutral terminal screw that comes loose in a plugtop, for instance. Is it ? Is this a 'well known fact' or something ? Are you actually serious ? Deadly. I check the mains plug on every bit of kit that comes across my bench, and in at least 50% of cases, one terminal screw will be loose, and that is *almost* invariably the neutral one. There has been discussion about this in trade magazines, so amongst proper service engineers, it would seem to be well known. Adrian C's explanation sounds quite convincing. Graham I think it was actually Mr Cook who ventured the detailed explanation, with Adrian's being just "vibration", but yes, it does indeed seem reasonable. So you see, with a bit of thought, not everything is as black and white as you suppose. Before seing an explanation that appealed to you as a possibility, you had already started to rubbish me on that one too ... Arfa |
Bridge Failures ...
One wild guess-- the negative side diodes are likely to be better heat-
sunk by their chassis side leads. That means there is a larger temperature drop across the diode, perhaps leading to more stress on the junction. The positive side diodes are more likely to be nice and warm, about equally on both sides of the junction. |
Bridge Failures ...
Adrian C wrote: Arfa Daily wrote: When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. Any thoughts on why this should be, rather than any one of the four failing at random ? I think now that I have posted physical theories to the last two (plugtop; xmas light) I might have a similar *physical* answer to the diode anomaly. Sinking away heat from the diode PN junction is more efficient with a large amount of ground plane to connect to which is the case with the negative half of the bridge. These diodes will run with a higher Vf and hence a higher power dissipation than the remaining diodes on the bridge given that both positive and negative halves will be conducting the same current. Where fault conditions exist on the DC side of the circuit, these harder running diodes may be the first to fail? I can blow that one away instantly. If there is a larger amount of pcb foil, it'll help cool those 2 diodes. Since they fail from over heating, that would suggest the positive diodes ought to fail first. Graham |
Bridge Failures ...
In article ,
msg wrote: Arfa Daily wrote: When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. Any thoughts on why this should be, rather than any one of the four failing at random ? An interesting observation; some thoughtful speculation and perhaps a few experiments may be useful. 1. perhaps the dominant failure mode in some equipment happens on the negative half cycle of input power, especially in switching applications. Doubtful for switchmode power supplies, as the switching regulator generally operates asynchronously to the line frequency. Possible for other switching control methods (e.g. triac or SCR phase control circuits), but most applications of those don't tend to involve bridge rectifiers. 2. perhaps in some areas, power line glitches occur more often on the negative half cycle. That's very unlikely to be the case in the USA, where the two halves of the usual 110/220 residential power feed are at 180 degree phase angles to each other. Half of the devices in any average house would see a positive glitch, and half a negative glitch, of approximately the same magnitude and form. Things may be different in e.g. the UK where the typical household power supply isn't composed of two out-of-phase legs. Are the secondaries of UK power distribution transformers center-tapped 440V windings, with different houses getting opposite phases, or just a single 220V winding? 3. perhaps the devices are manufactured with a deviation of thermal characteristics in the region of the negative arm making them more prone to failure there. Possible. It would be helpful to determine just what the usual failure modes are. If the initial event causing the destruction of the rectifier is a voltage spike, it implies that sudden spikes on the anode are better handled than sudden spikes on the cathode of the rectifier, the other leg being held (very roughly speaking) at a constant voltage. I'm not sure of a good reason why that would be, but I guess it's not really surprising that an asymmetric component behaves asymmetrically when subjected to unusual stresses. An interesting question indeed. -- Andrew Erickson "He is no fool who gives what he cannot keep to gain that which he cannot lose." -- Jim Elliot |
Bridge Failures ...
Andrew Erickson wrote: Are the secondaries of UK power distribution transformers center-tapped 440V windings, with different houses getting opposite phases, or just a single 220V winding? 230V actually and quite often still 240V which is what is was in the first place before Brussels decided it had to change for harmonisation reasons.. The 230V supply is actually a single phase of a 415V ? 3 phase supply. I believe that the houses in a street are connected to the phases sequentially so the first property will be on 'red' phase, the next on 'blue', then 'yellow' them back to red again and so on. Graham |
Bridge Failures ...
"Andrew Erickson" wrote in message ... In article , msg wrote: Arfa Daily wrote: When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. Any thoughts on why this should be, rather than any one of the four failing at random ? An interesting observation; some thoughtful speculation and perhaps a few experiments may be useful. 1. perhaps the dominant failure mode in some equipment happens on the negative half cycle of input power, especially in switching applications. Doubtful for switchmode power supplies, as the switching regulator generally operates asynchronously to the line frequency. Possible for other switching control methods (e.g. triac or SCR phase control circuits), but most applications of those don't tend to involve bridge rectifiers. 2. perhaps in some areas, power line glitches occur more often on the negative half cycle. That's very unlikely to be the case in the USA, where the two halves of the usual 110/220 residential power feed are at 180 degree phase angles to each other. Half of the devices in any average house would see a positive glitch, and half a negative glitch, of approximately the same magnitude and form. Things may be different in e.g. the UK where the typical household power supply isn't composed of two out-of-phase legs. Are the secondaries of UK power distribution transformers center-tapped 440V windings, with different houses getting opposite phases, or just a single 220V winding? 3. perhaps the devices are manufactured with a deviation of thermal characteristics in the region of the negative arm making them more prone to failure there. Possible. It would be helpful to determine just what the usual failure modes are. If the initial event causing the destruction of the rectifier is a voltage spike, it implies that sudden spikes on the anode are better handled than sudden spikes on the cathode of the rectifier, the other leg being held (very roughly speaking) at a constant voltage. I'm not sure of a good reason why that would be, but I guess it's not really surprising that an asymmetric component behaves asymmetrically when subjected to unusual stresses. An interesting question indeed. -- Andrew Erickson Some interesting thoughts from you and Michael. About the only thing that I would say is that it seems to be an 'in use' problem of the reccies, rather than something caused by a downstream failure of another component. I don't think that I can actually remember ever having a bridge failure - discrete diode or integrated 4-pin - that had occured in tandem with some other problem. If a discrete diode bridge has a single diode that's failed, and there are caps across the diodes, I always replace these as a matter of course though, just in case, as well as the other three diodes. One particular commercial board that I work on, has a perfectly conventional transformer - bridge - resevoir setup, although the cap is separated from the positive terminal of the bridge by a further diode, leaving a large ripple at that terminal, which is scaled and then goes off to a micro on the machine control board, presumably as some kind of sync or zero crossing signal. The bridge is perfectly well rated for the job in hand, although it does run quite hot. I repair around 25 of these boards a week, and I would say that I replace at least one bridge a month. The problem is always a short circuit diode in the bridge, and I can't remember the last time, if ever, that it was one of the pair in the positive arm, so that's how common it seems to be in this particular piece of equipment. Remember also, that this question was brought up by my colleague, completely unsolicited by me, and he works mainly on all types of TV set - CRT, back projection, plasma and LCD, and also VCRs, so if he has experienced a similar situation on the equipment that he works on, you would have to say that my board is tending to be a rule rather than an exception. The board in question does drive some DC motors with brushgear, so sparks abound, particularly when there is a problem with them, or they are overloaded by incorrect customer cleaning of the mechanical component that they drive, so either of those factors could have a hand in the bridge failing in the first place, but still interesting as to why it always seems to be the negative arm that fails. Arfa |
Bridge Failures ...
On Sep 18, 7:04 pm, "Arfa Daily" wrote:
"Andrew Erickson" wrote in message ... In article , msg wrote: Arfa Daily wrote: When a diode power bridge - discrete devices or four-legged package - fails, it's almost invariably one diode in the 'negative' arm which goes short circuit. Any thoughts on why this should be, rather than any one of the four failing at random ? An interesting observation; some thoughtful speculation and perhaps a few experiments may be useful. 1. perhaps the dominant failure mode in some equipment happens on the negative half cycle of input power, especially in switching applications. Doubtful for switchmode power supplies, as the switching regulator generally operates asynchronously to the line frequency. Possible for other switching control methods (e.g. triac or SCR phase control circuits), but most applications of those don't tend to involve bridge rectifiers. 2. perhaps in some areas, power line glitches occur more often on the negative half cycle. That's very unlikely to be the case in the USA, where the two halves of the usual 110/220 residential power feed are at 180 degree phase angles to each other. Half of the devices in any average house would see a positive glitch, and half a negative glitch, of approximately the same magnitude and form. Things may be different in e.g. the UK where the typical household power supply isn't composed of two out-of-phase legs. Are the secondaries of UK power distribution transformers center-tapped 440V windings, with different houses getting opposite phases, or just a single 220V winding? 3. perhaps the devices are manufactured with a deviation of thermal characteristics in the region of the negative arm making them more prone to failure there. Possible. It would be helpful to determine just what the usual failure modes are. If the initial event causing the destruction of the rectifier is a voltage spike, it implies that sudden spikes on the anode are better handled than sudden spikes on the cathode of the rectifier, the other leg being held (very roughly speaking) at a constant voltage. I'm not sure of a good reason why that would be, but I guess it's not really surprising that an asymmetric component behaves asymmetrically when subjected to unusual stresses. An interesting question indeed. -- Andrew Erickson Some interesting thoughts from you and Michael. About the only thing that I would say is that it seems to be an 'in use' problem of the reccies, rather than something caused by a downstream failure of another component. I don't think that I can actually remember ever having a bridge failure - discrete diode or integrated 4-pin - that had occured in tandem with some other problem. If a discrete diode bridge has a single diode that's failed, and there are caps across the diodes, I always replace these as a matter of course though, just in case, as well as the other three diodes. One particular commercial board that I work on, has a perfectly conventional transformer - bridge - resevoir setup, although the cap is separated from the positive terminal of the bridge by a further diode, leaving a large ripple at that terminal, which is scaled and then goes off to a micro on the machine control board, presumably as some kind of sync or zero crossing signal. The bridge is perfectly well rated for the job in hand, although it does run quite hot. I repair around 25 of these boards a week, and I would say that I replace at least one bridge a month. The problem is always a short circuit diode in the bridge, and I can't remember the last time, if ever, that it was one of the pair in the positive arm, so that's how common it seems to be in this particular piece of equipment. Remember also, that this question was brought up by my colleague, completely unsolicited by me, and he works mainly on all types of TV set - CRT, back projection, plasma and LCD, and also VCRs, so if he has experienced a similar situation on the equipment that he works on, you would have to say that my board is tending to be a rule rather than an exception. The board in question does drive some DC motors with brushgear, so sparks abound, particularly when there is a problem with them, or they are overloaded by incorrect customer cleaning of the mechanical component that they drive, so either of those factors could have a hand in the bridge failing in the first place, but still interesting as to why it always seems to be the negative arm that fails. Arfa- Hide quoted text - - Show quoted text - It seems like Graham's been pretty well subdued by most of the commenters who see a reasonable number of reasons why one diodes on one side of the bridge might fail more often. Not that it couldn't be a statistical anomaly, but there are other possibilities too, and I hope Graham now understands his trashing response was out of line. We need helpful comments, not trashing ones. H. R. Hofmann |
Bridge Failures ...
On Sep 18, 3:44 pm, Eeyore
wrote: Andrew Erickson wrote: Are the secondaries of UK power distribution transformers center- tapped 440V windings, with different houses getting opposite phases, or just a single 220V winding? 230V actually and quite often still 240V which is what is was in the first place before Brussels decided it had to change for harmonisation reasons.. The 230V supply is actually a single phase of a 415V ? 3 phase supply. I believe that the houses in a street are connected to the phases sequentially so the first property will be on 'red' phase, the next on 'blue', then 'yellow' them back to red again and so on. Graham So every residence gets its _own_ pole pig? Where I live in southern Cal, there are many houses on 1 phase and 10 houses share a pole pig. GG |
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On Tue, 18 Sep 2007 14:56:02 +0100, Eeyore
wrote: "hr(bob) " wrote: Graham: You obviously don't know very nmuch about electronic componentgs and circuits. It must be my imagination that I'm an electronics design consultant in that case ! --- Truer words were never spoken! -- JF |
Bridge Failures ...
Arfa Daily wrote:
Oh, sorry. I must be more stupid than I thought then. Do you honestly think that if I had not genuinely observed this, that I would be taking the trouble to post the question ? Sometimes, Graham (how long have you not been able to spell your own name BTW ? ) you can be a real contentious prat. Only on his good days. If you tell him the sky is blue, he'll insist that it's orange. :( -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
Bridge Failures ...
John Fields wrote:
On Tue, 18 Sep 2007 14:56:02 +0100, Eeyore wrote: "hr(bob) " wrote: Graham: You obviously don't know very nmuch about electronic componentgs and circuits. It must be my imagination that I'm an electronics design consultant in that case ! Even a donkey slips up and gets something right, once in a blue moon. -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
Bridge Failures ...
N Cook wrote:
There's a simple explanation for that one. The neutral retaining screw is connected to the prong that goes in and out of socket each time and vibrated each time. The live one is decoupled from a lot of that vibration by the fuse. But why do christmas tree lights always fail to light when reused the next year but were fine before packing away, at least one bulb is always loosened over that 11 months. ? Planned obsolecence. Most people are too lazy to find a bad bulb, so they get to sell a new string. ;-) -- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida |
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