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getting bit by my FT-101EE chassis
All,
I don't know if I am grounding my station correctly. The radials of my 20m vertical are connected to my trailer's electrical system ground rod. My coax shield is connected both to the radials and the ground rod. I plug my antenna into the Yaesu and turn it on. I can hear stations just fine, and I have no problems touching the chassis. However, the instant I disconnected the antenna but hang onto the coax, I got a mild shock on both arms if I should momentarily touch the chassis of the Yaesu. So, I understand I have a problem. Now I noticed that the Yaesu uses a 2-prong AC cord adapter, which is "before code" and therefore is unsafe by today's standards. If I rewrire the AC cord to 3-prong, should that remove the hazard? If so, what pinout do I use? The FT-101 Shop service manual does not list where positive, negative, and neutral should be on the Yaesu power plug.in Figure 1-2. Thanks, The Eternal Squire P.S. I hope I have not long-term defibrillated myself. Should I visit a hospital for cardiac system damage even if the shock was mild? I now realize that I probably could have been killed. Right now I have everything unplugged and disconnected until I can get better advice. |
getting bit by my FT-101EE chassis
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getting bit by my FT-101EE chassis
wrote:
I don't know if I am grounding my station correctly. The radials of my 20m vertical are connected to my trailer's electrical system ground rod. My coax shield is connected both to the radials and the ground rod. I plug my antenna into the Yaesu and turn it on. I can hear stations just fine, and I have no problems touching the chassis. However, the instant I disconnected the antenna but hang onto the coax, I got a mild shock on both arms if I should momentarily touch the chassis of the Yaesu. So, I understand I have a problem. So, DON'T DO THAT. Now I noticed that the Yaesu uses a 2-prong AC cord adapter, which is "before code" and therefore is unsafe by today's standards. If I rewrire the AC cord to 3-prong, should that remove the hazard? If so, what pinout do I use? The FT-101 Shop service manual does not list where positive, negative, and neutral should be on the Yaesu power plug.in Figure 1-2. A three-prong plug will make the radio safe, but in fact as long as the radio is plugged into the antenna, it's already safely grounded by the anntena system. A three-prong plug will make it meet code, though. BUT, the real problem is that you have current leaking to chassis, and your chassis has become hot. Look for an AC line filter or some ceramic disc capacitors between the AC line and the chassis, used to keep RF out of the power line (and out of the radio). It will be leaky. Replace it, even if you think it's good. P.S. I hope I have not long-term defibrillated myself. Should I visit a hospital for cardiac system damage even if the shock was mild? I now realize that I probably could have been killed. Right now I have everything unplugged and disconnected until I can get better advice. Keep your left hand in your pocket next time. The thing about electrical injuries is that there is really nothing doctors can do. When there is damage due to electrical power, cells become elongated and the cell membranes break down. As this process continues, the cell membranes break, the resistance of the tissue drops, and more and more current flows. All the doctors can see is the surface burn, they can't tell how bad the tissue damage is. So even in the case of very serious electrical injury, the normal procedure is basically to wait and see how much tissue dies. RF burns really terrify doctors, because they look like serious electrical burns but have little or no actual tissue damage (due to skin effect). So they look a lot worse than they really are. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
getting bit by my FT-101EE chassis
wrote in message ups.com... All, I If the radio has bypass caps on the line to chassis, and many do, you can develop sixty or so volts AC from chassis to ground because the two caps form a voltage divider. Measure the DC resistance between each of the power lugs to the chassis, you should see infinite resistance. Don't relay on the coax shell to provide a safety ground, you're only going to end up getting knocked on your butt repeatedly when working on the rig. The best bet is a three wire cord with safety ground. Pete |
getting bit by my FT-101EE chassis
This is indeed the case for the FT-101E whose schematic I just
examined. What I did was remove the 2-wire cord, and then connect a 3-wire cord where plus and minus hot were in former locations, then soldered the neutral wire of the cord to the plug's ground pin. Hope that would work. The voltage divider effect bears out in the fact that my original exposure to the AC was not immediately fatal. I think from now on, I should NEVER operate a rig powered by a 2 wire cord.... I should always replace with 3-wire on general principles. The Eternal Squire |
getting bit by my FT-101EE chassis
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getting bit by my FT-101EE chassis
I believe the important thing here is that a three wire plug be used and
that it gets wired correctly. I will never see why the neutral which is grounded and green wire which is ground cannot be tied together. The key here is that the plug can not get reversed like it could with the two wire plug so getting hot AC on the chassis can never happen. If the socket is miswired than as soon as you plug in your radio with the green and neutral tied together your main fuse will blow. I sure would like to know what certain wiring failure modes could energize the chassis ? Ground is Ground period. If the original two wire plug would have been polarized in the very beginning I expect that three wire plug would have never happened. Chuck Harris wrote: wrote: This is indeed the case for the FT-101E whose schematic I just examined. What I did was remove the 2-wire cord, and then connect a 3-wire cord where plus and minus hot were in former locations, then soldered the neutral wire of the cord to the plug's ground pin. Hope that would work. The voltage divider effect bears out in the fact that my original exposure to the AC was not immediately fatal. I think from now on, I should NEVER operate a rig powered by a 2 wire cord.... I should always replace with 3-wire on general principles. The Eternal Squire NO! Don't do that! The hot goes to the + hot, and the neutral goes to the - hot, and the green wire goes to the chassis. Never, never, never connect the neutral and the green wire together! (Did I mention never?) The only place in the whole house where that is supposed to happen is in the service panel where the power comes into the house. Everywhere else, it must remain separate. The bond wire (green) is purely for safety. It saves your butt when currents accidentally leak out to the chassis. If you have the bond connected to the neutral side of the powerline, it can energize the chassis in certain wiring failure modes. Please don't leave it that way, save some poor soul's bacon, and go back and fix it correctly. Thanks, -Chuck |
getting bit by my FT-101EE chassis
I believe the important thing here is that a three wire plug be used and
that it gets wired correctly. I will never see why the neutral which is grounded and green wire which is ground cannot be tied together. The key here is that the plug can not get reversed like it could with the two wire plug so getting hot AC on the chassis can never happen. If the socket is miswired than as soon as you plug in your radio with the green and neutral tied together your main fuse will blow. I sure would like to know what certain wiring failure modes could energize the chassis ? Ground is Ground period. If the original two wire plug would have been polarized in the very beginning I expect that three wire plug would have never happened. Chuck Harris wrote: wrote: This is indeed the case for the FT-101E whose schematic I just examined. What I did was remove the 2-wire cord, and then connect a 3-wire cord where plus and minus hot were in former locations, then soldered the neutral wire of the cord to the plug's ground pin. Hope that would work. The voltage divider effect bears out in the fact that my original exposure to the AC was not immediately fatal. I think from now on, I should NEVER operate a rig powered by a 2 wire cord.... I should always replace with 3-wire on general principles. The Eternal Squire NO! Don't do that! The hot goes to the + hot, and the neutral goes to the - hot, and the green wire goes to the chassis. Never, never, never connect the neutral and the green wire together! (Did I mention never?) The only place in the whole house where that is supposed to happen is in the service panel where the power comes into the house. Everywhere else, it must remain separate. The bond wire (green) is purely for safety. It saves your butt when currents accidentally leak out to the chassis. If you have the bond connected to the neutral side of the powerline, it can energize the chassis in certain wiring failure modes. Please don't leave it that way, save some poor soul's bacon, and go back and fix it correctly. Thanks, -Chuck |
getting bit by my FT-101EE chassis
Ron wrote:
and neutral tied together your main fuse will blow. I sure would like to know what certain wiring failure modes could energize the chassis ? Ground is Ground period. No, not really. You're thinking like an electrician saying the chassis is energized. That can happen too in a failure mode but the original poster's gist was that he got that normal low ma bite that one gets when one creates different ground points as opposed to a common ground. The answer here is to tie the grounds together as short as possible. Of course the OP is going to get a tingle when his rig is 'grounded' only via the AC with inherent leakage of caps/yadda/yadda versus his external antenna/trailer ground. Thats normal. Sorry to belabour but this has been addressed in most every electronic publication since electricity was 'invented'. I could ground all my stuff to the hilt but you would have to pay me to pound a separate ground rod and lick my fingers and put my hand between the rig and the new rod. Ground ISNT ground unless they are at the same potential. If OP wants a no-bite situation he should visualize the ground path via his coax versus the radio ground via the trailer AC wiring. Until the two are essentially the same a difference in potential exists. -Bill |
getting bit by my FT-101EE chassis
On Wed, 30 Nov 2005 18:18:48 -0500, " Uncle Peter"
wrote: wrote in message oups.com... All, I If the radio has bypass caps on the line to chassis, and many do, you can develop sixty or so volts AC from chassis to ground because the two caps form a voltage divider. Measure the DC resistance between each of the power lugs to the chassis, you should see infinite resistance. Don't relay on the coax shell to provide a safety ground, you're only going to end up getting knocked on your butt repeatedly when working on the rig. The best bet is a three wire cord with safety ground. Yup, as I said when in the earlier post where my FT101B tried to kill me with a bare copper wire tied to a ground rod. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com Pete Roger |
getting bit by my FT-101EE chassis
Ron wrote:
I believe the important thing here is that a three wire plug be used and that it gets wired correctly. I will never see why the neutral which is grounded and green wire which is ground cannot be tied together. The key here is that the plug can not get reversed like it could with the two wire plug so getting hot AC on the chassis can never happen. If the socket is miswired than as soon as you plug in your radio with the green and neutral tied together your main fuse will blow. I sure would like to know what certain wiring failure modes could energize the chassis ? Ground is Ground period. If the original two wire plug would have been polarized in the very beginning I expect that three wire plug would have never happened. Hi Ron, You are thinking like a newbie engineer... you haven't yet discovered multiple failures, and mistakes. If nothing fails, you are right, there is no harm in tieing the safety ground and neutral together. But let's first discuss the purpose of the safety ground: It is there to make it very unlikely that the cases of appliances could ever become elevated above earth ground. This is to protect a barefooted doofus from getting electrocuted when he is standing on the cement floor in the basement, and trys to operate his FT-101E. The *secondary* purpose of the safety ground is to provide a return that will blow the circuit breaker if the hot lead accidentally becomes shorted to the case of the FT-101E. The way the safety ground provides these protections is by being connected to the centertap of the pole pig (neutral), and to a grounding rod that sticks into the earth at the house. This connection is done at the service panel where power service enters the house. The grounding rod is there to make sure that the safety ground, and thus the cases of the appliances, stays at the same potential as the cement floor in your basement. Back in the old 2 wire days, when the neutral side of the plug wire was connected to the chassis, and you were expected to turn the plug around until it didn't tingle, if the cord's neutral wire broke, current would pass through the appliance's circuitry to the chassis connection, and as a result the chassis would become hot relative to the earth ground (Doofus's feet on the concrete slab). Doofus would be pushing up daisies. Let's move forward to the days of the 3 wire plug, and the safety ground... Saint Chuck has wired Doofus's FT101E so that the hot lead goes to Hot+, and the neutral lead goes to Hot-, and the safety ground lead goes to the chassis: Doofus, likes to unplug his FT101E whenever he isn't using it, and he likes to windup the cord to look just like it did when the radio was new-in-the-box. After doing this for a while, the hot, or neutral lead breaks. Doofus plugs in his radio, and turns it on, and it doesn't work! So he asks Saint Chuck to fix his radio, and life marches on. If, on the other hand, it wasn't the hot, or neutral lead that was broken, but rather it was the safety ground lead, Doofus wouldn't know it was broken, and would continue to operate, a little less safe, but still safe, because the radio was wired correctly... and if somewhere down the path, we added an additional wire to the broken safety ground, the radio would stop working, but would still be safe. Now, lets suppose that instead of Saint Chuck wiring Doofus's FT101E, it was wired by some squire. This squire wired the hot lead to Hot+, and then wired the neutral lead, safety ground lead, and chassis to Hot-. Back to Doofus: Doofus, likes to unplug his FT101E whenever he isn't using it, and he likes to windup the cord to look just like it did when the radio was new-in-the-box. After doing this for a while, the neutral lead breaks. Doofus plugs in his radio, and trys it out, and it works just fine! Doofus continues operating this way, and eventually, another wire in the cord breaks. If that wire happens to be the hot lead, the radio will quit, and barefoot Doofus will take the radio back to the squire for a rewire job. If that wire happens to be the safety ground lead, the chassis of the FT101E will now be at full power line potential (current passing from hot lead through the radio's circuits, to the chassis/hot- connection), and barefoot Doofus will be pushing up daisies. The safety ground must NEVER be connected to the neutral at the load! NEVER! Be safe, allow for multiple failures, and fix the cord so that the hot lead goes to hot+, the neutral goes to hot-, and the safety ground lead goes to the chassis. -Chuck Harris |
getting bit by my FT-101EE chassis
OK that is one case where your need two failures to cause a hot chassis.
Now for Doofus to get electrocuted he will also have to have one hand on this deaf radio and one hand on the radio that has a metal chassis that is plugged into a socket with a good ground. The problem you could also have a similar problem even if the neutral was wired correctly (not tied to ground). If the ground wire broke in the cord or inside the radio and then a capacitor or a transformer had an internal short to the chassis or there was a resistor from hot to chassis ground then the chassis would become hot. The so called safety ground is not a 100% sure thing in the case of a failure. Because safety grounds are as prone to fail as anything a third external wire tying all metal cabinet radios together is the only safety measure if one has a table full of these old AC powered beasts. Yes it is not a good policy to tie the ground and neutral together. I just felt that a good explanation of why not to do so was required instead of just a blanket statement stating "The safety ground must NEVER be connected to the neutral at the load !NEVER! " But he on the safe side and ground those boatanchors together. (you can buy a bigger boat that way). Thanks Ron WA0KDS Doofus, likes to unplug his FT101E whenever he isn't using it, and he likes to windup the cord to look just like it did when the radio was new-in-the-box. After doing this for a while, the neutral lead breaks. Doofus plugs in his radio, and trys it out, and it works just fine! Doofus continues operating this way, and eventually, another wire in the cord breaks. If that wire happens to be the hot lead, the radio will quit, and barefoot Doofus will take the radio back to the squire for a rewire job. If that wire happens to be the safety ground lead, the chassis of the FT101E will now be at full power line potential (current passing from hot lead through the radio's circuits, to the chassis/hot- connection), and barefoot Doofus will be pushing up daisies. |
getting bit by my FT-101EE chassis
Ron wrote:
OK that is one case where your need two failures to cause a hot chassis. Now for Doofus to get electrocuted he will also have to have one hand on this deaf radio and one hand on the radio that has a metal chassis that is plugged into a socket with a good ground. He won't know the radio is "deaf" until he trys to turn it on... and you know Doofus, he broke the on/off knob years ago, and he always turns the bare aluminum shaft while he is standing barefoot on the cement floor. The problem you could also have a similar problem even if the neutral was wired correctly (not tied to ground). If the ground wire broke in the cord or inside the radio and then a capacitor or a transformer had an internal short to the chassis or there was a resistor from hot to chassis ground then the chassis would become hot. The so called safety ground is not a 100% sure thing in the case of a failure. Nothing is ever 100% perfectly safe. But you do try and improve the odds as much as you can comfortably afford. Adding a safety wire system gives you much more bang for the buck in terms of safety than the simple addition of 33% more wire would appear to offer. Because safety grounds are as prone to fail as anything a third external wire tying all metal cabinet radios together is the only safety measure if one has a table full of these old AC powered beasts. Yes it is not a good policy to tie the ground and neutral together. I just felt that a good explanation of why not to do so was required instead of just a blanket statement stating "The safety ground must NEVER be connected to the neutral at the load !NEVER! " The problem here is I could write for the next week describing all of the failure modes I know about that can and do happen with power distribution grounds, and grounding. But I really don't have that kind of time. It is far easier for me to tell you that doing such a thing is unsafe, and that you should NEVER connect the safety ground to the neutral at the load. If I tell you that E = I * R are you going to make me prove it? Or can I just tell you from a position of assumed authority that this is a true relationship? You can go and find a book that will tell you E = I*R, and likewise, you can find a book, or do a google search, to find out why you should NEVER connect the safety ground to the neutral at the load. -Chuck |
getting bit by my FT-101EE chassis
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getting bit by my FT-101EE chassis
Ron wrote:
The so called safety ground is not a 100% sure thing in the case of a failure. Because safety grounds are as prone to fail as anything a third external wire tying all metal cabinet radios together is the only safety measure if one has a table full of these old AC powered beasts. I forgot to mention one additional tidbit: Safety ground wires are *not* as prone to failure as are the current carrying hot and neutral leads. I have repaired numerous power cords on portable appliances, drills, saws, etc. There is one type of failure that I see over and over again, a broken power lead inside of the cord, with no sign of failure on the outside. The failure is usually at a point of stress, such as just after the strain relief for the cord. When I take the cord apart (usually to shorten it, and reconnect it inside the appliance) I have always found the break to be one that looks as if someone snipped the wire off clean and square! There is some blackening from the arcing that invariably occurs, but the break is clean and square. This is not at all like the way a twisted rope fails. I believe the reason for this, is a single strand breaks due to flexing, a mfr. flaw, or stress. When this strand breaks, it increases the current density of the wire at that point. The wire now gets hotter at the break, and this makes it more prone to stress failures, and another strand breaks... then another, and pretty soon the wire is seriously overloaded, and the rest of the strands pop. If I find a break in the safety ground wire, it is always a physical failure caused by the wire getting wound up in the drill bit, or cut off by the saw, or sheared off by a tool box in the bed of the truck. -Chuck |
getting bit by my FT-101EE chassis
Chuck Harris wrote: Ron wrote: The so called safety ground is not a 100% sure thing in the case of a failure. Because safety grounds are as prone to fail as anything a third external wire tying all metal cabinet radios together is the only safety measure if one has a table full of these old AC powered beasts. I forgot to mention one additional tidbit: Safety ground wires are *not* as prone to failure as are the current carrying hot and neutral leads. I have repaired numerous power cords on portable appliances, drills, saws, etc. There is one type of failure that I see over and over again, a broken power lead inside of the cord, with no sign of failure on the outside. The failure is usually at a point of stress, such as just after the strain relief for the cord. When I take the cord apart (usually to shorten it, and reconnect it inside the appliance) I have always found the break to be one that looks as if someone snipped the wire off clean and square! There is some blackening from the arcing that invariably occurs, but the break is clean and square. This is not at all like the way a twisted rope fails. I believe the reason for this, is a single strand breaks due to flexing, a mfr. flaw, or stress. When this strand breaks, it increases the current density of the wire at that point. The wire now gets hotter at the break, and this makes it more prone to stress failures, and another strand breaks... then another, and pretty soon the wire is seriously overloaded, and the rest of the strands pop. If I find a break in the safety ground wire, it is always a physical failure caused by the wire getting wound up in the drill bit, or cut off by the saw, or sheared off by a tool box in the bed of the truck. -Chuck Good point and thanks I think a few others understand the problem now more than they did. |
getting bit by my FT-101EE chassis
Don Bowey wrote: On 11/30/05 10:29 PM, in article , "Ron" wrote: I believe the important thing here is that a three wire plug be used and that it gets wired correctly. I will never see why the neutral which is grounded and green wire which is ground cannot be tied together. You declare that you will never understand the requirement, and obviously have not searched for information about it, so why do you waste space with such a post? (snip) Just thought a little more info would be good for the group. I fully understand the issue of grounds. Have a good day and hope someone got a better feel for why AC grounds are important. Ron |
getting bit by my FT-101EE chassis
Chuck Harris wrote: Ron wrote: OK that is one case where your need two failures to cause a hot chassis. Now for Doofus to get electrocuted he will also have to have one hand on this deaf radio and one hand on the radio that has a metal chassis that is plugged into a socket with a good ground. He won't know the radio is "deaf" until he trys to turn it on... and you know Doofus, he broke the on/off knob years ago, and he always turns the bare aluminum shaft while he is standing barefoot on the cement floor. The problem you could also have a similar problem even if the neutral was wired correctly (not tied to ground). If the ground wire broke in the cord or inside the radio and then a capacitor or a transformer had an internal short to the chassis or there was a resistor from hot to chassis ground then the chassis would become hot. The so called safety ground is not a 100% sure thing in the case of a failure. Nothing is ever 100% perfectly safe. But you do try and improve the odds as much as you can comfortably afford. Adding a safety wire system gives you much more bang for the buck in terms of safety than the simple addition of 33% more wire would appear to offer. Because safety grounds are as prone to fail as anything a third external wire tying all metal cabinet radios together is the only safety measure if one has a table full of these old AC powered beasts. Yes it is not a good policy to tie the ground and neutral together. I just felt that a good explanation of why not to do so was required instead of just a blanket statement stating "The safety ground must NEVER be connected to the neutral at the load !NEVER! " The problem here is I could write for the next week describing all of the failure modes I know about that can and do happen with power distribution grounds, and grounding. But I really don't have that kind of time. It is far easier for me to tell you that doing such a thing is unsafe, and that you should NEVER connect the safety ground to the neutral at the load. If I tell you that E = I * R are you going to make me prove it? Or can I just tell you from a position of assumed authority that this is a true relationship? You can go and find a book that will tell you E = I*R, and likewise, you can find a book, or do a google search, to find out why you should NEVER connect the safety ground to the neutral at the load. -Chuck Chuck I think you did a very good job and hope a few others good a better understand of the problem. I just thought a little more info for the group would no hurt. Being an Engineer I fully understand the problem and Ohms law put most on this group I am sure are not and if a new person who is us to solidstate circuit starts playing with boatanchors it is totally different then being raised with them. Again thanks and have a good day. Ron .. |
getting bit by my FT-101EE chassis
Okay, I fail to understand.
Formerly, the 2-wire cord was connected to pins 2 and 4 of the Yaesu connector. These I assume correspond to the +hot and -hot of the 120V input winding to the step up transformer, leaving the ground floating. I looked at my 3-wire cord and determined that my hot wires were the black and white ones for the 3-wire cord, and that neutral (chassis ground) was green. So I connected wall ground through ground line of the cord to chassis ground pin of the plug, leaving the hot connections unchanged. Is there something I should be doing different? Thanks, The Eternal Squire |
getting bit by my FT-101EE chassis
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getting bit by my FT-101EE chassis
"Ron" wrote in message ... OK that is one case where your need two failures to cause a hot chassis. NEVER NEVER NEVER connect safety ground and neutral together on an exposed metal chassis, PERIOD! NEVER. What if some duffus uses a hardware store cheater on the radio, because he house ONLY has the older two slot wall sockets? 50/50 shot that the chassis and cabinet are hot with 120 VAC!!! The white neutral and black hot should go to the load, the green safety ground goes to the metal cabinet. Also, tieing the neutral and hot together defeats GFIs. Pete |
getting bit by my FT-101EE chassis
wrote in message ... I believe the important thing here is that a three wire plug be used and that it gets wired correctly. I will never see why the neutral which is grounded and green wire which is ground cannot be tied together. That's why you're dangerous. Sorry. Lot's of people use hardware store cheaters on safety cords so they can be plugged into older outlets. You REALLY want an AC hot chassis, or to kill some unsuspecting future user? Neutral and safety ground ARE NOT the same thing. Pete |
getting bit by my FT-101EE chassis
" Uncle Peter" wrote in message news:o8Njf.2627$4v.2258@fed1read03... One final comment, never assume that someone hasn't replaced older outlets with modern safety ground devices where no safety ground was available in the older two conductor cables! A second fatal assumption would be that the same outlet wasn't wired with the hot and neutral reversed. That's another reason why the neutral and ground aren't tied together at the load. Pete |
getting bit by my FT-101EE chassis
wrote in message
oups.com... This is indeed the case for the FT-101E whose schematic I just examined. What I did was remove the 2-wire cord, and then connect a 3-wire cord where plus and minus hot were in former locations, then soldered the neutral wire of the cord to the plug's ground pin. Hope that would work. Well keep wiring items like this and we may need to send flowers. Do you really understand what you are doing here? Sounds like you need an elmer - berfore you kill yourself. gb |
getting bit by my FT-101EE chassis
Hi Chuck,
I'm sorry I caused such a panic with my 'alien' terminology. In my physics class 'neutral' was the name of the wire in a circuit whose potential was midway between the peaks of an AC signal. In any case I had wired it as you said now that I understand standard terms and you understand alien terms :) Thanks, The Eternal Squire |
getting bit by my FT-101EE chassis
Ron wrote:
OK that is one case where your need two failures to cause a hot chassis. Now for Doofus to get electrocuted he will also have to have one hand on this deaf radio and one hand on the radio that has a metal chassis that is plugged into a socket with a good ground. The problem you could also have a similar problem even if the neutral was wired correctly (not tied to ground). If the ground wire broke in the cord or inside the radio and then a capacitor or a transformer had an internal short to the chassis or there was a resistor from hot to chassis ground then the chassis would become hot. The so called safety ground is not a 100% sure thing in the case of a failure. Because safety grounds are as prone to fail as anything a third external wire tying all metal cabinet radios together is the only safety measure if one has a table full of these old AC powered beasts. Yes it is not a good policy to tie the ground and neutral together. I just felt that a good explanation of why not to do so was required instead of just a blanket statement stating "The safety ground must NEVER be connected to the neutral at the load !NEVER! " But he on the safe side and ground those boatanchors together. (you can buy a bigger boat that way). Thanks Ron WA0KDS Ok, Ron here is another possible failure mode: The neutral from the pole pig goes high resistance or completely open. if both halves of the 240 VAC service are not balanced and the imbalance will cause a current to flow from the neutral wire, to the radio and back to the ground rod. If that current is very high the cord will smoke or burn. I had to replace a breaker box a few years ago after the neutral corroded to the point it exploded. I was outside at three in the morning repairing the damn thing to cool my bedroom down so i could go to work the next day, but nothing had the suggested wiring, or I could have lost my home. Also, you could have trouble collecting from your insurance company after a fire caused by your own work. -- ? Michael A. Terrell Central Florida |
getting bit by my FT-101EE chassis
Chuck Harris wrote:
The black wire is called Line, or we can call it hot+ The white wire is called neutral, or we can call it hot- The green wire is the safety ground, and it goes to pretty much any screw on a permanent part of the metal chassis. (eg. don't use a cover screw, if you can avoid it.) Technically, the green wire is supposed to have a crimped on lug that is a closed circle, rather than a fork. This is so that if the screw loosens, it won't fall off right away. If the FT101 doesn't have markings for line and neutral, it is usually a good idea to make sure that the line (black) goes to the fuse. If Yuasu did things correctly, the other side of the fuse should go to a switch, or relay contact. [Note, if the fuse is one of the type with a screw in, or bayonetted cap, the side of the fuse that goes closest to the power line should be the hidden center pin. This prevents you from getting zapped when you change the fuse. I have seen a lot of manufacturers get this wrong.] -Chuck Chuck, I worked as a production test tech at Microdyne on everything except the Scientific Atlanta telemetry product we subcontracted. A new employee in assembly mis-wired the round metal power connector and QA missed it: The white and green wires went to the main power switch, and the black was connected to the chassis. Another tech ignored the written test procedure and plugged it in for initial testing to see that it didn't come on. He leaned over to unplug it with one hand on the aluminum case and his other hand brushed against the bare metal outlet box where the radio was plugged in. He got a nasty shock and if it hadn't caused his muscles to contract violently, he would probably be dead. After that he never questioned the step that required the power cord to be checked with an ohm meter BEFORE the radio was plugged in. -- ? Michael A. Terrell Central Florida |
getting bit by my FT-101EE chassis
Michael A. Terrell wrote:
Yes it is not a good policy to tie the ground and neutral together. I just felt that a good explanation of why not to do so was required instead of just a blanket statement stating "The safety ground must NEVER be connected to the neutral at the load !NEVER! " But he on the safe side and ground those boatanchors together. (you can buy a bigger boat that way). Thanks Ron WA0KDS Ok, Ron here is another possible failure mode: The neutral from the pole pig goes high resistance or completely open. if both halves of the 240 VAC service are not balanced and the imbalance will cause a current to flow from the neutral wire, to the radio and back to the ground rod. If that current is very high the cord will smoke or burn. I had to replace a breaker box a few years ago after the neutral corroded to the point it exploded. I was outside at three in the morning repairing the damn thing to cool my bedroom down so i could go to work the next day, but nothing had the suggested wiring, or I could have lost my home. Also, you could have trouble collecting from your insurance company after a fire caused by your own work. Hi Michael, Yep, that is yet another good example of why you shouldn't break the rules. I could write all week, and still not cover all of the stupid dangerous things that have happened with ground failures and grounding errors. The NEC is the result of 100 years of experience with power distribution, and use. Their collective authors have seen some of the most bizarre failures, and the code has been designed to help prevent these types of failures. It is rather unsettling to have a line cord catch fire in the bedroom when your wife puts a piece of toast in the toaster oven in the kitchen. And we haven't even broached the subject of what happens when your antenna gets hit by lightning, and you have invited the ground currents into your neutral circuits! In case anyone thinks that losing the connection to the center tap (neutral) at the pole pig is an unlikely problem. Bear in mind that virtually all of these connections are to aluminum wire. The power companies make their own rules. They don't have to follow NEC, they have their own code. When they started using aluminum wire exclusively in the '60s, they didn't think about the corrosion and cold flowing characteristics of aluminum. The power companies use aluminum exclusively for all of the wiring on their side because aluminum has the highest conductivity per pound, and per dollar, of any known material. After they gained experience with aluminum, and knew all about its problems, I bet you think they went out, and upgraded all of the older connections, right? Nope! They left them alone. Power companies are profit driven, they didn't want to have to explain to their share holders why they would have to shoulder a billion dollar loss to fix a problem of the power company's making. So, they only fix the problem when *you* discover it. -Chuck |
getting bit by my FT-101EE chassis
Chuck Harris wrote:
Hi Michael, Yep, that is yet another good example of why you shouldn't break the rules. I could write all week, and still not cover all of the stupid dangerous things that have happened with ground failures and grounding errors. The NEC is the result of 100 years of experience with power distribution, and use. Their collective authors have seen some of the most bizarre failures, and the code has been designed to help prevent these types of failures. It is rather unsettling to have a line cord catch fire in the bedroom when your wife puts a piece of toast in the toaster oven in the kitchen. And we haven't even broached the subject of what happens when your antenna gets hit by lightning, and you have invited the ground currents into your neutral circuits! In case anyone thinks that losing the connection to the center tap (neutral) at the pole pig is an unlikely problem. Bear in mind that virtually all of these connections are to aluminum wire. The power companies make their own rules. They don't have to follow NEC, they have their own code. When they started using aluminum wire exclusively in the '60s, they didn't think about the corrosion and cold flowing characteristics of aluminum. The power companies use aluminum exclusively for all of the wiring on their side because aluminum has the highest conductivity per pound, and per dollar, of any known material. After they gained experience with aluminum, and knew all about its problems, I bet you think they went out, and upgraded all of the older connections, right? Nope! They left them alone. Power companies are profit driven, they didn't want to have to explain to their share holders why they would have to shoulder a billion dollar loss to fix a problem of the power company's making. So, they only fix the problem when *you* discover it. -Chuck After the hurricanes last year her in Florida they finally went through the whole subdivision and replaced every splice in the secondaries, as well as the 7200 volt primaries. I found a number of them on the ground and it was amazing that I even had electricity. Between the corrosion and the thermal expansion you could pull strands out of the crimps. After they finished my line voltage went up 10 volts, and is a lot more stable. -- ? Michael A. Terrell Central Florida |
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