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#1
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Why do stereo components lack ground plugs?
Does anyone know the main reason computers have 3-pronged plugs but
most consumer stereo gear doesn't? Is it less vulnerable to surges, even with all the microprocessors in modern receivers? JT P.S. I notice laptops rarely have ground plugs either. Must be a clue there. |
#2
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Why do stereo components lack ground plugs?
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#3
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Why do stereo components lack ground plugs?
Many years ago I read a technical article which stated that in a situation
where each component in a stereo is grounded, then there is the ground of the interconnecting signal cables, that can create a "ground loop" with a resulting hum. Some years ago when I used to service ATMs, such a dual grounded communications adapter box caused some interesting intermittent communications dropouts. Henry "J. Tyler" wrote in message om... Does anyone know the main reason computers have 3-pronged plugs but most consumer stereo gear doesn't? Is it less vulnerable to surges, even with all the microprocessors in modern receivers? JT P.S. I notice laptops rarely have ground plugs either. Must be a clue there. |
#5
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Why do stereo components lack ground plugs?
In article , Todd H. wrote:
(J. Tyler) writes: P.S. I notice laptops rarely have ground plugs either. Must be a clue there. Laptops differ from desktop computers in that their power supplies are isolated from the AC mains via battery isolation essentially. No, they are not. The battery provides NO isolation at all when the power supply/line cord is attached to the wall. Laptops don't have ground plugs because they have the internal design necessary to meet isolation standards. -- | Dick Pierce | | Professional Audio Development | | 1-781/826-4953 Voice and FAX | | | |
#6
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Why do stereo components lack ground plugs?
Richard D Pierce wrote:
In article , Todd H. wrote: (J. Tyler) writes: P.S. I notice laptops rarely have ground plugs either. Must be a clue there. Laptops differ from desktop computers in that their power supplies are isolated from the AC mains via battery isolation essentially. No, they are not. The battery provides NO isolation at all when the power supply/line cord is attached to the wall. Laptops don't have ground plugs because they have the internal design necessary to meet isolation standards. That's not the case either, except in the case of models that plug direclty into the wall. Most laptops use a wall wart. The wall wart is double insulated and is not required to have a ground pin. Using a wall wart relieves the computer manufacturer from all manner of regulatory problems. They've been taken care of by the wart vendor. As long as you keep the output voltage below 42.5V, your regulatory issues are very much easier to handle. mike -- Bunch of stuff For Sale and Wanted at the link below. laptops and parts Test Equipment 4in/400Wout ham linear amp. Honda CB-125S 400cc Dirt Bike 2003 miles $550 Police Scanner, Color LCD overhead projector Tek 2465 $800, ham radio, 30pS pulser Tektronix Concept Books, spot welding head... http://www.geocities.com/SiliconValley/Monitor/4710/ |
#7
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Why do stereo components lack ground plugs?
Todd H. ) writes:
(J. Tyler) writes: P.S. I notice laptops rarely have ground plugs either. Must be a clue there. Laptops differ from desktop computers in that their power supplies are isolated from the AC mains via battery isolation essentially. And rare is the power supply for a laptop that has a metal case. I don't know the answer to your interesting question though, but I think laptop power supplies having a 2 prong plug might be a red herring. Considering that someone might be plugging that laptop supply into any available outlet, I suspect convenience is one reason it would have a two-prong plug. Probably a lot of consumer equipment is done that way too for the same reason. Of course, that doesn't really address why some equipment routinely uses a third prong, only that there's a practical reason for some equipment having only two prongs. Michael |
#8
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Why do stereo components lack ground plugs?
"J. Tyler" wrote ...
Does anyone know the main reason computers have 3-pronged plugs but most consumer stereo gear doesn't? Partly tradition. And I suspect somewhat to avoid ground loops. Pro audio equipment tends to use 3-wire power cables, but then it is assumed that the user is better equipped to handle shielding and grounding problems like ground loops. Ground loops are rarely a problem with computers (except when we interconnect them with sound equipment!) Is it less vulnerable to surges, even with all the microprocessors in modern receivers? Doesn't really have anything to do with surge protection. P.S. I notice laptops rarely have ground plugs either. Must be a clue there. Most equipment that use wall-warts use 2-pin power plugs. Isolation is provided within the wall-wart. Laptop computers are little different than any other equipment that uses external mains power supplies/chargers. |
#9
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Why do stereo components lack ground plugs?
"rstlne" wrote ...
A AC Ground adapter that removes ground? .. I dont think that's verry wise.. Most law-making jurisdictions agree. Those ground-lifting adapters are illegal in most places these days. Doesn't prevent them from being useful in some situations, however. I used one to break a ground loop going to a video projector last summer. Note that if there weren't already TWO grounds, there wouldn't be a ground LOOP (by definition!) Maybee take an isolation transformer with you.. That also interrupts the ground. The battery probably provides isolation because it isnt connected to the same ground that the power company uses.. The "battery ground" is on the isolated side of the wall-wart. Ever held a battery in your hand? ever notice how a car battery wont shock you when your cleanign either terminal? Low-voltage batteries don't have enough voltage to push any kind of current through your high-impedance epidermis. I don't see the connection with the current discussion about power line grounding. I mean .. okay.. I might not be the brightest lightbulb but your statement seems a little silly to me so maybee I am reading it wrong You appear to be mixing several different issues together. If your removing the earth line from electronic equipment (on a professional basis) then I would say that your probably liable for damages if anyone gets shock'd, but that's just me Conventional wisdom, petty bureraucrats, and plantiff's attorneys all agree. :-) |
#10
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Why do stereo components lack ground plugs?
In article , "Richard Crowley" wrote:
"rstlne" wrote ... A AC Ground adapter that removes ground? .. I dont think that's verry wise.. Most law-making jurisdictions agree. Those ground-lifting adapters are illegal in most places these days. Doesn't prevent them from being useful in some situations, however. I used one to break a ground loop going to a video projector last summer. Note that The problem here is obviously the lack of isolation between signal ground and chassis ground which in most cases should always be separate. Don't forget, most commercially wired isolation transformers are sold with the ground tied to one leg of the output. This does not isolate ground, but does cut noise way down. greg |
#11
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Why do stereo components lack ground plugs?
"Henry Mydlarz" wrote in message u...
Many years ago I read a technical article which stated that in a situation where each component in a stereo is grounded, then there is the ground of the interconnecting signal cables, that can create a "ground loop" with a resulting hum. With CAR stereo ground leads (I've never had noise problems with interconnects) that's usually fixed by grounding all components at the same chassis location. That's DC though, and the components depend on grounding to complete their power circuits. It makes sense that you'd want to totally isolate AC-powered components. JT |
#12
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Why do stereo components lack ground plugs?
"J. Tyler" wrote in message
om... Does anyone know the main reason computers have 3-pronged plugs but most consumer stereo gear doesn't? Is it less vulnerable to surges, even with all the microprocessors in modern receivers? It's purely a design/economic decision. Having the earth connection can: 1. Make meeting emission limits easier since you can shunt common mode noise. 2. If low voltage secondaries are earthed then it reduces safety clearances (actually creepage distances) by half. If the product is designed for international use then reinforced insulation is required anyway so earthing the secondary doesn't reduce margins. Unless there's a good reason to earth the secondary (like ensuring SELV) the only advantage of having the third wire is for meeting emissions. If the product can be designed to meet SELV and emissions without the third wire the manufacturer can save money on the cord. Those molded IEC connectors are much more expensive than a hard wired cord with grommet. |
#13
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Why do stereo components lack ground plugs?
(Barry Mann) wrote in message . com...
In , on 09/09/03 at 11:13 PM, (J. Tyler) said: Does anyone know the main reason computers have 3-pronged plugs but most consumer stereo gear doesn't? Is it less vulnerable to surges, even with all the microprocessors in modern receivers? JT P.S. I notice laptops rarely have ground plugs either. Must be a clue there. Sometimes I wonder if anyone has a clue about this issue. The non-use of a grounding plug implies that the object to which it is connected is "double-insulated" so that a double fault must occur before the user can get an electrical shock (short of going swimming with the device plugged in - then the GFI circuit near the swiming pool or bathroom or whatever is supposed to protect the dumb fool that goes swimming). In the case of a computer, as noted earlier, the wall-wart provides double insulation for the electrical dc output that goes to the computer. If stereos, tvs, etc used wall-warts, they could also be provided with no grounding plugs. In fact, the tv sets use insulating techniques inside the tv sets that qualify them for the "double-insulating" ratings, as far as I know. It would be helpful if someone from UL was on the newsgroup. H. R. (Bob) Hofmann |
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