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A typical household RCB will trip on a 60 or 100mA difference in supply
current surges up to 60A. That's pretty good common-mode rejection! ========== Don't want to be pedantic but the RCDs in domestic switchboards in the UK (at least here in Scotland ) trip at 30 mA . I just had a look at my house's switch board made by SQUARE -D (England) to British Standard BS5486 pt 13 In UK industry I have come across RCDs which trip at 100 mA Frank GM0CSZ / KN6WH |
Paul Burridge wrote:
On Sat, 9 Aug 2003 09:01:05 +0100, "Ian White, G3SEK" wrote: A typical household RCB will trip on a 60 or 100mA difference in supply current surges up to 60A. That's pretty good common-mode rejection! It's better than that. 30mA is the standard currently. Sorry, I got mixed-up about that. Our house was wired under the older regulations which allowed the lights to be protected by a separate 100mA RCD, while the power outlets are protected at 30mA. The idea was that tripping a power circuit is less likely to plunge the whole house into darkness. The standard for new household installations is now 30mA all around, although 100mA units are still available for industrial uses. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
Paul Burridge wrote:
On Sat, 9 Aug 2003 09:01:05 +0100, "Ian White, G3SEK" wrote: A typical household RCB will trip on a 60 or 100mA difference in supply current surges up to 60A. That's pretty good common-mode rejection! It's better than that. 30mA is the standard currently. Sorry, I got mixed-up about that. Our house was wired under the older regulations which allowed the lights to be protected by a separate 100mA RCD, while the power outlets are protected at 30mA. The idea was that tripping a power circuit is less likely to plunge the whole house into darkness. The standard for new household installations is now 30mA all around, although 100mA units are still available for industrial uses. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
Roy Lewallen wrote:
No, the GFCI doesn't need the safety ground. Like the device you're describing, it measures the difference between the "hot" and "neutral" wires, by running the pair together through a transformer. A GFCI is supposed to trip in 1/40 of a second at 5 mA. In our system, like yours, the "hot" and "neutral" wires should always carry equal currents, and the safety ground shouldn't carry any. However, the safety ground is sized the same as the current-carrying conductors so it'll handle a fault current large enough to kick the circuit breaker. That is pretty much the same as our RCDs, right down to the large-sized 'protective earth' wire. Its primary function is to protect against something like the "hot" wire making contact with a metal appliance frame, which should be connected to the safety ground. An interesting thing happens when you switch off to isolate part of the house wiring, and then cut the "dead" three-wire cable. (We call it "flat twin and earth". It has PVC-insulated hot and neutral wires with a bare ground wire in between, all in a flattish grey or white PVC sheath. Is this what you call "Romex"?) If you cut the hot and ground wires together, nothing happens; but if you cut the neutral and ground wires together, the RCD trips. That's a puzzle the first time it happens, but it's because that cable isn't quite as "dead" as you think. the isolating switches interrupt only the hot wire, so the neutral and earth are still being shared with everything else that's switched on in the house. Does that happen in the USA, or do you have two-pole isolating switches for individual sub-circuits? This isn't totally idle curiosity. If there's an electrical problem while we're staying with the in-laws in Atlanta, I'm the one who's supposed to know about these things... When it comes to a GFCI, no assumption is made about how much of the imbalance current is returned via the safety ground and how much via the Earth or some other path. Exactly the same as our RCD, then... just a slightly ambiguous name. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
Roy Lewallen wrote:
No, the GFCI doesn't need the safety ground. Like the device you're describing, it measures the difference between the "hot" and "neutral" wires, by running the pair together through a transformer. A GFCI is supposed to trip in 1/40 of a second at 5 mA. In our system, like yours, the "hot" and "neutral" wires should always carry equal currents, and the safety ground shouldn't carry any. However, the safety ground is sized the same as the current-carrying conductors so it'll handle a fault current large enough to kick the circuit breaker. That is pretty much the same as our RCDs, right down to the large-sized 'protective earth' wire. Its primary function is to protect against something like the "hot" wire making contact with a metal appliance frame, which should be connected to the safety ground. An interesting thing happens when you switch off to isolate part of the house wiring, and then cut the "dead" three-wire cable. (We call it "flat twin and earth". It has PVC-insulated hot and neutral wires with a bare ground wire in between, all in a flattish grey or white PVC sheath. Is this what you call "Romex"?) If you cut the hot and ground wires together, nothing happens; but if you cut the neutral and ground wires together, the RCD trips. That's a puzzle the first time it happens, but it's because that cable isn't quite as "dead" as you think. the isolating switches interrupt only the hot wire, so the neutral and earth are still being shared with everything else that's switched on in the house. Does that happen in the USA, or do you have two-pole isolating switches for individual sub-circuits? This isn't totally idle curiosity. If there's an electrical problem while we're staying with the in-laws in Atlanta, I'm the one who's supposed to know about these things... When it comes to a GFCI, no assumption is made about how much of the imbalance current is returned via the safety ground and how much via the Earth or some other path. Exactly the same as our RCD, then... just a slightly ambiguous name. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
In article ,
mentioned... Chris1 wrote: In article , "Michael A. Terrell" wrote: I find that very interesting, since every chocolate bar I have ever had was wrapped in aluminum foil. I always thought it was just shiny paper. There's not much Aluminum there, if any. Chris A very thin aluminum foil, with a paper backing. Use an Ohm meter on a piece to see that it is conductive. I used to be able to do that with the nickle plated antistatic bags that parts came in back in 1980. The ohmmeter would measure several hundred ohms. But nowadays all I can measure is an open. I just tried it again, measured open even on the 200M range. -- @@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@ ###Got a Question about ELECTRONICS? Check HERE First:### http://users.pandora.be/educypedia/e...s/databank.htm My email address is whitelisted. *All* email sent to it goes directly to the trash unless you add NOSPAM in the Subject: line with other stuff. alondra101 at hotmail.com Don't be ripped off by the big book dealers. Go to the URL that will give you a choice and save you money(up to half). http://www.everybookstore.com You'll be glad you did! Just when you thought you had all this figured out, the gov't changed it: http://physics.nist.gov/cuu/Units/binary.html @@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@ |
Paul Burridge wrote:
On Fri, 08 Aug 2003 03:29:47 GMT, Eric Immel wrote: Paul, are you asking if anyone has been killed, then revived? That's pretty close to what I'm getting at. What I *am* actually get at is that theoretical physicists are coming around to the rather extraordinary view that one cannot from one's own perspective be killed by any sudden and dramatic life event. No matter how bad the shock, you will always 'come around' to find that you've survived. The tricky bit is that you'll probably have found yourself in a different reality to the one you left. In the one you've left, observers will see your cold, dead, smoking body lying sparko on the ground. Your relatives will grieve, your obituary will be written. But *you* won't know anything of that. You'll just believe you've had a lucky escape; you'll go home and tell your friends and family all about it and years later maybe you'll tell others via the Internet. Now that you've explained what you meant, I'll mention that I must be on at least my fifth parallel Universe. I told a few tales about my "teleportation experiments" here some time back, all involving from 220VAC @ 60 Hz to a few kV @ 400 Hz. I tend to jump rather than tear muscles because I'm skinny, you see. Mark L. Fergerson |
Paul Burridge wrote:
On Fri, 08 Aug 2003 03:29:47 GMT, Eric Immel wrote: Paul, are you asking if anyone has been killed, then revived? That's pretty close to what I'm getting at. What I *am* actually get at is that theoretical physicists are coming around to the rather extraordinary view that one cannot from one's own perspective be killed by any sudden and dramatic life event. No matter how bad the shock, you will always 'come around' to find that you've survived. The tricky bit is that you'll probably have found yourself in a different reality to the one you left. In the one you've left, observers will see your cold, dead, smoking body lying sparko on the ground. Your relatives will grieve, your obituary will be written. But *you* won't know anything of that. You'll just believe you've had a lucky escape; you'll go home and tell your friends and family all about it and years later maybe you'll tell others via the Internet. Now that you've explained what you meant, I'll mention that I must be on at least my fifth parallel Universe. I told a few tales about my "teleportation experiments" here some time back, all involving from 220VAC @ 60 Hz to a few kV @ 400 Hz. I tend to jump rather than tear muscles because I'm skinny, you see. Mark L. Fergerson |
In article , "K Wind"
writes: "Paul Burridge" wrote in message .. . The question seems daft, but bear with me, gentlemen. Has anyone ever had an electric shock that they feel lucky to have survived? Would 1,500VDC with 6mA capability flowing through one arm and out the other be considered lethal? At one time, I knew how much current was considered lethal, but have forgotten. Think of "30-30" as a mnemonic. If the source has over 30 Volts and can supply over 30 milliamperes through the cardiac region, you will go into cardiac fibrilation. High voltage with little supply current will affect the nerves and the resulting muscle spasms can cause other kinds of injuries, some that may be fatal. DON'T DO IT. PAY ATTENTION! Len Anderson still living in the same reality I was born into... |
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