h a l f b a k e r yRecalculations place it at 0.4999.
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Conventional power plugs in the US (and everywhere I've been abroad) are typically two or three pronged affairs. This arrangement makes it difficult to plug in devices when the socket is difficult to see (like plugging in a lamp in a dark room, or trying to mate plug to socket far behind a heavy piece
of furniture).
A single-pronged arrangement would be so much easier. Shaped much like a standard headphone plug, connecting the plug to power could be facilitated by wall plates that have a funnel shape around the socket.
This would also be a safer design, I think, as under the current arrangement, I usually have to put my finger on one of the prongs, and use it to find the appropriate side of the socket by touch. Always makes me nervous when I have to do that.
***Addendum*** - The issue of grounding before current can flow can easily be addressed by this sort of socket. Deep in the socket, the plug can make contact with a metal bit connected to ground. As the plug pushes the metal bit rearward, it activates a switch which allows current to flow through the positive and negative contacts of the plug (which, at this time, are safely sheathed inside the socket).
This way, even if a toddler does manage to stick a screwdriver into the socket, the current travels from the proximal end of the screwdriver towards its distal end, away from the curious child, before tripping the circuit breaker.
The socket could be made either too small for most children to put their fingers in, or too deep for their fingers to reach.
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Not 30 seconds, and fishboned already. Is that a record? |
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Boned: I'm *not* rewiring my house again! |
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[PeterSealy]: Baked!? Ever try to run a hair dryer from your stereo? Also, I've answered some of your objections in an addendum to the original idea. |
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The polarization issue takes care of itself. Cool... never having to flip the prongs again. It's a little thing, but it's mildly annoying when it happens every time. |
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Tv Aerial leads use a one 'prong' system and lots of Radio equiptment uses such leads to provide power. So, Baked-Baked-Baked-Baked-Baked. |
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Take care of the voltage and frequency, Kenneth, and it's worth a vote. |
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Not to mention the ubiquitous "barrel connectors" used to supply low-voltage DC to gadgets. |
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Sure would be nice if AC had a more convenient plug -- but of course it would be monumentally difficult to change now. |
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Oh, how charming, PeterSealy! |
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The reason why this may have been baked for earphones, aerial leads and stereo connectors is that they are all low voltage devices. When designing a mains plug one of the main design criteria has to be keeping the pins away from each other. So a single pin is more convenient but due too the danger involved no-one has tried to make one for mains voltages. |
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So this is NOT baked and unlikely to ever be so. |
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stef: The standards recommend a minimum creepage distance of 3mm between parts carrying mains voltage. Provided this can be met there is no reason not to arrange a mains plug and socket in mono fashion. |
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My kettle is of the type that docks into a base unit for kettling purposes, and removes for filling / emptying. The connector that connects it to the base is co-axial. I see not why this system should not be used for wall sockets, so it's bakeable, but it's already used for my kettle, so it's baked. |
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The two to three pronged units appear to help stabilize the mated plug to its counterpart, the wall i.e., a vacuum cleaning unit's plug stretching to a far reach of the room appears to be much more stable with the higher prong count. We would hate to have it pull itself out. Good day |
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Here are some things to keep in mind when designing an electrical plug for high-voltage/high-current. First, inserting the plug must never create a short-circuit, even momentarily. That rules out most tip-ring-sleeve varieties of plugs. Second, all live parts should be recessed to avoid accidental contact. This would require shortening the center pins of those barrel type coaxial connectors somewhat. Third, have a large contact surface area to ensure a good electrical connection. All the coaxial plugs I have seen fail this part miserably. The center pins can not be guaranteed to mate precisely with the plug, and so the surface of actual contact is hardly more than a pinpoint in the worst case. Under high current, this would make the plug get unacceptably hot. |
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Now, if a barrel type coaxial plug were made with a very wide (~1 cm) center and a relatively thin (2-3 mm) barrel shell, then the center stump (it's not really a pin any more) would have space for multiple contacts with independent springs to maintain a good electrical connection. This arrangement will allow the plug 360 degrees of rotation for ease of insertion and also high current capability, but it only works for hot/return type systems. |
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To accommodate systems requiring hot/neutral/earth, +hot/-hot/earth, and A_hot/B_hot/C_hot/earth, you would need an additional barrel shell at a wider (~2 cm) diameter. |
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(later)
Oh yeah, and add insulation to the external end of the center stump to prevent curious fingers from frying. You can even make this insulation cone-shaped to help with plug alignment. |
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For maximum safety, the earth contact is always the outside of the outermost shell. The contacts in the receptical should be arranged so that the earth conatct makes first and breaks last. |
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Yeah, my laptop power jack broke so I replaced it with a 1/8" phone jack. Guess what? It shorts every time you plug it in or unplug it. So your design would need moving parts if you were going to do a typical TRS kind of plug, with the contacts moving into position from insertion force. Moving parts aren't that reliable, though. The barrel connectors are a better idea, with one contact on the inside and one on the outside, but how would you make three connections? I guess you could have two connections at different radii, but make sure the barrel is definitely constrained by the point they are in contact range so that it can't tilt to the left or right and let one contact touch the wrong place. |
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