科学与数学amasci.com
为什么插头有三个脚？
Why three prongs?
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导读
这篇页面解释为什么插头要有第三个插脚（接地脚）：从早期未接地供电系统的风险讲起，说明中性线接地、设备外壳接地以及故障电流如何被导入大地，并指出相关做法是逐步演化出来的。它也澄清了“接地”并不神秘，核心是给故障电流提供一条低阻通路，避免人体成为通路。
为什么经久不衰：它把日常插头背后的电气安全原理和历史成因讲得清楚，而“接地到底是什么”至今仍是常见困惑，所以多年后仍值得读。
HN 评论精选
解释中性线接地、地线与中性线隔离，并提到地线孔朝上的安全考量与北美习惯。
简言之：中性线是接地的。插头的“嘴”（接地脚）是地线，并与中性线隔离，以防意外带电位。附注：通常认为把插座的地线孔装在上方更安全，但北美不常这么做，因为地线孔在下方看起来像一张小脸，而人喜欢脸。
linsomniac查看英文原文
Short form: Neutral is grounded. The "mouth" part of the plug is the ground and is isolated from the neutral to prevent inadvertent carrying of potential. Aside: it is generally considered safer to have the outlets ("receptacles") installed with the ground at the top, but we don't tend to do this in NA because ground at the bottom makes it look like a little face and humans like faces. Edit: Adding link to EETimes: https://www.eetimes.com/document.asp?doc_id=1272972#
质疑三脚插头是否绝对必要，以日本仍用两脚插座和电饭煲为例。
那么显而易见的后续问题是：为什么日本到今天还在用两脚插座？日本人触电死亡率比世界其他地方高很多吗？日本是不是只有完美电工？还是说这其实并不是这个（词源意义上的）神话所暗示的那么严重的问题？我唯一拥有的两脚电器是一台日本产电饭煲。你会觉得，如果有哪个设备需要三脚安全，那应该就是这种把水和市电结合起来的金属容器。
ken查看英文原文
The obvious follow up question, then, is: why does Japan use 2-prong outlets even today? Are Japanese people dying from electrical shock at a much higher rate than the rest of the world? Is Japan full of only Perfect Electricians? Or is this not actually the significant problem that this myth (in the etiological sense, not the fictional sense) would lead us to believe? The only 2-prong device I own is a (Japanese-made, of course) rice cooker. You'd think that if any device warranted 3-prong safety, it'd be a metal container which combines water and mains electricity.
表达普通读者对“接地”到底是什么、电流去哪里的常见困惑。
我一直很难理解“地”的概念。为什么电“想”流向大地？什么算“地”？把导线碰到混凝土算接地吗？不算？那必须埋下去？多深？碰到泥土才行？沙子呢？电最后“去”哪里了？我读了很多文章，还是没搞懂。
komali2查看英文原文
> There is a simple solution to these problems: connect your system to the Earth. Drive some long metal rods into the dirt, and connect them to your wires. That way, lightning currents will be directed into the Earth rather than spreading throughout your power lines. I have tried and failed many times to understand the concept of "ground." Why does electricity "want to go to the ground?" What constitutes "ground?" Can I touch wire to concrete, and that counts as "ground?" No? Must I then sink it? How deep? Until it touches dirt? What about sand? Where does the electricity "go" then? I've read plenty of articles, never got it.
对未接地系统下单线触电风险的推理提出技术质疑。
我对“未接地系统中单根导线不会电人”这个说法感到困惑。如果两根导线之间有 120V 交流电，那不就意味着至少有一根导线与大地之间至少有 60V 交流电位吗？作者是依赖“减半”后的电压来保证安全，还是依赖完整回路使另一根已连接导线总比大地更适合作为通路，还是他在某种我看不到的方式上是对的？
nkurz查看英文原文
> Before you "grounded" your system, the AC voltage in general acted pretty safe for your customers. The only way they could get a shock was if they touched both wires at the same time. This was a fairly rare occurrence. One single wire acted as if it was "safe," and it did not deliver shocks. I'm confused by the assertion that you could not get a shock from a single wire in an ungrounded system. If there is 120V AC between the two wires, doesn't this mean that there has to be at least 60V AC potential between at least one of the wires and earth ground? Is he depending on the "halved" voltage for safety, or depending on having an intact circuit so the other connected wire is always "better" than an earth ground, or is he right in some way that I'm not seeing?
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