有时，当技术规范“禁止”使用某个特定的配件时，可能会让人感到困惑，然而每个人似乎都认为使用有问题的配件是完全可以的。到底谁是对的？今天的超级用户问答帖子回答了一位忧心忡忡的读者的问题。

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

照片由丹尼斯S.赫德（Flickr）提供。

问题

超级用户读者muttley91想知道在USB外围设备上使用Y形电缆是否有任何风险：

I have been advised to use a Y-cable to power a portable USB hard drive from two ports since it is unable to draw enough power from a single port. Are there any risks or dangers of overloading or damaging the hard drive by using a Y-cable this way?

将Y形电缆与USB外围设备一起使用是否存在任何风险？

答案

超级用户贡献者misha256和Dmitry Grigoryev为我们提供了答案。首先，misha256：

The USB specification prohibits the use of Y-cables:

• Use of a Y-cable (a cable with two A-plugs) is prohibited on any USB peripheral. If a USB peripheral requires more power than allowed by the USB specification to which it is designed, then it must be self-powered.

But the real world said “forget your silly rules” and uses Y-cables all the time. Technically, there is pretty much zero risk of anything bad happening, just do not use Y-cables via an unpowered USB hub. Plug the connectors straight into the computer’s USB ports.

“Are there any risks or dangers of overloading or damaging the hard drive by using a Y-cable this way?”

Using a Y-cable does not increase the voltage, it only makes more current available, so it is all good. The hard drive will take as much current as it needs.

You are far more likely to damage the contents of a hard drive by running it under-powered. There is nothing worse than write operati*** failing midway through. So I implore you, use the Y-cable.

接着是德米特里·格里戈里耶夫的回答：

Y-cables are forbidden by the USB specification for a reason. Connecting the A-plugs of a Y-cable into two different host ports (i.e. two different computers, a computer and a hub, etc.) can lead to multiple electrical problems:

1. One of the hosts may be unpowered while the other one is powered on. This will result in the powered host pushing current to the unpowered one in the wrong direction, possibly resulting in damage.
2. Even if both hosts are powered, one will provide a slightly higher voltage than the other, resulting in a problem similar to problem #1 above (perhaps less severe).
3. If you are extremely unlucky, you may get two computers with poorly isolated PSUs connected to different mains (120V or 240V) networks. Connecting those with a common ground cable (which is a Y-shaped USB) will zap both computers instantly. Though in this case I would be more concerned about electrical safety in general rather than about Y-cable usage.

If you make sure to connect both A-plugs to the same USB host, using a Y-cable is fine (I have one myself). Do not worry about over-powering the drive, it will take just as much current as it needs.

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