USB hard drive connection order

Long ago, but not so very far away, the order in which computer components were powered up was important. Nobody worries about it now.

But are USB external hard drives in a different class? Does it matter in which order the various components get connected? There are three connections to worry about:

1. the power supply to the AC mains
2. the power supply to the USB drive
3. the USB drive to a USB port on the computer

Applying the logic of the bad old days, I would connect them in the order shown above, for these reasons:

• the power supply should have time to stabilize before it is connected to the hard drive so that it doesn't have a chance to pass a start-up spike to the drive's circuitry.
• the drive's logic circuitry should be alive when hot-plugged into the computer, so that it can respond to interrogation by the computer's USB drivers.

Are there other factors to consider? Do they dictate a different connection order?

And what about connecting a USB drive before starting the computer? Or leaving it connected until after shut-down? What considerations apply there?

 

Western Digital's page at <http://wdc.custhelp.com/cgi-bin/wdc.cfg/php/enduser/popup_adp.php?p_faqid=5316&p_sid=ceFdDpjk&p_lva=> suggests that the above order is correct, with one additional detail: when connecting the USB cable, connect the cable to the computer, then the external drive. WD does not say why that detail is significant, or whether it applies only to their external drives.

 

Hi Rob,

I always connect the power adapter to the hard drive, then the wall (it takes milliseconds to "stabilize", and the brick in the cord has safeguards to stop excess power from flooding the drive circuitry, it's a built in converter and mini surge protector... won't protect against much of a power surge), and then connect the USB cord to the hard drive, then the computer.

I have two external drives connected to my desktop that stay connected (to power and via USB to the computer) at all times. I use a surge protector, of course, between the wall and the drive power cords. I know there are a few models out there that don't do well with reboots of certain PCs, though.

 

I've no doubt that pretty much all AC adapters for external drives include the protective circuitry you describe -- which would be a good reason for not using an AC adapter not manufactured specifically for that use.

But if you have the option of entirely avoiding start-up spikes in the adapter's output by powering up the adapter before you connect it to anything, why would you rely on included circuitry to nullify any start-up spikes? I'll certainly grant you that most such protection circuitry is usually quite reliable -- but why take the chance of a failure that could take out the drive or the data on it?

 

With today's modern power grid, the only spikes occur with storms and line issues. The line issues are rare, and storms are pretty noticeable.

Why risk plugging ANYTHING directly into the wall? A power spike could destroy it! Seriously, it's not as sensitive of an issue as you're making it out to be.

 

It's not power-line spikes that I was speaking of, though if you want to minimize that risk, you'd plug the AC adapter into a good-quality surge bar or UPS, not the wall outlet. As I gather you do. Which is good -- power-line spikes can be generated just by shutting down an electric motor of any size. You really don't want to put sensitive electrical equipment on the same branch circuit as even a refrigerator without some protection.

But I digress. The risk I was speaking of was that of spikes that appear in the output of electrical equipment when it is powered up -- in those few milliseconds before the output stabilizes. They happen. AC adapters designed for external hard drives presumably include circuitry that prevents a spike from appearing in the output, but like all circuit elements, that protection can fail.

Sure, the probability of such a failure is quite low. And some risks one accepts because avoiding them is too troublesome or expensive. But I don't see any need to accept a risk that I can avoid merely by changing the order in which I make the connections.