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We have an upcoming scheduled power outage for maintenance.

UPS protects our servers. But it has been suggested that all PCs should be unplugged to prevent damage from power surges when power is restored. Is this precaution really necessary?

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3 Answers 3

up vote 10 down vote accepted

In my experience yes. The main problem is that often too many devices are left turned on and create quite a peak when power is back again, with potential damaging effects for the power supplies.

This is the reason why intelligent PDU for server racks often turn devices on in a staggered mode after a power loss.

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This is a big issue at big LAN Parties for example. Power goes down then back up and all the gamers turn their computers on at the same time, eager to frag. And BAM, the power goes right back down. And so on and so forth :) –  Antoine Benkemoun Aug 15 '11 at 9:05
    
@SvenW Thanks SvenW. But if the devices are already powered off should we still unplug them? –  RMNVM Aug 15 '11 at 14:15
    
Worth noting: some BIOSs have features such as "Auto-Power ON after power failure", "Wake-on-LAN", etc. –  deizel Aug 15 '11 at 15:27
    
If you can't really turn the PSUs off with a switch on the back, I would unplug them, as they are connected to the power grid even when soft-off. –  SvW Aug 15 '11 at 15:46

If you are not sure of the nature of the power outage, I recommend you to turn off the main breaker just before the outage, and restore it just after the outage (isolating your building from utility power, to prevent "short power-on" or any kind of undesired power problems during the outage that could damage something)

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That is often not enough, as the surges can be created in your own power grid because of too many devices left on that afterwards are turned on at the same time. –  SvW Aug 15 '11 at 8:48
    
In this case, you should rearm the different "sub-breakers" one after each other. But this problem is more a problem that we see in case of server room power outage (800+ servers starting at the same time = boom), I've never seen this in desktop environments. –  Kedare Aug 15 '11 at 20:15

If you're not going to unplug them when you leave work I'd say you're only elimiting part of the risk. Dirty power can cause severe problems on machine. One of my former employers did not have ups' on each desktop, despite the recomendation. One day we had terrible power problems and the power went out mutiple times after being up for 30 seconds or so. This ended up corrupting about 1/3 of the user profiles causing about a weeks worth of remediation.
Id say if the you cannot get the policy to unplug the machines when the user is not in the office, I would push to get a UPS for each desktop. UPS tend to provide protection from not just blackouts & brownouts but also Over voltage & spikes.

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