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programming and human factors
by Jeff Atwood
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A question recently came up on the internal Vertigo mailing list about surge protection for home equipment and computers:
The best source of information on this is Dan of the eponymously named Dan's Data. Let's start with his essential article on power conditioning:
Mains irregularities come in four flavours - surges, sags, spikes and outages.A surge is a lengthy (2.5 second or longer) increase in the supply voltage. A sag is a similarly lengthy decrease. By and large, computer power supplies deal with both of these quite well, though it of course depends on the severity of the irregularity, not to mention the quality of the power supply, and how much of its capacity is being used by the computer. The closer to maximum capacity a power supply is, the less likely it is to handle a given surge or sag. For this reason, a computer with a 300 watt (W) Power Supply Unit (PSU) is likely to deal better with line irregularities than one with a 235W PSU, although it may not ever need more than 200W of the PSU's possible output.
Outages are plain old blackouts, which are the Russian roulette of computing - you’ll probably get away with no damage or only minor system corruption if the power drops out, but if you’re writing to the only copy of an important file at the magic moment, you can kiss it goodbye.
Spikes are the real nasties. A spike is a brief increase in the supply voltage - less than 2.5 seconds, often a lot less. For a fraction of a second, a spike can easily subject your equipment to several hundred volts. If this doesn’t blow something up outright, it can progressively damage power supply and other components. So, after a few (or a few hundred) more spikes and surges, your PC dies, for no obvious reason. You may lose a power supply or modem; you may lose your motherboard; you may even lose your hard drive and everything on it.
If lightning directly strikes the power lines near your house, you will have a very exciting time and probably lose some gear, unless everything is unplugged. Fortunately, direct strikes to power lines are rare, because, by definition, a power line is well isolated from earth, and the lightning is looking for an earth. Buried power and telephone lines are a different story, though; lightning strikes a long way away can result in large induced spikes on these sorts of cables.
Dan goes on to describe the risks of garden variety cheap, generic surge protectors:
The plain surge/spike filter powerboards you can buy at various electronics, electrical and hardware stores are, arguably, worse than nothing. This is because they give you the impression you’re protected, when you probably aren’t - well, not for long, anyway.The chief surge-clamping component in a basic filter-board is a Metal-Oxide Varistor (MOV). MOVs pass current only when the voltage across them is above a set value, and they react very quickly (in a matter of microseconds, against the tens of milliseconds a circuit breaker takes). That’s the good news. The bad news is that MOVs wear out - they’re only good for a few uses, and the bigger the spike, the more damage is done.
Cheap power filters seldom give you any indication whether your MOV is alive or not. If the powerboard has an illuminated power switch, the switch light often goes off when the MOV has died. The switch lights generally last for decades, so no light almost definitely means no MOV - but since the light only shows the status of a fuse, and the fuse won’t blow if the MOV has been killed by lots of smaller surges, the light can keep glowing merrily when the MOV has long since kicked the bucket.
The key thing to take away from this article is that surge protectors wear out. They aren't good forever.
Personally, I recommend the Tripp Lite ISOBAR Ultra series of surge protectors. And yes, it has to be the Ultra, because of the little green "protection present" LED the Ultra adds. It lets you know that the MOV inside your power strip is still functioning.
The 6-outlet ISOBAR ultra is about $50 online, so they skew to the expensive side of the surge protection spectrum. But at least you won't get a false sense of security from a cheap power strip with a MOV that blew out three years ago. The howstuffworks article on surge protectors mentions that you should look for power strips with a UL 1449 certification, but I think it's more important to look for one with that "protection present" LED.
If you're really serious about protecting that bit of equipment, you won't bother with a surge protector. A surge protector can only protect you from spikes and surges, after all. What about sags and outages? To get full protection from the entire gamut of power problems, you need an Uninterruptible Power Supply.
And that's why, although I own and use many Tripp Lite Ultra power strips, all my home PCs are plugged into UPSes.
I don't have enough experience to recommend a specific brand of UPS, but this excellent Computer Power User article (may be behind paywall after first visit) has a few general recommendations for us:
Once you hook your device up to a true UPS, you've basically removed it from the power grid and hooked it into a custom electricity provider. The only use the UPS has for wall power is to charge its batteries. And be sure not to plug your UPS into any surge protection strip; plug it directly into the wall. I've seen some truly bizarre PC behavior resulting from daisy-chaining UPSes or surge protection strips.
So, in summary: if it's something you really care about, put it on a decent UPS. If it's something you want to protect, put it behind a decent surge protector with a "protection OK" indicator.
Posted by Jeff Atwood View blog reactions
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Many years ago, I worked at Shell, and my boss told me that the office had recieved an insurance discount because their hardware was plugged into isobar surge protectors. (And it had to be isobar to get the discount.)
Mike Swaim on July 12, 2006 12:18 PMThis bring up the question: IS the ISOBAR Ultra any better at supressing surges, or is it's only advantage that it accurately tells you when it's failed? If the latter, would we be better off just buying a truckload of cheap suppresser, and replacing than every 6 months?
As a side note: Remember to never plug a surge suppresser into a square-wave UPS --- the SS would consider the square waves lots of tiny surges and will be constantly trying to supress them -- greatly shortening it's life and possibly leading to overheating & fire.
James: Thanks! Jeff said it too, but i tend to ignore "Just don't do this" messages (opposite to "Don't do this because: ...") :)
Keff on July 12, 2006 01:50 PMOne interesting note: voltage regulation in a UPS is largely unnecessary with PCs due to the ability of the switching power supply to accomodate voltage swings. UPS manufactures push this dubious feature.
David Gustafson on July 12, 2006 02:07 PM"Outages are plain old blackouts, which are the Russian roulette of computing - you’ll probably get away with no damage or only minor system corruption if the power drops out, but if you’re writing to the only copy of an important file at the magic moment, you can kiss it goodbye."
That last statement is not true for most OS's. Journaling file systems like NTFS, the default for NT based Windows, and ReiserFS, the most popular default file system for Linux, handle these situations with relative ease. Unfortunately Windows 95 + 98 used Fat32 and tended to crash a lot, causing crippling file system errors, but that's old history. Similarly, most linux distros used ext2 back in the day, with a similar effect.
steveth45 on July 12, 2006 02:07 PMI have an APC UPS, and one of the features I like is that it keeps logs. Among other things it can report is how many surges and sags you've experienced, which is a useful thing to know. What I've learned is that the power to my house is pretty clean (essentially no anomalies beyond +/- a couple of volts), although of course the power just cuts out at odd intervals. For which I have the UPC.
My only complaint about it is that it supports only one USB port, so only one machine can be notified to do a clean shutdown, so I do that on my server. It would be nice if they powered themselves back up when the power came back, I suppose. :-)
mike on July 12, 2006 02:10 PM> James: Thanks! Jeff said it too
Well, not quite-- I didn't specify that you should avoid surge protectors both upstream AND downstream of the UPS. This is also an argument for a true UPS with realistic "sine wave" output.
> It would be nice if they powered themselves back up when the power came back, I suppose
There is a way to do this for power interruptions via the BIOS, but I don't know if a clean shutdown counts or not.
> would we be better off just buying a truckload of cheap suppresser, and replacing than every 6 months?
Well, maybe, but are you REALLY going to be conscientious about replacing a half-dozen surge suppressors every 6 months? What are you gonna do, write the date on them, like a box of baking soda in the fridge? ;) I think it's easier to have an "I still work" LED that you can eyeball. Who knows, maybe your surge suppressor will still be chugging along 3 years from now.
Jeff Atwood on July 12, 2006 02:36 PMAnother point of protection is to get a surge suppressor for your main power. It installs into your electrical panel.
foobar on July 12, 2006 02:46 PMOh, and don't forget to surge protect your cable and telephone lines.
foobar on July 12, 2006 02:48 PMGetting a UPS has increased the stability and life expectancy of various bits of computer equipment at my place.
For example, ADSL modems and other smaller equipment used to die with frightning regularity, apparently due to the poor power quality.
Another benefit is that I can use my cordless phones during a blackout (we've long since got rid of a "normal" corded phone), and keep some light on in the house for a considerable amount of time.
Will on July 12, 2006 04:04 PMRegarding the spike protection in case of lightning, there's a killer that's not on power at all:
Most people only disco the power and modem lines, because they obviously come from the outside.
But it's the network cables that often run in endless loops, making a perfect place for induction by the field(!) of the lightning.
If you disconnect, don't forget the network cables; and don't get "too long" network cables. A straight line is much less dangerous than a coil.
Bernd Haug on July 13, 2006 01:41 AMMike wrote: My only complaint about it is that it supports only one USB port, so only one machine can be notified to do a clean shutdown, so I do that on my server.
AFAIR APC has software for notifying several machines when the UPS detects a power outage. They probably want to sell it for extra money.
A different approach would be to read the status of the UPS via script and to shutdown all the machines via remote login.
Deltatango on July 13, 2006 04:16 AMThis made me actually look at the "protected" indicator on my old Belkin Surgemaster II.
Guess what: It's off :-(
These are meant to have a lifetime warranty, so I'll see what Belkin have to say.
Roddy on July 13, 2006 10:09 AMhttp://www.portlandgeneral.com/home/products/surge/meter_protection.asp
Michael Fitzpatrick on July 13, 2006 10:24 AMJeff said:
> I think it's easier to have an "I still work" LED that you can eyeball.
I think it would be even easier to have an "I *don't* work anymore" light -- blinking, if possible. It would be far more noticable than the lack of a light. (Crack that thing open and install a NOT gate!)
Atario on July 13, 2006 07:04 PMA little tangent, has anyone had any experience with
the isobar cutting out static from the power lines? I'm wondering if it will help reduce the noise from my speakers...which I believe may be coming from the outlet...
there's tomething to be said for hooking your coffee machine on the ups...
andy on July 14, 2006 09:40 AMandy: You can't hook a press pot to a UPS! Though perhaps something for boiling the water...
Adam Vandenberg on July 14, 2006 11:04 AMSurge Protectors prevent spikes in power shorting out expensive equipment because they take the hit, not the eletronic device. The protector will not help you out against a lightning strike because of the amount of voltage coming in as the lighting will flow until it grounded. It will eaily jump through the surge protector if it is inline from the strike. A lightning strike has a much higher amount of voltage coming in than the power lines off the street. If your worried about lightning, the best defense is a lightning rod grounded into the earth away from the power coming off the street.
If you leave your computer on all the time, a UPS is much better solution, because it regulates the voltage coming in from the street, stepping down the highs (sometime a higher amount of voltage will come in off the street) and stepping up the lows (brown outs). It will give you a nice even voltage flow and prolong the life of eletronic equipment, and it also gives you a limited time of power during a blackout for graceful shutdowns etc. This is in addition to surge protection.
Jon Raynor on July 14, 2006 12:26 PMAlso, has anyone ever had a power spike that the surge protector caught? Just wondering.
I never had, but I have had brown outs and over voltages occur on a regular basis that the UPS deals with.
Jon Raynor on July 14, 2006 12:31 PMsteveth45: Journalling file systems only protect the file system data. They do nothing for the data in the files themselves. That's why all reputable database systems require their own transaction logs. What that means is that you're extremely unlikely to lose the whole volume due to an inconsistent state, but you can lose the changes to a file if a write partially completed before the power failed. Also most journalled filesystems generally work in a write-back caching mode by default so changes that haven't yet been lazy-written will be lost. Windows provides flags to pass to CreateFile to tell it not to cache writes to this file.
My sister works in Exchange technical support. Her eyes nearly popped out when I explained the UNIX mbox format to her. Exchange uses a true database to contain your mailbox data. UNIX mbox is a flat file with no indexing and no protection against power or disk failure or concurrent access.
Note that Microsoft recommend the use of SCSI disks for SQL Server and Exchange because the drive manufacturers play fast and loose with the IDE/SATA specs - often they don't actually provide a genuine direct-to-disk write path, writing only to the drive's on-drive cache instead. This gets better benchmark results to the detriment of reliability.
Mike Dimmick on July 15, 2006 08:21 AMIf you protect your PC, monitor, etc, but NOT your peripherals (Printer, USB hub, speakers, router, etc), could a spike pass through the cabls and knock out the PC's USB or network cards?
Simon on July 17, 2006 11:05 AMSimon: Yes, especially if it's a surge due to a lightning strike.
I'm surprised that nobody's mentioned the difference between "power conditioning" devices and "surge protectors." Surge protectors (and most UPSes) do nothing to provide clean power. There's a reason why musicians and hospitals don't simply use tripp-lite or APC.
UL1449 is about the safety of the device, it's acceptable for a tested device to fail, but it shouldn't start a fire or create a shock hazard.
Excedrin on July 18, 2006 12:18 PMI got that isobar thing in the 90's and paid about $80 from Ingram Micro after reading an article where they surged different protectors and the vast majority of them totally failed except for the Tripp Lites. It's one of those instances of quality constrution with metal construction, a solid feeling switch and snug gripping receptacles. It's supposed to condition the power as well. I still use it... wonder if it's still good....better be I paid $80 for it.
Ben on July 20, 2006 06:44 AMVery enlightening stuff here.
I have been replacing circuit boards in my Raynor Flitestar garage door opener with regularity. I have replaced about 1 per year in 6 years, each time following a close lightning strike in the woods where I live.
I have always followed the directions from Raynor, and have the unti plugged into the "suppressor" they provided.
1. I know why that rascal is worthless now. Thanks to you.
2. I always felt that a UPS or similar equipment would help. (it would have to be screwed to the ceiling or in the panel)
3. The last time I think it came in the ground circuit. A stereo and oscilloscope that were plugged into a GFCI outlet that tripped were both fine. The door opener is not on a GFCI.
So I suppose I will get a UPS and screw it to the ceiling, but I found a company called brickwall, that has info on how its equipment works. It sounds cool, but it's pricey ($180 for a 15A 2-outlet)
My question is; with circuit boards at $85, do you think their "huge inductor and capacitors" filtering will help, or are my circuit boards the sacrificials here?
Mike Perry
mikep on August 20, 2006 07:52 AMThat last sentence was poorly worded.
The Flitestar boards are $85 each,
The brickwall power surge suppressor is $180,
and the real question is whether they are blowing smoke to sell products and if I should just keep replacing boards.
Thanks.
Mike Perry
mikep on August 20, 2006 07:55 AMMy firm is a specialized distributor of "Power Quality" products, ie we have leading technology for EVERY type of electrical disturbance. Rarely does one band-aid fix every problem.
UPS's are strictly for outages, brown-outs and loss of power. UPS units have transient spike protection to protect themselves, not your critical load. I strongly suggest adding a surge bar to the load side of your UPS in every case.
Whether the UPS is "stand-by" or "always-on" it diverts surges to ground to protect the battery, charger and rectifier. NO UPS re-creates the neutral or ground circuits but merely uses them as diversion pathes for damaging spikes. Spikes are bi-directional and the neutral is the incursion highway for spikes to enter your computer bus.
Official terminology is: a transient is 8ms or one half cycle.
Static electricity is a transient spike capable of as much as 5000volts. How is your UPS going to protect your PC tower if your touch you keyboard or PC chassis?
According to IBM over 88% of all electrical disturbances are transient spike related. If money is limited, dollars are far better spent on transient spike protection.
R Milner on December 12, 2006 04:31 PMI protect my server with a UPS. But I have lots of workstations that I'm not as worried about. After a UPS battery dies, would it make sense to use the serge protection side of the ups as just a surge protector?
tom on June 12, 2007 07:55 PMRight - short of a $200 Brick Wall, a proven supressor made with quality components and a real "Working" light (like a $50 Ultra) with a $50 Tripp Lite 550VA will offer a boatload of real world protection and short-term backup power.
But the surge suppressor protects the UPS, you don't want a SS after the UPS. Also nothing power hungry like a printer or lamp.
Thanks on July 30, 2007 12:35 AMThis is a little late, so I don't know if know when you get comments on old entries. You can now by power panels for your home that have surge protection built in. This will protect your entire house. I haven't looked into the specifics so I don't know if there is a part that you need to replace every now and then or if they use a different method. You can check your local Home Depot or other home store for them.
Mark Bernard on May 16, 2008 11:01 AMI have that same model as shown in your photograph. How do you get it to stop beeping? It's driving me up the wall.
caroline on July 14, 2008 08:48 AMHello Jeff, Nice article. I have always wondered as to how you guys manage those messy cables from monitors, keyboards, mouse, the CPU, DSL modem, computer speakers etc. I really have a very hard time organizing these cables neatly. Any suggestions or pointers?
prabhu on July 14, 2008 09:09 AMHi Jeff, I really appreciated your article about surge supressors.I think that I will buy one of the Tripp Lite Isobars that you suggested. My question is-does this unit have connections for coax in and out to PC? Can't tell by pic. If not, what to do? My existing suppressor has these connections,but it surely not as good as what you are describing. Thanks much.GRM
George on July 18, 2008 08:41 PM| Content (c) 2008 Jeff Atwood. Logo image used with permission of the author. (c) 1993 Steven C. McConnell. All Rights Reserved. |
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