This is possibly the most plausible explanation I've found about plugging a power strip into a UPS. I know that Metal Oxide Varistors are by design a sacrificial device. Their sole purpose in life is to protect the component or device that lies beyond them. Every time they do their job, even though they may not be destroyed completely, they do weaken over time. Kind of like bending a coat hanger back and forth. Bend it once, it just loses a little bit of shape, but it is still useable. Bend it a few times, and you'll notice it start to weaken. Bend it back and forth rapidly and you'll experience it get hot and break down right before your very eyes:
"What you shouldn't do is plug a surge protector into an UPS. I've never seen a great explanation as to why, but what I have read is that the dirty output of the UPS operating on battery will look like many small surges to the surge protector. This in turn will cause the surge protector to shunt power to the ground wire, quickly draining the UPS's battery and destroying the surge protector (most surge protectors are the MOV type, which are degraded every time they activate)." >From >http://www.hometheaterforum.com/forum/thread/213390/ups-plugged-into-a-surge-protector-bad And a comment posted to the article that started all of this. Based on what I know about electricity (My father is a EE and I've taken a number of courses on the subject as well), this guy knows exactly what he is talking about): Great post, but there's a bit of myth floating around, here - there's a HUGE difference between a strike hitting a structure, and the strike hitting a tree/pole that's 40 feet from a structure. First up, the "surge" from a true strike is ambient. Our old shop had a 100 foot tower attached to the building. It got struck twice, and I was charged with making us survive it. These are the realities: 1. Creating deliberate strike points, and CORRECT grounding of the strike points is key, lest you burn down your building. Having it grounded is not enough; run the cable wrong, and the cable will start a fire (or several fires) inside the walls and attic spaces. 2. When you see plasma flowing along the grids of your drop ceiling, you'll realize that the touting of surge protectors and "ground everything and it'll be fine" is a cute concept. 3. During an ACTUAL strike on the structure, the ambient step potential is several gazillion volts per foot for dozens of yards. Grounding does not mitigate this fact. Unplugging does not mitigate this fact. 4. Your hardware devices will live or die based on their shielding and orientation to the strikepoint/ground path, since every conductor in them is a low resistance path along that step potential. If there happens to be a little silicon in the way, well, there won't be when it's over. Note that we're talking KV per inch within a dozen yards of the strike point OR its grounding cable. Your UPS is not even relevant at this point; the grounding path is a huge inductor; every uncaged conductive sub-path in the area will have some amount of current induced, including inside the chip-level. 5. You will lose things like spare mice and keyboards that are not even plugged in, depending on orientation. And, you'll notice that the survival/loss is consistent with that orientation. :) 6. A faraday cage can work wonders, but only if it is done correctly. Many PCs with a cheap metal case will actually survive in some part, possibly enough to cannibalize. Plastic cased PCs will probably need to be removed from production unless the mainboard was exactly flat along the gradient; if they don't fail outright, they typically will before the month is over. Since most rack mounted devices have metal enclosures, the servers etc typically are ok regardless of the rack type, but connectivity may be lost depending on luck, cable shielding, etc. Fully enclosed (metallic all four sides) racks will generally fare slightly better as far as connectivity. Racks with plastic (or no) doors will typically lose NICs, switches, etc in bulk. As with any production, you already keep a stack of old NICs handy - so if lightning is likely, just keep them in a faraday cage of some type (metal storage box or foil wrap). For hubs, routers and switches... plastic case = dead device, doesn't matter how you ground/surge-protect it or the Cat5/6. So, revision of your quick summary: Surge protectors work fair for NEARBY strikes; they become mostly useless as the strike becomes a direct hit. Mitigation of a direct hit requires a different type of engineering (shielding, etc), since you're dealing with a huge ambient EMF gradient, and induced current, neither of which cares about grounding. posted by Steven, Tue Aug 03 2010, 18:02 Jonathan L. Raper, A+, MCSA, MCSE Technology Coordinator Eagle Physicians & Associates, PA [email protected] www.eaglemds.com -----Original Message----- From: Steven Peck [mailto:[email protected]] Sent: Tuesday, August 03, 2010 4:24 PM To: NT System Admin Issues Subject: Re: Guilty, will change after reading this. A surge protector generally lacks the electronics to care enough at the difference. It would have to be a fairly edge case to destroy something. If a stepped sine wave won't destroy an PSU then a surge protector should for hte most part be fine. Steven Peck http://www.blkmtn.org On Tue, Aug 3, 2010 at 12:34 PM, John Hornbuckle <[email protected]> wrote: > I know pretty much nothing about electricity, so this is news to me. I've > done this before, like others, in order to allow UPSs to support more > devices (without overloading them, of course-I only get the kind with load > meters on them). > > > > So, a step sine wave created by a UPS could destroy a surge protector, but > wouldn't harm equipment plugged directly into the UPS? > > > > > > > > > > > > John Hornbuckle > > MIS Department > > Taylor County School District > > www.taylor.k12.fl.us > > > > > > > > From: David Lum [mailto:[email protected]] > Sent: Tuesday, August 03, 2010 1:01 PM > To: NT System Admin Issues > Subject: Guilty, will change after reading this. > > > > - do not plug surge protectors into a UPS. If they UPS runs on batteries it > will usually generate a step sine wave which may destroy surge protectors > (in particular tricky to find power strips without surge protector) > > > > http://isc.sans.edu/diary.html?storyid=9319 > > > > David Lum // SYSTEMS ENGINEER > NORTHWEST EVALUATION ASSOCIATION > (Desk) 971.222.1025 // (Cell) 503.267.9764 > > > > > > > > > > > > NOTICE: Florida has a broad public records law. Most written communications > to or from this entity are public records that will be disclosed to the > public and the media upon request. E-mail communications may be subject to > public disclosure. > ~ Finally, powerful endpoint security that ISN'T a resource hog! ~ ~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~ ________________________________ Any medical information contained in this electronic message is CONFIDENTIAL and privileged. It is unlawful for unauthorized persons to view, copy, disclose, or disseminate CONFIDENTIAL information. 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