Electrical misshaps in PC PSUs - Page 1
Forum section: electronics / general

author: Eliminateur
author_rank: Regular Contributor
timestamp: January 27, 2011, 05:54:47 pm
content: Customer called that when doing electrical work in the plant, the "electrician" swapped neutral with Live on the 380v switchboard, result?, pure WIN!at least 9 Dell PC burnt, assorted monitors, scanners, photocopiers, etc.I have the 9 PSUs for repair, interesting fact is that -apart from 1 from an SFF Dell Optiplex that uses a weird input board- protections worked botchily depending on how they where designed.Allow me to explain with an autopsy:All PSUs had burnt fuses, that's goodAll PSUs had burnt varistors to some degrees(the main cap varistors blew in all units, but the AC input survived mostly)Some PSUs ALSO had severely exploded main capsOf those, some blew only one of the capsNONE had rectifier/downstream damageNONE of the input AC filtering circuitry blew, even when some of the X/Y caps are rated below the peak output they where subject toOf the exploded caps, none blew traumatically, they all broke the venting slots on top/outgassed/bled except one that also bulged the plastic wrapping like a dry fruitAll the units contain a protection topology that has one inrush limiter thermistor(it didn't fail in any of them), and 2 main caps in series, rated 220v~, with a varistor in parallel to each cap AND a main varistor in parallel to the output of the input filtering stageWhat amazed me are some units that all 3 varistors exploded violently(even unsoldering themselves and burning through part of the PCB) and still didn't prevent the main caps from blowing.so i have to say that whilst varistors did their job by blowing up, it wasn't very useful to protect completely and the fuses where slow to react and didn't prevent cap damage.Only in one unit(the one with all the movs failing and the worst capacitor damage) that appears to have taken a much higher energy spike did the protection appears to be innefective.watch the pretty pictures:http://img406.imageshack.us/g/27012011431.jpg/

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 27, 2011, 07:13:39 pm
content: Why would swapping line and neutral cause such damage? looks more like over voltage to me.Edit> Just noticed it was 380v board (Three Phase).That explains it.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: January 27, 2011, 07:22:52 pm
content: You are a lucky man ... you got lots of " easy repairs " .About the poor electrician who made the mistake,he has my sympathy too, I bet that he will pay the bill.

author: Eliminateur
author_rank: Regular Contributor
timestamp: January 27, 2011, 07:33:59 pm
content: haha, "relatively easy", only one of the units is shorted out and i think i can pronounce it pretty dead(and it uses some sort of nonstandard mini-atx connector too).they sent us the PSUs in a cardboard box, when i opened it, it smelled like "napalm in the morning" hahahai'm pretty sure they canned the electrician guy, at least from the tone of the IT guy who was desperate for a quote on new PSUs i'm pretty sure he was...

author: saturation
author_rank: Super Contributor
timestamp: January 27, 2011, 08:47:23 pm
content: Interesting. No surge protectors on those electronics to provide a layer of protection after the mains?

author: RayJones
author_rank: Frequent Contributor
timestamp: January 27, 2011, 09:43:42 pm
content: Yeah, electricians and switchboards - never a good combination.We had a radar site install (just across the road from Dave's work actually) that borrowed 3 phase power from the adjacent golf club for a while until the "authority" installed our own meter - yes we did pay the golf club for the power prior.Said "authority" turned up and installed said shiny new meter and power was restored.After a few hours we realised, gee it is starting to get warm. Checked out the air con and found the compressors were running damn hot. Yep the 3 phase was now rotating in reverse and the pump design does not like that and stalls. Lucky we were on site, could have been a 2x $5000 pump replacement, plus labour.Normally it doesn't matter too much, but with motors, oh yeah.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 27, 2011, 09:45:53 pm
content: Quote from: Eliminateur on January 27, 2011, 07:33:59 pmFor years in the uk the standard colour code for three phase systems was Red, Yellow, Blue with Black as the neutral conductor. In their infinite wisdom (All hail the wise one's) the standards committee decided to roll out a new EU standard colour code Brown, Black, Gray and Blue for neutral. Small wonder that the phase and neutral can become crossed especially in an existing (Old) installation with a new feeder cable as the old neutral is black with one of the phases blue and the new cable is neutral blue with one of the phases black just asking for trouble really. Don't know about the original colours in the rest of the EU but this new colour scheme seems to address a problem that does not exist.Just how many people travel around the EU wiring up 3ph systems? It's caused more problems than it's solved.

author: RayJones
author_rank: Frequent Contributor
timestamp: January 27, 2011, 09:51:23 pm
content: Quote from: FreeThinker on January 27, 2011, 09:45:53 pmOuch - that is pure nonsense.We have had similar issue with stuff imported from the US, with AU mains GPO sockets fitted.They used black for active, and white for neutral, and they always had Neutral/Active transposed on the GPO's.Those little 3 light testers are always handy for a quick check, but yeah you don't expect it all to change in an existing install.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 27, 2011, 09:53:08 pm
content: Quote from: RayJones on January 27, 2011, 09:43:42 pmTo be honest I would suspect the 'Temp' supply from the golf course to be the culprit either crossed at your end or at the golf clubs as the supply authority will ALWAYS follow the same phase rotation and verify before turning on the supply, Major legal issues if they get it wrong.

author: RayJones
author_rank: Frequent Contributor
timestamp: January 27, 2011, 09:56:15 pm
content: Quote from: FreeThinker on January 27, 2011, 09:53:08 pmYeah that's what we first thought too, but nope, apparently they did screw it up.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 27, 2011, 10:11:24 pm
content: Quote from: RayJones on January 27, 2011, 09:51:23 pmIndeed and it doesn't stop there.The Regs change so quickly now (and are sometimes contradictory, a requirement being superceded by another that states just the opposite) that is is very hard to keep compliant.Quote from: RayJones on January 27, 2011, 09:51:23 pmThey are handy for single phase but not for 3ph. We used to have a phase rotation meter for checking for crossed phases (not sure how it worked exactly)

author: RayJones
author_rank: Frequent Contributor
timestamp: January 27, 2011, 10:19:22 pm
content: Quote from: FreeThinker on January 27, 2011, 10:11:24 pmCan't be too hard, electricians use them, (or should)I suppose simplistically in terms of digital logic, you could transform all phases into simple positive/negative square waves, and use the rising edge (zero crossing) of a phase to latch the state of another phase (positive or negative)?You would need to ensure that all three phases are unique too.Hey we could go overkill and use a micro

author: Eliminateur
author_rank: Regular Contributor
timestamp: January 27, 2011, 10:35:47 pm
content: ah mini update, 3 of the AC varistors where poof as well.Varistors where:for caps: 150VAC/200VDC breakdown (and a nice side note, Dell heatshrinks all the small varistors to direct the blast up/downwards -and it worked quite well at containing the blast as they're flanked by the main caps), the big 1.5cm AC one doesn't but that's a biggie one anyway)for AC: *can't remember DC*/395VAC breakbownI don't know if surge protection devices have sustained 380VAC in mind, i think they're made with lightning discharge in mind, or i could be wrong...And no, they probably don't ave anything like that, i don't think they even have multistrips(that sometimes have a small thermal reseteable fuse) as it's probably all directly connected neat and tidy.got new varistors from a local shop but for the small ones they sold be an incorrect rating one, bummer, have to go back tomorrow....Caps are a chore, all i can get here are "generic cheapo" caps and this PSUs are very cramped and use very specific sizes, luckily i could scrounge some from the "bin of broken PSUs" and in the shop found some of same voltage/size but not capacity, oh well it will have to doRay: what kind of radar requires TWO HVAC units with 5K$ compressors?!?, a military SAR ICBM air search radar?!?

author: RayJones
author_rank: Frequent Contributor
timestamp: January 27, 2011, 10:42:55 pm
content: Quote from: Eliminateur on January 27, 2011, 10:35:47 pmA weather surveillance radar, running a 850kW klystron transmitter.The tx tube and supporting magnetic field solenoid exhaust a sizable volume of hot air (typ > 50C) (can't remember the CFM)This air is actually exhausted outside, and the replacement fresh air still needs to be chilled.Usually only one unit runs, the second is a failover or fires up on hotter days.The air con plant is actually much larger than the radar transmitter!BTW, 380V had me confused for a while, then I realised 220V mains, not the usual 240/415V we have in Australia.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 27, 2011, 10:50:32 pm
content: Quote from: RayJones on January 27, 2011, 10:19:22 pmI know how to USE them just not the theory of How they work....Cheek!.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 27, 2011, 10:55:56 pm
content: Quote from: FreeThinker on January 27, 2011, 09:45:53 pmThis was just a completely insane decision. If there's one thing that really just doesn't evr need harmonising between countries it's fixed wiring. These people have too much time on their hands.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: January 27, 2011, 11:04:22 pm
content: Quote from: mikeselectricstuff on January 27, 2011, 10:55:56 pmI know that, You know that but they need to justify there jobs somehow.Too bent bananas is another nonsense but don't get me started on the waste in the food industry (BILLIONS of ££££ of perfectly good food going to landfill every year) boggles the mind.

author: Eliminateur
author_rank: Regular Contributor
timestamp: January 27, 2011, 11:14:46 pm
content: Ah, no wonder it required that fancy cooling equipment.hah, yeah, we have 220v as norm here but we use the same plugs as you and everything is compatibles.With your 415V, ohoho that would've been even funnier!Quote from: RayJones on January 27, 2011, 10:42:55 pm

author: RayJones
author_rank: Frequent Contributor
timestamp: January 27, 2011, 11:20:43 pm
content: Quote from: Eliminateur on January 27, 2011, 11:14:46 pmNow that is interesting. I never knew the Australian GPO was used beyond New Zealand, let alone Argentina way across the Pacific. You learn something everyday.I wonder if a wiki page exists that shows the mains plugs used in each country around the world?

author: Eliminateur
author_rank: Regular Contributor
timestamp: January 27, 2011, 11:25:50 pm
content: actually there is:http://users.telenet.be/worldstandards/electricity.htm#plugsWe use the type I as well, but: "The most important difference from the Australasian plug is that the Argentinian plug is wired with the live and neutral contacts reversed."andhttp://en.wikipedia.org/wiki/AC_power_plugs_and_socketsthe type I is the new one in law, but we used the europlug before, very unsafe

author: RayJones
author_rank: Frequent Contributor
timestamp: January 27, 2011, 11:30:13 pm
content: Wow, at least they kept the earth in the same placeIn theory active/neutral reversals should not matter (as in the euro plug standard), but how do you go with equipment that may single pole switch on the neutral?Makes the case for double pole switching more compelling.

author: Eliminateur
author_rank: Regular Contributor
timestamp: January 27, 2011, 11:35:37 pm
content: hmm dunno what the law is for power switches, i can't say i've taken notice either....i guess if it's fully isolated, it doesn't matters what pole you switch....

author: RayJones
author_rank: Frequent Contributor
timestamp: January 27, 2011, 11:40:40 pm
content: FWIW, I learnt this in the early days, doesn't apply for Argentina though!/\ |\|/-\ |\||-|-|-ie, you makeActive,Neutral andEarth from the front view of the socket.

author: Psi
author_rank: Super Contributor
timestamp: January 28, 2011, 12:44:09 am
content: Got to wonder what the hell the guy who desinged this socket was thinking.I dont think you could make it more inviting to children even if you tried.I guess thats why it has a cover.

author: RayJones
author_rank: Frequent Contributor
timestamp: January 28, 2011, 12:48:20 am
content: Looks like a classic "design by committee" result.BTW, the plug looks boring, but that socket would be enticing for a childAnd yeah the cover seems like very good idea due to the facial similarity.

author: Psi
author_rank: Super Contributor
timestamp: January 28, 2011, 06:23:53 am
content: Quote from: RayJones on January 28, 2011, 12:48:20 amyeah, i meant to say socket

author: Eliminateur
author_rank: Regular Contributor
timestamp: January 28, 2011, 11:31:24 am
content: "Hey Kids, let's have fun with Mr. Mains!, poke Mr. Mains in the eye and start dancing wildly!"Quote from: Psi on January 28, 2011, 12:44:09 am

author: Fryguy
author_rank: Regular Contributor
timestamp: January 29, 2011, 12:32:55 am
content: We have a nice powerplug / socket type here in Germany that has become forgotten and i can't see why .It's called the "Perilex" connector .The design is really great - it's a 3phase/n/gnd connector rated 400V 16A or 25A . It is polarised , current coded , touchproof and small compared to other 3phase connectors .You can still buy it and it was not banned by the authorities - it just did disappear from regular use about 30 !!! years ago and nobody seems to know it still exists . . .My grandfathers oven used this connector - hmmmm - the wallsocket might still be there . . . (now i am curious)We go a little bit off topic here but who cares . . . - nice blown PSUs - looks like a lot of fun

author: the_raptor
author_rank: Regular Contributor
timestamp: January 29, 2011, 05:15:49 am
content: Quote from: Psi on January 28, 2011, 12:44:09 amHappy socket is happy*!* to murder your children.

author: Hypernova
author_rank: Unknown
timestamp: January 29, 2011, 07:16:05 am
content: Quote from: Fryguy on January 29, 2011, 12:32:55 amWell. domestic 3 phase is overkill and that design looks a bit expensive.

author: Zero999
author_rank: Super Contributor
timestamp: January 29, 2011, 12:51:32 pm
content: Did you get any compensation from the cowboy electrician? He should have liability insurance.X and Y capacitors shouldn't fail even if you put 1kV across them.